Method for epitaxial growth of silicon-based germanium with low dislocation densityTechnical Field
The invention belongs to the technical field of semiconductor material preparation, and relates to an epitaxial growth method of a silicon-based germanium material with low dislocation density.
Background
Germanium (Ge) and silicon (Si) belong to the same IV group semiconductor material, the electron mobility and the hole mobility of Ge are respectively 2 times and 4 times of those of Si, the forbidden bandwidth of Ge is smaller than that of Si, the forbidden bandwidth is about 0.67eV at room temperature, and the Ge has greater potential in the aspects of reducing the power supply voltage and reducing the power consumption in equal proportion; more importantly, the Ge device process is compatible with the standard Si process, so that the Ge material becomes one of important alternative materials for preparing high-performance MOS devices in the future. In addition, Ge has better photoelectric properties than Si, for example, Ge has high absorption coefficient in a communication waveband of 1.3-1.5 um, and can be used for manufacturing an infrared photoelectric detector; the difference between the direct band bottom and the indirect band bottom of Ge is very small, only about 136meV, and the Ge is a collimating band gap material and is expected to become a gain medium of a light-emitting device based on energy band modification engineering; the lattice mismatch degree of Ge and GaAs is only 0.07%, so Ge can also be used as a transition layer for epitaxially growing III-V semiconductor materials on a Si substrate. Silicon-based Ge materials are one of the most important silicon-based heteroepitaxial materials in recent years. However, the biggest challenge in epitaxially growing Ge materials on Si substrates is the large lattice mismatch between Si and Ge, which easily causes high surface roughness and high dislocation density. The rough surface increases the process difficulty of device manufacturing; high dislocation density will increase device leakage current and reduce device performance. Therefore, reducing surface roughness and reducing dislocation density are key to the epitaxial growth of high quality Si-based Ge materials.
Disclosure of Invention
The invention aims to provide a method for epitaxially growing silicon-based germanium with low dislocation density, which has the beneficial effect that a pure Ge layer with the thickness of about 1.5 mu m is epitaxially grown on a Si (100) substrate by adopting a two-step method of low-temperature growth and high-temperature annealing. The structure of the compound is characterized by X-ray double-crystal diffraction, a scanning electron microscope and an atomic force microscope. The test result shows that under the optimized conditions, the full width at half maximum of the X-ray double-crystal diffraction curve of the epitaxial Ge is 283arc sec, the surface root mean square roughness is 0.57nm (the scanning range is 5 mu m multiplied by 5 mu m), and the dislocation density obtained by the chemical etching dislocation pit method is about 8.25 multiplied by 106cm-2(20. mu. m.times.20 μm). The grown Si-based Ge material has good crystallization quality and can be applied to Si-based photoelectronic devices. The epitaxial growth method used by the invention has the advantages of low production cost, good controllability, continuous production, easy industrial production and the like.
The invention adopts the technical scheme that a reduced pressure chemical vapor deposition system is utilized for epitaxial growth, a growth gas source comprises high-purity digermane and hydrogen, a P-type Si substrate is cleaned by a standard semiconductor silicon wafer cleaning process (standard RCA process) and then is conveyed into a vacuum sample feeding chamber, when the growth is started, a silicon wafer is conveyed into a growth chamber again, the substrate is slowly heated and kept in the hydrogen for a period of time, pollutants such as oxygen atoms and the like on the silicon wafer are removed to form a clean growth surface, and the growth can be started by reducing the temperature of the substrate to a proper value after the oxygen is removed.
Further, the growth process is that a germanium layer is grown firstly, and then the temperature is raised to carry out high-temperature annealing in a hydrogen atmosphere.
Further, a 150mmP type Si substrate with the resistivity of 4-10 omega cm is adopted, the substrate is transferred into a vacuum sample chamber after standard RCA cleaning, when the silicon wafer starts to grow, the silicon wafer is transferred into a growth chamber again, the substrate is slowly heated to 1000 ℃ and kept in hydrogen for 2 minutes, pollutants such as oxygen atoms on the silicon wafer are removed to form a clean growth surface, and the vacuum is kept at 10 ℃ in the process4Pa。
Further, the growth process is to grow germanium layer at 400 deg.c and then to raise the temperature to 650 deg.c or 850 deg.c at a temperature raising rate of 6.5 deg.c/min for high temperature annealing in hydrogen atmosphere.
Drawings
FIG. 1 is an SEM image of a sample;
FIG. 2 shows the dislocation density of the sample at 1.38X 107cm-2;
FIG. 3 shows the dislocation density of the sample at 1.25X 107cm-2;
FIG. 4 shows the dislocation density of the sample at 8.25X 106cm-2;
FIG. 5 is an X-ray bimorph diffraction rocking curve of a sample;
FIG. 6 is an AFM surface topography of a sample with a surface roughness RMS of 2.50nm for a scan range of 5 μm by 5 μm;
FIG. 7 is an AFM surface topography map of the sample with a surface roughness RMS of 0.57nm for a scan range of 5 μm by 5 μm;
AFM surface topography for the sample of FIG. 8, surface roughness RMS was 0.46nm for a scan range of 5 μm.
Detailed Description
The present invention will be described in detail with reference to the following embodiments.
The silicon-based germanium material of the present invention is epitaxially grown using a Reduced Pressure Chemical Vapor Deposition (RPCVD) system. The growth gas source is high-purity digermane (Ge)2H6) And hydrogen (H)2). Cleaning a 150mm P-type Si (100) substrate (with resistivity of 4-10 omega cm) by a standard semiconductor silicon wafer cleaning process (standard RCA process), transferring into a vacuum sample chamber, transferring the silicon wafer into a growth chamber, slowly heating the substrate to 1000 deg.C, maintaining in hydrogen (H) gas2) Maintaining for 2 min to remove contaminants such as oxygen atoms from the wafer and form a clean growth surface, and maintaining the vacuum at 10 deg.C4Pa. After deoxidation, the growth can be started by lowering the substrate temperature to a suitable value. The growth process is as follows: a germanium layer is grown at 400 c and then a high temperature anneal in a hydrogen atmosphere is performed by raising the temperature to 650 c or 850 c at a ramp rate of about 6.5 c/min. Table 1 shows the silicon-based germanium material growth and annealing conditions.
TABLE 1
FIG. 1 is an SEM image of a sample; FIG. 2 shows the dislocation density of sample No. 1, 1.38X 107cm-2(ii) a FIG. 3 shows the dislocation density ofsample 2# 1.25X 107cm-2(ii) a FIG. 4 shows the dislocation density of sample No. 3, 8.25X 106cm-2(ii) a FIG. 5 is an X-ray bimorph diffraction rocking curve of the sample. FIG. 5 is an X-ray bimorph diffraction rocking curve of a sample; FIG. 6 is an AFM surface topography of a sample with a surface roughness RMS of 2.50nm for a scan range of 5 μm by 5 μm; FIG. 7 is an AFM surface topography map of the sample with a surface roughness RMS of 0.57nm for a scan range of 5 μm by 5 μm; AFM surface topography for the sample of FIG. 8, surface roughness RMS was 0.46nm for a scan range of 5 μm.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not intended to limit the present invention in any way, and all simple modifications, equivalent variations and modifications made to the above embodiments according to the technical spirit of the present invention are within the scope of the present invention.