CN100451162C - Method of chemical gas phase precipitation for growing carbon doped silicon germanium alloy buffer layer and germanium film - Google Patents

Abstract

The present invention relates to a chemical vapor deposition method for growing carbon, germanium and silicon alloy buffer layers, and growing germanium films. GeH4 and C2H4 are used as reaction gas sources at the temperature of 700 to 850 DEG C of a substrate, and the pressure intensity of a cavity is maintained within 10 to 100 Pa, wherein the C2H4 has the pressure component of 0.01 to 0.15 Pa, and the GeH4 has the pressure component of 0.10 to 1.10 Pa. The gas sources and a Si outwards diffused from the substrate carry out an extension reaction and are combined with Ge in an epitaxial layer to diffuse towards the substrate. Finally, a layer of Si <1-x> Ge <x> with a gradually varied Ge component grows on the surface of the substrate. The thickness of a C buffer layer is from 0.5 to 10 microns. A Ge film subsequently grows. The pressure intensity of the cavity is maintained within 15 to 100 Pa at the temperature of lower than 400 to 600 DEG C, and the GeH4 has the pressure component of 0.17 to 1.11 Pa. On the Si<1-x>Ge<x> with the gradually varied Ge component, a Ge film is outwards extended on the C buffer layer. Because of the existence of the buffer layer, a series of low mismatching limiting surfaces is formed on the Si substrate, and the degression of the dislocation density and the heat mismatching is realized. Thus, continuous strain relaxation is realized.

Description

Chemical vapor deposition growth carbon-doped silicon-germanium alloy buffer layer and growth germanium thin film method

1. Technical field

The invention relates to the preparation of a carbon-doped silicon-germanium alloy (Si _{1-x Gex} :C) buffer layer on a Si substrate with a gradually changing composition of germanium (Ge) by chemical vapor deposition (CVD), and then on the Si _{1- x} Ge _x : Method for epitaxial growth of single crystal Ge film on C buffer layer.

2. Background technology

As a first-generation semiconductor material, Ge has the advantage of high carrier mobility compared to Si; epitaxial growth of Ge and Si _1-x Ge _x alloys with high Ge composition on Si can be used for high cut-off frequency ( >100G Hz) Si _1-x Ge _x /Si heterojunction bipolar transistors and long-wavelength photodetectors and other new devices.

There is a 4.2% lattice mismatch and a 5.6% thermal mismatch between Ge and Si. The Ge thin film obtained directly on the Si substrate has high density of structural defects, poor single crystal and photoelectric properties, and low film thickness. Due to the disadvantages such as critical thickness, it is difficult to put into practical application. Therefore, epitaxial growth of buffer layer to reduce lattice mismatch and thermal mismatch is an effective way to obtain high-quality single crystal Ge thin films.

At present, the common buffer layer is Si _1-x Ge _x alloy buffer layer with Ge composition gradient. This method maintains a constant gradient rate of the Ge composition in the epitaxial film by continuously increasing the flow rate of the Ge source in the growth of multilayer Si _1-x Ge _x alloy, and then realizes high Ge composition Si _1-x Ge _x alloy film and single Epitaxy of Ge thin films. The existence of the buffer layer forms a series of low-mismatch interfaces on the Si substrate to realize the gradual reduction of dislocation density and thermal mismatch, thereby realizing continuous strain relaxation. However, this method has high requirements on the precise control of the flow rate of the reaction gas source, and the process is complicated and the cost is high.

In the present invention, we adopt the CVD method to react with the Si expanded from the Si substrate to the surface through the reaction gas source at a relatively high temperature, thereby forming a Si _1-x Ge _x :C alloy buffer with a gradually changing Ge composition. layer, followed by epitaxy on the buffer layer to obtain a single crystal Ge thin film with high crystal quality.

3. Contents of the invention

The purpose of the present invention is to grow Si _1-x Ge _x :C alloy thin film with Ge composition gradient on Si substrate by CVD method as a buffer layer, and then realize CVD epitaxial growth of single crystal Ge thin film with higher crystal quality.

The technical solution of the present invention is: at an appropriate reaction temperature, the reaction gas source reacts with the Si expanded outwardly of the substrate to form a Si _1-x Ge _x :C alloy with a gradual change in Ge composition, and use it as a buffer layer epitaxy Growth of Ge thin films. Specifically: at a substrate temperature of 700-850°C, using GeH ₄ as the Ge reaction gas source, CH ₄ , C ₂ H ₂ , C ₂ H ₄ , C ₂ H ₆ , C ₃ H ₆ or C ₃ H ₈ is the C reaction gas source; keep the chamber pressure at 10-100Pa, the partial pressure of C ₂ H ₄ is 0.01-0.15Pa, and the partial pressure of GeH ₄ is 0.10-1.10Pa. The Ge in the epitaxial layer diffuses to the substrate, and finally grows a layer of Si _1-x Ge _x :C buffer layer with a Ge composition gradient on the substrate surface, and the thickness of the buffer layer is 0.5-10 microns; then grows a Ge thin film; especially The method is to keep the chamber pressure at 15-100Pa at 400-600°C, and the partial pressure of GeH ₄ at 0.17-1.11Pa, and epitaxial Ge thin film on the Si _{1-xGex :} C buffer layer with Ge composition gradient.

The mechanism and characteristics of the present invention are: using CVD method to epitaxially grow high-quality single-crystal Ge thin film on Si substrate, and first using CVD method to prepare Si _1-x Ge _x : C alloy with gradually changing Ge composition as a buffer layer. The _buffer layer includes: Si ₁ -xGex:C epitaxial layer and Si _{1- xGex} :C _epitaxial layer and Si _{1- x} Ge _x : the Si _1-x Ge _x layer formed by the metal Ge atoms in the C epitaxial layer diffusing toward the substrate to fill the vacancies left by the diffusion of Si to the surface; the buffer layer is a Sil- The xGex:C buffer layer forms a series of low-mismatch interfaces on the Si substrate to realize the gradual reduction of dislocation density and thermal mismatch, thereby realizing continuous strain relaxation and greatly reducing the crystal defects in the epitaxial Ge thin film, It is possible to obtain high-quality single-crystal Ge thin films; doping a small amount of C (<10 ²⁰ at.cm ^-3 ) in Si _1-x Ge _x alloys can effectively suppress the diffusion of B atoms in Si _1-x Ge _x , so as to effectively improve the performance of the device; the doping of C can also adjust the strain between Si and Ge, realize strain relaxation, and improve the crystal quality of the buffer layer.

4. Description of drawings

Fig. 1 is a schematic diagram of the growth of Si _1-x Ge _x :C buffer layer with Ge composition gradient in the present invention,

Figure 1(a) shows the diffusion of metal Ge atoms in the Si _1-x Ge _x :C epitaxial layer towards the substrate,

Figure 1(b) shows the Si _1-x Ge _x layer formed under the CVD epitaxial Si _1-x Ge _x :C film,

Figure 1(c) shows a Si _1-x Ge _x :C buffer layer with a Ge composition gradient obtained on a Si substrate;

Fig. 2 is the Auger electron spectrum of Ge/Si _1-x Ge _x :C/Si sample of the present invention

Fig. 3 is the X-ray diffraction spectrum (XRD) of Ge/Si _1-x Ge _x of the present invention:C/Si sample

Fig. 4 is the Raman scattering spectrum of Ge/Si sample and Ge/Si _1-x Ge _x :C/Si sample of the present invention

5. Specific implementation

In Fig. 1, the growth process of the Si _{1-x Gex} :C buffer layer is described as follows: On the surface of the sample, Si reacts with the reaction gas source (GeH ₄ , C ₂ H ₄ ) to form Si _{1-x Gex} : C film, the higher growth temperature causes the Si atoms in the substrate to diffuse to the surface, thus maintaining the epitaxial growth of the Si _1-x Ge _x :C film on the sample surface (as shown in Figure 1(a)); at the same time, the Si The metal Ge atoms in the _1-x Ge _x : C epitaxial layer diffuse toward the substrate to fill the vacancies left by the diffusion of Si to the surface, thus forming Si under the CVD epitaxial Si _1-x Ge _x :C film _1-x Ge _x layer (as shown in Fig. 1(b)). As a result of the above growth process, a Si _1-x Ge _x : C buffer layer with a Ge composition gradient was obtained on the Si substrate (as shown in Figure 1(c)).

The invention adopts CVD method, germane (GeH ₄ ) is used as germanium source, ethylene (C ₂ H ₄ ) is used as carbon source, hydrogen is used as carrier gas, and Si (100) wafer is used as substrate.

The present invention scheme mainly comprises the following steps:

1. Before the growth, first clean the Si substrate, then use a diluted hydrofluoric acid solution (HF:H ₂ O = 1:10) to remove the natural oxide layer on the substrate surface, and finally dry the Si substrate with high-purity nitrogen, Put it into the CVD reaction chamber.

2. At a substrate temperature of 700-850°C, keep the cavity pressure at 10-100Pa, C ₂ H ₄ partial pressure 0.01-0.15Pa, GeH ₄ partial pressure 0.10-1.10Pa, GeH ₄ , C ₂ H ₄ and substrate The bottom-extended Si undergoes an epitaxial reaction, combines with Ge in the epitaxial layer to diffuse to the substrate, and finally grows a Si _1-x Ge _x :C buffer layer with a Ge composition gradient on the substrate surface. The thickness control of the buffer layer is determined by the growth time, generally 0.5-10 microns; the substrate temperature range of 700-850°C has no significant effect.

3. Keep the cavity pressure at 15-100Pa at 400-600°C, and the partial pressure of GeH ₄ at 0.17-1.11Pa, epitaxial Ge thin film on Si _1-x Ge _x :C buffer layer with Ge composition gradient, so as to obtain Ge/ Si _1-x Ge _x : C/Si structure.

Through the above method, the present invention has successfully obtained a single crystal Ge thin film with higher crystal quality, which is specifically characterized as follows:

Ge/Si _1-x Ge _x : The Auger electron spectrum of the C/Si sample (Fig. 2) shows the change trend of the atomic concentration of Ge, Si, and C in the film from the surface to the substrate, from which it can be seen that the Ge group A two-layer structure of a graded Si _1-x Ge _x :C buffer layer and epitaxial Ge film on it. The atomic concentration of Ge in the buffer layer is up to 90%, while the atomic concentration of Ge in the epitaxial Ge thin film is close to 100% (excluding the error caused by background noise in the measurement), and the thickness is about 60nm (obtained by sputtering rate and sputtering time ), far exceeding the critical thickness of direct epitaxial Ge films on Si.

Fig. 3 is the X-ray diffraction spectrum (XRD) of the Ge/Si _1-x Ge _x :C/Si sample. The diffraction peak at 2θ=65.9° corresponds to the Ge(400)Kα diffraction peak of the Ge epitaxial layer. Compared with other peaks originating from the epitaxial layer, the diffraction peak has a large intensity and a small half-maximum width (FWHM), indicating that the obtained The crystal orientation of the Ge thin film is relatively single, and the crystal quality is high. However, in the XRD spectrum of the Ge thin film sample (Ge/Si) epitaxy directly on the Si substrate, no characteristic diffraction peaks related to Ge were observed. The difference in the XRD results of the two samples indicates that the lattice mismatch between Ge and Si makes the crystal quality of the resulting epitaxial film poor when the Ge film is directly grown on Si with a thickness greater than the critical thickness, while the Si _{1 -x} Ge _x :C buffer layer and regrown Ge epitaxial layer can effectively improve the crystal quality of Ge thin film.

Fig. 4 shows the Raman scattering (Raman) measurement results of the Ge/Si sample and the Ge/Si _{1-x Gex} :C/Si sample. The Si-Si peak (520cm ^-1 , FWHM=5cm ^-1 ) from the substrate and the Ge-Ge peak (301cm ^-1 ) from the Ge epitaxial layer can both be observed, and the Ge-Ge peak intensity and There is a large difference in half-height width. Comparison found that: Ge/Si _1-x Ge _x :C/Si sample Ge-Ge peak intensity and half-width (FWHM=7cm ^-1 ) are equivalent to Si-Si peak; compared with Ge/Si sample The Ge-Ge peak intensity is very low, and the half-width (FWHM=19cm ^-1 ) is relatively large. This shows that the crystal quality of Ge thin films epitaxially obtained on Si _1-x Ge _x : C buffer layer is obviously better than that obtained directly on Si epitaxially. This is consistent with the XRD evaluation results of the crystal quality of epitaxial Ge thin films.

The Hall effect measurement was carried out on the Ge/Si _1-x Ge _x :C/Si sample at room temperature (300K), and the results showed that the conductivity type of the obtained Ge thin film was n-type, and the carrier concentration was 1.0×10 ¹⁹ cm At ^-3 , the Hall mobility μ=300 cm ² /V·s. This value is significantly higher than the electron mobility of the n-type bulk Si material at the same doping concentration, and is comparable to the electron mobility of the bulk Ge material at the same doping concentration. This indicates that the epitaxial Ge thin film material on the Si _1-x Ge _x : C buffer layer has ideal electrical transport properties.

The present invention adopts CVD method, by strictly controlling reaction temperature and reaction gas partial pressure, growing Si _1-x Ge _x : C alloy with Ge composition gradient on Si(100) substrate as a buffer layer, and then epitaxy on it to obtain Ge thin films with high crystal quality were obtained. The carbon source of the present invention has no special requirements, and CH ₄ , C ₂ H ₄ , C ₂ H ₆ and the like are all acceptable.

Claims (1)

1, chemical vapor deposition growth carbon doped silicon germanium alloy buffer layer and growth germanium film method, on the Si substrate with CVD method growth Si _1-xGe _x: the C buffer layer, the Ge film of growing then is characterized in that under 700～850 ℃ underlayer temperature, with GeH ₄For the Ge reactant gas source, with CH ₄, C ₂H ₂, C ₂H ₄, C ₂H ₆, C ₃H ₆Or C ₃H ₈Be the C reactant gas source; Keep chamber pressure 10～100Pa, dividing potential drop 0.01～the 0.15Pa of C reactant gas source, the extension reaction takes place in the dividing potential drop 0.10～1.10Pa of Ge reactant gas source, the Si that source of the gas and substrate extend out, spread final Si at substrate surface growth one deck Ge content gradually variational to substrate in conjunction with the Ge in the epitaxial film _1-xGe _x: C buffer layer, the thickness of buffer layer are 0.5～10 micron; Then the Ge film of growing; The condition of growth Ge film is: keep chamber pressure 15～100Pa, GeH down at 400～600 ℃ ₄Dividing potential drop 0.17～1.11Pa is at the Si of Ge content gradually variational _1-xGe _x: extension Ge film on the C buffer layer.

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