Method for improving thickness uniformity of polycrystalline diamond

Abstract

The invention provides a method for improving the thickness uniformity of polycrystalline diamond, and belongs to the technical field of semiconductors, and the method comprises the following steps: carrying out chamfering grinding on an edge intersection angle area of a silicon substrate; covering polycrystalline diamond seed crystals on the surface of the silicon substrate subjected to chamfering treatment; growing polycrystalline diamond on the polycrystalline diamond seed crystal; polishing to enable the thickness deviation between the edge intersection angle area and the central area of the polycrystalline diamond to be 1t; 10 m. By means of the method, the thickness deviation of the edge intersection angle area and the center area of the polycrystalline diamond can be reduced, the thickness uniformity of the polycrystalline diamond is improved, the cracking problem caused by the temperature deviation of the edge intersection angle area and the center area is prevented, the finished product quality is improved, and the rejection rate and the production cost are reduced.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology, and particularly relates to a method for improving the thickness uniformity of polycrystalline diamond. Background Art

[0002] The growth substrate for preparing polycrystalline diamond is generally a silicon substrate. The surface and the side edge of the silicon substrate intersect vertically to form a 90° edge intersection angle region. At present, the main method for preparing high-quality polycrystalline diamond is the MPCVD method. The growth environment of the MPCVD method is hydrogen plasma, which has an edge effect, that is, the hydrogen plasma encounters the edge intersection angle region of the silicon substrate and generates tip discharge. A local hot spot will be formed in this edge intersection angle region, resulting in the temperature of the edge intersection angle region of the silicon substrate being dozens to several hundred degrees higher than that of the central region. The resulting consequences are as follows: The growth rate of the edge intersection angle region of the silicon substrate is higher than that of the central region, and the thickness of the edge intersection angle region of the polycrystalline diamond is greater than that of the central region, forming a thickness deviation.

[0003] This thickness deviation will cause the following problems: (1) It will cause uneven stress distribution between the edge intersection angle region and the central region of the polycrystalline diamond. During the cooling process after the growth of the polycrystalline diamond is completed, the shrinkage of the edge intersection angle region and the central region is different, which may cause the polycrystalline diamond to crack. See Figure 1 .

[0004] (2) In addition, the different thicknesses of the edge region and the central region of the polycrystalline diamond will also increase the subsequent polishing processing cycle. Summary of the Invention

[0005] An embodiment of the present invention provides a method for improving the thickness uniformity of polycrystalline diamond, aiming to solve the problems of large thickness deviation between the edge region and the central region of the polycrystalline diamond, uneven stress distribution, different shrinkage between the edge intersection angle region and the central region of the polycrystalline diamond thickness, and possible cracking of the polycrystalline diamond.

[0006] To achieve the above object, the technical solution adopted by the present invention is: to provide a method for improving the thickness uniformity of polycrystalline diamond, the method comprising the following steps: Step 1, chamfer and grind the edge intersection angle region of the silicon substrate, and perform a primary polishing; Step 2, cover polycrystalline diamond seeds on the surface of the silicon substrate after chamfering; Step 3, grow polycrystalline diamond on the polycrystalline diamond seeds; Step 4, perform secondary polishing to make the thickness deviation between the edge intersection angle region and the central region of the polycrystalline diamond < 10 µm.

[0007] In an implementable manner, Step 1, chamfer and grind the edge intersection angle region of the silicon substrate, and perform a primary polishing includes: Fix a chamfering fixture with a grinding head on the side of the silicon substrate; wherein, the inner angle of the chamfering fixture has an arc inner angle adapted to the chamfer of the silicon substrate; the grinding head is in a circular arc shape adapted to the arc inner angle of the chamfering fixture, and the grinding head has a circular arc grinding surface; The silicon substrate rotates with the rotating disk, and the circular arc grinding surface of the grinding head contacts the chamfer of the silicon substrate for grinding to achieve rough forming of the chamfer; The chamfer radius is 0.5 mm - 2 mm.

[0008] In an achievable manner, during primary polishing, fix a polishing pad on the arc inner angle of the chamfering fixture and press the chamfering fixture tightly against the side of the silicon substrate; The silicon substrate rotates with the rotating disk, and the polishing pad contacts the chamfer for primary polishing to achieve fine forming of the chamfer.

[0009] In an achievable manner, after primary polishing of the chamfer, use an atomic force microscope to test any 10 μm × 10 μm range on the substrate surface, and the roughness RMS < 0.5 nm; if the test does not meet the requirements, repeat step one and polish again.

[0010] In an achievable manner, in step two, covering polycrystalline diamond seeds on the surface of the silicon substrate after chamfering treatment includes: Select polycrystalline diamond powder to prepare a suspension. The particle diameter of the polycrystalline diamond powder is 20 nm - 20 µm, and deionized water is used to prepare the suspension until the concentration of the suspension is 0.1 wt% to 5 wt%; Immerse the silicon substrate in the suspension and place it in an ultrasonic cleaner for ultrasonic treatment.

[0011] In an achievable manner, during the ultrasonic treatment process in the ultrasonic cleaner, heat the water bath to between 30 - 80 ºC, with a power of 60 - 900 W and a time of 10 - 60 min.

[0012] In an achievable manner, after ultrasonic treatment, use a nitrogen gun to blow the surface of the silicon substrate, then place it in an oven for heating until the surface of the silicon substrate is dry, and cover a layer of polycrystalline diamond seeds on the surface of the silicon substrate.

[0013] In an achievable manner, in step three, growing polycrystalline diamond on the polycrystalline diamond seeds includes: Place the silicon substrate covered with polycrystalline diamond seeds into a microwave plasma chemical vapor deposition device, evacuate to below 5.0E - 6 mbar, use hydrogen as a carrier, heat by microwave during the growth process, and introduce a gaseous carbon source to form a polycrystalline diamond / silicon composite substrate.

[0014] In one feasible way, in step three, the hydrogen flow rate is 200 - 300 sccm; the gaseous carbon source is any one or a combination of methane, ethane, ethylene, acetylene, and propane, and the carbon-hydrogen ratio is the ratio of the gaseous carbon source flow rate to the hydrogen flow rate, which is controlled between 1% and 5%.

[0015] In one feasible way, in step three, it is heated to 700 - 900 °C by microwave heating, and the pressure is controlled between 100 - 200 mbar; the growth time is 10 - 300 hours.

[0016] The method for improving the thickness uniformity of polycrystalline diamond provided by the present invention, compared with the prior art, has the beneficial effects that: First, chamfering the edge intersection area of the silicon substrate can effectively change the geometric shape of the edge intersection area of the silicon substrate, avoid the problem of tip discharge in the edge intersection area of the silicon substrate, and thus avoid the formation of local hot spots in the edge intersection area. Therefore, the problem that the growth rate in the edge intersection area is higher than that in the central area can be avoided, so that the growth rate in the edge intersection area of the silicon substrate is the same as that in the central area, the thickness of the polycrystalline diamond is uniform from the central area to the edge intersection area, and the stress distribution is uniform. Thus, during the cooling process after the growth of the polycrystalline diamond is completed, the shrinkage rate in the edge intersection area is the same as that in the central area, avoiding the risk of cracking and scrapping of the polycrystalline diamond, which makes it unusable.

[0017] (2)By chamfering the edge intersection area of the silicon substrate, the growth thickness of the polycrystalline diamond in the central area and the edge intersection area of the silicon substrate can be made uniform, thereby reducing the time required for subsequent polishing.

[0018] The chamfering treatment process of the silicon substrate in the present invention increases the overall cost very little, is simple and easy to implement, can significantly improve the thickness uniformity of polycrystalline diamond, and can significantly reduce the temperature deviation between the edge area and the central area caused by tip discharge of hydrogen plasma at the edge of the silicon substrate. The present invention is suitable for preparing silicon-based polycrystalline diamond with a thickness ≥ 100 µm to prevent cracking caused by the temperature deviation between the edge area and the central area. Description of the Drawings

[0019] Figure 1 Schematic diagram of the structure where the polycrystalline diamond cracks due to different shrinkages in the edge area and the central area of the polycrystalline diamond on the silicon substrate (a is the cracking position); Figure 2 Flow chart of the silicon substrate chamfering and primary polishing process provided by the embodiment of the present invention; Figure 3 Flow chart of the polycrystalline diamond secondary polishing process provided by the embodiment of the present invention; Figure 4 Schematic diagram of the structure of the first embodiment of the chamfering fixture provided by the embodiment of the present invention; Figure 5 Schematic diagram of the second embodiment of the chamfering fixture provided by the embodiment of the present invention; Explanation of reference numerals: 1. Silicon substrate; 2. Chamfering fixture. Specific implementation manners

[0020] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0021] Please refer to Figure 2 , and now a method for improving the thickness uniformity of polycrystalline diamond provided by the present invention will be described.

[0022] Embodiment 1 The method for improving the thickness uniformity of polycrystalline diamond provided by the present invention includes the following steps: Step 1, silicon substrate 1 chamfering treatment process. A single-crystal silicon substrate is selected, and the substrate crystal plane is the (001) plane. As shown in Figure 2 , Figure 4 and Figure 5 , the chamfer is processed by using a chamfering fixture 2 adapted to the chamfer of the silicon substrate. The silicon substrate chamfer polishing is divided into two parts: silicon substrate chamfer grinding treatment and silicon substrate chamfer polishing.

[0023] Among them, the inner angle of the chamfering fixture 2 has an arc inner angle adapted to the chamfer of the silicon substrate; the grinding head is in a circular arc shape adapted to the arc inner angle of the chamfering fixture 2, and the grinding head has a circular arc grinding surface. The chamfering fixture is in a groove shape, and the inner corner part of the chamfering fixture has an arc curved surface adapted to the chamfer shape after the final forming of the silicon substrate edge; the grinding head is fixed at the arc curved surface, and the grinding head has an arc curved surface adapted to the final forming chamfer shape.

[0024] Silicon substrate chamfer grinding treatment: Place the silicon substrate on the rotating disk, fix the chamfering fixture with the grinding head on the side of the silicon substrate, fix the lower end of the chamfering fixture on the workbench, the rotating disk is located on the workbench, the chamfering fixture is in an L shape or a groove shape, and the vertical inner side surface of the chamfering fixture does not contact the side surface of the silicon substrate, and only the circular arc grinding surface of the grinding head contacts the chamfer of the silicon substrate.

[0025] The silicon substrate rotates with the rotating disk, and the inner grinding head of the chamfering fixture chamfers the intersection angle area of the front surface edge of the silicon substrate. The edge chamfer of the front surface of the silicon substrate is chamfered from the original 90° angle to form an arc chamfer, realizing the preliminary forming or rough forming of the chamfer, and the chamfer radius is controlled within 0.5 mm - 2 mm.

[0026] Chamfer polishing treatment: The silicon substrate after chamfering treatment is polished. When the silicon substrate is chamfered and polished, the polishing pad is fixed inside the chamfer fixture. The polishing pad is made of a flexible material that can adapt to the inner arc angle of the chamfer fixture. The polishing pad contacts the chamfer arc of the silicon substrate, and by rotating the rotating disk, the surface of the chamfered silicon substrate can be finely polished; The polished chamfered silicon substrate is cleaned; the atomic force microscope is used to measure any 10μm×10μm range on the substrate surface, and the roughness (RMS) = 0.45nm; If the test does not meet the requirements, repeat step one and polish again.

[0027] Step two, covering the polycrystalline diamond seed crystal process. Select polycrystalline diamond powder to prepare a suspension. The particle diameter of the polycrystalline diamond powder is 20nm, the liquid is deionized water, and the concentration of the polycrystalline diamond powder suspension is 0.1wt%.

[0028] The chamfered silicon substrate is immersed in the suspension, placed in an ultrasonic cleaner for ultrasonic treatment, heated in a water bath to 30ºC, with a power of 600W and a time of 10min; the chamfered silicon substrate after ultrasonic treatment is taken out of the suspension, the excess suspension is blown off with a nitrogen gun, and then placed in an oven for heating until it is taken out after the surface is dry; thus, a layer of polycrystalline diamond seed crystals is evenly covered on the surface of the chamfered silicon substrate.

[0029] Step three, polycrystalline diamond growth process. The silicon substrate covered with polycrystalline diamond seed crystals is placed in an MPCVD device, and the vacuum is pumped to 4.50E-6mbar; hydrogen is introduced as the carrier gas, and the hydrogen flow rate is 200sccm.

[0030] The microwave power source is turned on, the temperature is raised to 700ºC, and the pressure is controlled at 100mbar; a gaseous carbon source is introduced, methane is used as the gaseous carbon source, and the carbon-hydrogen ratio (C / H) is the ratio of the gaseous carbon source flow rate to the hydrogen flow rate, which is 1%, and the growth time is 10 hours.

[0031] The microwave power is turned off, the hydrogen and the gaseous carbon source are stopped, and the temperature is slowly lowered to room temperature in a hydrogen environment to form a polycrystalline diamond / silicon composite substrate; Step four, polycrystalline diamond secondary polishing process, see Figure 3 .. The polycrystalline diamond / silicon composite substrate is taken out, high-temperature heat-conducting silicone grease is applied to the silicon material side of the polycrystalline diamond / silicon composite substrate, and then it is pasted on the polishing machine head with the polycrystalline diamond side facing outwards.

[0032] The polishing machine head is placed flat, the polycrystalline diamond contacts the polishing disk, a certain pressure is applied to the polishing machine head, and the rotation speed of the polishing disk is adjusted. As the polishing process progresses, the thickness deviation between the edge intersection angle area and the central area of the polycrystalline diamond is <10µm until the polycrystalline diamond surface can be polished to a mirror surface.

[0033] After thickness testing, the thickness deviation between the edge region and the central region of the polycrystalline diamond is 9 µm, and the polishing process is completed.

[0034] MPCVD is the abbreviation of Microwave Plasma Chemical Vapor Deposition, and its Chinese meaning is microwave plasma chemical vapor deposition. The MPCVD equipment is a device used to grow single-crystal and polycrystalline diamonds in batches.

[0035] Example Two The method for improving the thickness uniformity of polycrystalline diamond provided by the present invention includes the following steps: Step 1, chamfering process of the silicon substrate 1. Select a single-crystalline silicon substrate with the substrate crystal plane being the (001) plane. As shown in the attachment Figure 2 The chamfer is processed using a chamfering fixture adapted to the silicon substrate chamfer. The silicon substrate chamfer polishing is divided into two parts: silicon substrate chamfer grinding and silicon substrate chamfer polishing.

[0036] Using an atomic force microscope to test any 10 µm × 10 µm range on the substrate surface, the roughness (RMS) = 0.42 nm; Step 2, process of covering polycrystalline diamond seeds. Select polycrystalline diamond powder to prepare a suspension. The particle diameter of the polycrystalline diamond powder is 20 µm, the liquid is deionized water, and the concentration of the polycrystalline diamond powder suspension is 5 wt%.

[0037] Immerse the chamfered silicon substrate in the suspension, put it into an ultrasonic cleaner for ultrasonic treatment, heat it in a water bath to 80 °C, with a power of 900 W and a time of 60 min; take out the ultrasonic-treated chamfered silicon substrate from the suspension, use a nitrogen gun to blow off the excess suspension, and put it into an oven for heating until it is taken out after the surface is dry; thus, a layer of polycrystalline diamond seeds is evenly covered on the surface of the chamfered silicon substrate.

[0038] Step 3, polycrystalline diamond growth process. Put the silicon substrate covered with polycrystalline diamond seeds into the MPCVD equipment, evacuate to 4.0E-6 mbar; introduce hydrogen as the carrier gas with a hydrogen flow rate of 200 sccm.

[0039] Turn on the microwave power source, heat up to 900 °C, and control the pressure at 200 mbar; introduce gaseous carbon sources, methane, ethane, and ethylene as gaseous carbon sources, and the carbon-hydrogen ratio (C / H) is the ratio of the gaseous carbon source flow rate to the hydrogen flow rate, which is 1%, and the growth time is 300 hours.

[0040] Turn off the microwave power supply, stop the hydrogen and gaseous carbon sources, and slowly cool down to room temperature in a hydrogen environment to form a polycrystalline diamond / silicon composite substrate; Step 4, the polycrystalline diamond secondary polishing process, see Figure 3 Take out the polycrystalline diamond / silicon composite substrate, apply high-temperature heat-conducting silicone grease on the silicon material side of the polycrystalline diamond / silicon composite substrate, and then paste it on the polishing machine head with the polycrystalline diamond side facing outwards. Lay the polishing machine head flat so that the polycrystalline diamond contacts the polishing disc.

[0041] Apply a certain pressure to the polishing machine head and adjust the rotation speed of the polishing disc. As the polishing process proceeds, the thickness deviation between the edge intersection angle area and the center area of the polycrystalline diamond is <10 µm, and further polish the polycrystalline diamond surface to a mirror surface.

[0042] After thickness testing, the thickness deviation between the edge area and the center area of the polycrystalline diamond is 6 µm, and the polishing process ends.

[0043] Example 3 The method for improving the thickness uniformity of polycrystalline diamond provided by the present invention includes the following steps: Step 1, the chamfering process of the silicon substrate 1. Select a single-crystalline silicon substrate with the substrate crystal plane being the (001) plane. As shown in the appendix Figure 2 , use a chamfering fixture adapted to the silicon substrate chamfering to process the chamfer. The silicon substrate chamfer polishing is divided into two parts: the silicon substrate chamfer grinding process and the silicon substrate chamfer polishing process; use an atomic force microscope to test any 10 µm×10 µm range on the substrate surface, and the roughness (RMS) = 0.40 nm; Step 2, the process of covering polycrystalline diamond seeds. Select polycrystalline diamond powder to prepare a suspension. The particle diameter of the polycrystalline diamond powder is 10 µm, the liquid is deionized water, and the concentration of the polycrystalline diamond powder suspension is 1 wt%.

[0044] Immerse the chamfered silicon substrate in the suspension, put it into an ultrasonic cleaner for ultrasonic treatment, heat it in a water bath to 50 ºC, with a power of 100 W and a time of 30 min; take out the chamfered silicon substrate after ultrasonic treatment from the suspension, use a nitrogen gun to blow off the excess suspension, and put it into an oven for heating until it is taken out after the surface is dry; thus, a layer of polycrystalline diamond seeds is evenly covered on the surface of the chamfered silicon substrate.

[0045] Step 3, the polycrystalline diamond growth process. Put the silicon substrate covered with polycrystalline diamond seeds into the MPCVD equipment and evacuate it to 4.3E-6 mbar; introduce hydrogen as the carrier gas with a hydrogen flow rate of 200 sccm.

[0046] Turn on the microwave power source, heat up to 850 ºC, and control the pressure at 120 mbar; introduce gaseous carbon sources, acetylene and propane as gaseous carbon sources, and the carbon-hydrogen ratio (C / H) is the ratio of the gaseous carbon source flow rate to the hydrogen flow rate, which is 2%, and the growth time is 100 hours.

[0047] Turn off the microwave power supply, stop the hydrogen gas and gaseous carbon source, and slowly cool down to room temperature in a hydrogen environment to form a polycrystalline diamond / silicon composite substrate; Step 4: The secondary polishing process of polycrystalline diamond, refer to Figure 3 . Take out the polycrystalline diamond / silicon composite substrate, apply high-temperature heat-conducting silicone grease on the silicon material side of the polycrystalline diamond / silicon composite substrate, and then paste it on the polishing machine head with the polycrystalline diamond side facing outwards. Place the polishing machine head flat so that the polycrystalline diamond contacts the polishing disc.

[0048] Apply a certain pressure to the polishing machine head and adjust the rotation speed of the polishing disc. As the polishing process progresses, the thickness deviation between the edge intersection area and the central area of the polycrystalline diamond is <10 µm, and further polish the polycrystalline diamond surface to a mirror surface.

[0049] After thickness testing, the thickness deviation between the edge area and the central area of the polycrystalline diamond is 8 µm, and the polishing process ends.

[0050] In the above embodiments, the descriptions of each embodiment have their own focuses. For the parts not detailed or recorded in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0051] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for improving the thickness uniformity of polycrystalline diamond, characterized in that: The method comprises the following steps: Step 1, chamfering and grinding the edge corner area of ​​the silicon substrate (1), and performing a polishing operation; Step 2, covering the surface of the chamfered silicon substrate (1) with polycrystalline diamond seed crystals; Step 3, growing polycrystalline diamond on the polycrystalline diamond seed crystal; Step 4: secondary polishing to make the thickness deviation between the edge corner area and the center area of ​​the polycrystalline diamond less than 10µm.

2. The method for improving the thickness uniformity of polycrystalline diamond according to claim 1, characterized in that: Step 1, chamfering and grinding the edge corner area of ​​the silicon substrate (1), and performing a polishing process, including: A chamfering fixture (2) having a grinding head is fixed to the side of a silicon substrate; wherein the inner side angle of the chamfering fixture (2) has an arc inner angle adapted to the chamfering of the silicon substrate; the grinding head is in an arc shape adapted to the arc inner angle of the chamfering fixture (2), and the grinding head has an arc-shaped grinding surface; The silicon substrate rotates with the rotating disk, and the arc-shaped grinding surface of the grinding head contacts and grinds the chamfer of the silicon substrate to achieve rough forming of the chamfer; The chamfer radius is 0.5mm-2mm.

3. The method for improving the thickness uniformity of polycrystalline diamond according to claim 2, characterized in that: During a single polishing operation, the polishing pad is fixed on the inner corner of the circular arc of the chamfering fixture (2), and the chamfering fixture (2) is pressed tightly against the side of the silicon substrate; The silicon substrate (1) rotates with the rotating disk, and the polishing pad contacts the chamfer of the silicon substrate (1) to perform a polishing operation, thereby achieving fine shaping of the chamfer.

4. The method for improving the thickness uniformity of polycrystalline diamond according to claim 3, characterized in that: After the chamfer is polished once, the roughness RMS is <0.5nm in any 10μm×10μm range of the substrate surface tested by atomic force microscopy; If the test fails, repeat step 1 and polish again.

5. The method for improving the thickness uniformity of polycrystalline diamond according to claim 1, characterized in that: Step 2, covering the chamfered silicon substrate surface with polycrystalline diamond seed crystals, comprising: Select polycrystalline diamond powder to prepare suspension, the particle diameter of polycrystalline diamond powder is 20nm-20µm, and use deionized water to prepare suspension to a concentration of 0.1wt% to 5wt%; The silicon substrate is immersed in the suspension and placed in an ultrasonic cleaning machine for ultrasonic treatment.

6. The method for improving the thickness uniformity of polycrystalline diamond according to claim 5, characterized in that: The ultrasonic treatment process is carried out in an ultrasonic cleaning machine, with the water bath heated to between 30-80ºC, the power being 60-900W, and the time being 10-60min.

7. The method for improving the thickness uniformity of polycrystalline diamond according to claim 5, characterized in that: After the ultrasonic treatment, the surface of the silicon substrate is purged with a nitrogen gun and then placed in an oven for heating until the surface of the silicon substrate is dry, and a layer of polycrystalline diamond seed crystals is covered on the surface of the silicon substrate.

8. The method for improving the thickness uniformity of polycrystalline diamond according to claim 1, characterized in that: Step 3, growing polycrystalline diamond on the polycrystalline diamond seed crystal, comprising: The silicon substrate covered with polycrystalline diamond seed crystals is placed in a microwave plasma chemical vapor deposition device, evacuated to below 5.0E-6mbar, hydrogen is used as a carrier, microwave heating is adopted in the growth process, and a gaseous carbon source is introduced to form a polycrystalline diamond / silicon composite substrate.

9. The method for improving the thickness uniformity of polycrystalline diamond according to claim 8, characterized in that: In step three, the flow rate of hydrogen is 200-300 sccm; the gaseous carbon source is any one or more combinations of methane, ethane, ethylene, acetylene and propane, and the carbon-hydrogen ratio is the ratio of the gaseous carbon source flow rate to the hydrogen flow rate, and is controlled between 1% and 5%.

10. The method for improving the thickness uniformity of polycrystalline diamond according to claim 8, characterized in that: In step 3, microwave heating is used to raise the temperature to 700-900°C, and the pressure is controlled between 100-200 mbar; the growth time is 10-300 hours.

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