A silicon high uniformity wet etching device and method

Abstract

The purpose of the present invention is to provide a silicon high uniformity wet etching device and method, belonging to the field of semiconductor chip manufacturing technology, the device includes a water bath, a beaker is provided in the water bath, a fixture made of polytetrafluoroethylene material for clamping silicon wafers is provided in the beaker, the fixture includes a clamp, the clamp includes an upper clamp and a lower clamp connected by bolts, an upper screw is provided at the top of the upper clamp, a filter plate is provided at the bottom of the clamp, the lower clamp is connected to the filter plate by a middle screw, and a lower screw is provided at the bottom of the filter plate. Through the device and method, the uniformity of wet etching can be improved, the morphology of wet etching can be improved, and the generation of precipitates and gas overflow can be accelerated by relieving the flow rate of the etching liquid, so as to achieve the effect of improving the uniformity of deep silicon etching of the whole wafer while improving the morphology.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor chip manufacturing, and in particular relates to a silicon high-uniformity wet etching device and method. Background Art

[0002] In the process of semiconductor chip manufacturing, etching silicon wafers is a common step in the semiconductor manufacturing process. Etching is mainly divided into wet etching and dry etching. The equipment used for dry etching is expensive and has poor uniformity. At present, the deep silicon etching error of MEMS process dry etching equipment is ±3%. The wet etching process is simple to operate, the equipment cost is low, and the uniformity is good. With the development of MEMS technology, the critical size is getting smaller and smaller, and the etching uniformity requirements for the entire silicon wafer are getting higher and higher, so wet etching has been widely used.

[0003] The silicon wet etching process is often carried out in a water bath, which makes the silicon wafer heated more evenly in the solution and the etching rate more controllable. Commonly used etching solutions include potassium hydroxide (KOH), sodium hydroxide (NaOH) and tetramethylammonium hydroxide (TMAH). TMAH, as a commonly used organic alkaline solution, avoids metal pollution in the process environment. TMAH reacts with silicon to generate orthosilicic acid precipitate and hydrogen. Both orthosilicic acid and hydrogen will adhere to the silicon surface to form a local mask, resulting in an uneven surface of the silicon, which will not only affect the corrosion morphology, but also affect the corrosion uniformity. Summary of the invention

[0004] The object of the present invention is to provide a high-uniformity wet etching device and method for silicon. Through the device and method, the uniformity of wet etching can be improved, the wet etching morphology can be improved, and the generation of precipitates and gas overflow can be accelerated by reducing the flow rate of the etching liquid, so as to achieve the effect of improving the uniformity of deep silicon etching of the entire wafer while improving the morphology.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A high uniformity wet etching device for silicon comprises a water bath, a beaker is arranged in the water bath, a fixture made of polytetrafluoroethylene material for clamping a silicon wafer is arranged in the beaker, the fixture comprises a clamping piece, the clamping piece comprises an upper clamping piece and a lower clamping piece connected by bolts, an upper screw is arranged at the top of the upper clamping piece, a filter plate is arranged at the bottom of the clamping piece, the lower clamping piece and the filter plate are connected by a middle screw, and a lower screw is arranged at the bottom of the filter plate.

[0007] Furthermore, a groove is provided on an end surface of the lower clamping member close to the upper clamping member.

[0008] Furthermore, the cross sections of the clamping member and the filter plate are both circular.

[0009] Furthermore, there are two upper screw rods, which are symmetrically arranged relative to the center of the clamping member.

[0010] Furthermore, the number of the middle screws is four, and they are arranged in a cross-symmetric manner relative to the center of the clamping member.

[0011] Furthermore, the number of the lower screws is four, and they are arranged in a cross-symmetric manner relative to the center of the filter plate.

[0012] Furthermore, the diameter of the filter plate is greater than the diameter of the clamping member.

[0013] A high uniformity wet etching method for silicon comprises the following steps:

[0014] The first step is to provide a single-polished silicon wafer, on both sides of which silicon oxide and silicon nitride are grown by low-pressure chemical vapor deposition as a masking layer for substrate silicon corrosion;

[0015] The second step is to pattern the front side of the silicon wafer through coating, pre-baking, exposure, development, stripping and post-baking.

[0016] The third step is to use reactive ion etching to remove the silicon nitride and silicon oxide in the exposed part of the silicon wafer after the patterning process in the second step, so as to complete the hole opening;

[0017] Step 4: Add deionized water to the water bath, place the beaker containing the corrosive solution into the water bath, turn on the power and set the temperature, and wait for the temperature to stabilize for half an hour;

[0018] Step 5: Place the silicon wafer with the polished surface facing downward in a fixture, place the fixture in a beaker, turn on the rotor and start wet etching;

[0019] Step 6. After the etching depth is reached, the silicon wafer is taken out and placed in a glass container filled with deionized water for ultrasonic cleaning and then blown dry with nitrogen.

[0020] Furthermore, in the first step, the thickness of the silicon oxide is 300 nm, and the thickness of the silicon nitride is 300 nm.

[0021] Furthermore, in the third step, the silicon nitride is removed by etching the silicon nitride with CF4 for 10 minutes and etching the silicon oxide with CHF3 for 20 minutes.

[0022] The working principle of the water bath used for wet etching is to use the bottom heating element to heat the water to a set temperature, and then maintain a constant temperature through the heat capacity and heat conduction characteristics of the water. When the heating element starts to heat the water, the water temperature gradually rises until the set temperature is reached. After reaching the set temperature, the heating element will stop heating, but the water bath will continue to maintain a constant temperature because the heat capacity and heat conduction characteristics of water can help maintain temperature stability. In the water bath, the closer the silicon wafer is to the bottom heating element, the higher the corrosion temperature, the worse the corrosion morphology and uniformity, resulting in the actual corrosion depth not being consistent with the expected corrosion depth. In the present invention, the silicon wafer is placed in the fixture groove, and the clamp is supported by a screw, so that it is at a certain distance from the bottom heating element of the water bath, while leaving enough space for the rotor to rotate.

[0023] TMAH reacts with silicon to generate orthosilicic acid precipitate and hydrogen. The two substances will form a local mask on the silicon surface. In addition to using additives, the silicon wafer can also be placed face down so that the liquid below can directly contact the corrosion surface when heated and move upward. The orthosilicic acid precipitate produced by corrosion falls with gravity and avoids adhering to the silicon surface. The rotation of the rotor accelerates the flow of liquid and accelerates the overflow of precipitate and hydrogen.

[0024] When the rotor rotates, water flow and heat flow are generated obliquely upward, making the bottom of the silicon corrosion uneven. In the present invention, the filter plate below the clamp can slow down the flow rate of the liquid and prevent the impact of the water flow on the side wall of the silicon corrosion.

[0025] This invention can control the absolute error of etching depth within 1 μm.

[0026] The beneficial effects of the present invention are as follows:

[0027] The wet etching device of the present invention is simple to operate to control the uniformity of corrosion, and the control method does not require additional additives, nor does it require replacement of parts of the corrosion equipment or adjustment of corrosion parameters, thereby reducing the cost of process adjustment. The present invention can effectively control the corrosion depth of wet corrosion, improve the uniformity of wet corrosion, and improve the morphology of wet corrosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a flow chart of the wet etching method of the present invention;

[0029] Figure 2 It is a structural schematic diagram of the wet etching device of the present invention;

[0030] Figure 3 It is a structural schematic diagram of the clamp of the present invention;

[0031] Figure 4 It is a schematic diagram of the exploded structure of the clamp of the present invention;

[0032] Figure 5A schematic diagram of the corrosion structure of a silicon wafer according to an embodiment of the present invention;

[0033] Figure 6 is an actual etching diagram of a silicon wafer according to an embodiment of the present invention;

[0034] Among them: 1-water bath; 2-beaker; 3-clamp; 31-upper screw; 32-clamping piece; 321-bolt; 322-upper clamping piece; 323-lower clamping piece; 33-middle screw; 34-filter plate; 35-lower screw; 4-silicon; 5-silicon oxide; 6-silicon nitride. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] like Figures 1 to 4 As shown, a high uniformity wet etching device for silicon comprises a water bath 1, wherein a beaker 2 is arranged in the water bath 1, wherein a fixture 3 made of polytetrafluoroethylene material for clamping a silicon wafer is arranged in the beaker 2, wherein the fixture 3 comprises a clamp 32, wherein the clamp 32 comprises an upper clamp 322 and a lower clamp 323 connected by bolts 321, wherein an upper screw 31 is arranged at the top of the upper clamp 322, wherein a filter plate 34 is arranged at the bottom of the clamp 32, wherein the lower clamp 323 is connected to the filter plate 34 by a middle screw 33, and wherein a lower screw 35 is arranged at the bottom of the filter plate 34.

[0037] Furthermore, a groove is provided on an end surface of the lower clamping member 323 close to the upper clamping member 322 .

[0038] Furthermore, the cross sections of the clamping member 32 and the filter plate 34 are both circular.

[0039] Furthermore, there are two upper screw rods 31 , which are symmetrically arranged relative to the center of the clamping member 32 .

[0040] Furthermore, there are four middle screws 33 , which are arranged in a cross-symmetric manner relative to the center of the clamping member 32 .

[0041] Furthermore, there are four lower screw rods 35 , which are arranged in a cross-symmetric manner relative to the center of the filter plate 34 .

[0042] Furthermore, the diameter of the filter plate 34 is greater than the diameter of the clamping member 32 .

[0043] Example

[0044] A high uniformity wet etching method for silicon comprises the following steps:

[0045] 1: Provide a single-polished silicon wafer, both sides of which use low-pressure chemical vapor deposition (LP-CVD) to grow silicon oxide and silicon nitride as a masking layer for substrate silicon corrosion; C1232 model, double-polished N-type silicon wafer, silicon crystal orientation <100> , resistivity 2-4, silicon wafer thickness 500±15μm, oxide layer 300nm, nitride layer 300nm;

[0046] 2: Graphic processing is performed on the front side of the silicon wafer through coating, pre-baking, exposure, development, stripping and post-baking;

[0047] (1) Use Cee200XCB coating machine for coating, use photoresist 6130, and the coating parameters are 6130-1000r;

[0048] (2) Pre-bake on a hot plate at 100°C for 1 minute;

[0049] (3) Exposure with EVG610, exposure dose 160mj / cm 2 ;

[0050] (4) Use IoN Wave 10 for debonding, gas type O2, power 300W, 2min;

[0051] (5) Bake on a hot plate at 120°C for 15 minutes;

[0052] 3: Use reactive ion etching (RIE) to remove the silicon nitride and silicon oxide in the exposed area in step 2 respectively to complete the hole opening; use CF4 to etch silicon nitride for 10 minutes (overetching), and CHF3 to etch silicon oxide for 20 minutes (overetching);

[0053] 4: Add an appropriate amount of deionized water to the water bath, place the beaker containing the corrosive solution into the water bath, turn on the power and set the temperature, and wait for the temperature to stabilize for half an hour;

[0054] 5: Open the wet etching fixture, place the silicon wafer face down into the groove between the upper clamp and the lower clamp, put in a gasket made of fluororubber to fix the silicon wafer in the groove, then tighten the bolts and screws, put it into the etching liquid beaker in the water bath, and turn on the rotor for stirring;

[0055] 6: After a certain period of time, when the corrosion depth is reached, take out the silicon wafer, put it into a glass container filled with deionized water, and ultrasonically clean it for 5 minutes, and then blow it dry with nitrogen.

[0056] Schematic diagram of corrosion structure Figure 5As shown in the figure, in order to obtain the accurate corrosion rate of the (111) surface, the lateral corrosion distance d1 is measured using a microscope. Since the angle θ between the (111) surface and the (100) surface is 54.7°, the corrosion distance d2 of the (111) surface is d1sin54.7°. The actual corrosion inclination is Figure 6 As shown, it is 54.2°, which is close to the theoretical value of 54.7°.

[0057] At 80°C, the wet etching with 25 wt% TMAH for 8.5 hours reached a corrosion depth of 236.7 μm. The electron microscope image is shown in Figure 6 As shown. According to the corrosion time t, the formula for calculating the corrosion rate of the (111) surface is obtained:

[0058] V （111） =d1sin54.7° / t.

[0059] The corrosion depth h of the (100) surface is measured using a step profiler, and the corrosion rate formula of the (100) surface is obtained from the corrosion time t: V （100） =h / t.

Claims

1. A silicon high uniformity wet etching device, characterized in that: The invention comprises a water bath (1), wherein a beaker (2) is arranged in the water bath (1), wherein a fixture (3) made of polytetrafluoroethylene material for clamping a silicon wafer is arranged in the beaker (2), wherein the fixture (3) comprises a clamping member (32), wherein the clamping member (32) comprises an upper clamping member (322) and a lower clamping member (323) connected by bolts (321), wherein an upper screw rod (31) is arranged at the top of the upper clamping member (322), and a filter plate (34) is arranged at the bottom of the clamping member (32), and wherein the lower clamping member (323) is provided with a filter plate (34). The holder (323) and the filter plate (34) are connected via a middle screw (33), and a lower screw (35) is provided at the bottom of the filter plate (34); the diameter of the filter plate (34) is larger than the diameter of the holder (32), and the filter plate (34) below the clamp (3) can slow down the flow rate of the liquid and prevent the impact of the water flow on the silicon-corroded side wall; the holder (32) is supported by a screw so that it is at a certain distance from the heating element at the bottom of the water bath (1), while leaving enough space for the rotor to rotate; A groove is provided on an end surface of the lower clamping piece (323) close to the upper clamping piece (322), and the silicon wafer is placed in the groove with the front side facing downwards; The clamping member (32) and the filter plate (34) are both in an annular shape.

2. The high uniformity wet etching device for silicon according to claim 1, characterized in that: The number of the upper screw rods (31) is two, and they are arranged symmetrically relative to the center of the clamping member (32).

3. The high uniformity wet etching device for silicon according to claim 1, characterized in that: The number of the middle screw rods (33) is four, and they are arranged in a cross-symmetrical manner relative to the center of the clamping member (32).

4. The high uniformity wet etching device for silicon according to claim 1, characterized in that: The number of the lower screw rods (35) is four, and they are arranged in a cross-symmetrical manner relative to the center of the filter plate (34).

5. A method for high uniformity wet etching of silicon using the device as claimed in claim 1, characterized in that: The steps include: The first step is to provide a single-polished silicon wafer, on both sides of which silicon oxide and silicon nitride are grown by low-pressure chemical vapor deposition as a masking layer for substrate silicon corrosion; The second step is to pattern the front side of the silicon wafer through coating, pre-baking, exposure, development, stripping and post-baking. The third step is to use reactive ion etching to remove the silicon nitride and silicon oxide in the exposed part of the silicon wafer after the patterning process in the second step, so as to complete the hole opening; Step 4: Add deionized water to the water bath, place the beaker containing the corrosive solution into the water bath, turn on the power and set the temperature, and wait for the temperature to stabilize for half an hour; Step 5: Place the silicon wafer with the polished surface facing downward in a fixture, place the fixture in a beaker, turn on the rotor and start wet etching; Step 6. After the etching depth is reached, the silicon wafer is taken out and placed in a glass container filled with deionized water for ultrasonic cleaning and then blown dry with nitrogen.

6. The method for high uniformity wet etching of silicon according to claim 5, characterized in that: In the first step, the thickness of the silicon oxide is 300 nm, and the thickness of the silicon nitride is 300 nm.

7. The method for high uniformity wet etching of silicon according to claim 5, characterized in that: In the third step, the silicon nitride is removed by etching the silicon nitride with CF4 for 10 minutes and etching the silicon oxide with CHF3 for 20 minutes.

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