A method for lateral growth of single crystal diamond

Abstract

The application discloses a single-crystal diamond transverse expansion method, which comprises the following steps: firstly, performing growth pretreatment on a single-crystal diamond seed crystal; then, setting a groove in the center of a molybdenum support obtained, wherein the depth of the groove is 0.3mm≤d≤1mm, the width of the groove is 1mm≤w≤2.5mm, the distance between the edge of the groove and the edge of the single-crystal diamond seed crystal is 1mm≤s≤5mm, and the thickness of the diamond seed crystal is h d . H d H +1mm, wherein 0.3mm≤d≤1mm, 1mm≤w≤2.5mm, 1mm≤s≤5mm, and h H h ≤2.5mm, h is the thickness of the diamond seed crystal, H is the thickness of the diamond seed crystal after transverse expansion, the distance between the edge of the groove and the edge of the single-crystal diamond seed crystal is 1mm-5mm; finally, single-crystal diamond growth is performed by using an MPCVD method, so that the single-crystal diamond transverse expansion is realized. The method effectively inhibits polycrystal growth at the edge of the single-crystal diamond and realizes stable transverse expansion.​​​

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of single crystal diamond CVD growth, and particularly relates to a single crystal diamond lateral growth method. BACKGROUND

[0002] As an ultra-wide bandgap semiconductor material, diamond has the advantages of large bandgap, high carrier mobility, large carrier saturation drift speed, large critical breakdown field strength, high thermal conductivity, etc., and is very suitable for preparing high-frequency, high-power, high-temperature-resistant and radiation-resistant electronic devices and deep ultraviolet band optoelectronic devices, and has wide application prospects in new energy, 6G communication, space science and other fields. Therefore, diamond, which has multiple excellent performances, is considered as an ideal next-generation power device material, and has great application prospects in electric vehicles, photovoltaics, military and other fields.

[0003] In order to realize the industrial application of diamond, the efficient and low-cost preparation technology of high-quality and large-area single crystal substrates is still a challenge for the commercial application of diamond materials and devices.

[0004] The CVD method for growing single crystal diamond usually takes single crystal diamond as a substrate. In the growth process, in addition to the growth of the upper surface to thicken the diamond, the growth of the side surface can also expand the size of the diamond. However, due to process control problems, the diamond edge tends to grow polycrystalline during the growth process. In addition to limiting the lateral growth of diamond, polycrystalline will also produce defects and stress in the diamond, reducing the quality of the original diamond.

[0005] The patent document with the publication number CN107059120A discloses a method for inhibiting polycrystalline diamond growth at the edge of diamond by using a square slot inlaid type substrate holder, which comprises the following steps: first, a substrate holder is made, two concentric square slots are opened in the central position of the surface of the substrate holder; the surface of the substrate holder and the slots are polished; ultrasonic cleaning is performed with anhydrous ethanol, and then plasma cleaning is performed; the single crystal diamond substrate is ultrasonically cleaned with acetone, placed in the slot of the substrate holder, and then loaded into a growth device; the substrate is plasma cleaned in the device; then methane is added, and single crystal diamond growth is performed. The technical route of the application is to use graphite deposition between the substrate and the substrate, and the side edge of the substrate is in contact with the substrate holder, which increases the cooling effect of the edge of the substrate, thereby optimizing the overall temperature uniformity of the single crystal diamond substrate, and greatly avoiding polycrystalline growth at the edge of the substrate. Although the application avoids polycrystalline growth at the edge of the substrate, it does not disclose how to realize lateral growth of single crystal diamond.

[0006] The patent document with the publication number CN119287501A discloses a large-area single crystal diamond expansion method. The application realizes the iterative growth of a single crystal diamond substrate by continuously replacing a molybdenum table with a larger recessed area in the middle, thereby obtaining a large-area single crystal diamond substrate suitable for use in the semiconductor field. After each growth of the single crystal diamond substrate, a thin slice is cut along the maximum expansion surface in the transverse direction, as many single crystal diamonds grown in the transverse direction as possible are retained, and the waste of materials is reduced. The application realizes the growth of a single crystal diamond through multiple iterations. Although the application realizes the expansion of a large-area single crystal diamond, it relies on traditional multiple post-cutting to suppress polycrystal growth, which is low in efficiency.

[0007] Therefore, finding a convenient method that not only suppresses the growth of edge polycrystals during the growth of a single crystal diamond but also realizes the lateral expansion of a single crystal diamond is still the key research direction for preparing a large-area single crystal diamond substrate suitable for use in the semiconductor field. SUMMARY

[0008] In view of the deficiencies of the prior art, the application provides a single crystal diamond lateral expansion method, which not only suppresses the growth of edge polycrystals during the growth of a single crystal diamond but also realizes the lateral expansion of a single crystal diamond.

[0009] The single crystal diamond lateral expansion method provided by the application comprises the following steps:

[0010] (1) Pre-treating a single crystal diamond seed crystal;

[0011] (2) Setting a recess in the center of a molybdenum support, the depth of the recess is d for: H ≤ d ≤ H +1mm, wherein 0.3mm≤ H - h ≤2.5mm, h is the thickness of the diamond seed crystal, H is the thickness of the diamond seed crystal after lateral expansion, the distance between the edge of the recess and the edge of the single crystal diamond seed crystal is 1mm-5mm;

[0012] (3) Using the MPCVD method to grow a single crystal diamond to realize the lateral expansion of a single crystal diamond.

[0013] Compared with the conventional recess design of a molybdenum support, the application cooperatively regulates the recess depth and the edge distance, optimizes the relative position relationship between the single crystal diamond seed crystal and the recess, ensures the more uniform distribution of plasma in the single crystal diamond growth zone, suppresses the heat and temperature aggregation at the edges and corners, thereby suppressing the polycrystal growth at the edges of the diamond and realizing efficient lateral expansion.

[0014] If the depth of the groove is too deep, the single crystal diamond seed expands slowly, and polycrystal grows at the edge of the groove, and then in the case of not meeting the expansion requirement, the polycrystal grown at the edge of the groove interferes with the laterally expanded single crystal diamond, scratches appear, and even the single crystal diamond cannot be taken out.

[0015] If the depth of the groove is too shallow, there is not enough space for single crystal growth, resulting in polycrystal growing outside the groove, the lateral size is small, and the lateral expansion effect is poor.

[0016] The 0.3mm≤ H - h ≤2.5mm, wherein the groove is arranged H - h ≥0.3mm, because when the target diamond grown is too thin, the polycrystal grown at the edge of the diamond is less, and the groove is not needed; the groove is arranged H - h ≤2.5mm, because when the target diamond grown is too thick, multiple diamond growth forms need to be used, and the single diamond growth thickness needs to be ≤2.5mm at this time, otherwise the crystal quality and growth efficiency of the diamond cannot be ensured.

[0017] The present application provides a suitable distance between the edge of the groove and the edge of the single crystal diamond seed, which can prevent the polycrystal grown at the edge of the molybdenum support from being pressed by the polycrystal at the edge of the diamond during lateral expansion, causing cracks or even breaking in the diamond, reducing the risk of polycrystal grown at the edge of the groove spreading to the surface of the diamond, and ensuring that the confinement of the plasma by the edge of the groove effectively covers the edge of the single crystal diamond, inhibiting the generation of polycrystal at the edge of the diamond and the adhesion of the polycrystal diamond film of the molybdenum support to the diamond seed, thereby ensuring that the plasma is reasonably confined by the edge of the groove, and effectively promoting the lateral growth of the single crystal diamond.

[0018] Preferably, the upper and lower surfaces of the single crystal diamond seed are square, and the single side length of the single crystal diamond seed is 3mm-50mm.

[0019] In this size range, the single crystal diamond seed can be uniformly covered by the plasma in the groove, and the risk of temperature difference between the center and the edge of the small size single crystal diamond seed being enlarged is minimized, which induces the generation of edge polycrystal, and at the same time, the large size single crystal diamond seed does not exceed the capacity of the MPCVD cavity, and the plasma distribution is out of control.

[0020] Further preferably, the center of the single crystal diamond seed is located at the center of the groove, and the shape of the groove is square.

[0021] The present application can make the edges of the single crystal diamond seed crystal correspond to the edge spacing of the groove by limiting the position of the single crystal diamond and the shape of the groove, further eliminate the local plasma density fluctuation of the single crystal diamond seed crystal, ensure the uniform distribution of the plasma at the edge of the single crystal diamond seed crystal, inhibit the local polycrystal growth at the edge, and better crystal expansion can be realized.

[0022] Further preferably, the side length of the groove is: l + 2*( H-h ) +2mm≤ L ≤ l + 2*( H-h ) +5mm, l is the side length of the single crystal diamond seed crystal, L is the side length of the groove.

[0023] Preferably, the lateral expansion of the diamond refers to the size of the single crystal region of the diamond growth surface after growth is greater than the size of the diamond before growth.

[0024] Preferably, the plane size of the groove is L 2-10mm larger than the size of the diamond sheet. l

[0025] Preferably, the specific steps of step (1) include: using a mixed solution prepared by mixing concentrated sulfuric acid and concentrated nitric acid at a volume ratio of 1:1 to acid wash the single crystal diamond seed crystal, rinsing with deionized water, and then sequentially ultrasonic cleaning in acetone, alcohol, and deionized water, and finally blowing dry with nitrogen for standby.

[0026] Further preferably, the single crystal diamond seed crystal has no notched or cracks on the four sides, and the thickness is 0.2-1mm.

[0027] Further preferably, the soaking time of the acid washing is 2-8 hours, and the soaking temperature is 150-250℃.

[0028] Preferably, the specific steps of step (3) are: first, vacuumize the MPCVD equipment to below the target value, then ignite under hydrogen atmosphere, then increase the power and pressure to increase the substrate temperature to 800-900℃, etch the diamond surface, and finally introduce methane and nitrogen for diamond growth.

[0029] Further preferably, the etching gas is hydrogen and oxygen, the hydrogen flow is 100-1000sccm, the oxygen ratio in the total gas is 0-3%, 0% means no oxygen, and the etching time is 10-60 minutes. Before introducing methane, hydrogen is used to etch the diamond surface to remove impurities and defects on the surface, so that the single crystal diamond seed crystal can grow normally and stably.

[0030] ​Further preferably, the growth conditions of the MPCVD device are: the gas introduced is hydrogen, methane and nitrogen, the hydrogen flow is 100-1000 sccm, the proportion of methane in the total gas is 1-10%, the proportion of nitrogen in the total gas is 0-100 ppm, 0 ppm means no nitrogen is introduced.

[0031] Further preferably, the growth conditions of the MPCVD device are: the growth temperature of the single crystal diamond seed crystal is 850-1100℃, the power is 3-6 kW, and the pressure is 10-18 kPa, wherein the power and the pressure are jointly adjusted according to the required growth temperature.

[0032] Further preferably, the growth temperature of the single crystal diamond seed crystal is 900-1000℃.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] The present application optimizes the groove geometry parameters of the molybdenum support and the single crystal diamond growth process in a synergistic manner, accurately controls the relative spatial position of the single crystal diamond seed crystal and the groove according to the initial side length, thickness and thickness after growth of the seed crystal, ensures uniform distribution of the growth zone plasma, effectively suppresses polycrystal growth at the edge of the single crystal diamond, and realizes stable lateral crystal expansion. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a perspective view of the shape and position relationship between the diamond seed crystal and the groove of the molybdenum support in Example 1 of the present application;

[0036] Figure 2 is a front view full-section structure schematic view of the shape and position relationship between the diamond seed crystal and the groove of the molybdenum support in Example 1 of the present application;

[0037] Figure 3 is a side view of the single crystal diamond grown in Example 1 of the present application;

[0038] Figure 4 is a top view of the single crystal diamond grown in Example 1 of the present application;

[0039] Figure 5 is a side view of the single crystal diamond grown in Example 2 of the present application;

[0040] Figure 6 is a top view of the single crystal diamond grown in Example 2 of the present application;

[0041] Figure 7 is a side view of the diamond grown in Comparative Example 1 of the present application;

[0042] Figure 8 is a top view of the diamond grown in Comparative Example 1 of the present application;

[0043] Figure 9 is a top view of diamond grown by the present comparative example 2;

[0044] Figure 10 is a top view of diamond grown by the present comparative example 3;

[0045] Figure 11 is a top view of diamond grown by the present comparative example 4. DETAILED DESCRIPTION

[0046] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0047] The present application is a method for lateral expansion of single crystal diamond, which realizes the lateral expansion of single crystal diamond by optimizing the design of single crystal diamond molybdenum support and growth parameters to suppress the growth of polycrystal at the edge of single crystal diamond. Through this method and continuous iteration, large-area single crystal diamond growth can be realized, and large-area single crystal diamond substrates suitable for use in the semiconductor field can be prepared.

[0048] In order to suppress the growth of polycrystal at the edge of single crystal diamond, a groove is provided in the middle of the molybdenum table, and the single crystal substrate is grown in the groove of the molybdenum support. By setting the distance between the edge of the diamond and the edge of the groove and the depth of the groove, the plasma in the diamond growth area can be made more uniform, and the plasma density at the edge of the diamond can be reduced, thereby avoiding the generation of polycrystal at the edge of the diamond, and at the same time, the lateral growth area of CVD single crystal diamond can be increased.

[0049] Example 1

[0050] (1) The single crystal diamond seed crystal is subjected to pre-growth treatment, including:

[0051] The single crystal diamond prepared by HTHP is selected to make the substrate, and the edge length size of the substrate seed crystal is 3 mm, and the thickness of the substrate is 0.9 mm;

[0052] The single crystal diamond substrate is soaked in a mixed solution of concentrated sulfuric acid and concentrated nitric acid at a volume ratio of 1:1 at 200°C for 4 hours. After soaking, the diamond substrate is taken out with a polytetrafluoroethylene tweezers and washed clean with deionized water. The cleaned substrate is then sequentially ultrasonically cleaned in acetone, alcohol and deionized water for 15 minutes each, and the cleaned substrate is dried with nitrogen for standby, so as to remove the metal impurities introduced in the processing process.

[0053] (2) Prepare the molybdenum support, including:

[0054] Prepare a molybdenum table, and process a recess with an area larger than that of the single crystal diamond substrate to be grown at the center of the upper surface of the molybdenum table, clean the surface impurities after processing, and dry after cleaning, wherein the recess size is 8.5mmx8.5mm, the depth is 2.5mm, the thickness of the diamond seed crystal is less than the depth of the recess, the diamond is placed in the center of the recess, and the distance from the edge of the recess is 2.5mm, Figure 1 、 2 The diamond seed crystal and the shape and position relationship of the recess of the molybdenum table are shown in the full view of the schematic diagram, Figure 1 、 2 1, 2 and 3 in the figure respectively refer to the molybdenum support, the recess and the single crystal diamond seed crystal.

[0055] (3) Based on the MPCVD device, the single crystal diamond is grown, including:

[0056] The single crystal diamond substrate after cleaning treatment is etched in the MPCVD device; to remove the surface impurities, defects, internal stress, so that it can grow normally and stably. The etching conditions in the MPCVD device are: the gas is hydrogen and oxygen, the hydrogen flow is 400sccm, the oxygen flow is 8sccm, the etching temperature is 850℃, and the etching time is 30 minutes. After etching, the power and pressure are increased to increase the substrate temperature to 920℃, and then methane and nitrogen gas are introduced for diamond growth. After growing for a suitable time, the device is turned off, the diamond is taken out, and the analysis test is carried out. The side view and top view of the grown diamond are as follows Figure 3 and Figure 4 .

[0057] As can be seen from the figure, the seed crystal size a of the diamond before growth is 3mm, and the seed crystal size b of the diamond after growth is expanded to 7mm, and the thickness c is 2.3mm. The diamond size is increased by more than one time, and at the edge of the diamond, no obvious polycrystalline growth is observed due to the limitation of the recess.

[0058] Example 2

[0059] Compared with Example 1, the difference of Example 2 is that it includes:

[0060] In step (1), CVD diamond growth is selected, the diamond seed crystal size is 11mmx11mm, the thickness is 0.5mm, and the four sides of the seed crystal are (100) faces.

[0061] The surface recess size of the molybdenum support used is 17mmx17mm, and the depth is 2.5mm. The diamond is placed in the center of the recess for diamond growth, and the distance from the edge of the recess is 3mm.

[0062] The etching temperature of the diamond is 900°C, hydrogen is 400 sccm, no oxygen is introduced, and the etching time is 20 minutes. The diamond growth conditions are as follows: temperature is 940-960°C, hydrogen is 400 sccm, methane is 40 sccm, and nitrogen is 5 sccm. After growing for a suitable time, the device is turned off, the diamond is taken out, and analysis and testing are performed. The side view and top view of the grown diamond are as shown in Figure 5 and Figure 6 .

[0063] From Figure 5 , 6 It can be seen that the seed crystal size a of the diamond before growth is 11 mm, the seed crystal size b of the grown diamond is expanded to 15 mm, and the thickness c of the grown diamond is 2.2 mm. At the edge of the diamond, no obvious polycrystal growth is observed due to the limitation of the groove.

[0064] Examples 1 and 2 show that by optimizing the shape matching degree between the groove of the molybdenum support and the substrate and the distance between the diamond and the edge of the groove, the edge heat and temperature aggregation during growth can be effectively inhibited, the generation of edge polycrystal can be avoided, the growth quality can be improved, and the polycrystalline diamond on the substrate after growth can be prevented from growing together with the polycrystalline diamond on the molybdenum table and being unable to be taken out.

[0065] Comparative Example 1

[0066] Compared with Example 1, the difference of Comparative Example 1 includes:

[0067] The diamond seed crystal size is 11 mm x 11 mm, the thickness is 0.6 mm, and the four sides of the seed crystal are (100) planes. The surface groove size of the molybdenum support used is 20 mm x 20 mm, the depth is 1 mm, and the edge of the diamond is 7 mm away from the edge of the groove. The seed crystal size a of the diamond before growth is 11 mm, the size b of the grown diamond is expanded to 14 mm, the thickness c of the diamond is 2.2 mm, and exceeds the depth of the groove.

[0068] The side view and top view of the grown diamond are as shown in Figure 7 , Figure 8 It can be seen that as the diamond grows, the thickness of the diamond will gradually be higher than the edge of the groove, resulting in a large number of polycrystalline layers at the edge of the grown diamond. After deducting the thickness of the polycrystalline layer, the lateral size of the diamond almost does not increase.

[0069] Comparative Example 2

[0070] Compared with Example 1, the difference of Comparative Example 2 includes:

[0071] Diamond seed size 18 mm x 18 mm, thickness 0.5 mm. The groove size on the molybdenum holder surface is 22 mm x 22 mm, depth 3 mm, and the edge of the diamond is 2 mm away from the edge of the groove. The thickness of the grown diamond is 1.2 mm.

[0072] Figure 9 For the top view of the grown diamond on the sample stage, it can be seen that due to the deep groove, the longitudinal growth of the diamond is relatively slow, the polycrystalline growth on the edge of the molybdenum holder groove is fast, which will block the growth window, reduce the diamond growth rate, and the diamond is difficult to take out.

[0073] Comparative Example 3

[0074] Compared with Example 1, the difference of Comparative Example 3 is that it includes:

[0075] Diamond seed size 12 mm x 12 mm, thickness 0.6 mm. The groove size on the molybdenum holder surface is 15 mm x 15 mm, depth 2 mm, and the edge of the diamond is 0.8 mm away from the edge of the groove. The thickness of the grown diamond is 1.7 mm.

[0076] Figure 10 For the top view of the grown diamond on the sample stage. Figure 10 In the middle, when the edge of the diamond is very close to the edge of the groove, due to the mismatch of the thermal expansion coefficient of the diamond on the molybdenum holder and the molybdenum holder, after cooling, the diamond film is thick and will crack and separate from the molybdenum holder, there is polycrystalline on the edge of the grown diamond, and the edge of the molybdenum holder will also grow polycrystalline, the transverse growth of the two will form extrusion to cause the generation of internal cracks in the diamond. A clear internal crack in the diamond can be seen in the left lower-right upper direction.

[0077] Comparative Example 4

[0078] Compared with Example 1, the difference of Comparative Example 4 is that it includes:

[0079] Diamond seed size 12 mm x 12 mm, thickness 0.6 mm. The groove size on the molybdenum holder surface is 22 mm x 22 mm, depth 2 mm, and the edge of the diamond is 6 mm away from the edge of the groove. The thickness of the grown diamond is 1.6 mm.

[0080] Figure 11 For the top view of the grown diamond on the sample stage, it can be seen that due to the distance between the edge of the diamond and the edge of the groove, the edge of the diamond will still grow polycrystalline, and at the same time, if the contact surface between the diamond and the molybdenum holder is relatively flat, the polycrystalline diamond film grown on the molybdenum holder may be connected together with the diamond seed, and finally cannot be taken out.

[0081] In combination with the above examples and comparative examples, it is shown that when the shape of the groove and the shape of the substrate are properly matched, by controlling the relative position relationship between the single crystal diamond seed and the groove of the molybdenum holder, the corner heat and temperature aggregation in the growth process can be controlled, the generation of corner polycrystal can be avoided, the growth quality can be improved, and the polycrystalline diamond on the grown substrate and the polycrystalline diamond on the molybdenum table can be prevented from growing together and cannot be taken out.

Claims

1. A method for lateral expansion of single-crystal diamond, characterized in that, include: (1) Pre-treatment of single-crystal diamond seed crystals before growth; (2) A groove is provided in the center of the obtained molybdenum support, the depth of the groove being... d for: H ≤ d ≤ H +1mm, where 0.3mm≤ H - h ≤2.5mm, h The thickness of the diamond seed crystal. H The thickness of the diamond seed crystal after lateral expansion is given. The distance between the edge of the groove and the edge of the single-crystal diamond seed crystal is 1mm-5mm, and the side length of the groove is: l + 2*( H - h +2mm≤ L ≤ l +2*( H - h +5mm, l The side length of the single-crystal diamond seed crystal. L The length of the groove side; (3) Use MPCVD method to grow single crystal diamond to achieve lateral expansion of single crystal diamond.

2. The method for lateral expansion of single-crystal diamond according to claim 1, characterized in that, The top and bottom surfaces of the single-crystal diamond seed crystal are square, and the length of one side of the single-crystal diamond seed crystal is 3mm-50mm.

3. The method for lateral expansion of single-crystal diamond according to claim 1, characterized in that, The center of the single-crystal diamond seed crystal coincides with the center of the groove, and the groove is square in shape.

4. The method for lateral expansion of single-crystal diamond according to claim 1, characterized in that, The specific steps of step (1) include: using a mixture of concentrated sulfuric acid and concentrated nitric acid in a 1:1 volume ratio to acid-wash the single-crystal diamond seed crystal, rinsing it with deionized water, and then ultrasonically cleaning it in acetone, alcohol, and deionized water in sequence, and finally drying it with nitrogen gas for later use.

5. The method for lateral expansion of single-crystal diamond according to claim 4, characterized in that, The pickling soaking time is 2-8 hours, and the soaking temperature is 150-250℃.

6. The method for lateral expansion of single-crystal diamond according to claim 1, characterized in that, The specific steps of step (3) are as follows: First, the MPCVD equipment is evacuated to below the target value, then it is ignited in a hydrogen atmosphere, and then the power and pressure are increased to raise the substrate temperature to 800-900℃, the diamond surface is etched, and finally methane and nitrogen are introduced to grow diamond.

7. The method for lateral expansion of single-crystal diamond according to claim 6, characterized in that, The etching process uses hydrogen and oxygen as the gas, with a hydrogen flow rate of 100-1000 sccm and an oxygen content of 0-3% (0% indicates no oxygen is introduced). The etching time is 10-60 minutes.

8. The method for lateral expansion of single-crystal diamond according to claim 1, characterized in that, The growth conditions of the MPCVD equipment are as follows: the introduced gases are hydrogen, methane and nitrogen, the hydrogen flow rate is 100-1000 sccm, the proportion of methane in the total gas is 1-10%, the proportion of nitrogen in the total gas is 0-100 ppm, and 0 ppm indicates that no nitrogen is introduced.

9. The method for lateral expansion of single-crystal diamond according to claim 1, characterized in that, The growth conditions of the MPCVD equipment are as follows: the growth temperature of the single crystal diamond seed crystal is 850-1100℃, the power is 3-6kW, and the pressure is 10-18 kPa.

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