Passivation Characteristics of New Silicon Oxide

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

Abstract—Surface passivation on silicon is one of the hot topics for research in the field of silicon solar cells. Single layers of silicon oxide prepared by thermal oxidation, O3 oxidation or chemical oxidation and the stack layer of silicon oxide combined with other dielectric layers as passivation layers have been widely used to reduce surface carrier recombination in silicon solar cells.

This paper provides a new method for preparing silicon oxide that realizes an excellent passivation effect, in which perhydropolysilazane was used as a spin-coating precursor. The effective minority carrier lifetime for n-type silicon passivated by a SiOx layer increases with SiOx thickness and can reach 1 ms when thickness is up to 100 nm. Moreover, when SiO_x layers with a thickness of 100 nm or more were capped by an AlOx or SiNx

layer, the effective minority carrier lifetime could get a value above 2 ms, which is much higher than the value for single SiNx or AlOx (approximately 500–750 μs). This may result from the high positive fixed charge in the SiOx layer and high hydrogenation of silicon surface induced by H diffusion from AlOx or SiNx to SiOx

and stored in it.

Index Terms—interface fixed charge, passivation, perhydropolysilazane, silicon oxide

I. INTRODUCTION

At the silicon solar cell surface, due to the destruction of the crystal periodic structure, dangling bonds are generated, forming defect levels in the forbidden band, which seriously affect the minority carrier lifetime[1]. With the thickness of silicon solar cells continuing to decrease in order to save cost, the diffusion length of minority carriers may be close to or even larger than the thickness of the wafer; so, some carriers will diffuse to the surface to recombine, leading to surface passivation on silicon more important than before. Surface recombination is realized by a combination of the electric field effect and chemical components[2]. The fixed charge in the passivation film forms an electric field on the surface of the substrate, causing the energy band to bend and inhibit the movement of the minority carrier to the surface, thus leading to the field-effect passivation; however, the dangling bonds can be saturated by hydrogen atoms during the preparation and annealing of the passivation layers, reducing the interface state density D and increasing the minority carrier lifetime. SiNx, AlOx and SiOx are widely used as passivation materials [3-5].

Additionally, Si–SiO2 has a lattice-matched interface and

This work was supported by the research project 61874120 supported by National Natural Science Foundation of China and the research project 261574 granted by Norwegian Research Council.

L. Gong, C.L. Zhou and W.J. Wang are with the Key Laboratory of Solar Thermal Energy and Photovoltaic System, Institute of Electrical Engineering, Chinese Academy of Science (CAS), Beijing 100190, PR China and University of Chinese Academy of Sciences, Beijing 100190, PR China (e-mail:

gonglei@mail.iee.ac.cn; zhouchl@mail.iee.ac.cn; wangwj@mail.iee.ac.cn).

J.J. Zhu is with the Solar Energy Department, Institute for Energy Technology, Kjeller, Norway (e-mail: Junjie.Zhu@ife.no).

positive to provide chemical passivation and field-effect passivation, respectively [6, 7]. Most of the silicon solar cells adopt a multi-layer film structure to ensure both the passivation and anti-reflection in practical applications.

The most popular preparation methods of silicon oxide include thermal oxidation, wet chemical oxidation, plasma-enhanced chemical vapor deposition (PECVD), and plasma oxidation [8-10]. Thermal oxidation requires high temperature at 900–1200 °C; silicon atoms on the silicon surface are oxidized to SiO2 in different atmospheres. However, the thermal oxidation requires large energy consumption, and the oxidation of the silicon wafer generates self-gap silicon atoms and form bulk defects. Wet chemical oxidation mainly includes H2O2, H2SO4, and HNO3 oxidants[11]. The low growth rate of the wet chemical oxidation layer limits its application range, and using oxidants such as HNO3 requires treatment of the waste, which increases the cost and could be harmful to the ecological environment. PECVD uses SiH and N O or O as a precursor to grow silicon oxide on the substrate, which requires a vacuum environment and a complicated process. In this paper, we use perhydropolysilazane (PHPS) as the spin-coating precursor to prepare a silicon oxide film, it is a low-temperature and uncomplicated process.

PHPS is mainly composed of Si–N and Si–H. It is mainly used for ceramic precursors, ceramic matrix composites and coating materials[12]. PHPS can be cured in an ultraviolet environment, and the –(SiH2–NH)– unit undergoes a hydrolysis reaction to form ammonia gas and Si(OH)4 as an intermediate state[13]. During the subsequent heat treatment, portions of O and H overflow such that Si(OH)4 forms a SiOx

grid. The principle of hydrolysis reaction is as follows[12]:

—(SiH2–NH)n— + 4nH2O → nSi(OH)4 + 2nH2 + nNH3 . (1) It can also be cured at appropriate temperature and form SiOx

directly with oxygen in the atmosphere:

—(SiH2-NH) n— + nxO → nSiOx + nNH3. (2) Nagayoshi introduced a 100 nm SiOx film which was made from the PHPS precursor into TiO2 back reflector to promote the surface passivation on silicon[14], but that film is seldom used in solar cells. In this work, we explore the spin coating of a SiOx film from a precursor of PHPS for surface passivation. We have studied the effect of annealing temperature and thickness of SiOx films on the chemical component. In addition, the contribution of a single SiOx layer on silicon surface passivation has been discussed. Finally, double layers of SiOx/AlOx:H, or SiNx/SiOx:H made by capping the SiOx layer with plasma-enhanced atomic layer deposition (PE-ALD) AlOx and PECVD SiNx layers were investigated. The result shows that improvements were observed in the two stacks compared to the single passivation layer of SiOx, AlOx, and SiNx.

Passivation Characteristics of New Silicon Oxide

Lei Gong, Chunlan Zhou, Junjie Zhu, Wenjing Wang

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spin

annealing at moderate temperature in atmosphere.

double

resistivity of 1~10 H2

in DI water; finally, the surface oxide layer was removed using 1% HF. A

n-

4500 r/min for 60 s by the spin

film was baked at 150 °C for 3 min and then annealed in air atmosphere for 1

temperature was changed from 300 °C to 900 °C to obtain a single

structure of the stack layer, after depositing SiO front and back surfaces of the sil

PE

1(B1)) and an 80 nm PECVD SiN capped on the SiO

passivated silicon wafer were used as references. The SiO

exchanging the preparing order of AlO two

SiOx/AlOx:H, and SiO 400 °C for 10 min, and SiN

annealed at 450 °C for 10 min in atmosphere. AlO

deposited at 200 °C with TMA and oxygen as the reaction precursor, and PECVD SiN

with SiH and the thickne

infrared spectroscopy (FTIR) spectroscopy and ellipsometer, respectively. The effective minority carrier lifetime of a passivated silicon wafer and fixed charge in the dielectric film were measured through tr

using WT

was tested by Time of Flight Secondary Ion Mass Spectrometry

(TOF

A.

after annealing are shown in Fig. 2. This shows that the chemical component changes after annealing. The spectra for the as

with the N Si

Fig. 1.

SiOx stack

and C is a SiOx/SiNx:H

In this experiment, a silicon oxide film was formed by spin-coating a PHPS film on Si (100) substrates and using annealing at moderate temperature in atmosphere.

double-sided polished c resistivity of 1~10

2SO4:H2O2 = 4:1 (volume ratio) at 85 °C for 10 min and rinsed in DI water; finally, the surface oxide layer was removed using 1% HF. After being dried in N

-butyl ether, was double 4500 r/min for 60 s by the spin

film was baked at 150 °C for 3 min and then annealed in air atmosphere for 1

temperature was changed from 300 °C to 900 °C to obtain a single-layer SiO

structure of the stack layer, after depositing SiO front and back surfaces of the sil

PE-ALD AlOx

1(B1)) and an 80 nm PECVD SiN capped on the SiO

passivated silicon wafer were used as references. The SiOx/AlOx:H stack shown in Fig. 1(C) was obtained by exchanging the preparing order of AlO

two-side deposition on silicon wafer, the single AlO SiOx/AlOx:H, and SiO

400 °C for 10 min, and SiN

deposited at 200 °C with TMA and oxygen as the reaction precursor, and PECVD SiN

with SiH4 and NH

and the thickness of the film were tested by Fourier transform infrared spectroscopy (FTIR) spectroscopy and ellipsometer, respectively. The effective minority carrier lifetime of a passivated silicon wafer and fixed charge in the dielectric film were measured through tr

using WT-2000 instrument. The distribution of H in the film was tested by Time of Flight Secondary Ion Mass Spectrometry

(TOF-SIMS).

III.

A. Film component

The absorption FTIR spectra of the SiO

after annealing are shown in Fig. 2. This shows that the chemical component changes after annealing. The spectra for the as-deposited sample show the absorption peaks associated with the N–H peak (3,400 cm

Si-O peak (1,080 cm

Fig. 1. Sample structures in the experiment; A is the structure of single SiOx-passivated Si wafer, B1 is a double

stack-passivated Si wafer, B2 is a AlOx/SiOx:H stack and C is a SiOx/SiNx:H

II. EXPERIMENTS

In this experiment, a silicon oxide film was formed by coating a PHPS film on Si (100) substrates and using annealing at moderate temperature in atmosphere.

sided polished c-Si substrate was adopted with resistivity of 1~10 Ω ∙ cm. First, a wafer was immersed in

= 4:1 (volume ratio) at 85 °C for 10 min and rinsed in DI water; finally, the surface oxide layer was removed using

fter being dried in N

butyl ether, was double-sided coated on the silicon surface at 4500 r/min for 60 s by the spin

film was baked at 150 °C for 3 min and then annealed in air atmosphere for 15 min in a box furnace. The annealing temperature was changed from 300 °C to 900 °C to obtain a layer SiOx sample (as shown in Fig. 1 (a)); as for the structure of the stack layer, after depositing SiO

front and back surfaces of the sil

with a thickness of 15 nm (as shown in Fig.

1(B1)) and an 80 nm PECVD SiN capped on the SiOx layers. Single AlO

passivated silicon wafer were used as references. The :H stack shown in Fig. 1(C) was obtained by exchanging the preparing order of AlO

side deposition on silicon wafer, the single AlO SiOx/AlOx:H, and SiOx/AlO

400 °C for 10 min, and SiN

deposited at 200 °C with TMA and oxygen as the reaction precursor, and PECVD SiNx

and NH3 as the reaction precursor. The components ss of the film were tested by Fourier transform infrared spectroscopy (FTIR) spectroscopy and ellipsometer, respectively. The effective minority carrier lifetime of a passivated silicon wafer and fixed charge in the dielectric film were measured through transient micro

2000 instrument. The distribution of H in the film was tested by Time of Flight Secondary Ion Mass Spectrometry

III. RESULTS AND DISCUSSIO

Film components

after annealing are shown in Fig. 2. This shows that the chemical component changes after annealing. The spectra for deposited sample show the absorption peaks associated

H peak (3,400 cm ,080 cm^-1), and the Si

Sample structures in the experiment; A is the structure of single ssivated Si wafer, B1 is a double

passivated Si wafer, B2 is a AlOx/SiOx:H stack and C is a SiOx/SiNx:H-passivated Si wafer.

XPERIMENTS

In this experiment, a silicon oxide film was formed by coating a PHPS film on Si (100) substrates and using annealing at moderate temperature in atmosphere.

Si substrate was adopted with . First, a wafer was immersed in

= 4:1 (volume ratio) at 85 °C for 10 min and rinsed in DI water; finally, the surface oxide layer was removed using fter being dried in N2, PHPS which was diluted with sided coated on the silicon surface at 4500 r/min for 60 s by the spin-coating process. The as film was baked at 150 °C for 3 min and then annealed in air

5 min in a box furnace. The annealing temperature was changed from 300 °C to 900 °C to obtain a sample (as shown in Fig. 1 (a)); as for the structure of the stack layer, after depositing SiO

front and back surfaces of the silicon wafer and annealing, with a thickness of 15 nm (as shown in Fig.

1(B1)) and an 80 nm PECVD SiNx layer (Fig. 1(B2)) were layers. Single AlO

passivated silicon wafer were used as references. The :H stack shown in Fig. 1(C) was obtained by exchanging the preparing order of AlO

side deposition on silicon wafer, the single AlO /AlOx:H stacks were annealed at 400 °C for 10 min, and SiNx layers, SiN

deposited at 200 °C with TMA and oxygen as the reaction layers were deposited at 400 °C as the reaction precursor. The components ss of the film were tested by Fourier transform infrared spectroscopy (FTIR) spectroscopy and ellipsometer, respectively. The effective minority carrier lifetime of a passivated silicon wafer and fixed charge in the dielectric film ansient micro-photoconductive decay 2000 instrument. The distribution of H in the film was tested by Time of Flight Secondary Ion Mass Spectrometry

ESULTS AND DISCUSSIO

after annealing are shown in Fig. 2. This shows that the chemical component changes after annealing. The spectra for deposited sample show the absorption peaks associated

H peak (3,400 cm^-1), the Si-H peak (2,145 cm ), and the Si-N peak (860 cm

Sample structures in the experiment; A is the structure of single ssivated Si wafer, B1 is a double-

passivated Si wafer, B2 is a AlOx/SiOx:H stack passivated Si wafer.

In this experiment, a silicon oxide film was formed by coating a PHPS film on Si (100) substrates and using annealing at moderate temperature in atmosphere. An N

Si substrate was adopted with . First, a wafer was immersed in

= 4:1 (volume ratio) at 85 °C for 10 min and rinsed in DI water; finally, the surface oxide layer was removed using , PHPS which was diluted with sided coated on the silicon surface at coating process. The as-coated film was baked at 150 °C for 3 min and then annealed in air 5 min in a box furnace. The annealing temperature was changed from 300 °C to 900 °C to obtain a sample (as shown in Fig. 1 (a)); as for the structure of the stack layer, after depositing SiOx film on the icon wafer and annealing, with a thickness of 15 nm (as shown in Fig.

layer (Fig. 1(B2)) were layers. Single AlOx and SiNx

passivated silicon wafer were used as references. The :H stack shown in Fig. 1(C) was obtained by exchanging the preparing order of AlOx and SiOx. After

side deposition on silicon wafer, the single AlO :H stacks were annealed at

layers, SiNx/SiOx:H, annealed at 450 °C for 10 min in atmosphere. AlOx layers were deposited at 200 °C with TMA and oxygen as the reaction layers were deposited at 400 °C as the reaction precursor. The components ss of the film were tested by Fourier transform infrared spectroscopy (FTIR) spectroscopy and ellipsometer, respectively. The effective minority carrier lifetime of a passivated silicon wafer and fixed charge in the dielectric film photoconductive decay 2000 instrument. The distribution of H in the film was tested by Time of Flight Secondary Ion Mass Spectrometry

ESULTS AND DISCUSSIONS

The absorption FTIR spectra of the SiOx film before and after annealing are shown in Fig. 2. This shows that the chemical component changes after annealing. The spectra for deposited sample show the absorption peaks associated

H peak (2,145 cm N peak (860 cm^-1). After

Sample structures in the experiment; A is the structure of single -sided SiOx/AlOx:H passivated Si wafer, B2 is a AlOx/SiOx:H stack-passivated Si wafer,

In this experiment, a silicon oxide film was formed by coating a PHPS film on Si (100) substrates and using An N-type Si substrate was adopted with . First, a wafer was immersed in

= 4:1 (volume ratio) at 85 °C for 10 min and rinsed in DI water; finally, the surface oxide layer was removed using , PHPS which was diluted with sided coated on the silicon surface at coated film was baked at 150 °C for 3 min and then annealed in air 5 min in a box furnace. The annealing temperature was changed from 300 °C to 900 °C to obtain a sample (as shown in Fig. 1 (a)); as for the film on the icon wafer and annealing, with a thickness of 15 nm (as shown in Fig.

layer (Fig. 1(B2)) were layers passivated silicon wafer were used as references. The :H stack shown in Fig. 1(C) was obtained by . After side deposition on silicon wafer, the single AlOx, :H stacks were annealed at :H, were layers were deposited at 200 °C with TMA and oxygen as the reaction layers were deposited at 400 °C as the reaction precursor. The components ss of the film were tested by Fourier transform infrared spectroscopy (FTIR) spectroscopy and ellipsometer, respectively. The effective minority carrier lifetime of a passivated silicon wafer and fixed charge in the dielectric film photoconductive decay 2000 instrument. The distribution of H in the film was tested by Time of Flight Secondary Ion Mass Spectrometry

before and after annealing are shown in Fig. 2. This shows that the chemical component changes after annealing. The spectra for deposited sample show the absorption peaks associated H peak (2,145 cm^-1), ). After

annealing at 300 °C for 15 min, the N disappeared, whereas the Si significantly, and the Si intensity. As the anneali of the Si

a low level. This reveals that the Si were broken, and the Si

reacting with the oxygen in the atmosph

peak (a) and the ratio of the Si peak’s height (b) as a function of the

Their peak position moves toward a higher wavenumber with increasing annealing temperature; this indicates that the composition of the film is closer to chemical stoichiometry SiO

of Si

bond more easily transfers to the Si

temperature. The PHPS film could be defined as SiO

atomic ratios of Si, O, and N can be calculated from the area of the

composition of SiO relationship

and

[

calculated by coefficient 10

[Si], we find that x continues to increase and y continues to decrease as the annealing temperature increases. The value of x is 1.95 at 300

0.07 to 0.02.

released to the outside of the film in the form of H

during annealing, and the components of the film are mainly dominated by Si

the stoichiometric SiO

Fig. 2

Sample structures in the experiment; A is the structure of single sided SiOx/AlOx:H passivated Si wafer,

annealing at 300 °C for 15 min, the N disappeared, whereas the Si significantly, and the Si intensity. As the anneali

of the Si–O peak became higher, and the Si a low level. This reveals that the Si were broken, and the Si

reacting with the oxygen in the atmosph

Fig. 3 shows the peak of the Si peak (a) and the ratio of the Si peak’s height (b) as a function of the

Their peak position moves toward a higher wavenumber with increasing annealing temperature; this indicates that the composition of the film is closer to chemical stoichiometry SiO2. When the annealing temperature is up to 600 °C, the of Si–O bond increases significantly, indicating that the Si bond more easily transfers to the Si

atomic ratios of Si, O, and N can be calculated from the area of Si–O and Si

composition of SiO relationship [15]:

and

=

[ − ] is the absolute concentration of the bond and can be calculated by [

coefficient

. After calculating the value of [O] / [Si] and [N] / [Si], we find that x continues to increase and y continues to decrease as the annealing temperature increases. The value of x is 1.95 at 300°C and 1.98 at 900°C, and that

0.07 to 0.02. Therefore, the result reveals that N and H are released to the outside of the film in the form of H

during annealing, and the components of the film are mainly dominated by Si–

the stoichiometric SiO

Fig. 2. The FTIR spectrum for SiO

annealing at 300 °C for 15 min, the N disappeared, whereas the Si

significantly, and the Si–N peak still appeared with lower intensity. As the annealing temperature increased, the intensity

O peak became higher, and the Si a low level. This reveals that the Si

were broken, and the Si–O bond was formed by Si bonds reacting with the oxygen in the atmosph

Fig. 3 shows the peak of the Si peak (a) and the ratio of the Si peak’s height (b) as a function of the

Their peak position moves toward a higher wavenumber with increasing annealing temperature; this indicates that the composition of the film is closer to chemical stoichiometry

. When the annealing temperature is up to 600 °C, the O bond increases significantly, indicating that the Si bond more easily transfers to the Si

atomic ratios of Si, O, and N can be calculated from the area of O and Si–N peaks in the FTIR spectrum. For the composition of SiOxNy, x and y satisfy the following

:

=[ ] [ ]=

[ −

=[ ] [ ]=4

3· [

is the absolute concentration of the bond and can be [ − ] =

= 1.5 × 10

After calculating the value of [O] / [Si] and [N] / [Si], we find that x continues to increase and y continues to decrease as the annealing temperature increases. The value of x

°C and 1.98 at 900°C, and that

Therefore, the result reveals that N and H are released to the outside of the film in the form of H

during annealing, and the components of the film are mainly –O bonds. So, the film is gradually chan the stoichiometric SiO2 during annealing.

The FTIR spectrum for SiOx

annealing at 300 °C for 15 min, the N–H and Si

disappeared, whereas the Si–O peak intensity increased N peak still appeared with lower ng temperature increased, the intensity O peak became higher, and the Si–N peak remained at a low level. This reveals that the Si–N, N–H, and Si

O bond was formed by Si bonds reacting with the oxygen in the atmosphere during annealing.

Fig. 3 shows the peak of the Si–O normalized by Si peak (a) and the ratio of the Si–O peak’s height to the Si peak’s height (b) as a function of the annealing temperature.

. When the annealing temperature is up to 600 °C, the O bond increases significantly, indicating that the Si bond more easily transfers to the Si–O bond under higher temperature. The PHPS film could be defined as SiO

atomic ratios of Si, O, and N can be calculated from the area of N peaks in the FTIR spectrum. For the , x and y satisfy the following

2[ − ] [ − ] + [ −

is the absolute concentration of the bond and can be

∫ ^{( )} = , and

°C and 1.98 at 900°C, and that

Therefore, the result reveals that N and H are released to the outside of the film in the form of H

during annealing, and the components of the film are mainly O bonds. So, the film is gradually chan

during annealing.

(280 nm) before and after annealing

H and Si–H peaks almost O peak intensity increased N peak still appeared with lower ng temperature increased, the intensity N peak remained at H, and Si–H bonds O bond was formed by Si bonds

ere during annealing.

O normalized by Si O peak’s height to the Si

annealing temperature.

. When the annealing temperature is up to 600 °C, the O bond increases significantly, indicating that the Si

O bond under higher temperature. The PHPS film could be defined as SiOxNy:H, the atomic ratios of Si, O, and N can be calculated from the area of N peaks in the FTIR spectrum. For the , x and y satisfy the following

]

− ].

is the absolute concentration of the bond and can be

= , the

, and = 2

°C and 1.98 at 900°C, and that of y changes from Therefore, the result reveals that N and H are released to the outside of the film in the form of H2 and NH during annealing, and the components of the film are mainly

O bonds. So, the film is gradually changed to

H peaks almost O peak intensity increased N peak still appeared with lower ng temperature increased, the intensity N peak remained at H bonds O bond was formed by Si bonds ere during annealing.

O normalized by Si–N O peak’s height to the Si-N annealing temperature.

Their peak position moves toward a higher wavenumber with increasing annealing temperature; this indicates that the composition of the film is closer to chemical stoichiometry ratio O bond increases significantly, indicating that the Si–N O bond under higher :H, the atomic ratios of Si, O, and N can be calculated from the area of N peaks in the FTIR spectrum. For the , x and y satisfy the following

is the absolute concentration of the bond and can be , the 2.1 × After calculating the value of [O] / [Si] and [N] / [Si], we find that x continues to increase and y continues to decrease as the annealing temperature increases. The value of x of y changes from Therefore, the result reveals that N and H are and NH3

during annealing, and the components of the film are mainly ged to

(3)

B.

SiO

In the low temperature range (200 quite small and rise slightly; then, more than 1200 μs at 700 °C. However,

as the temperature further increases to 800 °C and above.

find the reasons for the decline, the corona charge test was performed on the films.

method. By applying a charge of opposite polarity to the charge Q

passivation is weakened, and the minority carrier lifetime is thus

charge provides a passivation effect that causes

rise, forming a complete corona charge curve as shown in Fig. 5.

The amount of charge applied at the lowest point of the curve is approximately regarded as the interface fixed charge Q the minimum effective minority carrier lifetime ( curv

is related to the interface state density D +1

Fig.

normalized with the height of the Si ratio of Si

(b); the dash line is only for guidance.

B. Surface passivation quality

The effective minority carrier lifetime

SiOx as a function of annealing temperature is shown in Fig. 4.

s the temperature further increases to 800 °C and above.

The corona charge method is a non

method. By applying a charge of opposite polarity to the charge Qf to the surface of the sample, the field effect passivation is weakened, and the minority carrier lifetime is thus lowered; as the charge is continuously applied, the excess charge provides a passivation effect that causes

ise, forming a complete corona charge curve as shown in Fig. 5.

The amount of charge applied at the lowest point of the curve is approximately regarded as the interface fixed charge Q the minimum effective minority carrier lifetime (

curve corresponds to the effect of chemical passivation, which is related to the interface state density D

Fig. 7 shows that the fixed charge density is approximately 1~2 × 10

Fig. 3. FTIR spectrum of films annealed at different temperatures are normalized with the height of the Si

ratio of Si-O and Si

(b); the dash line is only for guidance.

Surface passivation quality

as a function of annealing temperature is shown in Fig. 4.

The corona charge method is a non

method. By applying a charge of opposite polarity to the to the surface of the sample, the field effect passivation is weakened, and the minority carrier lifetime is

lowered; as the charge is continuously applied, the excess charge provides a passivation effect that causes

e corresponds to the effect of chemical passivation, which is related to the interface state density D

Fig. 7 shows that the fixed charge density is approximately , which is much higher than that in thermal

FTIR spectrum of films annealed at different temperatures are normalized with the height of the Si

O and Si-N peaks varying with annealing t (b); the dash line is only for guidance.

Surface passivation quality

as a function of annealing temperature is shown in Fig. 4.

In the low temperature range (200–500 °C), the value of quite small and rise slightly; then, τ increases significantly to more than 1200 μs at 700 °C. However, τ

find the reasons for the decline, the corona charge test was The corona charge method is a non-contact measurement method. By applying a charge of opposite polarity to the

to the surface of the sample, the field effect passivation is weakened, and the minority carrier lifetime is

lowered; as the charge is continuously applied, the excess charge provides a passivation effect that causes

e corresponds to the effect of chemical passivation, which is related to the interface state density Dit.

Fig. 7 shows that the fixed charge density is approximately , which is much higher than that in thermal

FTIR spectrum of films annealed at different temperatures are normalized with the height of the Si–N peak and are shown in (a); the height

N peaks varying with annealing t (b); the dash line is only for guidance.

The effective minority carrier lifetime τ for 280 nm as a function of annealing temperature is shown in Fig. 4.

500 °C), the value of increases significantly to

begins to decrease s the temperature further increases to 800 °C and above.

find the reasons for the decline, the corona charge test was contact measurement method. By applying a charge of opposite polarity to the

to the surface of the sample, the field effect passivation is weakened, and the minority carrier lifetime is

lowered; as the charge is continuously applied, the excess charge provides a passivation effect that causes τ to begin to ise, forming a complete corona charge curve as shown in Fig. 5.

The amount of charge applied at the lowest point of the curve is approximately regarded as the interface fixed charge Q the minimum effective minority carrier lifetime (min) of the

e corresponds to the effect of chemical passivation, which Fig. 7 shows that the fixed charge density is approximately , which is much higher than that in thermal

FTIR spectrum of films annealed at different temperatures are N peak and are shown in (a); the height N peaks varying with annealing temperature is shown in

for 280 nm as a function of annealing temperature is shown in Fig. 4.

500 °C), the value of τ is increases significantly to begins to decrease s the temperature further increases to 800 °C and above. To find the reasons for the decline, the corona charge test was contact measurement method. By applying a charge of opposite polarity to the fixed to the surface of the sample, the field effect passivation is weakened, and the minority carrier lifetime is lowered; as the charge is continuously applied, the excess to begin to ise, forming a complete corona charge curve as shown in Fig. 5.

The amount of charge applied at the lowest point of the curve is approximately regarded as the interface fixed charge Qf, and ) of the e corresponds to the effect of chemical passivation, which Fig. 7 shows that the fixed charge density is approximately , which is much higher than that in thermal

oxidation of SiO

gradually increases as the temperature

annealed at higher temperature has better field effect passivation. As for the

all the temperatures; so, the chemical passivation is very limited. The figure also shows that the relations

τ

temperature.

800

FTIR spectrum of films annealed at different temperatures are N peak and are shown in (a); the height emperature is shown in

Fig. 4.

annealing temperature; the dash line is only for guidance.

Fig 5.

700°C.

Fig 6. •

annealed at different temperatures; the dashed line is only for guidance.

oxidation of SiO2

annealed at higher temperature has better field effect passivation. As for the

all the temperatures; so, the chemical passivation is very limited. The figure also shows that the relations

and temperature is quite similar to that of temperature.

Therefore, it can

800–900 °C mainly because of the increase of

Fig. 4. The effective minority carrier lifetime of a 280 nm SiO annealing temperature; the dash line is only for guidance.

Fig 5. An example of the corona charge curve of 280 nm SiO 700°C.

Fig 6. •τmin and Qf for the 280 nm single

2 of +3 × 10

annealed at higher temperature has better field effect passivation. As for the τ , it is approximately 1/10 of all the temperatures; so, the chemical passivation is very limited. The figure also shows that the relations

and temperature is quite similar to that of

Therefore, it can be concluded that the decrease of 900 °C mainly because of the increase of

The effective minority carrier lifetime of a 280 nm SiO annealing temperature; the dash line is only for guidance.

An example of the corona charge curve of 280 nm SiO

for the 280 nm single

[16]. The charge density gradually increases as the temperature increases, so the film annealed at higher temperature has better field effect

it is approximately 1/10 of all the temperatures; so, the chemical passivation is very limited. The figure also shows that the relations

and temperature is quite similar to that of

be concluded that the decrease of 900 °C mainly because of the increase of

The effective minority carrier lifetime of a 280 nm SiO annealing temperature; the dash line is only for guidance.

An example of the corona charge curve of 280 nm SiO

for the 280 nm single-layer SiOx-passivated silicon wafer annealed at different temperatures; the dashed line is only for guidance.

The charge density increases, so the film annealed at higher temperature has better field effect

it is approximately 1/10 of τ all the temperatures; so, the chemical passivation is very limited. The figure also shows that the relationship between

and temperature is quite similar to that of τ

be concluded that the decrease of τ 900 °C mainly because of the increase of D . So we chose

The effective minority carrier lifetime of a 280 nm SiOx varies with annealing temperature; the dash line is only for guidance.

An example of the corona charge curve of 280 nm SiOx film annealed at

passivated silicon wafer annealed at different temperatures; the dashed line is only for guidance.

The charge density increases, so the film annealed at higher temperature has better field effect for all the temperatures; so, the chemical passivation is very hip between and

τ at . So we chose

varies with

film annealed at

passivated silicon wafer

(4)

the temperature of 700 °C as the annealing temperature for single SiO

of PHPS with N

ratio increases, the thickness of the film gradually decreases from 280 nm to less than 10 nm.

film thickness is plotted in Fig. 8. When the film is 15 nm,

increases quickly as the film thickness increases and reaches 1100

the upward trend of

280 nm. It has been pointed out that when the lower thickness of the PHPS is thermal

uniform, and cracks are likely to occur; this may be a cause of the serious decrease in the passivation effect

combining with other passivation layers, we prepared the stack layers of SiO

to the silicon surface and AlO

be noted that for the stack layer, after studying the effec annealing temperature of SiO

quality of SiO

optimized annealing temperature of SiO the stacks preparation, the annealing of SiO 450 °C. T

Fig. 7. The thickness of SiOx varies with dilution ratio after annealing at 700 °C for 15

Fig 8. Effective minority carrier lifetime as a function of single SiOx layer’s thickness after annealing at 700 °C for 15 min.

the temperature of 700 °C as the annealing temperature for single SiOx layer in the following study.

The relationship between film thickness and of PHPS with N

ratio increases, the thickness of the film gradually decreases from 280 nm to less than 10 nm.

film thickness is plotted in Fig. 8. When the film is 15 nm, τ is maintained at approximately 220

increases quickly as the film thickness increases and reaches 1100 μs at 80 nm. As the film thickness continuously increases, the upward trend of

280 nm. It has been pointed out that when the lower thickness of the PHPS is thermal

uniform, and cracks are likely to occur; this may be a cause of the serious decrease in the passivation effect

To investigate the passivation properties of the SiO combining with other passivation layers, we prepared the stack layers of SiOx/AlO

to the silicon surface and AlO

quality of SiO

optimized annealing temperature of SiO the stacks preparation, the annealing of SiO 450 °C. The SiO

Fig. 7. The thickness of SiOx varies with dilution ratio after annealing at 700 °C for 15 min.

the temperature of 700 °C as the annealing temperature for layer in the following study.

The relationship between film thickness and

of PHPS with N-butyl ether is shown in Fig. 7. As the dilution ratio increases, the thickness of the film gradually decreases from 280 nm to less than 10 nm.

film thickness is plotted in Fig. 8. When the film is is maintained at approximately 220

increases quickly as the film thickness increases and reaches at 80 nm. As the film thickness continuously increases, the upward trend of τ becomes slow and reaches 1250 280 nm. It has been pointed out that when the lower thickness of the PHPS is thermal-treated, the film formation is less uniform, and cracks are likely to occur; this may be a cause of the serious decrease in the passivation effect

To investigate the passivation properties of the SiO combining with other passivation layers, we prepared the stack

/AlOx:H and SiO to the silicon surface and AlO

quality of SiOx/AlOx:H and SiO optimized annealing temperature of SiO the stacks preparation, the annealing of SiO

he SiOx/AlOx:H stack was prepared with different

Fig. 7. The thickness of SiOx varies with dilution ratio after annealing at

the temperature of 700 °C as the annealing temperature for layer in the following study.

The relationship between film thickness and

butyl ether is shown in Fig. 7. As the dilution ratio increases, the thickness of the film gradually decreases from 280 nm to less than 10 nm. The τ

film thickness is plotted in Fig. 8. When the film is is maintained at approximately 220

increases quickly as the film thickness increases and reaches at 80 nm. As the film thickness continuously increases,

becomes slow and reaches 1250 280 nm. It has been pointed out that when the lower thickness

treated, the film formation is less uniform, and cracks are likely to occur; this may be a cause of the serious decrease in the passivation effect

:H and SiOx/SiNx:H, in which SiO

to the silicon surface and AlOx, SiNx is the cap layer. It should be noted that for the stack layer, after studying the effec annealing temperature of SiOx layer on the surface passivation

:H and SiOx/SiNx:H, we found the optimized annealing temperature of SiOx to be 450 °C. Then, in the stacks preparation, the annealing of SiO

:H stack was prepared with different

the temperature of 700 °C as the annealing temperature for The relationship between film thickness and dilution ratio butyl ether is shown in Fig. 7. As the dilution ratio increases, the thickness of the film gradually decreases as a function of the film thickness is plotted in Fig. 8. When the film is thinner than

is maintained at approximately 220 μs; then, increases quickly as the film thickness increases and reaches

at 80 nm. As the film thickness continuously increases, becomes slow and reaches 1250 280 nm. It has been pointed out that when the lower thickness

treated, the film formation is less uniform, and cracks are likely to occur; this may be a cause of the serious decrease in the passivation effect[17].

:H, in which SiOx is close is the cap layer. It should be noted that for the stack layer, after studying the effec

layer on the surface passivation :H, we found the to be 450 °C. Then, in the stacks preparation, the annealing of SiOx was conducted at :H stack was prepared with different

Fig 8. Effective minority carrier lifetime as a function of single SiOx layer’s

the temperature of 700 °C as the annealing temperature for dilution ratio butyl ether is shown in Fig. 7. As the dilution ratio increases, the thickness of the film gradually decreases as a function of the thinner than

; then, τ increases quickly as the film thickness increases and reaches

at 80 nm. As the film thickness continuously increases, becomes slow and reaches 1250 μs at 280 nm. It has been pointed out that when the lower thickness treated, the film formation is less uniform, and cracks are likely to occur; this may be a cause of

To investigate the passivation properties of the SiOx film combining with other passivation layers, we prepared the stack is close is the cap layer. It should be noted that for the stack layer, after studying the effect of layer on the surface passivation :H, we found the to be 450 °C. Then, in was conducted at :H stack was prepared with different

thicknesses of the SiO thicknesses of SiO

respectively. The result for SiO The function of effect

thickness is basically the same as that of single SiO evident that

wafers are higher than those for SiO

smaller thickness, the passivation effect is very limited, whether it is a SiO

stack; for example, the SiO

nm, and the stack layers have a poorer s effect compared with single AlO However, the

SiO

more than 2200 μs when the thickness of SiO

whereas the value is approximately 1 ms for single 80 nm SiO The interface fixed charge of the stack measured by a corona charge method is maintained at approximately 10

with single SiO

significantly lower, but the than that of the SiO

passivation is much stronger. As a result, the field effect passivation is relatively weaken

passivation in the stack.

the SiO the SiO

peaks at 2200 cm

shown here). This may indicate that the diffusion of hydrogen from AlO

on the surface of the substrate to eliminate such recombination centers. To investigate the distribution of H in

used a TOF nm)/AlO AlO

intensity of H

increase until at the surface of Si. As for the stack of SiO

than in AlO

closer to the substrate, even thoug

have disappeared after annealing at 450 °C, which means that the H in AlO

the surface of the Si substrate. This H saturates the dangling bonds to reduce

In other words, this confirms that the excellent passivation of the SiO

chemical passivation. This implies that higher concentration of H effusing from the AlO

especially at the SiO

concentrations provide better chemical passivation on silicon’s surface than that passivated by single SiO

However, combining the TOF of the SiO

that the effective effusion and storage H in SiO that the thickness of SiO

thickness has less influence when the it closes 100 nm or more.

It is interesting that when coating 80 nm SiO

and after annealing at 400 °C for 10 min, the minority carrier lifetime also increased from 750 μs for the AlO

Fig 8. Effective minority carrier lifetime as a function of single SiOx layer’s

thicknesses of the SiO thicknesses of SiO

respectively. The result for SiO The function of effect

thickness is basically the same as that of single SiO evident that eff values for SiO

wafers are higher than those for SiO

smaller thickness, the passivation effect is very limited, whether it is a SiO

stack; for example, the SiO

nm, and the stack layers have a poorer s effect compared with single AlO However, the τ

SiOx thickness is more than 50 nm; furthermore, it can reach more than 2200 μs when the thickness of SiO

whereas the value is approximately 1 ms for single 80 nm SiO The interface fixed charge of the stack measured by a corona charge method is maintained at approximately

when the SiO with single SiO

significantly lower, but the than that of the SiO

passivation is much stronger. As a result, the field effect passivation is relatively weaken

passivation in the stack.

the SiOx film and SiO

the SiOx film after annealing at 450 °C does not show obvious peaks at 2200 cm^-

shown here). This may indicate that the diffusion of hydrogen from AlOx films during annealing saturates the dangling bonds on the surface of the substrate to eliminate such recombination centers. To investigate the distribution of H in

used a TOF-SIMS test and got the spectrum of the SiO nm)/AlOx (15 nm) stack as shown in Fig. 10; a result of a 15nm AlOx film is used as reference. In the single AlO

intensity of H⁺ and SiH

increase until at the surface of Si. As for the stack of SiOx/AlOx:H, there are more H

than in AlOx layer, and an evident peak exists at the position closer to the substrate, even thoug

have disappeared after annealing at 450 °C, which means that the H in AlOx can diffuse into the SiO

the surface of the Si substrate. This H saturates the dangling bonds to reduce D

In other words, this confirms that the excellent passivation of the SiOx/AlOx:H stack was mainly due to the enhancement of chemical passivation. This implies that higher concentration of H effusing from the AlO

especially at the SiO

concentrations provide better chemical passivation on silicon’s surface than that passivated by single SiO

However, combining the TOF

of the SiOx/AlOx:H stack shown in Fig. 9, it could be concluded that the effective effusion and storage H in SiO

that the thickness of SiO

thickness has less influence when the it closes 100 nm or more.

s interesting that when coating 80 nm SiO

thicknesses of the SiOx film, whereas for SiO

thicknesses of SiOx and SiNx were fixed at 280 nm and 80 nm, respectively. The result for SiO

The function of effective minority carrier lifetime with SiO thickness is basically the same as that of single SiO

values for SiOx/AlO wafers are higher than those for SiO

smaller thickness, the passivation effect is very limited, whether it is a SiOx film (as shown in Fig. 8) or an SiO

stack; for example, the SiOx layer’s thickness is smaller than 50 nm, and the stack layers have a poorer s

effect compared with single AlO

of the stack layer exceeds that of AlO thickness is more than 50 nm; furthermore, it can reach more than 2200 μs when the thickness of SiO

when the SiOx thickness is above 80 nm. Compared with single SiOx layer, Qf

significantly lower, but the τ

than that of the SiOx film; this means that the chemical passivation is much stronger. As a result, the field effect passivation is relatively weaken

passivation in the stack. By comparing the FTIR spectrum of film and SiOx/AlOx:H stack, we find that the FTIR of film after annealing at 450 °C does not show obvious

-1 (Si–H), but the SiO

shown here). This may indicate that the diffusion of hydrogen films during annealing saturates the dangling bonds on the surface of the substrate to eliminate such recombination centers. To investigate the distribution of H in

SIMS test and got the spectrum of the SiO (15 nm) stack as shown in Fig. 10; a result of a 15nm film is used as reference. In the single AlO

and SiH⁺ remains at a low value and begins to increase until at the surface of Si. As for the stack of

:H, there are more H⁺

layer, and an evident peak exists at the position closer to the substrate, even thoug

have disappeared after annealing at 450 °C, which means that can diffuse into the SiO

the surface of the Si substrate. This H saturates the dangling D and achieve effective

In other words, this confirms that the excellent passivation of :H stack was mainly due to the enhancement of chemical passivation. This implies that higher concentration of H effusing from the AlOx layer can be stored i

especially at the SiOx/Si interface; these higher H concentrations provide better chemical passivation on silicon’s surface than that passivated by single SiO

However, combining the TOF-

:H stack shown in Fig. 9, it could be concluded that the effective effusion and storage H in SiO

that the thickness of SiOx is not less than 50 nm, and the thickness has less influence when the it closes 100 nm or more.

film, whereas for SiO

were fixed at 280 nm and 80 nm, respectively. The result for SiOx/AlOx:His shown in the Fig. 9.

ive minority carrier lifetime with SiO thickness is basically the same as that of single SiO

/AlOx:H stack

wafers are higher than those for SiOx; however, in the case of smaller thickness, the passivation effect is very limited,

film (as shown in Fig. 8) or an SiO

layer’s thickness is smaller than 50 nm, and the stack layers have a poorer surface passivation effect compared with single AlOx layer (

of the stack layer exceeds that of AlO thickness is more than 50 nm; furthermore, it can reach more than 2200 μs when the thickness of SiO

thickness is above 80 nm. Compared of the SiOx

of the stack is 10 times higher film; this means that the chemical passivation is much stronger. As a result, the field effect passivation is relatively weakened, but with higher chemical By comparing the FTIR spectrum of :H stack, we find that the FTIR of film after annealing at 450 °C does not show obvious

H), but the SiOx/AlOx

shown here). This may indicate that the diffusion of hydrogen films during annealing saturates the dangling bonds on the surface of the substrate to eliminate such recombination centers. To investigate the distribution of H in

SIMS test and got the spectrum of the SiO (15 nm) stack as shown in Fig. 10; a result of a 15nm film is used as reference. In the single AlO

remains at a low value and begins to increase until at the surface of Si. As for the stack of

+ or SiH⁺ bonds in the SiO layer, and an evident peak exists at the position closer to the substrate, even though the Si–

have disappeared after annealing at 450 °C, which means that can diffuse into the SiOx layer and accumulate at the surface of the Si substrate. This H saturates the dangling and achieve effective chemical passivation.

In other words, this confirms that the excellent passivation of :H stack was mainly due to the enhancement of chemical passivation. This implies that higher concentration of

layer can be stored i

/Si interface; these higher H concentrations provide better chemical passivation on silicon’s surface than that passivated by single SiOx

-SIMS results with the

:H stack shown in Fig. 9, it could be concluded that the effective effusion and storage H in SiO

is not less than 50 nm, and the thickness has less influence when the it closes 100 nm or more.

film, whereas for SiOx/SiNx:H, the were fixed at 280 nm and 80 nm, is shown in the Fig. 9.

ive minority carrier lifetime with SiO thickness is basically the same as that of single SiOx layer. It is

:H stack-passivated silicon

; however, in the case of smaller thickness, the passivation effect is very limited,

film (as shown in Fig. 8) or an SiOx/AlO layer’s thickness is smaller than 50

urface passivation layer (τ ≈ 750 of the stack layer exceeds that of AlOx as the thickness is more than 50 nm; furthermore, it can reach more than 2200 μs when the thickness of SiOx is 80 nm or more, whereas the value is approximately 1 ms for single 80 nm SiO The interface fixed charge of the stack measured by a corona charge method is maintained at approximately +

thickness is above 80 nm. Compared

x/AlOx:H stack is of the stack is 10 times higher film; this means that the chemical passivation is much stronger. As a result, the field effect ed, but with higher chemical By comparing the FTIR spectrum of :H stack, we find that the FTIR of film after annealing at 450 °C does not show obvious

x:H stack does (not shown here). This may indicate that the diffusion of hydrogen films during annealing saturates the dangling bonds on the surface of the substrate to eliminate such recombination centers. To investigate the distribution of H in the stack, we

SIMS test and got the spectrum of the SiOx

(15 nm) stack as shown in Fig. 10; a result of a 15nm film is used as reference. In the single AlOx film, the remains at a low value and begins to increase until at the surface of Si. As for the stack of bonds in the SiOx layer layer, and an evident peak exists at the position –H bonds in SiO have disappeared after annealing at 450 °C, which means that

layer and accumulate at the surface of the Si substrate. This H saturates the dangling chemical passivation.

In other words, this confirms that the excellent passivation of :H stack was mainly due to the enhancement of chemical passivation. This implies that higher concentration of layer can be stored in the SiOx layer, /Si interface; these higher H concentrations provide better chemical passivation on silicon’s

x and AlOx layers.

SIMS results with the τ result :H stack shown in Fig. 9, it could be concluded that the effective effusion and storage H in SiOx should require is not less than 50 nm, and the thickness has less influence when the it closes 100 nm or more.

s interesting that when coating 80 nm SiOx on 15 nm AlO and after annealing at 400 °C for 10 min, the minority carrier lifetime also increased from 750 μs for the AlOx layer to about :H, the were fixed at 280 nm and 80 nm, is shown in the Fig. 9.

ive minority carrier lifetime with SiOx

layer. It is passivated silicon

; however, in the case of smaller thickness, the passivation effect is very limited, /AlOx:H layer’s thickness is smaller than 50 urface passivation μs).

as the thickness is more than 50 nm; furthermore, it can reach more, whereas the value is approximately 1 ms for single 80 nm SiOx. The interface fixed charge of the stack measured by a corona +3 × thickness is above 80 nm. Compared

:H stack is of the stack is 10 times higher film; this means that the chemical passivation is much stronger. As a result, the field effect ed, but with higher chemical By comparing the FTIR spectrum of :H stack, we find that the FTIR of film after annealing at 450 °C does not show obvious :H stack does (not shown here). This may indicate that the diffusion of hydrogen films during annealing saturates the dangling bonds on the surface of the substrate to eliminate such recombination the stack, we

x (80 (15 nm) stack as shown in Fig. 10; a result of a 15nm film, the remains at a low value and begins to increase until at the surface of Si. As for the stack of layer layer, and an evident peak exists at the position H bonds in SiOx

have disappeared after annealing at 450 °C, which means that layer and accumulate at the surface of the Si substrate. This H saturates the dangling chemical passivation.

In other words, this confirms that the excellent passivation of :H stack was mainly due to the enhancement of chemical passivation. This implies that higher concentration of layer, /Si interface; these higher H concentrations provide better chemical passivation on silicon’s layers.

result :H stack shown in Fig. 9, it could be concluded should require is not less than 50 nm, and the thickness has less influence when the it closes 100 nm or more.

on 15 nm AlOx

and after annealing at 400 °C for 10 min, the minority carrier layer to about