A silicon wafer cleaning method and system

Abstract

The present invention relates to a silicon wafer cleaning method and system. The method includes: S1. putting the silicon wafer into a first cleaning tank, adding air into the pure water in the first cleaning tank, and jointly acting with megasonic waves to remove large particle impurities on the silicon wafer; S2. putting the silicon wafer processed in step S1 into a second cleaning tank, adding ozone into the pure water in the second cleaning tank, and jointly acting with megasonic waves to remove atomic, molecular and ionic impurities on the silicon wafer; S3. putting the silicon wafer processed in step S2 into a third cleaning tank, adding air and ozone into the pure water in the third cleaning tank, and jointly acting with megasonic waves to remove residual atomic, molecular and ionic impurities on the silicon wafer. In this way, efficient cleaning of the silicon wafer can be achieved, and no chemical agents are used in the whole cleaning process, with low cleaning cost, simplified processes, short cleaning time, less wastewater generation, and low energy consumption and breakage rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon wafer production, and particularly relates to a silicon wafer cleaning method and system. Background Art

[0002] Currently, in the process of silicon wafer production and processing, the commonly used silicon wafer cleaning method in the industry is to chemically clean the residual substances (atoms, molecules, ions, etc.) on the silicon wafer surface with a mixed alkali agent, NaOH, KOH, H2O2 and other alkaline solvents in a certain ratio under medium and high temperature and ultrasonic conditions; then use pure water to perform fine cleaning on the silicon wafer under high temperature and ultrasonic conditions to remove the residual chemical substances. The existing silicon wafer cleaning process needs to be carried out under high temperature and ultrasonic conditions, and the energy consumption of large-scale cleaning processes is high. In addition, a large amount of chemical alkali agents are required in the silicon wafer cleaning process, the cleaning cost is high and it is not conducive to environmental protection. Summary of the Invention

[0003] In order to solve the above problems existing in the prior art, the present invention provides a silicon wafer cleaning method and system.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] In the first aspect, a silicon wafer cleaning method of the present invention includes:

[0006] S1. Put the silicon wafer into the first cleaning tank, add air to the pure water in the first cleaning tank, and act together with megasonic waves to remove large particle impurities on the silicon wafer;

[0007] S2. Put the silicon wafer processed in step S1 into the second cleaning tank, add ozone to the pure water in the second cleaning tank, and act together with megasonic waves to remove atomic, molecular and ionic impurities on the silicon wafer; S3. Put the silicon wafer processed in step S2 into the third cleaning tank, add air and ozone to the pure water in the third cleaning tank, and act together with megasonic waves to remove the remaining atomic, molecular and ionic impurities on the silicon wafer.

[0008] Further, in step S1, air is input into the pure water from the bottom of the first cleaning tank in the form of small-diameter bubbles, the addition speed is 17 ml / L to 21 ml / L at room temperature, and the frequency of the megasonic wave is 1000 kHz to 1200 kHz.

[0009] Further, in step S2, ozone is added to the pure water in the second cleaning tank in the form of high-pressure and high-concentration micron bubbles under the condition of 0.3 to 0.5 Mpa, the addition ratio is 0.037 L / L of water, and the frequency of the megasonic wave is 1500 kHz to 2000 kHz.

[0010] Further, in step S3, ozone is added to the pure water in the third cleaning tank in the form of high-pressure and high-concentration micron bubbles under the condition of 0.4 Mpa, the addition ratio is 0.021 L / L of water, and the frequency of the megasonic wave is 1500 kHz to 1700 kHz.

[0011] In a second aspect, the present invention also provides a silicon wafer cleaning system based on the silicon wafer cleaning method described above, including:

[0012] A first cleaning tank, the bottom of which is provided with a first air pipe with holes on the circumferential surface and a first megasonic wave generating device, and the first air pipe is connected to a first air pump;

[0013] A second cleaning tank, the bottom of which is provided with a first ultra-fine and dense bubble generator device and a second megasonic wave generating device;

[0014] And a third cleaning tank, the bottom of which is provided with a second air pipe with holes on the circumferential surface, a second ultra-fine and dense bubble generator device and a third megasonic wave generating device, and the second air pipe is connected to a second air pump.

[0015] Further, the frequency of the megasonic wave generated by the first megasonic wave generating device is 1000 kHz to 1200 kHz, the frequency of the megasonic wave generated by the second megasonic wave generating device is 1500 kHz to 2000 kHz, and the frequency of the megasonic wave generated by the third megasonic wave generating device is 1500 kHz to 1700 kHz.

[0016] Through the above technical solutions, the present invention has the following beneficial effects:

[0017] 1. There is no need to use chemical agents, and the cleaning cost is low;

[0018] 2. The process of removing chemical agents is saved, the process is simplified, and the cleaning time is shorter;

[0019] 3. The generation of wastewater during the cleaning process is reduced, and the wastewater treatment cost is lowered;

[0020] 4. The entire cleaning process is completed at medium and low temperatures, while reducing energy consumption and the fragmentation rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic flow chart of the silicon wafer cleaning method described in the present invention;

[0022] Figure 2 is a data graph of the experimental test results of the silicon wafer cleaning method described in the present invention;

[0023] Figure 3 is a schematic diagram of the principle of removing impurities on the surface of the silicon wafer by megasonic waves in the silicon wafer cleaning method described in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, 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.

[0025] As Figure 1 shown, a silicon wafer cleaning method according to the present invention includes the following steps:

[0026] Step S1. Place the silicon wafer into the first cleaning tank, add air to the pure water in the first cleaning tank, and jointly act with

[0027] megasonic waves to remove large particle impurities on the silicon wafer. Specifically: Place the silicon wafer into the first cleaning tank, and then at room temperature, input air into the pure water from the bottom of the first cleaning tank in the form of small-diameter bubbles at a speed of 17 ml / L to 21 ml / L, and at the same time generate megasonic waves in the pure water through a megasonic wave generator. The frequency of the megasonic waves is 1000 kHz to 1200 kHz. The small-diameter bubbles escaping are torn into smaller bubbles by the megasonic waves; the impact force generated by the rupture of the smaller bubbles during the rising process removes large particle impurities on the surface of the silicon wafer.

[0028] In a possible implementation scheme, the bottom of the first cleaning tank is provided with a first air pipe with holes on the peripheral surface and a first megasonic wave generating device, and then a first air pump is used to supply gas to the air pipe, and the gas escapes from the holes on the peripheral surface of the air pipe to form small-diameter bubbles.

[0029] Step S2. Place the silicon wafer processed in step S1 into the second cleaning tank, add ozone to the pure water in the second cleaning tank, and jointly act with megasonic waves to remove atomic, molecular and ionic impurities on the silicon wafer; specifically: Place the silicon wafer processed in step S1 into the second cleaning tank, and then add ozone to the pure water in the second cleaning tank in the form of high-pressure and high-concentration micron bubbles at a ratio of 0.037 L / L of water under the condition of 0.3 to 0.5 Mpa. The diameter of the micron bubbles of the ozone is less than 50 microns; at the same time, megasonic waves are added to the pure water in the second cleaning tank through a megasonic wave generator. The frequency of the megasonic waves is 1500 kHz to 2000 kHz; during the cleaning process, the added ozone micron bubbles float in the pure water, diffuse to the periphery of the silicon wafer and rupture under the action of the megasonic waves. The impact force generated by the rupture also plays a certain role in removing impurities on the surface of the silicon wafer, and the ozone released by the rupture reacts with water to neutralize or react with the atomic, molecular and ionic substances on the surface of the silicon wafer, and then the impact force generated by the megasonic waves causes the reaction products to fall off from the surface of the silicon wafer, achieving the purpose of cleaning and realizing the removal of most atomic, molecular and ionic impurities on the surface of the silicon wafer.

[0030] In a possible implementation, a first ultra-fine dense bubble generator device and a second megasonic wave generating device are provided at the bottom of the second cleaning tank. The ultra-fine dense bubble generator device belongs to the prior art and will not be elaborated here in detail. For example, the high-pressure jet micro-nano bubble generator device with models NANO-JET-01T, NANO-JET-10T, or NANO-JET-50T sold by Shanghai Xingheng Technology Co., Ltd. Ozone is input into pure water from the bottom of the second cleaning tank in the form of high-pressure and high-concentration micron bubbles through the ultra-fine dense bubble generator device.

[0031] Step S3. Place the silicon wafer processed in step S2 into the third cleaning tank. Add air and ozone to the pure water in the third cleaning tank and act together with the megasonic wave to remove the remaining atomic, molecular, and ionic impurities on the silicon wafer. Specifically: Place the silicon wafer processed in step S2 into the third cleaning tank, and then add ozone in the form of high-pressure and high-concentration micron bubbles to the pure water in the third cleaning tank at a ratio of 0.021 L / L of water under the condition of 0.4 Mpa. At the same time, generate megasonic waves in the pure water in the third cleaning tank through a megasonic wave generator. The frequency of the megasonic wave is 1500 kHz to 1700 kHz. Tear the escaping small-diameter bubbles into smaller bubbles through the megasonic wave, and then the smaller bubbles burst during the rising process, and the generated impact force removes the large-particle impurities remaining on the surface of the silicon wafer. At the same time, diffuse and burst the added ozone micron bubbles to the surrounding of the silicon wafer through the megasonic wave. On the one hand, the impact force generated by the bursting plays a certain role in removing the small-particle impurities remaining on the surface of the silicon wafer. On the other hand, the ozone released by the bursting reacts with water to generate mono-oxygen ions to neutralize or react with the atomic, molecular, and ionic substances remaining on the surface of the silicon wafer, and then the impact force generated by the megasonic wave causes the reaction products to fall off from the surface of the silicon wafer, achieving a thorough cleaning effect.

[0032] In a possible implementation, a second air pipe with holes on the peripheral side surface, a second ultra-fine dense bubble generator device, and a third megasonic wave generating device are provided at the bottom of the third cleaning tank, and the

[0033] second air pipe is connected to a second air pump.

[0034] In this way, through the silicon wafer cleaning method of the present invention, efficient cleaning of the silicon wafer can be achieved (specifically, by using megasonic waves of different frequencies in combination with air bubbles and / or ozone microbubbles to remove impurities on the surface of the silicon wafer), and no chemical agents are required during the entire cleaning process. Compared with the existing cleaning methods that use a large amount of chemical alkalis, on the one hand, the cleaning cost can be reduced, on the other hand, the process of removing chemical agents can be saved, the process is simplified, and the cleaning time is shorter (through experimental tests, the total cleaning time of the silicon wafer cleaning method of the present invention is about 42 seconds, and the cleaning times of S1 - S3 are 15 seconds, 10 seconds, and 17 seconds respectively. Compared with the existing process with a total cleaning time of about 90 seconds, the cleaning time is saved by 53.33%, and the cleaning efficiency is increased by more than double). On the third hand, the generation of wastewater during the cleaning process can be reduced, and the wastewater treatment cost can be lowered. On the fourth hand, the entire cleaning process is completed at medium and low temperatures, which not only reduces energy consumption but also avoids the problem of wafer breakage caused by high temperatures, effectively reducing the breakage rate.

[0035] Due to the brittle nature of the silicon wafer material, there are certain requirements for the vibration frequency of the megasonic wave.

[0036] The principle of megasonic wave cleaning is that the ultrasonic power supply emits a high-frequency oscillating current, which is converted into a mechanical vibration wave by the transducer and transmitted into the cleaning medium, thereby generating two phenomena of cavitation and acoustic streaming in the liquid. Under the combined action of these two phenomena, the particles attached to the surface of the wafer are removed. The intensity of the cavitation effect is determined by the size and density of the bubbles formed in the liquid. When the frequency is low, the bubble size is large and the density is low; when the frequency increases, the bubble size decreases and the density increases. The larger the bubble size, the greater the impact force generated when it collapses, and the stronger the ability to remove particles, but at the same time, the greater the damage to the surface of the silicon wafer.

[0037] Therefore, in the three steps of the above cleaning method, this principle is followed, and different megasonic wave frequencies are used for different cleaning time periods on the surface of the silicon wafer. The larger the particle, the relatively smaller the density of the large particles; the smaller the particle, the relatively larger the density of the small particles. During the cleaning process, the large particles will be impacted by energy

[0038] and become smaller. Therefore, different frequencies of megasonic waves are used at different cleaning time periods to thoroughly clean the particles on the surface of the silicon wafer.

[0039] The force analysis of the particles is as follows Figure 3 :

[0040] M R : The peeling moment received by the particle;

[0041] M A : The adhesion moment;

[0042] F Drag : The peeling force;

[0043] F Adhesion : Adhesion force (electrostatic force and van der Waals force);

[0044] F elec double layer : Double electric layer force;

[0045] R: Particle radius;

[0046] a: Contact radius between the particle and the silicon wafer surface.

[0047] M R : Stripping torque on the particle, which includes the torque when the resultant force generated during the cavitation and acoustic streaming chemical and physical reaction processes acts on the particle.

[0048] Let Eth: Thermal energy generated during cavitation;

[0049] Eel: Light radiation energy generated during cavitation;

[0050] Eme: Mechanical energy generated by acoustic waves during cavitation;

[0051] Ech: Chemical energy generated during cavitation;

[0052] q: Cavitation intensity;

[0053] Then the energy of the bubble is WE = Eth + Eel + Eme + Ech =

[0054]

[0055] From the cavitation intensity formula I = WE / △t△v ≈ (P0 / T)q,

[0056] we get q(x, y, z, t) = (t)

[0057] Therefore, when setting the megasonic frequency, precise calculation, testing, and verification are required, and the following data are obtained after multiple tests:

[0058] The first stage (step S1): 1000 kHz - 1200 kHz;

[0059] The second stage (step S2): 1500 kHz - 2000 kHz;

[0060] The third stage (step S1): 1500 kHz - 1700 kHz;

[0061] The cleaning effect is the best when the following process parameters are selected, especially for silicon wafers with a processing size of 158 mm - 230 mm and a thickness of 180 µm - 110 µm.

[0062] In addition, by assembling the above-mentioned first cleaning tank, second cleaning tank and third cleaning tank of the present invention together in sequence, a silicon wafer cleaning device can be formed.

[0063] The silicon wafer cleaning method of the present invention is applied to a production line for experimental detection. The specific operation is as follows:

[0064] Step 1: Place the silicon wafer into the first cleaning tank, then input air in the form of small-diameter bubbles from the bottom of the first cleaning tank into pure water, and then tear the small-diameter bubbles into smaller bubbles through megasonic waves; when the smaller bubbles burst during the rising process, the generated impact force removes large-particle impurities on the surface of the silicon wafer.

[0065] Step 2: Place the silicon wafer cleaned in the first cleaning tank into the second cleaning tank, and then add ozone in the form of high-pressure and high-concentration micron bubbles to pure water. Under the action of megasonic waves, the ozone micron bubbles are diffused to the periphery of the silicon wafer and burst, and the generated impact force removes impurities on the surface of the silicon wafer

[0066] Moreover, the ozone released by the burst reacts with water to neutralize or react with atoms, molecules, and ionic substances on the surface of the silicon wafer, and then falls off from the surface of the silicon wafer under the impact force generated by megasonic waves, achieving the cleaning purpose.

[0067] Step 3: Place the silicon wafer cleaned in the second cleaning tank into the third cleaning tank, and then add air, ozone, and megasonic waves to the pure water in the third cleaning tank. On the one hand, the impact force generated by the bursting of small bubbles is used to remove residual large-particle impurities on the surface of the silicon wafer. On the other hand, the impact force generated by the bursting of ozone micron bubbles and the ozone released by the reaction with water are used, and then megasonic waves are used to further clean the surface of the silicon wafer to remove residual atomic, molecular, and ionic impurities.

[0068] Perform the cleaning experiment according to the above steps for a certain period of time, and detect the silicon wafers after cleaning and the silicon wafers cleaned by the existing silicon wafer cleaning process described in the background art of the present invention before. The detection results are as Figure 2 shown. The defective wafer rate of the silicon wafer cleaning method of the present invention can be reduced to less than 0.22%, while the defective wafer rate of the existing silicon wafer cleaning process can only reach 0.31%. It can be seen that the silicon wafer cleaning method of the present invention can achieve efficient cleaning of silicon wafers.

[0069] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. A silicon wafer cleaning method, characterized in that Including: S1. Place the silicon wafer into the first cleaning tank, add air to the pure water in the first cleaning tank, and cooperate with megasonic waves to remove large-particle impurities on the silicon wafer. S2. Place the silicon wafer processed in step S1 into the second cleaning tank, add ozone to the pure water in the second cleaning tank, and cooperate with megasonic waves to remove atomic, molecular, and ionic impurities on the silicon wafer. S3. Place the silicon wafer processed in step S2 into the third cleaning tank, add air and ozone to the pure water in the third cleaning tank, and cooperate with megasonic waves to further remove residual atomic, molecular, and ionic impurities on the silicon wafer.

2. The method according to claim 1, wherein In step S1, air is input into the pure water from the bottom of the first cleaning tank in the form of small-diameter bubbles, and the addition speed is 17 ml / L - 21 ml / L at room temperature, and the frequency of the megasonic wave is 1000 kHz - 1200 kHz.

3. The method according to claim 1, wherein In step S2, ozone is added to the pure water in the second cleaning tank in the form of high-pressure and high-concentration micron-sized bubbles under the condition of 0.3 - 0.5 Mpa, and the addition ratio is 0.037 L / L of water, and the frequency of the megasonic wave is 1500 kHz - 2000 kHz.

4. The method according to claim 1, wherein In step S3, ozone is added to the pure water in the third cleaning tank in the form of high-pressure and high-concentration micron-sized bubbles under the condition of 0.4 Mpa, and the addition ratio is 0.021 L / L of water, and the frequency of the megasonic wave is 1500 kHz - 1700 kHz.

5. A silicon wafer cleaning system based on the silicon wafer cleaning method according to any one of claims 1-4, characterized in that, Including: The first cleaning tank, at the bottom of which there is a first air pipe with holes on the peripheral surface and a first megasonic wave generating device, and the first air pipe is connected to a first air pump; The second cleaning tank, at the bottom of which there is a first ultra-fine and dense bubble generator device and a second megasonic wave generating device; And the third cleaning tank, at the bottom of which there is a second air pipe with holes on the peripheral surface, a second ultra-fine bubble generator device, and a third megasonic wave generating device, and the second air pipe is connected to a second air pump.

6. The system according to claim 5, characterized in that, The megasonic wave generated by the first megasonic wave generating device has a frequency of 1000 kHz - 1200 kHz, the megasonic wave generated by the second megasonic wave generating device has a frequency of 1500 kHz - 2000 kHz, and the megasonic wave generated by the third megasonic wave generating device has a frequency of 1500 kHz - 1700 kHz.

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