Device for regulating substrate curvature during growth of an epitaxial film

Abstract

The present invention relates to epitaxial film grown on a foreign substrate. More particularly, the present invention relates to a device for generating a desired provisional curvature of a substrate prior to the growth of an epitaxial film. After the growth of the epitaxial film, the device gradually reduces the curvature of the substrate proportionally to the thermal shrinkage of the epitaxial film and the substrate. The desired provisional curvature of the substrate is generated using a layered underlay positioned beneath the substrate, said underlay having a specific ratio of the thicknesses of an active and a passive layer, which lends the substrate a curvature of the desired size at a given temperature. To form a convex substrate, the layered underlay (1) is placed beneath the substrate (5) with the active layer facing upwards (Fig. 2). To form a concave substrate, the layered underlay is placed with the active layer facing downwards, and the substrate is drawn downwards at the centre thereof using a stud, a bolt or a lever.

Description

[0001] A device for controlling the bending of the substrate during the growth of an epitaxial film.

[0002] Field of technology

[0003] The present invention relates to layered structures, namely, to epitaxial films grown on foreign substrates. More specifically, the present invention relates to a device that forms the necessary bending of the substrate before growing an epitaxial film on it, with the aim of reducing the bending of the final layered structure.

[0004] State of the art

[0005] As is known, difficulties arise when growing an epitaxial film on a foreign substrate due to the mismatch of the thermal expansion coefficients (TEC) of the substrate and the epitaxial film. Promising semiconductors such as GaAs, SiC and GaN are often grown on foreign substrates. For example, GaN epitaxial films are grown on sapphire, SiC and Si substrates. The epitaxial film is grown at high temperatures. After cooling the resulting layered structure to room temperature, many defects appear in the epitaxial film due to the mismatch of the TEC of the epitaxial film and the substrate. These defects worsen the emitting properties of LEDs, reduce electron mobility, lower the breakdown voltage, and lead to rapid degradation of devices made on their basis. In addition, due to the mismatch of the TEC of the epitaxial film and the substrate, the resulting layered structure bends: it becomes concave or convex.According to modern technical requirements, the bending of the substrate for further processing in technological lines should not exceed a certain value. For example, according to SEMI Ml - 0600 standards, the bending value of a substrate with a diameter of 150 mm should not exceed 60 μm.

[0006] A method known as "Method for controlling bending in a semiconductor structure, semiconductor structure and semiconductor device" (Patent Application WO 2022 / 185067 A1.) The proposed method for controlling bending in a layered semiconductor structure includes the steps of: providing a layered semiconductor structure comprising a first layer of III-nitride semiconductor material on a substrate, wherein the layered semiconductor structure has a first bend. Then forming a porous region of III-nitride semiconductor material over the first layer of III-nitride semiconductor material. In this case, the layered semiconductor structure containing the porous region has a second bend different from the first bend. The semiconductor structure with controlled bending comprises a first layer of III-nitride semiconductor material on a substrate and a porous region of III-nitride semiconductor material over the first layer of III-nitride semiconductor material.A layered semiconductor structure comprising a porous region has a second bend, and the second bend can be tuned by tuning the porosity and / or thickness of the porous region.

[0007] Also known is the method "Reducing Wafer Bending in Growing Epitaxial Films" (US 2018 / 0358221 A1). The work describes designs and methods for reducing substrate bending during heteroepitaxial growth. Microgrooves can be formed on the substrate surface and filled with a polycrystalline material. Stress-relieving material regions can be grown on top of the polycrystalline material in a layer of semiconductor material during heteroepitaxy.

[0008] The disadvantages of the above mentioned methods are that it is necessary to perform additional technological operations with the substrate or epitaxial film, which leads to additional production costs.

[0009] The closest analogue of the proposed device is the method described in the application "Curvature-compensating substrate and method for forming the same" (US 20150035123A1). In this method, a curvature control material (CCM) is formed on one side of the substrate before forming the Group III nitride material on the other side of the substrate. The CCM has a coefficient of thermal expansion (CTE) that is lower than the CTE of the substrate and is stable at elevated growth temperatures required to form the Group III nitride material. In some embodiments, the CCM deposition provides flat plate conditions for the Group III nitride material, maximizing the uniformity of the emission wavelength of the Group III nitride material. The use of the CCM also reduces the bending of the final structure during cooling, which leads to a decrease in the convex curvature of the substrate.In some embodiments, the final curvature of the structure can be further designed to be concave by properly selecting the properties of the SCM, and by controlled selective etching of the SCM, this method allows the final structure to be made flat.

[0010] The disadvantage of this method is that it is necessary to deposit additional curvature control material on the back side of the substrate, which leads to additional production costs.

[0011] Disclosure of invention

[0012] The technical result of the present invention is a device that creates the necessary preliminary bending of the substrate before growing an epitaxial film on it. Then, after growing the epitaxial film, it gradually reduces the bending value of the substrate, proportionally with the thermal contraction of the epitaxial film and the substrate, which will allow obtaining a higher-quality layered structure with less bending and defects.

[0013] As is known, when growing an epitaxial film on a foreign substrate, the manufactured layered structure bends, and the bending value can be calculated using formula (1) given in the work of Hideo Aida et al 2012 Jpn. J. Appl. Phys. 51 016504. DOI: 10.1143 / JJAP.51.016504.

[0014] Where E su b and E epi - Young's modulus of the substrate and film, t su b and t epi - thickness of the substrate and film, a su b and a epi- coefficient of thermal expansion of the substrate and film, d - substrate diameter, AT - difference between growth temperature and room temperature. Or, you can pre-grow an epitaxial film on a flat substrate under normal conditions, and measure the bending of the resulting structure.

[0015] If, before growing an epitaxial film, the substrate is bent in the opposite direction to the bending that is formed during conventional growth, and equal in magnitude, then a structure with a smaller bend or even a flat structure can be obtained.

[0016] As is known, during epitaxial film growth, the crystallographic orientation of the substrate and film coincide. When bending a single-crystal substrate before growing an epitaxial film, the crystallographic plane of the substrate is bent. The crystallographic plane of the epitaxial film grown on such a substrate will also be bent, repeating the bend of the crystallographic plane of the substrate. The proposed device bends the substrate with the required bending value before growing the epitaxial film, and after growing the epitaxial film, during cooling of the manufactured layered structure, reduces the bending, proportionally with the thermal contraction of the epitaxial film and the substrate. Thus, the crystallographic planes of the substrate and epitaxial film are gradually straightened after growth. As a result, at room temperature, there will be less bending and residual stresses in the crystallographic structure of the epitaxial film and the substrate.

[0017] The proposed device consists of a layered lining, which has layers with different coefficients of thermal expansion. The layered lining in the form of a round washer, having the same diameter as the substrate, is installed under the substrate (Fig. 1). Thermally stable materials are used to manufacture the layered lining. In particular, the layered structure can be bimetal. Molybdenum can be used as a passive material, i.e. a material with a lower CTE. Tantalum, nickel or other suitable materials can be used as an active material - a material with a higher CTE. If such a bimetallic lining (1) (Fig. 1) is installed on a substrate holder (4), under the substrate (5), with the active layer facing up (Fig. 2), then when heated, the bimetallic lining takes a convex shape and will also give the substrate a convex shape. The edges of the substrate (5) and the bimetallic lining (1) are pressed to the substrate holder (4) by a fixing ring (6).Since the bimetallic lining bends during heating and does not fully contact the flat graphite support, the bimetallic lining (1) is heated directly by an induction or infrared heater (7) (Fig. 2) to prevent the formation of a temperature gradient in the substrate. (For clarity, the bending of the substrates in the figures is not to scale. In real scale, the bending of the substrates will be barely noticeable). With the correct design of the bimetallic lining, it will give the substrate the required bending value at the growth temperature. After reaching the required bending value of the substrate, an epitaxial film (8) is grown on it (Fig. 3). After cooling to room temperature, the resulting structure has a flat shape (Fig. 4). When manufacturing a bimetallic lining in advance, according to formula (1), the ratio of the thicknesses of the active and passive layers is calculated.For example, if it is necessary to grow a 5 µm thick GaN epitaxial film on a 350 µm thick Si substrate with a diameter of 10 cm at a temperature of 1050°C, then the possible bending of such a layered structure can be calculated using formula (1). According to literature data, Esi = 165 GPa, Eoai = 210 GPa, asi = 3.59 10'. 6 / °С, ac,aN = 5.59- 10' 6 / °С. If t epi =5mkm, t su b = 350 µm, dsub = Yusm = 10 5 μm, AT = 1025 °C, then the bending of the layered structure calculated by formula (1) is Bow = 796 μm. To obtain the final flat layered structure, it is necessary to place a bimetallic lining under the Si substrate, which will give the substrate a convex shape with a bending value of 796 μm, at 1050 °C, before growing the epitaxial GaN film on it. According to calculations using formula (1), a bimetallic lining with a diameter of 10 cm, consisting, for example, of a 400 μm molybdenum passive layer and a 13.5 μm tantalum active layer, can perform such a function.

[0018] In another variant, one of the layers of the layered lining may consist of the material of the substrate. In this case, contamination of the substrate by the material of the layered lining at high temperatures is reduced. If monocrystalline silicon with a thickness of 350 μm and a diameter of 10 cm is used as the passive layer, and tantalum is used as the active layer. Then, according to formula (1), it is possible to calculate the thickness of the tantalum layer, at which the manufactured layered lining forms a bend equal to 796 μm at 1050 °C. According to literature data, Esi = 165 GPa, asi = 3.59- 10' 6 / °С, Е Та =190GPa, and Та =7- 10' 6 / °С. If, t si =350 µm, d si = Yusm = 10 5 µm, AT = 1025 °C, Bow = 796 µm, then the thickness of the tantalum layer, calculated using formula (1) will be Cha = 3.67 µm.

[0019] It should be noted that the metal layer is deposited on the silicon substrate at room temperature. For example, by electrochemical deposition or other methods of gluing layers, so that at room temperature the manufactured layered lining has a flat shape.

[0020] In order to use silicon as an active layer, it is necessary to attach a material with a CTE lower than that of silicon, such as quartz, to silicon. Then, to form a convex substrate, such a layered lining can be installed with the silicon layer facing up, which pollutes the silicon substrate located on such a layered lining less.

[0021] To form a concave substrate, small holes with a diameter of 1-2 mm are formed in the center of the substrate and the layered lining (Fig. 5), and they are fastened together using a bolt (9). The hole in the center of the layered lining has an internal thread corresponding to the thread of the bolt (9). Here, the layered lining (1) is installed with the active layer down. When heated, the layered lining (1) pulls the center of the substrate (5) down using the bolt (9), and gives the substrate the necessary concavity. If the hole in the center of the substrate interferes with further processing of the substrates, it can be closed using the substrate gluing technology.

[0022] In the second option, in order not to make a hole in the substrate, you can temporarily attach a small pin (rod with external thread) (10) (Fig. 6), perpendicular to the substrate, from below, in the center, screw the layered lining to the pin and in this way form a concave substrate.

[0023] In the third variant of forming a concave substrate, a bracket-shaped lever (11) is used (Fig. 7), the end of one arm of which rests on the center of the layered lining (1) from below, and the end of the other arm rests on the center of the substrate (5) from above by means of an adjusting bolt (12). Here, the layered lining (1) is installed with the active layer down. The location of the axis of the lever (13) is selected so that when the substrate rotates around its axis by the rotating mechanism, the lever remains stationary and parallel to the gas flow in the reactor, which will have less effect on the gas flow.

[0024] In another embodiment, the device consists of two rods that are stable at the temperature of epitaxial film growth and have different CTEs, and a clamp that fastens these rods together.

[0025] The device for forming a convex substrate consists of two rods (15) and (16) (Fig. 8) with different CTE, which are located perpendicular to the substrate (5), in the center, on the lower side, and a clamp (17), which fastens these rods together. The upper end of the rod with a smaller CTE (15) is fixed to the support (18), which is located parallel to the substrate (5) and fixed to the substrate holder (4). The rod with a larger CTE (16) is located parallel to the rod with a smaller CTE (15), perpendicular to the substrate (5), and passing through the hole in the support (18) rests against the center of the lining (14) on the lower side (Here the lining is ordinary, not layered). The rods are fastened together by a clamp (17). The location of the clamp can be changed by moving it up or down. To move the clamp, it is necessary to first loosen the clamp fixing bolt (27) (Fig. 24). When the substrate begins to heat up in preparation for epitaxial growth, the rods also begin to heat up.In this case, the rod with the smaller CTE (15) is extended downwards together with the clamp (17). The clamp is lowered downwards by a distance ALi=aiLAT. The rod with the larger CTE (16) is extended upwards by a distance AL2 = 012LAT from the clamp attachment point. Since o > oc, then AL2 >ALi, therefore, the device raises the center of the substrate by a value of H = AL2 - ALi. When using molybdenum as a rod with the smaller CTE, with a CTE equal to a. m = 5 10' 6 / °C, and as a rod with a high CTE - stainless steel of the austenite grade with a CTE equal to a s = 17.3 10' 6 / °C the following results can be obtained.

[0026] The bending value can be calculated using formula (2). At a growing temperature of 1050°C and a rod length of L= 5 cm, the calculated H = 633 µm.

[0027] Н= 012LAT- aiLAT= (а.2- aJLAT. (2) L = H / (a2. ai)AT (3)

[0028] As shown above, during conventional growth of a 5-μm-thick GaN epitaxial film on a 350-μm-thick, 10-cm-diameter Si substrate at 1050°C, the resulting structure bends Bow = 796 μm. Since oiGaN > dsi, such a structure is concave. To obtain a flat final structure, the silicon substrate must be given a convex shape with a bend value of 796 μm before growing the epitaxial film. In this case, it is necessary to use 7-cm-long rods in the device. Then the maximum bend that such a device can make, calculated using formula (2), is H = 882 μm. This is sufficient for the required preliminary bending of the silicon substrate. According to formula (3), at H = 796 μm, L = 6.33CM. Moving the clamp by 0.5 mm changes the bending value of the substrate by approximately - 6 microns.

[0029] In this variant, the device and the substrate are heated by one common heater (7) (Fig. 10). Therefore, after the end of growth, the device gradually reduces the substrate bending, proportionally with the thermal contraction of the epitaxial film and the substrate. Under the substrate there is a thermally stable, thin and flexible lining (14) (not layered), which bends together with the substrate (5). This lining can be heated by induction (RF) or infrared heating (IR). The lining is in close contact with the substrate at any bending of the substrate. This promotes more uniform heating of the substrate, formation of a spherical shape of the substrate bending and prevents damage to the substrate by the rod.

[0030] When growing an epitaxial film with a lower CTE on a substrate with a higher CTE, the resulting final layered structure has a convex shape. To obtain a final flat structure, before growing the epitaxial film, it is necessary to give the substrate a concave shape with the required bending value. For example, if before growing the GaN epitaxial film on a sapphire substrate, the substrate is given a concave shape with the required bending value, then it will be possible to obtain a structure with a minimum bending.

[0031] There are two options for forming a concave substrate. If it is possible to form a hole with a diameter of 1-2 mm in the center of the substrate, then through such a hole it will be possible to pull the center of the substrate down (Fig. 11) using a pin (10) and a nut (19). In this case, the rods with different CTE (15) and (16) in the device are swapped. The pin (10) is attached to the upper end of the rod with a smaller CTE (15). When heated, the device pulls the nut (19) down, and forms a concave substrate.

[0032] If it is impossible to make a hole in the substrate, the device can be installed under the lining, parallel to the substrate, and using the angular lever (11) press along the center of the substrate (5) from top to bottom by means of the adjusting bolt (12) (Fig. 12). In this version, the rod with a large CTE (16) pushes the vertical arm of the angular lever (I). The perpendicular arrangement of the device rods can accommodate the reactor structure. In this case, the device rods can be located parallel to the substrate, under the substrate holder (Fig. 12), or on the side (Fig. 13), which takes up significantly less space. The device can be located in any convenient place, and the mechanical action of the rods along the center of the substrate can be carried out through the lever. The adjusting bolt (12) is installed at the end of the horizontal arm of the angular lever (I).This bolt is used to ensure that after the substrate (5) is installed in the substrate holder (4), there is no gap between the lever (11) and the device rod, as well as between the adjusting bolt (12) and the substrate (5). The location of the lever axis (13) in the reactor is selected in such a way as to minimize the influence of the lever on the reactor design, as well as to optimize the ratio of the lever arms. The substrate and the device can be heated by a common heater (7) (Fig. 13) or by separate heaters (7) and (22) (Fig. 14). With separate heating of the device, it will be possible to adjust the substrate curvature on site, with high accuracy. The amount of substrate curvature can be measured on site using a substrate curvature measurement system. For example, the Advanced EpiCurve® TT - wafer curvature measurements system. By measuring the amount of bending with the device and adjusting the bending of the substrate by adjusting the temperature of the device, it will be possible to determine the amount of initial bending of the substrate with great accuracy.A change in the temperature of the device by one degree will result in a change in the bending value of approximately 0.5-1 micron.

[0033] Fig. 19 shows a longitudinal section of the rods of the device that creates a pushing force along the lever (I). Here, the CTE (15) of the rod is smaller, and the CTE (16) of the rod is larger. The front (20) and rear (21) supports serve to secure and guide the rods.

[0034] Fig. 20 shows a longitudinal section of the rods of the device that creates a pulling force along the lever (9). In this case, the rods with a larger and smaller CTE in the device are swapped relative to Fig. 19.

[0035] In modern planetary MOCVD reactors, substrate holders rotate around the axis during growth. For such reactors, another version of the device can be used, which consists of a tube (24) with a lower CTE and a rod (16) with a higher CTE, which is located inside the tube (Fig. 21). Such a device can be installed in the rotating shaft (23) of the planetary reactor. In order to form the required substrate bend at a certain temperature of the device, it is necessary to calculate the length of the tube (24) and rod (16), taking into account the difference in their CTE. With a sufficient length of the tube (24) and rod (16), as well as with a sufficient difference in their CTE, the required substrate bend can be formed by heating the device to 300 - 350 ° C. Fig. 21 shows a section of a device for forming a convex substrate, using a tube (24) and a rod (16) as a control device, with separate heaters for the substrate (7) and for the device (22).Thermal insulation couplings (26) serve to reduce thermal heating of the upper and lower parts of the shaft (23). When heating the device consisting of a tube (24) with a lower CTE and a rod (16) with a higher CTE, the rod (16) is extended more than the tube (24) and by means of a rod (25) raises the center of the lining (14) to a certain height. With such a design of the device, one device can bend one substrate or several substrates simultaneously.

[0036] Fig. 22 shows a section of the device for forming a concave substrate. Here, the CTE of the tube (24) is greater than the CTE of the rod (15), therefore, when the device is heated, the rod pulls the center of the substrate (5) downwards by means of the pin (10) and nut (19), and forms a concave substrate.

[0037] Fig. 23 shows a section of the device for forming several convex substrates simultaneously. Here, the CTE of the tube (24) is greater than the CTE of the rod (15). Consequently, when the device is heated, the tube (24) is extended more than the rod (15), thus, the rod (15) pulls the ends of the levers (11) downwards and forms convex substrates (5).

[0038] Fig. 24 shows a cross-section of the clamp with rods. The bolt (27) serves to tighten the clamp to fasten the rods (15) and (16) with the clamp (17). Fig. 25 shows a longitudinal section of the clamp with rods. The area of ​​the clamp (17) in contact with the rods (15) and (16) is narrow. This design will allow the clamp to be localized with high accuracy.

[0039] When using a device consisting of two rods, or a tube with a rod, it is possible to regulate the amount of bending of the substrate by adjusting the temperature of the device on site. Such a device can impart a bend of any value to a substrate of any diameter. That is, the device is more universal. But when installing such a device in a reactor, some technical difficulties arise. The version of the device consisting of a layered lining is relatively simple and does not require significant design changes when installed in a reactor. But such a device does not allow you to regulate the amount of bending of the substrate directly on site. It bends a substrate of a certain diameter, by a pre-calculated amount at the growth temperature, depending on the ratio of the thicknesses of the active and passive layers.

[0040] To prevent contamination of the substrate by the liner material at high temperatures, a thin spacer consisting of the substrate material can be installed between the substrate and the liner. This spacer prevents the diffusion of atoms from the liner to the substrate at high temperatures.

[0041] Brief description of the drawings.

[0042] Fig. 1. Section of a layered lining (1), with active (2) and passive (3) layers.

[0043] Fig. 2. Section of the device for forming a convex substrate, consisting of: a substrate holder (4), a layered lining (1), a substrate (5), a fixing ring (6) and a heater (7).

[0044] Fig. 3. Section of the device for forming a convex substrate, consisting of: a substrate holder (4), a layered lining (1), a substrate (5) and a fixing ring (6). At the growth temperature, after growing the epitaxial film (8).

[0045] Fig. 4. Section of the device for forming a convex substrate, consisting of: a substrate holder (4), a layered lining (1), a substrate (5) and a fixing ring (6). After growing the epitaxial film and cooling to room temperature.

[0046] Fig. 5. Section of the device for forming a concave substrate, consisting of: a substrate holder (4), a layered lining (1), a substrate (5) and a fastening bolt (9). The layered lining is installed with the active layer facing down.

[0047] Fig. 6. Section of the device for forming a concave substrate, consisting of: a substrate holder (4), a layered lining (1) and a pin (10) temporarily attached to the substrate (5). The layered lining is installed with the active layer facing down.

[0048] Fig. 7. Section of the device for forming a concave substrate, consisting of; a substrate holder (4), a layered lining (1) and a bracket-shaped lever (I). The layered lining is installed with the active layer down. Fig. 8. Section of the device for forming a convex substrate, with general heating of the substrate and the device.

[0049] Fig. 9. Section of the device for forming a convex substrate with common heating of the substrate and the device. At the growth temperature, after growing the epitaxial film (8).

[0050] Fig.10. Section of the device for forming a convex substrate with common heating of the substrate and the device. After growing the epitaxial film (8) and cooling to room temperature.

[0051] Fig. 11. Section of the device for forming a concave substrate, with general heating of the substrate and the device.

[0052] Fig. 12. Section of the device for forming a concave substrate, with the rods positioned under the substrate, parallel to the substrate.

[0053] Fig. 13. Section of the device for forming a concave substrate with the rods positioned on the side, parallel to the substrate holder, with general heating of the substrate and the device (heater 7).

[0054] Fig. 14. Section of the device for forming a concave substrate with the rods positioned on the side, parallel to the substrate holder, with separate heating of the substrate and the device (heaters 7 and 22).

[0055] Fig.15. Section of the device for forming a concave substrate. At the growth temperature, before growing the epitaxial film.

[0056] Fig. 16. Section of the device for forming a concave substrate, at the growth temperature, after growing the epitaxial film.

[0057] Fig.17. Section of the device for forming a concave substrate. After growing the epitaxial film and cooling to room temperature.

[0058] Fig. 18. Section of the device for forming a convex substrate, with the rods positioned on the side, parallel to the substrate holder.

[0059] Fig. 19. Longitudinal section of the rods of the device that creates a pushing force along the lever (I).

[0060] Fig.20. Longitudinal section of the rods of the device creating a pulling force along the lever (I). Fig.21. Section of the device for forming a convex substrate, using a tube (24) and a rod (16) as a regulating device, with separate heating of the substrate (7) and the device (22).

[0061] Fig. 22. Section of the device for forming a concave substrate, using a tube (24) and a rod (15) as a control device, with separate heating of the substrate (7) and the device (22).

[0062] Fig. 23. Section of the device for simultaneous adjustment of the convexity of several substrates, using a tube (24) and a rod (15) as an adjustment device.

[0063] Fig. 24. Cross-section of the device consisting of a clamp (17), rods (15 and 16) and a bolt (27).

[0064] Fig. 25. Longitudinal section of a device consisting of a clamp (17) with rods (15 and 16).

[0065] The best embodiment of the invention

[0066] The device consists of a layered substrate. Molybdenum is used as a passive material. Tantalum is used as an active material. When growing GaN films 5 μm thick on a Si substrate 350 μm thick and 10 cm in diameter, at a temperature of 1050 ° C, the resulting layered structure has a concave shape with a bend value of 796 μm. Therefore, to obtain the final flat layered structure, before growing GaN films, the Si substrate must be given a convexity of 796 μm. To create a bimetallic substrate, which will be located under the substrate and give the Si substrate a convexity of 796 μm, at 1050 ° C, take a round molybdenum plate 10 cm in diameter and, for example, 400 μm thick. A layer of tantalum is deposited onto this plate using an electrochemical method at room temperature, or other methods of producing bimetals, so that the bimetal produced at room temperature has a flat shape.Taking into account the Young's moduli and CTE for these materials, the required thickness of tantalum can be calculated using formula (1). Em. о = 300GPa, Et а =190GPa, amo =5-10' 6 / °С, а-|а =7- 10' 6 / °С. According to calculations, the tantalum thickness is 13.5 μm. If the tantalum thickness changes by 0.1 μm, the bimetal bending value will change by approximately 5 μm. Of course, these calculations are preliminary. The optimal ratio of the active and passive layer thicknesses is determined experimentally. If we take into account that the bimetal must press on the Si substrate with a certain force, then the thickness of the active layer will need to be made slightly larger than the calculated one. Fig. 1 shows a cross-section of the layered lining (1) consisting of a lower molybdenum layer (3) with a thickness of 400 μm and an upper tantalum layer (2) with a thickness of 13.5 μm. Fig. 2 shows a cross-section of the device consisting of; a substrate holder (4), a layered lining (1), a substrate (5) and a fixing ring (6). The layered lining (1) and the substrate (5) are attached to the substrate holder using the fixing ring (6). The device works as follows: To form a convex substrate, a layered lining is installed in a substrate holder, with the active layer facing up.When heated by the heater (7) to the growth temperature, the layered lining (1) will impart the necessary convexity to the substrate (5). Then the epitaxial film (8) is grown (Fig. 3). After the epitaxial film is grown, the reactor is cooled to room temperature, and the resulting structure has a flat shape (Fig. 4).

[0067] Example 2

[0068] The device consists of two thermally stable rods (15) and (16) with different CTEs, fastened together with a clamp (17) (Fig. 8). Before starting to grow an epitaxial film on a foreign substrate, the possible bending of the resulting structure is calculated using formula (1). The device is adjusted so that at the growth temperature the device bends the substrate in the direction opposite to the direction of the structure bending during conventional growth, and equal in magnitude. For this, the location of the clamp on the rods is calculated using formula (3).

[0069] Here H is the substrate bending, ar and o c are the CTE of the rods, AT is the difference between the growing temperature and room temperature, L is the distance from the end of the rod (15), fixed to the support (18), to the clamp (17). When using a lever in the device, the ratio of the lever arm lengths is taken into account to calculate L.

[0070] The necessity of forming a convex or concave substrate depends on the ratio of the CTE of the substrate and the film. For example, when growing an epitaxial GaN film on a SiC or Si substrate, the resulting final structure forms a concave shape, since the CTE of GaN is greater than the CTE of SiC and Si. Therefore, to obtain a final structure with minimal bending, it is necessary to give the substrate a convex shape before growing the epitaxial film on it. The value H, by which it is necessary to raise the center of the substrate, is determined by formula (1) or by preliminary experiments.

[0071] Before starting epitaxial growth, a heat-resistant, flexible lining (14) is installed on the substrate holder (4) (Fig. 8), which can be heated by induction (RF) or infrared irradiation (IR). The substrate (5) is installed on top of this lining. The substrate is pressed to the substrate holder by a fixing ring (6). The role of the fixing ring (6) is to hold the edges of the substrate (5) and lining (14) pressed to the substrate holder (4) when the center of the lining is raised upward by a rod (16). Rods with different CTEs (15) and (16) are located below the substrate, perpendicular to it, in the center. The rods are fastened together by a clamp (17). The upper end of the rod with a smaller CTE (15) is attached to the support (18), which is located parallel to the substrate (5) and is attached to the substrate holder (4). The substrate and the rods of the device are heated by the heater (7) to the growing temperature (Fig. 9). In this case, the rods (15) and (16) are lengthened.The clamp (17) is lowered by a distance ALi=aiLAT, due to the thermal expansion of the rod with a smaller CTE (15) downwards. The rod with a larger CTE (16) is extended upwards from the clamp (17) fastening point by a distance AL2=a2LAT. Since the CTE of the rod (16) is greater than the CTE of the rod (15), then AL2> ALx. Consequently, the center of the substrate is raised by a value of H = AL2 - ALi. After reaching the required growth temperature and measuring the substrate bending value in situ, the epitaxial film is grown. If the initial substrate bending value H is greater or less than the required value, then it will be necessary to move the clamp (17) upwards or downwards. It should be noted that in the variant of arranging the device not under the substrate, but on the side (Fig. 14), when the substrate and the device are heated by separate heaters (7) and (22), there is no need to change the location of the clamp. In this version, fine adjustment of the substrate bending can be achieved by adjusting the temperature of the device.After the epitaxial film growth is complete, the substrate and device are cooled proportionally to room temperature (Fig. 10). The resulting composite structure has less bending.

[0072] Example 3. When the CTE of the epitaxial film is less than the CTE of the substrate, the resulting structure has a convex shape. For example, the CTE of GaN is less than the CTE of sapphire. Therefore, the structure consisting of the epitaxial GaN film and the sapphire substrate has a convex shape. To reduce the bending of the final structure, the sapphire substrate must be given a concave shape before growing the epitaxial GaN film on it. There are two options for forming a concave substrate.

[0073] If it is possible to form a hole with a diameter of 1-2 mm in the center of the substrate, then through such a hole it will be possible to pull the center of the substrate downwards. Fig. 11 shows a cross-section of the device for forming a concave substrate in this way. It should be noted that in this version of the device, the rods with different CTE (15) and (16) are swapped, that is, the rod with a larger CTE is attached to the support (18), and the rod with a smaller CTE (15) is located below the hole in the center of the lining (14). The pin (10) is attached to the upper end of the rod with a smaller CTE (15). When heated, the device pulls the center of the substrate downwards using the nut (19). The nut (19) is screwed to the stud (10) after installing the lining (14) and the substrate (5) on the substrate holder (4), so that there is no gap between the substrate (5) and the nut (19).

[0074] When heated, the rod (16) extends downwards and lowers the clamp (17) by a distance AL2=a2LAT. The rod (15) extends upwards from the point of attachment to the clamp by a distance ALi=aiLA. Since ag > ac, then AEg > ALi. Consequently, the center of the substrate is lowered by a distance H = AEg - ALi.

[0075] If the technical conditions do not allow making a hole in the center of the substrate, then the substrate can be pressed down in the center from top to bottom using an angular lever. To form a concave substrate, use the device shown in Fig. 12. It should be noted that in the version shown in Fig. 12, the device pushes the vertical arm of the lever (11) by means of a rod with a large CTE (16). Fig. 13 shows a device that pulls the vertical arm of the lever (11) by means of a rod with a smaller CTE (15), since in this case rods (15) and (16) in the device are swapped.

[0076] Here, as in example 2, the bending value H is calculated using formula (1) or determined from experimental data. Then, L is calculated using formula (3), and the clamp (17) is set in the desired position (Fig. 14). When heated, the device pulls the vertical lever arm. In this case, the horizontal lever arm (11) presses on the center of the substrate using the adjusting bolt (12). If, when measuring the concavity on site, it is found that the concavity does not correspond to the required value, then the concavity of the substrate is adjusted by adjusting the temperature of the device. When the required concavity of the substrate is achieved, the growth of the epitaxial film (8) begins (Fig. 15). After the epitaxial film growth is complete (Fig. 16), the substrate and device begin to cool proportionally so that the thermal contraction of the epitaxial film and the substrate is proportional to the decrease in the concavity of the substrate. After cooling to room temperature, the bending will be significantly reduced (Fig. 17).

[0077] Example 4

[0078] Fig. 23 shows a section of a device for simultaneously adjusting the convexity of several substrates, using a tube (24) and a rod (15) as a regulating device. Here, the device, consisting of a tube (24) with a large CTE and a rod (15) with a smaller CTE, can simultaneously form several convex substrates (5) using levers (I). The lower end of the rod (15) is attached to the bottom of the tube (24). The device operates as follows: When the device is heated, the tube (24) is extended more than the rod (15), and as a result, the rod pulls the end of the levers (11) downwards using the T-shaped end. The levers (11) with their other shoulders, by means of bolts (12), press along the center of the pads (14) from the bottom up. As a result, the device forms several convex substrates (5) simultaneously. The amount of convexity can be adjusted by adjusting the temperature of the device using the heater (22). After achieving the required bending of the substrates (5), the growth of epitaxial films (8) begins.After growing epitaxial films, the temperature of the substrates and device is proportionally reduced to room temperature.

Claims

Invention formula 1. A device for bending a substrate on which an epitaxial film will subsequently be grown, characterized in that the bending of the substrate is carried out using a layered lining (1) (Fig. 1), consisting of layers with different coefficients of thermal expansion, with the required ratio of the thicknesses of the active and passive layers, located under the substrate (5) (Fig. 2), with the active layer facing up, which will give the substrate the required convexity at the growth temperature.

2. The device according to claim 1, wherein the layered lining may be, in particular, a bimetal or one of its layers may consist of a substrate material.

3. The device according to paragraph 1, characterized in that a thin gasket is installed between the layered lining and the substrate, which consists of the substrate material.

4. The device according to claim 1, characterized in that, in order to form a concave substrate, the layered lining (1) (Fig. 5) is located under the substrate, with the active layer down, and is fastened to the substrate (5) by means of a bolt (9), wherein the bolt passes through holes in the center of the substrate, and is screwed to a threaded hole in the center of the layered lining.

5. The device according to item 1, characterized in that, in order to form a concave substrate, the layered lining (1) is located with the active layer down, and also to the substrate (5) (Fig. 6), from below, in the center, perpendicularly, a pin (10) is attached, wherein the layered lining, which has a hole with an internal thread in the center, is screwed to the pin.

6. The device according to claim 1, characterized in that the device for forming a concave substrate consists of a layered lining (1) (Fig. 7), located under the substrate (5), with the active layer down, and a bracket-shaped lever (I), resting with the end of one arm in the center of the layered lining, from below, and with the end of the other arm in the center of the substrate, from above, by means of an adjusting bolt (12).

7. A device for controlling the bending of a substrate on which an epitaxial film will subsequently be grown, characterized in that the control of the bending of the substrate is carried out directly on site, during the growth of the epitaxial film, by means of two thermally stable rods (15 and 16) (Fig. 8) with different coefficients of thermal expansion, fastened between a clamp (17), located perpendicular to the substrate (5), in the center, on the bottom side, wherein the upper end of the rod with a smaller coefficient of thermal expansion (15) is attached to a support (18), located parallel to the substrate (5) and attached to the substrate holder (4), and the rod with a larger coefficient of thermal expansion (16), passing through the hole in the support (18), rests against the center of the lining (14), located under the substrate (5).

8. The device according to item 7, characterized in that the location of the rods with different coefficients of thermal expansion (15 and 16) (Fig. 14) in the device changes, and the rod with a lower coefficient of thermal (15) expansion, when heated, pulls the vertical arm of the angular lever (11), and presses with the horizontal arm of the lever along the center of the substrate from top to bottom in order to give the substrate the necessary concavity.

9. The device according to item 7, characterized in that the device can be located in any convenient place, heated by a separate heater, and pressed in the center of the substrate using a lever.

10. A device for controlling the bending of a substrate on which an epitaxial film will subsequently be grown, characterized in that the control of the bending of the substrate is carried out on site using a tube (24) (Fig. 21) and a rod (16) located inside the tube, which have different coefficients of thermal expansion and are located under the substrate (5), perpendicular to it, in the center, at a certain distance, wherein the tube is attached to the substrate holder through a shaft (23) and a support (18), which makes it possible to regulate the temperature of the substrate and the device using separate heaters (7 and 22), and when the device is heated, the rod (16) by means of a rod (25) raises the center of the substrate (5) to the required height.

11. The device according to item 10, characterized in that in the device the tube (24) (Fig. 22) has a higher coefficient of thermal expansion, and the rod (15) has a lower coefficient of thermal expansion, and is attached to the bottom of the tube in such a way that when the device is heated, it is pulled down the center of the substrate (5) by means of the pin (10) and nut (19).

12. The device according to paragraph 10, characterized in that one device can simultaneously regulate the bending of several substrates (5) (Fig. 23) using several levers (I). CORRECTED SHEET (RULE 91)

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