An efficient doping HFCVD device based on dual gas flows

Abstract

An efficient doping HFCVD device based on dual gas flows, comprising a reaction chamber and a gas introduction structure. The gas introduction structure includes four gas pipelines and upper and lower gas inlets. The first gas pipeline is for introducing reaction gas, and the second gas pipeline is for introducing carrier gas. The gases in the first and second gas pipelines are mixed and then introduced into the reaction chamber through the first gas inlet pipe and the upper gas inlet, and the upper gas inlet is located at the central position of the top of the reaction chamber. There is a hot wire between the upper gas inlet and the substrate stage. The third gas pipeline is for introducing doping gas, and the fourth gas pipeline is for introducing carrier gas. The gases in the two pipelines are mixed and then introduced into the reaction chamber through the second gas inlet pipe and the lower gas inlet. The lower gas inlet is located at the central position below the substrate stage and is in the shape of a horn. The orthographic projection planes of the upper and lower gas inlets and the substrate stage are concentric structures. The present invention effectively improves the utilization efficiency of doping gas in the growth of diamond films and realizes efficient doping in diamond film samples.

Description

Technical Field

[0001] The present invention relates to the field of hot filament chemical vapor deposition, and discloses a high-efficiency doping HFCVD device based on a dual-gas-flow technology. In particular, the device has a dual-gas-flow gas input structure. Background Art

[0002] Diamond has many advantages such as high hardness, high melting point, high insulation, wide bandgap, high thermal conductivity, good chemical stability, and resistance to acid and alkali corrosion, and has broad prospects in the fields of force, sound, light, electricity, magnetism, heat, and chemistry. At present, the performance of synthetic diamond films is already close to that of natural diamonds, and certain properties can be improved by doping with different elemental particles, and there are many applications in high-tech fields, such as cutting tools and wear-resistant materials, components such as p-n diodes and thermistors, high-power IGBT devices, high-voltage high-speed optoelectronic switches, aerospace materials, etc., and are increasingly attracting people's attention. The diamond films prepared by chemical vapor deposition (CVD) method have many excellent properties such as wide bandgap, high breakdown electric field, high resistivity, high electron mobility, high electron saturation rate, low dielectric constant, high thermal conductivity, strong hardness, low friction coefficient, and low thermal expansion coefficient, and are the most promising semiconductor materials and new coating materials. The hot filament chemical vapor deposition (HFCVD) method is a relatively mature method for synthesizing diamond coatings, and has many advantages such as low cost, simple operation, mature process, and fast film formation speed. It is easy to control the temperature and doping of the substrate, and it is easier to prepare diamond films with better quality.

[0003] At present, conventional HFCVD devices are mainly used in the manufacture of tools such as drill bits, blades, and abrasives to increase the mechanical properties of the tools, and there is no doping process. By directly depositing diamond coatings on the surface of tools through the HFCVD method, it can be deposited on tool substrates of any shape and applied to the processing of high-hardness materials. The quasi-isotropy of the polycrystalline characteristics of diamond films results in uniform wear of the die holes when making wire drawing dies, which is superior to the use performance of diamond single crystal wire drawing dies, and the current technology has been relatively mature.

[0004] When diamond films are applied in semiconductor materials and devices, their electrical properties should be improved. For example, boron-doped diamond (BDD) has more excellent uses, and its conductivity is improved by efficient boron doping. In the laboratory, the following problems exist when using conventional HFCVD devices to fabricate diamond films and BDD samples:

[0005] 1. The HFCVD device adopts a single air inlet design. The air inlet of the HFCVD device is far from the hot filament. The doping gas introduced from the air inlet moves everywhere in the reaction chamber along with the carrier gas, and the concentration diffused to the substrate position is relatively low, resulting in low doping efficiency and unable to achieve the effect of high-efficiency doping.

[0006] 2. To meet the high-efficiency doping requirements of diamond films, especially the high-efficiency boron doping requirements for increasing the conductivity of BDD (boron-doped diamond) films, the HFCVD equipment needs to introduce doping gases at a relatively high concentration, which will greatly increase the raw material cost. In addition, the commonly used doping gas diborane is highly toxic and has high chemical activity. It is extremely easy to react chemically with various inorganic and organic molecules and is extremely prone to spontaneous combustion and explosion when mixed with air. The waste gas generated during the preparation of diamond films will pollute and harm the environment, and the pollution treatment cost will also increase significantly. Summary of the Invention

[0007] The object of the present invention is to propose a method for realizing an efficient doping HFCVD equipment based on a dual-gas flow technology in view of the problems existing in the existing HFCVD equipment. The reaction chamber of this HFCVD equipment adopts the dual-gas flow technology, that is, the single upper gas inlet in the HFCVD equipment is upgraded to upper and lower dual gas inlets, and the reaction gas and the doping gas are independently introduced into the growth area from the upper and lower two gas inlets respectively. The key is to solve the problem of the gas inlet structure of the lower doping gas, reduce its influence on the distribution of the reaction gas, and at the same time can significantly increase the concentration of the doping gas above the substrate table, realize the high-efficiency doping of diamond films, and meet the actual requirements of high-efficiency doping in the application of various diamond films, especially BDD films. The schematic diagram of the equipment structure is as Figure 1 shown.

[0008] The technical solution of the present invention is: An efficient doping HFCVD equipment based on a dual-gas flow technology, including a reaction chamber and a gas introduction structure. The gas introduction structure includes four gas pipelines and upper and lower two gas inlets. The first gas pipeline introduces the reaction gas, and the second gas pipeline introduces the carrier gas. The gases in the first and second gas pipelines are mixed and then introduced into the reaction chamber from the first gas inlet through the upper gas inlet. The upper gas inlet is located at the center of the top of the reaction chamber. There is a hot wire between the upper gas inlet and the substrate table. The third gas pipeline introduces the doping gas, and the fourth gas pipeline introduces the carrier gas. The two gases are mixed and then introduced into the reaction chamber from the second gas inlet through the lower gas inlet 8. The second gas inlet pipe is connected to the lower gas inlet under the substrate table. The lower gas inlet is located at the center under the substrate table and has a horn shape. The orthographic projection surfaces of the upper and lower gas inlets and the substrate table are concentric structures;

[0009] The upper gas inlet is located at the center of the top of the reaction chamber, and the aperture of the upper gas inlet is controlled in the range of 1 cm to 2 cm to control the flow rate of the reaction gas on the substrate table within a suitable range.

[0010] There is a hot wire at a height position of 7 cm to 9 cm below the upper gas inlet, and the reaction gas can be evenly radiated onto the hot wire.

[0011] The hot wire is located above the substrate stage, and the height between the hot wire and the substrate stage is controlled within the range of 0.4 cm to 1.5 cm, so as to control the temperature on the surface of the substrate stage within a suitable range.

[0012] The lower air inlet is located at the center of the substrate stage and is shaped like a horn. The upper and lower air inlets and the substrate stage are concentric structures. The horizontal height difference between the mouth of the lower air inlet and the substrate stage is between -0.5 cm and -1 cm. The flare angle of the lower air inlet (the angle between the inclined wall of the lower air inlet and the vertical line) is within the range of 0° to 60°. The doped gas radiates from the center to the surroundings, realizing a relatively uniform distribution of the doped gas on the surface of the substrate stage, as shown in Figure 2.

[0013] The aperture of the lower air inlet is controlled within the range of 0.2 cm to 1 cm, avoiding excessive aperture that may cause gas divergence, realizing a uniform distribution of the doped gas on the substrate stage, and at the same time avoiding affecting the growth gas.

[0014] The inlet pipe is connected to the lower air inlet at the lower part of the substrate stage, and the inlet pipe can be made of stainless steel or molybdenum metal.

[0015] Advantageous effects: When preparing diamond, especially boron-doped diamond thin films, the present invention requires a higher concentration of doped gas to be introduced for HFCVD. The concentration ratio of the BH3 group in the dual-gas-flow technology HFCVD equipment is significantly increased compared with that in the conventional HFCVD equipment, reaching 5 to 10 times. Figure 5a 、 Figure 5b In comparison, the concentration of the CH3 group in the dual-gas-flow technology HFCVD equipment is not much different from that in the conventional HFCVD equipment. The present invention can greatly reduce the raw material cost and has high production efficiency, overcoming the deficiencies of the existing technology in producing BDD (boron-doped diamond) thin films, and has obvious and unexpected effects compared with HFCVD in producing ordinary diamond thin films and boron-doped diamond thin films. Description of the Drawings

[0016] Figure 1 It is a schematic diagram of the reaction chamber and gas introduction structure of the dual-gas-flow technology HFCVD equipment of the present invention;

[0017] Figure 2a It is a schematic cross-sectional view of the lower air inlet of the dual-gas-flow technology HFCVD equipment of the present invention;

[0018] Figure 2b It is a schematic top view of the lower air inlet of the dual-gas-flow technology HFCVD equipment of the present invention;

[0019] Figure 3a It is a concentration distribution diagram of the BH3 group of the dual-gas-flow technology HFCVD equipment of the present invention;

[0020] Figure 3bIt is the concentration distribution diagram of CH3 groups of the dual-gas-flow technology HFCVD equipment of the present invention;

[0021] Figure 4 It is a schematic diagram of the reaction chamber and gas inlet structure of the conventional HFCVD equipment in the comparative example;

[0022] Figure 5a It is a comparison diagram of the BH3 group concentration distribution between the dual-gas-flow technology HFCVD equipment and the conventional HFCVD equipment in the example.

[0023] Figure 5b It is a comparison diagram of the CH3 group concentration distribution between the dual-gas-flow technology HFCVD equipment and the conventional HFCVD equipment in the example. Specific embodiments

[0024] To further elaborate on the technical means of the present invention, the following combines the drawings and examples to detail the specific embodiments of the present invention. The specific embodiments described herein are only used to illustrate and explain the technical solutions of the present invention and are not used to limit the present invention.

[0025] In the present invention, the reaction chamber of the dual-gas-flow technology HFCVD equipment adopts a cylindrical structure. As Figure 1 shown, the reaction chamber adopts the dual-gas-flow technology, that is, the single upper gas inlet in HFCVD is upgraded to upper and lower double gas inlets. The reaction gas and doping gas are independently introduced into the growth area from the upper and lower gas inlets respectively. The key is to solve the gas inlet structure problem of the doping gas at the lower gas inlet, reduce its influence on the distribution of the reaction gas, and at the same time can significantly increase the doping gas concentration above the substrate table to achieve efficient doping of diamond films.

[0026] Figure 1 Shown: It includes a reaction chamber and a gas inlet structure. The gas inlet structure includes four gas pipelines, two gas inlets and a first inlet pipe. The first gas pipeline introduces the reaction gas, and the second gas pipeline introduces the carrier gas. The gases in the first and second gas pipelines are mixed and then introduced into the reaction chamber through the first inlet pipe and the upper gas inlet. The upper gas inlet is located at the center of the top of the reaction chamber; there is a hot wire between the upper gas inlet and the substrate table; the third gas pipeline introduces the doping gas, and the fourth gas pipeline introduces the carrier gas. The two gases are mixed and then introduced into the reaction chamber through the second inlet pipe and the lower gas inlet 8. The second inlet pipe is connected to the lower gas inlet under the substrate table. The lower gas inlet is located at the center under the substrate table and has a horn shape. The orthographic projection surfaces of the upper and lower gas inlets and the substrate table are concentric structures; the upper gas inlet 4 is connected to the first gas pipeline 2 and the second gas pipeline 3. The aperture of the upper gas inlet is controlled within the range of 1 cm to 2 cm to control the flow rate of the reaction gas on the substrate table within a suitable range.

[0027] The intake pipe 7 is connected to the third gas pipeline 5 and the fourth gas pipeline 6. The intake pipe is connected to the lower intake port at the lower part of the substrate stage. The intake pipe can be made of stainless steel or molybdenum metal. The total flow rate of the doped mixed gas introduced into the intake pipe ranges from several SCCM to dozens of SCCM. Substrate stage 9. A hot wire 10 is arranged at a height position of 7 cm to 9 cm below the upper intake port (mouth part).

[0028] The gases in the first and second gas pipelines are mixed and then introduced into the reaction chamber through the first intake pipe and the upper intake port. The upper intake port is located at the center of the top of the reaction chamber; the first and second gas pipelines are perpendicular to the first intake pipe, that is, the upper intake port. According to experiments, the angle between the first and second gas pipelines and the first intake pipe is preferably about 90 degrees, especially 90 degrees ± 20 degrees, which will make the mixing of methane and hydrogen in the second gas pipeline more uniform. The third gas pipeline introduces a doped gas, and the fourth gas pipeline introduces a carrier gas. The two gases are mixed and then introduced into the reaction chamber through the second intake pipe and the lower intake port 8; the angle between the third and fourth gas pipelines and the second intake pipe is about 90 degrees (as shown in the figure). However, the angle between the third and fourth gas pipelines and the second intake pipe can be 90 degrees ± 45 degrees.

[0029] Embodiment:

[0030] A small hole is opened in the lower center of the substrate stage 9, and the upper part is made into a trumpet shape as the lower intake port 8. The upper and lower intake ports of the lower intake port and the substrate stage are concentric structures. The upper mouth of the lower intake port does not need special treatment. The flare angle of the lower intake port (the angle between the inclined wall of the lower intake port and the vertical line) ranges from 0 degrees to 60 degrees. The doped gas radiates from the center to the surroundings, realizing a relatively uniform distribution of the doped gas on the surface of the substrate stage. As shown in Figure 2.

[0031] The lower intake port is located at the center of the substrate stage and is shaped like a trumpet. The upper and lower mouths of the lower intake port and the substrate stage are concentric structures. The horizontal height difference between the lower intake port and the substrate stage is between -0.5 cm and -1 cm (the negative sign means lower than the horizontal line of the substrate stage). The flare angle of the lower intake port (the angle between the inclined wall of the lower intake port and the vertical line) ranges from 0 degrees to 60 degrees, and it is better between 30 - 50 degrees. The doped gas radiates from the center to the surroundings, realizing a relatively uniform distribution of the doped gas on the surface of the substrate stage.

[0032] The aperture of the lower intake port of the above-mentioned lower intake port is controlled within the range of 0.2 cm to 1 cm, avoiding excessive aperture resulting in gas divergence, realizing a uniform distribution of the doped gas on the substrate stage, and at the same time avoiding affecting the growth gas.

[0033] The upper air inlet 4 is connected to the first gas pipeline 2 and the second gas pipeline 3. The aperture diameter of the upper air inlet is controlled within the range of 1 cm to 2 cm to control the flow rate of the reaction gas on the substrate table within a suitable range.

[0034] The inlet pipe 7 is connected to the third gas pipeline 5 and the fourth gas pipeline 6. The inlet pipe is connected to the lower air inlet at the lower part of the substrate table. The inlet pipe can be made of stainless steel or molybdenum metal. The total flow rate of the doped mixed gas introduced into the inlet pipe is within the range of several SCCM to dozens of SCCM. Substrate table 9.

[0035] A hot wire 10 is arranged at a height position 7 cm to 9 cm below the upper air inlet to ensure that the reaction gas is evenly radiated onto the hot wire.

[0036] The hot wire is above the substrate table. The height position between the hot wire and the substrate table is controlled within the range of 0.4 cm to 1.5 cm to control the temperature on the surface of the substrate table within a suitable range.

[0037] Methane is introduced into the first gas pipeline, and hydrogen is introduced into the second gas pipeline. After the two gases are mixed, the reaction mixed gas is introduced into the reaction chamber 1 through the upper air inlet. Among them, the hydrogen flow rate is generally controlled between several hundred SCCM and several thousand SCCM, and the methane flow rate is generally controlled between several SCCM and dozens of SCCM. The methane concentration ratio in the reaction mixed gas is controlled between 1% and 10%.

[0038] After the reaction mixed gas enters the reaction chamber, it diffuses towards the substrate table under the action of gravity and air flow, and decomposes under the high temperature of the hot wire to form carbon groups required for diamond film growth.

[0039] Diborane is introduced into the third gas pipeline, and hydrogen is introduced into the fourth gas pipeline. After the two gases are mixed, they are introduced into the reaction chamber through the inlet pipe and the lower air inlet. Among them, the hydrogen flow rate is controlled between several SCCM and dozens of SCCM, and the diborane concentration ratio is controlled between dozens of ppm and tens of thousands of ppm.

[0040] The total flow rate of the doped mixed gas is controlled within dozens of SCCM so that the gas diffuses around at a sufficient flow rate, resulting in better doping uniformity and having little impact on the reaction gas.

[0041] To verify the effect of the dual-gas-flow technology HFCVD equipment of the present invention, through simulation modeling, the height of the reaction chamber is set to 22 cm, the diameter of the reaction chamber is 22 cm, the diameter of the substrate table is 20 cm, the aperture of the upper gas inlet is 2 cm, the horizontal height difference between the lower opening of the lower gas inlet and the substrate table is -0.5 cm, the flare angle of the lower gas inlet is 30 degrees, the aperture of the lower opening of the lower gas inlet is 0.6 cm, the hot wire is located 8 cm below the lower gas inlet, the vertical height from the hot wire to the substrate table is 1.5 cm, the temperature of the hot wire is 2773 K, the temperature of the substrate table is 1173 K, the pressure in the reaction chamber is 4 kPa, the methane flow rate at the upper gas inlet is 20 sccm, the hydrogen flow rate is 500 sccm, the diborane flow rate in the lower gas inlet is 0.1 sccm, and the hydrogen flow rate is 9.9 sccm.

[0042] In the simulation, the specific indicators for measuring the growth rate and doping rate are the concentrations of -CH3 groups and -BH3 groups on the substrate table. Generally, the higher the concentration of -CH3 groups, the faster the growth rate of the diamond film, and the higher the concentration of -BH3 groups, the higher the doping concentration of the diamond film.

[0043] The simulation results are as Figure 3a 、 Figure 3b shown. The concentration distributions of -CH3 groups and -BH3 groups are relatively uniform in the range of 2.5 cm to 9.5 cm from the center on the surface of the substrate table.

[0044] Comparative example:

[0045] The comparative example is a conventional single-gas-inlet HFCVD equipment, and its reaction chamber 1 and gas introduction structure are as Figure 4 shown.

[0046] The single gas inlet 4 is connected to the first gas pipeline 2, the second gas pipeline 3, and the third gas pipeline 5. The aperture of the upper gas inlet is controlled in the range of 1 cm to 2 cm to control the flow rate of the reaction gas on the substrate table 9 within a suitable range.

[0047] One (or more) hot wires 10 are arranged at a height position of 7 cm to 9 cm below the single gas inlet to ensure that the reaction gas is evenly radiated onto the hot wires.

[0048] The hot wire is above the substrate table, and the height position between the hot wire and the substrate table is controlled in the range of 0.4 cm to 1.5 cm to control the temperature on the surface of the substrate table within a suitable range.

[0049] Methane is introduced into the first gas pipeline, hydrogen is introduced into the second gas pipeline, and diborane is introduced into the third gas pipeline. The three gases are mixed and then introduced into the reaction chamber through the single gas inlet.

[0050] The hydrogen flow rate in the mixed gas is generally controlled between several hundred sccm and several thousand sccm, while the methane flow rate is generally controlled between several sccm and several tens of sccm, and the concentration ratio of diborane is controlled between several tens of ppm and several tens of thousands of ppm. The methane concentration ratio in the reaction mixed gas is controlled between 1% and 10%.

[0051] After the mixed gas enters the reaction chamber, it diffuses towards the substrate table under the action of gravity and gas flow, and decomposes under the high temperature of the hot wire to form the carbon groups required for diamond film growth and the boron groups required for doping.

[0052] To verify the improvement effect of the dual-gas-flow technology HFCVD equipment of the present invention on high-efficiency boron doping, through simulation modeling and several implementation benchmarks, the -CH3 groups and -BH3 groups of the dual-gas-flow technology HFCVD equipment and the conventional HFCVD equipment are compared.

[0053] Set the reaction chamber height to 22 cm, the reaction chamber diameter to 22 cm, the substrate table diameter to 20 cm, the single inlet aperture to 2 cm, the hot wire is located 8 cm below the lower inlet, the vertical height from the substrate table is 1.5 cm, the hot wire temperature is 2773 K, the substrate table hot wire temperature is 1173 K, the reaction chamber pressure is 4 kPa, the methane flow rate of the single inlet is 20 sccm, the hydrogen flow rate is 500 sccm, and the diborane flow rate is 0.1 sccm.

[0054] According to the simulation results, the concentration distributions of the -CH3 groups and -BH3 groups of the dual-gas-flow technology HFCVD equipment and the conventional HFCVD equipment are relatively uniform in the range of 2.5 cm to 9.5 cm from the center on the surface of the substrate table. As Figure 5a shown, the concentration ratio of the -BH3 groups of the dual-gas-flow technology HFCVD equipment is significantly increased compared with that of the -BH3 groups of the conventional HFCVD equipment, reaching 5 to 10 times. As Figure 5b shown, the concentration of the -CH3 groups of the dual-gas-flow technology HFCVD equipment is not much different from that of the -CH3 groups of the conventional HFCVD equipment.

[0055] Through the simulation analysis of the examples and comparative examples, it shows that the present invention can be applied to the sample preparation of high-efficiency doping of diamond films. Compared with the single-gas-flow technology, the utilization efficiency of the doping gas is increased by 5 to 10 times, and high-efficiency doping in diamond film samples can be achieved. The inventor of the present invention carried out the dual-gas-flow technology transformation on the existing HFCVD equipment in the laboratory. After many experiments, it was proved that the HFCVD equipment with dual-gas-flow technology increased the boron doping concentration of diamond films by more than 5 times.

[0056] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An efficient doping HFCVD device based on dual gas flows, characterized in that, It includes a reaction chamber and a gas inlet structure. The gas inlet structure includes four gas pipelines and upper and lower gas inlets. The first gas pipeline is for introducing reaction gas, and the second gas pipeline is for introducing carrier gas. The gases in the first and second gas pipelines are mixed and then introduced into the reaction chamber through the first inlet pipe and the upper gas inlet. The upper gas inlet is located at the center of the top of the reaction chamber. There is a heating wire between the upper gas inlet and the substrate stage. The third gas pipeline is for introducing doping gas, and the fourth gas pipeline is for introducing carrier gas. The gases in these two pipelines are mixed and then introduced into the reaction chamber through the second inlet pipe and the lower gas inlet. The second inlet pipe is connected to the lower gas inlet below the substrate stage. The lower gas inlet is located at the center below the substrate stage and is in a horn shape. The orthographic projection surfaces of the upper and lower gas inlets and the substrate stage are concentric structures. The upper gas inlet is located at the center of the top of the reaction chamber, and the aperture of the upper gas inlet is controlled within the range of 1 cm to 2 cm, so as to control the flow rate of the reaction gas on the substrate stage within a suitable range. A heating wire is provided at a height position of 7 cm to 9 cm below the upper gas inlet, and the reaction gas can be evenly radiated onto the heating wire. The heating wire is located above the substrate stage, and the height between the heating wire and the substrate stage is controlled within the range of 0.4 cm to 1.5 cm, so as to control the temperature on the surface of the substrate stage within a suitable range.

2. The high-efficiency doping HFCVD device based on dual airflows according to claim 1, wherein The lower gas inlet is located at the center of the substrate stage and is in a horn shape. The upper and lower gas inlets and the substrate stage are concentric structures. The horizontal height difference between the lower gas inlet and the substrate stage is between -0.5 cm and -1 cm. The flare angle of the lower gas inlet, that is, the angle between the inclined wall of the lower gas inlet and the vertical line, is within the range of 0° to 60°. The doping gas radiates from the center to the surroundings, achieving a relatively uniform distribution of the doping gas on the surface of the substrate stage.

3. The high-efficiency doping HFCVD device based on dual gas flows according to claim 1, characterized in that, The aperture of the lower gas inlet is controlled within the range of 0.2 cm to 1 cm, avoiding excessive divergence of the gas caused by too large an aperture, achieving a uniform distribution of the doping gas on the substrate stage, and at the same time avoiding affecting the growth gas.

4. The high-efficiency doping HFCVD device based on dual gas flows according to claim 1, wherein, The inlet pipe is connected to the lower gas inlet below the substrate stage, and the inlet pipe is made of stainless steel or molybdenum metal.

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