Crystallinity Investigation of Compositionally Graded SiGe ... · e-mail: [email protected]...

The 5th International Symposium on Advanced Science and Technology of Silicon Materials (JSPS Si Symposium, Abstracts), Nov. 10-14, 2008, Kona, Hawaii, USA

Sample-ASample-B

Strained Si layerThickness

(nm)

9.39.3

Maximum Geconcentration

at top SiGe step(%)

13.914.1

Graded SiGelayer thickness

(nm)

77453757

Grading Ratein SiGe layer(Ge% μm–1)

1.83.7

Sample-ASample-B


(nm)

9.39.3


at top SiGe step(%)

13.914.1


(nm)

77453757


1.83.7

Table I. Construction of s-Si wafers evaluated by SIMS.

Sample-ASample-B


(nm)

9.39.3


at top SiGe step(%)

13.914.1


(nm)

77453757


1.83.7

Sample-ASample-B


(nm)

9.39.3


at top SiGe step(%)

13.914.1


(nm)

77453757


1.83.7

Table I. Construction of s-Si wafers evaluated by SIMS.

Crystallinity Investigation of Compositionally Graded SiGe Layers by Synchrotron X-ray Cross-Sectional Diffraction Takeshi Senda1, 2, Koji Izunome1, Yoshiyuki Tsusaka2, Kazunori Fukuda2, Kazuki Hayashi2, Maiko Abe2, Sayuri Takahata2, Hidekazu Takano2, Yasushi Kagoshima2, and Junji Matsui2

1 Covalent Materials Corporation, 6-861-5 Higashi-ko, Niigata 957-0197, Japan 2 Graduate School of Material Science, University of Hyogo, 3-2-1 Koto, Kamigori, Hyogo 678-1297, Japan

e-mail: [email protected] [email protected] [email protected]

[email protected] [email protected] [email protected]

Abstract

We have investigated the crystallinity of compositionally graded SiGe layers of strained Si wafers (s-Si) in the

growth direction by irradiating a synchrotron X-ray microbeam with a high parallelism on a cross section of s-Si

wafers. As a result, we can confirm the presence of surface parallel SiGe lattice rotation and lattice rotation

distribution (LRD). The surface parallel LRD and relaxation ratio of SiGe start to decrease in the depth direction

below approximately 3 μm from the wafer surface. It is inferred that the insufficient relaxation of SiGe near the

wafer surface is caused by the characteristics of the free wafer surface. Furthermore, such characteristics are thought

to lead to a reduction in LRD near the wafer surface.

1. Introduction

Many researchers have studied the crystallinity of epitaxially grown SiGe layers. Moreover, it is reported that SiGe

layers have a large lattice tilt variation distribution (LTVD), and s-Si 2-6) grown on SiGe layers also inherits this

LTVD. 7) However, the crystallinity aggravation mechanism of the micron order in the growth direction for

compositionally graded SiGe layers has not yet been elucidated. In this study, we have investigated the crystallinity

of compositionally graded SiGe layers of s-Si wafers in the growth direction by irradiating a synchrotron X-ray

microbeam with a high parallelism on a cross section of the s-Si wafers.

2. Experiment

2.1 Sample preparation

SiGe and s-Si epitaxy was carried out in a commercial

single-wafer chemical vapor deposition (CVD) epitaxial

reactor at a low pressure (15 Torr). A p-type single

Si(001) crystal substrate with a diameter of 200 mm was used. Initially, the Si substrate was ramped and maintained

at 1000 ºC to remove Si native oxides and carbon from the substrate surface. Subsequently, SiGe and Si were

successively deposited on the Si substrate. The source gases employed for Ge and Si were GeH4 and SiH4,

respectively, with H2 as the carrier gas. The compositionally graded SiGe layers have a stepwise structure that

facilitates the investigation of the crystallinity of each SiGe step in the growth direction. The growth temperature of

the SiGe layers was 900 ºC, and the Ge concentration varied from 0% on the Si substrate to 14% at the top SiGe

layer. Next, s-Si layers with a thickness of approximately 9 nm were deposited on the SiGe layers at 750 ºC. The Ge


concentration depth profiles for the s-Si wafers were evaluated by secondary ion mass spectroscopy (SIMS). Table 1

and Fig. 1 show, respectively, the details of the SiGe structure and the Ge concentration depth profiles of the s-Si

wafers obtained by SIMS. Two samples—Sample-A and

Sample-B—with different grading rates in the SiGe layers were

prepared. The average Ge concentrations at the top SiGe steps

of Sample-A and Sample-B obtained by SIMS were 13.9% and

14.1%, respectively. On the other hand, the grading rates in the

SiGe layer of Sample-A and Sample-B were 1.8 and 3.7 Ge%

μm–1, respectively.

2.2 Incident X-ray optics

The synchrotron X-ray microbeam was constructed in hatch

C2 of BL24XU in SPring-8. 8) The experimental arrangement

of the microbeam optics is schematically illustrated in Fig. 2. 9)

The synchrotron radiation generated by a figure-8 undulator

was monochromatized to 15 keV using a Si double crystal

monochromator of the horizontal dispersion type with 111

symmetric reflections. The X-ray microbeam was primarily

focused in the vertical direction on the sample surface using an

Rh-coated bent cylindrical mirror for analyzing each step of the

compositionally graded SiGe layers more precisely. As a result,

the beam size was 3.9 μm (H) × 0.8 μm (V), and the angular

divergence in the horizontal direction was 2.2 arcsec on the

specimen.

2.3 Measurement procedure

First, in order to determine the thickness of the SiGe layer, we acquired contour maps of the 440 reflection

intensity distribution from a set of -scans (rocking curves) at each position in the vertical direction (Z). Next, by

putting the analyzer crystal behind the specimen, as shown in Fig. 2, we confirmed the center depth of each SiGe

step by the Z-scan. Here, we define the center depth of each SiGe step determined by the Z -scan as the depth of each

SiGe step. The 2 - scan of 440 reflections was successively performed at the depth of each SiGe step. The lattice

constants of the SiGe layers were determined by the above-mentioned 2 peak positions of each SiGe step. The

relaxation ratio of each SiGe step was calculated by lattice constants of the fully relaxed SiGe obtained from

Vegard’s law and the average Ge concentration of each SiGe step obtained by SIMS. The rocking curve of the 440

reflection using the analyzer crystal was obtained for the depth of each SiGe step. The central positions of the

rocking curve peaks revealed a SiGe lattice rotation angle (LRA) parallel to the Si substrate surface. On the other

hand, the width of the rocking curve peaks revealed a SiGe lattice rotation distribution (LRD) showing the

distribution range of lattice orientation parallel to the Si substrate surface. In this study, we define the parallel and

vertical directions for the Si substrate surface as “surface parallel” and “surface normal,” respectively. Moreover, the

full width at half maximum (FWHM) of each rocking curve fitted by a Gaussian function is also defined as an LRD.

Fig. 2. Setup of optical system producing a highly parallel X-ray microbeam.

Double CrystalMonochromator

15 keVChannel-Cut Crystals

Si (111)

Four-Quadrant Slit100 (H) 20 (V) μm2

Analyzer Crystal

Bent Cylindrical Mirror

Scintillation Counter

Sample Stage

2

Z



Si (111)


Analyzer Crystal



Sample Stage

2

Z

Fig. 2. Setup of optical system producing a highly parallel X-ray microbeam.



Si (111)


Analyzer Crystal



Sample Stage

2

Z



Si (111)


Analyzer Crystal



Sample Stage

2

Z

Fig. 1. Ge concentration depth profiles for SiGe layers as function of distance from wafer surface determined by SIMS. The grading rates of Sample-A and Sample-B are 1.8 and 3.7 Ge% μm–1, respectively.

0

5

10

15

20

0 1 2 3 4 5 6 7 8 9 10 Distance from Wafer Surface ( m)

Ge

Con

cent

ratio

n (A

t.%)

Sample-B

Sample-A

Top SiGe step

Graded SiGe layer

Wafer Surface

Fig. 1. Ge concentration depth profiles for SiGe layers as function of distance from wafer surface determined by SIMS. The grading rates of Sample-A and Sample-B are 1.8 and 3.7 Ge% μm–1, respectively.

0

5

10

15

20

0 1 2 3 4 5 6 7 8 9 10 Distance from Wafer Surface ( m)

Ge

Con

cent

ratio

n (A

t.%)

Sample-B

Sample-A

Top SiGe step

Graded SiGe layer

Wafer Surface


Fig. 4. Results of 2 - scan for 440 reflections obtained by putting analyzer crystal behind specimen: (a) Sample-A and (b) Sample-B. Each profile was obtained at the depth of a SiGe step.

0.959 0.960 0.961 0.962 0.963 0.964 0.965 0.966101

102

103

104

105Si-sub. 8.5 7.5 6.9 5.6 4.7 3.7 2.6 1.6 0.6

Inte

nsity

(cps

)

Lattice Constant (440)

0.959 0.960 0.961 0.962 0.963 0.964 0.965 0.966101

102

103

104

105Si-sub. 5.5 5.0 4.5 4.1 3.6 3.1 2.0 0.6

Inte

nsity

(cps

)


(a) (b)depth (μm)

0.959 0.960 0.961 0.962 0.963 0.964 0.965 0.966101

102

103

104

105Si-sub. 8.5 7.5 6.9 5.6 4.7 3.7 2.6 1.6 0.6

Inte

nsity

(cps

)


0.959 0.960 0.961 0.962 0.963 0.964 0.965 0.966101

102

103

104

105Si-sub. 5.5 5.0 4.5 4.1 3.6 3.1 2.0 0.6

Inte

nsity

(cps

)


(a) (b)

0.959 0.960 0.961 0.962 0.963 0.964 0.965 0.966101

102

103

104

105Si-sub. 8.5 7.5 6.9 5.6 4.7 3.7 2.6 1.6 0.6

Inte

nsity

(cps

)


0.959 0.960 0.961 0.962 0.963 0.964 0.965 0.966101

102

103

104

105Si-sub. 5.5 5.0 4.5 4.1 3.6 3.1 2.0 0.6

Inte

nsity

(cps

)


(a) (b)depth (μm)

Fig. 4. Results of 2 - scan for 440 reflections obtained by putting analyzer crystal behind specimen: (a) Sample-A and (b) Sample-B. Each profile was obtained at the depth of a SiGe step.

0.959 0.960 0.961 0.962 0.963 0.964 0.965 0.966101

102

103

104

105Si-sub. 8.5 7.5 6.9 5.6 4.7 3.7 2.6 1.6 0.6

Inte

nsity

(cps

)


0.959 0.960 0.961 0.962 0.963 0.964 0.965 0.966101

102

103

104

105Si-sub. 5.5 5.0 4.5 4.1 3.6 3.1 2.0 0.6

Inte

nsity

(cps

)


(a) (b)depth (μm)

0.959 0.960 0.961 0.962 0.963 0.964 0.965 0.966101

102

103

104

105Si-sub. 8.5 7.5 6.9 5.6 4.7 3.7 2.6 1.6 0.6

Inte

nsity

(cps

)


0.959 0.960 0.961 0.962 0.963 0.964 0.965 0.966101

102

103

104

105Si-sub. 5.5 5.0 4.5 4.1 3.6 3.1 2.0 0.6

Inte

nsity

(cps

)


(a) (b)

0.959 0.960 0.961 0.962 0.963 0.964 0.965 0.966101

102

103

104

105Si-sub. 8.5 7.5 6.9 5.6 4.7 3.7 2.6 1.6 0.6

Inte

nsity

(cps

)


0.959 0.960 0.961 0.962 0.963 0.964 0.965 0.966101

102

103

104

105Si-sub. 5.5 5.0 4.5 4.1 3.6 3.1 2.0 0.6

Inte

nsity

(cps

)


(a) (b)depth (μm)

Fig. 5. Rocking curve results of 440 reflections obtained by putting analyzer crystal behind specimen: (a) Sample-A and (b) Sample-B. The numbers shown indicate the depth of each SiGe step in μm.

-200 -100 0 100 200

5000

10000

15000

Si sub.

depth

5.55.04.5

3.63.1

4.1

0.62.0

Inte

nsity

(cps

)

Lattice Rotation Distribution (arcsec)-200 -100 0 100 200

5000

10000

15000

20000

Si sub.

Inte

nsity

(cps

)

Lattice Rotation Distribution (arcsec)7.56.95.64.73.72.61.6

depth

(a) (b)

-200 -100 0 100 200

5000

10000

15000

Si sub.

depth

5.55.04.5

3.63.1

4.1

0.62.0

Inte

nsity

(cps

)


5000

10000

15000

20000

Si sub.

Inte

nsity

(cps

)


depth

(a) (b)

Fig. 5. Rocking curve results of 440 reflections obtained by putting analyzer crystal behind specimen: (a) Sample-A and (b) Sample-B. The numbers shown indicate the depth of each SiGe step in μm.

-200 -100 0 100 200

5000

10000

15000

Si sub.

depth

5.55.04.5

3.63.1

4.1

0.62.0

Inte

nsity

(cps

)


5000

10000

15000

20000

Si sub.

Inte

nsity

(cps

)


depth

(a) (b)

-200 -100 0 100 200

5000

10000

15000

Si sub.

depth

5.55.04.5

3.63.1

4.1

0.62.0

Inte

nsity

(cps

)


5000

10000

15000

20000

Si sub.

Inte

nsity

(cps

)


depth

(a) (b)

3. Results and Discussion

Figures 3(a) and 3(b) show the contour maps of

the 440 reflection intensity distributions of

Sample-A and Sample-B, respectively. For both

Sample-A and Sample-B, we can confirm that the

peak position of the SiGe layers shifts to the

low-angle side as the Ge concentration in the SiGe

layers increases. Figure 4 shows the results of the

2 - scan of 440 reflection obtained by putting the

analyzer crystal behind the specimen. The vertical

and horizontal axes represent the intensity

detected by a scintillation counter and the (440)

lattice constant equivalent to 2 positions,

respectively. Each profile in the figure was

obtained at the depth of each SiGe step; the depths

are indicated in μm. Figure 5 shows the rocking

curve results of 440 reflection obtained by putting

the analyzer crystal behind the specimen. The

numbers shown in Fig. 5 indicate the depth in

μm of each SiGe step. For both Sample-A and

Sample-B, we can confirm that there are

differences in the peak positions of the rocking

curve between the SiGe layers and the Si

substrate.

Figure 6 shows the LRDs and relaxation ratios

for the SiGe (440) lattice constant as a function of

the distance from the wafer surface. The two sets

of these values shown in Fig. 6 are obtained from

Figs. 4 and 5. The LRDs of Sample-A and

Sample-B increase to approximately 100 and 140

arcsec, respectively, as the SiGe layers are

deposited on the Si substrates. These LRD values

are significantly larger than the value of 2 arcsec

for the Si substrate used in this study. However, as can be observed in Fig. 6, the LRDs and relaxation ratios of

Sample-A and Sample-B start to decrease in the depth direction from approximately 3 μm to the wafer surface.

Particularly in Sample-B, the decreases in the ratio of LRD and relaxation ratio are large, and we can confirm the

peak of LRD and relaxation ratio at a depth of about 4 μm.

Figure 7 shows the Ge concentration depth profiles evaluated by SIMS and cross-sectional transmission electron

microscopy (TEM) images of the SiGe layers. As can be observed from the TEM images of Sample-A and Sample-B

Fig. 3. Contour maps of 440 reflection intensity distribution of (a) Sample-A and (b) Sample-B obtained from set of -scans at each position in vertical direction.

-700 -600 -500 -400 -300 -200 -100 0-20

-15

-10

-5

0

(arcsec)

Z (

m)

1.0E0

4.5E0

2.0E1

8.9E1

4.0E2

1.8E3

8.0E3

-700 -600 -500 -400 -300 -200 -100 0-20

-15

-10

-5

0

(arcsec)

Z (

m)

1.0E0

4.5E0

2.0E1

8.9E1

4.0E2

1.8E3

8.0E3

SiG

eL

ayer

Si su

b.

Inte

nsity

(cps

)

(arcsec) (arcsec)

(b)(a)

-700 -600 -500 -400 -300 -200 -100 0-20

-15

-10

-5

0

(arcsec)

Z (

m)

1.0E0

4.5E0

2.0E1

8.9E1

4.0E2

1.8E3

8.0E3

-700 -600 -500 -400 -300 -200 -100 0-20

-15

-10

-5

0

(arcsec)

Z (

m)

1.0E0

4.5E0

2.0E1

8.9E1

4.0E2

1.8E3

8.0E3

SiG

eL

ayer

Si su

b.

Inte

nsity

(cps

)

(arcsec) (arcsec)-700 -600 -500 -400 -300 -200 -100 0

-20

-15

-10

-5

0

(arcsec)

Z (

m)

1.0E0

4.5E0

2.0E1

8.9E1

4.0E2

1.8E3

8.0E3

-700 -600 -500 -400 -300 -200 -100 0-20

-15

-10

-5

0

(arcsec)

Z (

m)

1.0E0

4.5E0

2.0E1

8.9E1

4.0E2

1.8E3

8.0E3

SiG

eL

ayer

Si su

b.

Inte

nsity

(cps

)

(arcsec) (arcsec)

(b)(a)

Fig. 3. Contour maps of 440 reflection intensity distribution of (a) Sample-A and (b) Sample-B obtained from set of -scans at each position in vertical direction.

-700 -600 -500 -400 -300 -200 -100 0-20

-15

-10

-5

0

(arcsec)

Z (

m)

1.0E0

4.5E0

2.0E1

8.9E1

4.0E2

1.8E3

8.0E3

-700 -600 -500 -400 -300 -200 -100 0-20

-15

-10

-5

0

(arcsec)

Z (

m)

1.0E0

4.5E0

2.0E1

8.9E1

4.0E2

1.8E3

8.0E3

SiG

eL

ayer

Si su

b.

Inte

nsity

(cps

)

(arcsec) (arcsec)

(b)(a)

-700 -600 -500 -400 -300 -200 -100 0-20

-15

-10

-5

0

(arcsec)

Z (

m)

1.0E0

4.5E0

2.0E1

8.9E1

4.0E2

1.8E3

8.0E3

-700 -600 -500 -400 -300 -200 -100 0-20

-15

-10

-5

0

(arcsec)

Z (

m)

1.0E0

4.5E0

2.0E1

8.9E1

4.0E2

1.8E3

8.0E3

SiG

eL

ayer

Si su

b.

Inte

nsity

(cps

)

(arcsec) (arcsec)-700 -600 -500 -400 -300 -200 -100 0

-20

-15

-10

-5

0

(arcsec)

Z (

m)

1.0E0

4.5E0

2.0E1

8.9E1

4.0E2

1.8E3

8.0E3

-700 -600 -500 -400 -300 -200 -100 0-20

-15

-10

-5

0

(arcsec)

Z (

m)

1.0E0

4.5E0

2.0E1

8.9E1

4.0E2

1.8E3

8.0E3

SiG

eL

ayer

Si su

b.

Inte

nsity

(cps

)

(arcsec) (arcsec)

(b)(a)

Fig. 6. Dependence on distance from wafer surface for (a) SiGe LRD and (b) relaxation ratios of SiGe lattice constant (440).

80

90

100

0 5 10 15Depth from Wafer Surface (μm)

Rel

axat

ion

Rat

io o

f SiG

e L

ayer

(%)

SiGe

Sample-ASample-B

SiGe0

50

100

150


Lat

tice

Rot

atio

n D

istr

ibut

ion

(arc

sec)

SiGe

Sample-ASample-B

SiGe

(a) (b)

80

90

100


Rel

axat

ion

Rat

io o

f SiG

e L

ayer

(%)

SiGe

Sample-ASample-B

SiGe0

50

100

150


Lat

tice

Rot

atio

n D

istr

ibut

ion

(arc

sec)

SiGe

Sample-ASample-B

SiGe

(a) (b)

Fig. 6. Dependence on distance from wafer surface for (a) SiGe LRD and (b) relaxation ratios of SiGe lattice constant (440).

80

90

100


Rel

axat

ion

Rat

io o

f SiG

e L

ayer

(%)

SiGe

Sample-ASample-B

SiGe0

50

100

150


Lat

tice

Rot

atio

n D

istr

ibut

ion

(arc

sec)

SiGe

Sample-ASample-B

SiGe

(a) (b)

80

90

100


Rel

axat

ion

Rat

io o

f SiG

e L

ayer

(%)

SiGe

Sample-ASample-B

SiGe0

50

100

150


Lat

tice

Rot

atio

n D

istr

ibut

ion

(arc

sec)

SiGe

Sample-ASample-B

SiGe

(a) (b)


shown in Fig. 7, the misfit dislocation densities at

the interface of each SiGe step remain nearly

constant as the SiGe layers are deposited from the Si

substrate to a depth of about 1 μm. However, these

dislocations are hardly observed at the interface

between the top and second SiGe steps for Sample-A

and Sample-B. This result represents a decrease in

SiGe relaxation ratio at the top SiGe step and is in

good agreement with the results of relaxation ratios

obtained by X-ray diffraction.

When a top SiGe step with a large Ge concentration is deposited on the second SiGe step with a smaller Ge

concentration, the surface strain of the top SiGe step is released at the wafer surface since there is no significant

stress on the wafer surface. Moreover, the top SiGe step with an insufficient relaxation ratio gives compressive stress

to the second SiGe step resulting in a decrease in relaxation ratio. We assume that this phenomenon of decrease in

relaxation ratio continues from the wafer surface to certain depths. Therefore, it appears that the decrease in the

relaxation ratio of the SiGe layer near the wafer surface is attributable to this free surface property. In practice, the

s-Si layers with a thickness of about 9 nm exist on the top SiGe steps; however, we assume that the s-Si layers have

little effect on the relaxation of top SiGe steps because the s-Si layers thickness are hardly smaller than the top SiGe

step thicknesses of about 1 μm. On the other hand, the reason LRD decreases near the wafer surface may be

explained as follows. SiGe steps with an insufficient relaxation ratio near the surface give rise to a compressive

stress in the lower SiGe steps, and it appears that this compressive stress plays a role in decreasing SiGe LRD.

Moreover, we assume that the effect of top SiGe compressive stress is easily transmitted in the depth direction in

Sample-B with a smaller thickness of about 0.5 μm than Sample-A with a thickness of about 1.0 μm. Therefore, the

larger decrease in ratio is confirmed in Sample-B.

Figure 8 shows the surface parallel SiGe LRAs, which indicate the peak position of the SiGe rocking curve with

respect to that of the Si substrate in the reciprocal lattice space. For both Sample-A and Sample-B, we can confirm

that the absolute values of surface parallel SiGe LRA slightly increase as the SiGe layers are deposited on the Si

substrates. However, the values tend to decrease

near the surface of the s-Si wafers. This result

implies that the surface parallel crystal orientation of

SiGe rotates around that of the Si substrate and

tends to be almost equal to that near the wafer

surface. We assume that the lattice rotations are

caused by the changes in LRD and relaxation ratio

because the peaks of lattice rotation are nearly

identical to that of LRD and relaxation ratio,

particularly in Sample-B. The change in the LRA of

SiGe near the wafer surface is small in Sample-B.

Because the relaxation of the top SiGe step is

Fig. 7. (a) Ge concentration depth profiles for SiGe layers as function of distance from wafer surface determined by SIMS. Cross-sectional TEM images of SiGelayers of (b) Sample-B and (c) Sample-A.

0 5 10 15 20

01

23

45

67

89

10 D

istance from W

afer Surface (m

)

Ge Concentration (atomic%)

Sample-B

Sample-A

(b) TEM (Sample-B) (c) TEM (Sample-A)(a) SIMS

Top SiGe Step

0 5 10 15 20

01

23

45

67

89

10 D

istance from W

afer Surface (m

)


Sample-B

Sample-A


Top SiGe Step

Fig. 7. (a) Ge concentration depth profiles for SiGe layers as function of distance from wafer surface determined by SIMS. Cross-sectional TEM images of SiGelayers of (b) Sample-B and (c) Sample-A.

0 5 10 15 20

01

23

45

67

89

10 D

istance from W

afer Surface (m

)


Sample-B

Sample-A


Top SiGe Step

0 5 10 15 20

01

23

45

67

89

10 D

istance from W

afer Surface (m

)


Sample-B

Sample-A


Top SiGe Step

Fig. 8 Surface parallel SiGe LRA, which indicates peak position of SiGe rocking curve relative to that of Si substrate crystal orientation in reciprocal lattice space, as function of distance from wafer surface.

-25-20-15-10-505

10152025

0 2 4 6 8 10Distance from wafer surface (μm)

Lat

tice

Rot

atio

n A

ngle

(arc

sec)

Si sub.

SiGe

Sample-ASample-B

SiGe

Fig. 8 Surface parallel SiGe LRA, which indicates peak position of SiGe rocking curve relative to that of Si substrate crystal orientation in reciprocal lattice space, as function of distance from wafer surface.

-25-20-15-10-505

10152025

0 2 4 6 8 10Distance from wafer surface (μm)

Lat

tice

Rot

atio

n A

ngle

(arc

sec)

Si sub.

SiGe

Sample-ASample-B

SiGe


insufficient, it is thought that the top SiGe step grows along the crystal orientation direction of the lower SiGe step in

an almost pseudomorphic state.

4. Conclusions

We have investigated the crystallinity of compositionally graded SiGe layers of s-Si in the growth direction by

irradiating a synchrotron X-ray microbeam with a high parallelism on a cross section of s-Si wafers. As a result, we

can confirm the presence of surface parallel SiGe lattice rotation and LRD similar to the surface normal SiGe LTVD,

as reported previously. The surface parallel LRD and relaxation ratio of SiGe start to decrease in the depth direction

below approximately 3 μm from the wafer surface. On the other hand, the absolute values of surface parallel SiGe

LRA slightly increase as the SiGe layers are deposited on the Si substrates. However, the values tend to decrease

near the surface of the s-Si wafers. This result implies that the surface parallel crystal orientation of SiGe rotates

around that of the Si substrate and tends to be equal to that near the wafer surface. It is estimated that the insufficient

relaxation of SiGe near the wafer surface is caused by the characteristics of the free wafer surface. Furthermore, such

characteristics are thought to lead to a reduction in LRDs near the wafer surface.

Acknowledgements

We express our appreciation to Mr. Shinichi Mitani and coworkers of NuFlare Technology Inc. for cooperation in

the s-Si epitaxial growth in their machine “HT3000.” This work was performed at SPring-8 with the approval of the

Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. C03B24XU-5043N).

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