Method for rapidly corroding silicon dioxide on edge of back surface of polished wafer

Abstract

The invention discloses a method for quickly corroding silicon dioxide on the edge of the back surface of a polished wafer, which comprises the following steps: (1) adding hydrofluoric acid into a liquid tank which is provided with a gas inlet pipeline for introducing high-purity nitrogen below the liquid level of the hydrofluoric acid; one end of the air outlet pipeline is positioned above the liquid level, and the other end of the air outlet pipeline is introduced into a corrosion tank of the suction cup type edge removing machine; (2) putting the suction cup with the wafer into a suction cup type edge removing machine, and transferring a point position to place the wafer at a specified position of an etch tank; (3) sealing the liquid tank, then introducing high-purity nitrogen into the liquid tank, and conveying the nitrogen carrying HF gas into the corrosion tank from another pipeline to react with silicon dioxide at the edge of the wafer; (4) after the reaction is finished, rotating the rotating shaft to drive the sucking disc to enter a specified cleaning agent for cleaning; and (5) after cleaning is completed, taking out the wafer, and spin-drying the wafer in a spin-drying barrel. The silicon dioxide film edge corrosion consistency and qualification rate can be improved, the cost is low, the production efficiency is high, and the practicability is high.

Description

Technical Field

[0001] The invention relates to a back side silicon dioxide processing technology of a semiconductor polishing sheet, in particular to a method for rapid etching of silicon dioxide at the back side edge of a polishing sheet, and belongs to the technical field of semiconductor materials. Background Art

[0002] The processing of polished wafers generally includes slicing, chamfering, grinding and etching, back treatment, edge polishing, polishing, cleaning and other processes, among which the back treatment includes annealing, back sealing and edge silicon dioxide etching. When heavily doped silicon single crystal is used as the substrate, due to the concentration gradient and high temperature, there is a common phenomenon of dopant migration between the substrate and the highly doped area of ​​the epitaxial layer. In order to suppress the influence of self-doping, the process requires a layer of silicon dioxide film to be deposited on the back of the heavily doped substrate and the back is back-sealed. In order to meet the needs of self-doping, some manufacturers will also use two layers of deposited polycrystalline and silicon dioxide films for back sealing.

[0003] Although the substrate treated with back sealing can greatly reduce the occurrence of self-doping, the silicon dioxide film on the edge will greatly reduce the yield of edge polishing and subsequent epitaxy. Due to the silicon dioxide residue on the chamfered surface and the positive bevel during the back sealing process, even the silicon dioxide residue on the edge of the back of the wafer can become the nucleation center during the epitaxial growth process, forming polycrystalline and amorphous at the edge, affecting the quality and yield of epitaxy, and the lattice defects on the edge after epitaxy can cause low edge yield of subsequent devices. Therefore, edge silicon dioxide corrosion treatment is of great significance to the processing process of polished wafers, and plays a vital role in the yield of edge polishing and subsequent epitaxy.

[0004] At present, the domestic wafer fab back edge silicon dioxide removal process methods mainly include the following three methods:

[0005] (1) Film-type edge removal process. This method uses a manual film-sticking method. First, select a suitable blue film according to product requirements, then manually align and adhere the blue film to the back of the wafer, place the wafer in a hydrofluoric acid solution, remove the exposed silicon dioxide at the edge, and further place the wafer with the blue film in a specific chemical solution to remove the blue film. Finally, dry the wafer to achieve the effect of etching the silicon dioxide at the edge. However, due to manual alignment, this process has low alignment accuracy and relatively poor edge consistency. At the same time, manual operation has a greater impact on the state of the back and will cause certain damage to the back. At the same time, due to the large number of blue film specifications, it has a certain negative effect on production, and the cost of blue film is high, so there are many disadvantages in actual production.

[0006] (2) Roller-type edge removal process: This method is to place the wafer on a wafer rack, align it with a roller, and use the roller to drive the wafer rack to rotate. At the same time, hydrofluoric acid is placed under the roller. As the roller rotates, the wafer also rotates, so that the edge of the wafer contacts the hydrofluoric acid to achieve the corrosion effect. Although it can protect part of the silicon dioxide from being corroded, the edge corrosion width is difficult to control, the accuracy is poor, and the qualified rate is low.

[0007] (3) Reaction chamber edge removal process: This process uses HF gas in the reaction chamber to etch away the silicon dioxide at the edge of the wafer. This process has the following disadvantages: the amount of HF gas is difficult to control, the edge etching width accuracy is difficult to control, and it is easy to cause harm to the operator.

[0008] Therefore, how to overcome the shortcomings of the above-mentioned edge removal process while retaining its advantages to achieve higher edge silicon dioxide removal accuracy and higher qualified rate has become a problem that needs to be solved urgently. Summary of the invention

[0009] The purpose of the present invention is to provide a method for rapid etching of silicon dioxide at the edge of the back side of a polishing sheet, so as to improve the consistency and qualified rate of etching of the edge of the silicon dioxide film.

[0010] To achieve the above object, the present invention adopts the following technical solutions:

[0011] A method for rapid etching of silicon dioxide at the back edge of a polishing sheet comprises the following steps:

[0012] (1) adding hydrofluoric acid into a liquid tank, the liquid tank being provided with an air inlet pipe for introducing high-purity nitrogen below the liquid level of the hydrofluoric acid; and an air outlet pipe, one end of which is located above the liquid level and the other end of which is introduced into the etching tank of the suction cup type edge removal machine;

[0013] (2) Place the suction cup with the wafer into the suction cup edge removal machine, rotate the shaft to make the suction cup pause on the etching tank, and then adjust the point to place the wafer at the specified position in the etching tank;

[0014] (3) The liquid tank is sealed, and then high-purity nitrogen is introduced into the liquid tank. The nitrogen carries the HF gas from another pipeline and is transported to the etching tank to react with the silicon dioxide at the edge of the wafer;

[0015] (4) After the reaction is completed, the rotating shaft is rotated to drive the suction cup into the designated cleaning agent for cleaning;

[0016] (5) After cleaning, take out the wafer and place it in a spin dryer to dry it.

[0017] Preferably, in step (1), 2L±0.5L of hydrofluoric acid is added to the liquid tank, the purity of the hydrofluoric acid is ≥49%, UP grade; the MFC flow rate of nitrogen is maintained at 3000±100, and at the same time, in order to prevent the excess hydrofluoric acid from polluting the workshop environment, the remaining hydrofluoric acid is collected through the air intake port, and recovered or discharged into the environment after treatment, and the hydrofluoric acid exhaust value is controlled at 0.1±0.05kPa.

[0018] Preferably, in step (3), the reaction time is controlled to be 30s±5s, and the vacuum pressure of the suction cup is controlled to be -20±5kPa. When the vacuum pressure of the suction cup is too low, the silicon dioxide corrosion width will be too large. When the vacuum pressure of the suction cup is too high, the silicon dioxide will not be completely corroded.

[0019] Preferably, in step (4), the cleaning agent is a mixed solution of ammonia water, hydrogen peroxide and water, the volume ratio of ammonia water, hydrogen peroxide and water is 1:1-2:15, and the operating temperature range is 25-35°C.

[0020] Preferably, in step (5), a hot air flow is introduced into the drying barrel, the temperature is controlled to be 25-30°C, and the drying speed is controlled to be 1000r for 30s, 1200r for 20s, and 1400r for 20s.

[0021] Preferably, the hydrofluoric acid in the liquid tank is replaced every 400 pieces processed to keep the concentration and flow rate of the hydrofluoric acid stable.

[0022] The beneficial effects of the present invention are:

[0023] The method of the present invention controls the corrosion rate of hydrofluoric acid on the wafer surface by passing high-purity nitrogen into hydrofluoric acid to form HF bubbling liquid, thereby achieving the purpose of controlling the suction cup type edge removal machine to remove the silicon dioxide film at the edge of the back side of the wafer, breaking through the technical bottleneck. The method of the present invention can be used for the preparation of polishing sheets used for large-scale integrated circuits and discrete devices. The method of the present invention has low cost, high production efficiency, strong practicality, and is suitable for removing the silicon dioxide film at the edge of the back side of large-scale industrial production of polishing sheets. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the positional relationship between the etching tank and the suction cup used in the present invention.

[0025] Figure 2 It is a schematic structural diagram of the HF bubbling liquid generating device of the present invention.

[0026] Figure 3 It is an edge effect diagram of the comparative example and the embodiment, wherein: Figure 3 (a) is the edge effect diagram of the comparative example. Figure 3(b) is an edge effect diagram of the embodiment. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but is not intended to limit the protection scope of the present invention.

[0028] like Figure 1 As shown, it is a schematic diagram of the positional relationship between the etching tank and the suction cup used in the present invention. The suction cup 1 is placed in the etching tank 2, about 2 cm away from the bottom of the etching tank, and the silicon wafer is adsorbed on the suction cup under vacuum operation (as shown in the figure, vacuum is drawn through the vacuum pipeline 3 on the suction cup). There are holes at the bottom of the etching tank 2, and the HF bubbling liquid is transported by the pipeline 4 and enters the etching tank through the holes at the bottom of the etching tank to perform a corrosion reaction on the silicon wafer.

[0029] like Figure 2 As shown, it is a schematic diagram of the structure of the HF bubbling liquid generating device in the present invention. The liquid tank containing hydrofluoric acid is provided with an air inlet pipe for introducing high-purity nitrogen below the hydrofluoric acid liquid level; and an air outlet pipe, one end of which is located above the liquid level, and the other end is introduced into the etching tank of the suction cup type edge remover. High-purity nitrogen is introduced through the air inlet pipe, and the nitrogen carries HF gas into the etching tank of the suction cup type edge remover to react with silicon dioxide at the edge of the wafer.

[0030] According to the method of the present invention, hydrofluoric acid and high-purity nitrogen are prepared into HF bubbling liquid according to the principle that the running speeds of gas and liquid on the solid surface are inconsistent, and the HF bubbling liquid reacts with silicon dioxide at the edge of the wafer. Compared with the traditional hydrofluoric acid etching of silicon dioxide at the edge, the HF bubbling liquid prepared by the method of the present invention can effectively inhibit the flow of hydrofluoric acid at the edge of the wafer, thereby reducing the etching of the wider edge of the wafer, thereby ensuring the consistency of edge corrosion. This etching liquid breaks through the bottleneck of uneven edges and low processing qualification rate that are difficult to overcome by the traditional suction cup type edge removal technology. On the basis of making up for this deficiency, the suction cup type edge removal technology has obvious advantages over other edge removal technologies: compared with the roller type edge removal technology, the concentration and dosage of hydrofluoric acid can be easily controlled, thereby ensuring the consistency of the edge corrosion of the silicon dioxide film and having a high qualification rate; compared with the film-sticking type edge removal technology, no expensive plastic blue film is required and it is no longer restricted by its specifications, which not only saves costs, but also overcomes the limitations of manual precision by using semi-automatic equipment.

[0031] Example

[0032] The specific preparation process of using HF bubbling liquid to remove silicon dioxide from the edge of the wafer is as follows:

[0033] As a raw material, a single crystal wafer of 8 inches (200 mm in diameter) with a thickness of 625±15 μm, doped with As, a <100> crystal orientation, and a resistivity of 0.01-0.02 is prepared after back damage and back sealing.

[0034] Prepare HF bubbling liquid. The preparation method is as follows: first add 2L hydrofluoric acid (purity is 49%, UP grade) into the liquid tank, then introduce a high-purity nitrogen gas into the liquid tank below the hydrofluoric acid liquid level, and add another pipeline into the liquid tank, this pipeline is above the hydrofluoric acid liquid level, and then introduce this pipeline into the corrosion tank of the suction cup type edge removal machine.

[0035] Use the wafer sorter to sort the wafers, the cradle to cradle, align the reference surface, and then load the wafers. Put the basket with the wafers on the loading table of the suction cup type edge removal machine, and then use the robot to place the wafer on the centering table, further adjust the position of the suction cup, and adsorb the wafer on the suction cup. Turn the shaft to place the suction cup carrying the wafer in the etching tank, then open the high-purity nitrogen valve, control the MFC flow rate to 3000, and control the hydrofluoric acid exhaust value at 0.1±0.05kPa. High-purity nitrogen carries HF to the etching tank, and the suction cup is rotated to make the HF bubbling liquid react evenly with the silicon dioxide at the edge of the wafer, and the reaction time is controlled to 30s±5s.

[0036] After the removal process is completed, the suction cup carrying the wafer is placed in a cleaning agent (a mixed solution of ammonia, hydrogen peroxide and water, with a volume ratio of 1:1:15), and the hydrofluoric acid remaining on the surface of the wafer is rinsed off with the cleaning agent, and then the wafer is spun dry (a hot air flow is passed into the drying barrel to control the temperature at 25-30°C, and the drying speed is controlled to 1000r for 30s, 1200r for 20s, and 1400r for 20s), and finally the edge removal effect is checked.

[0037] After processing every 400 pieces, the hydrofluoric acid in the liquid tank is replaced and the flow rate of high-purity nitrogen is monitored to keep the concentration and flow rate of the HF bubbling liquid stable.

[0038] Comparative Example

[0039] The HF bubbling liquid after the removal treatment in the above embodiment is poured out, and then hydrofluoric acid with a purity of 49% and UP grade is filled into the etching tank. The conventional hydrofluoric acid etching process is used for etching, and the cleaning and drying steps in the embodiment are performed after etching, and finally the effect of removing edge silicon dioxide is tested.

[0040] Figure 3 The edge effect diagram of the embodiment and the comparative example of the present invention is shown in Figure 1. The edge effect after de-edging is visually inspected at 200 times magnification using an OLYMPUS MX50 microscope. Figure 3As shown in (a), after the comparative example is processed by the traditional hydrofluoric acid etching process, the edge is not smooth, the jagged state is serious, and the edge is uneven and the consistency is poor. Figure 3 As shown in (b), after the embodiment is processed by HF bubbling liquid, the edge is smooth, there is no unevenness, and the edge consistency is good.

[0041] According to the method of the embodiment, a small batch production of 1000 wafers was further carried out. After inspection, the qualified rate reached more than 95%, indicating that the method is a technology suitable for removing the back silicon dioxide film of polishing wafers in large-scale industrial production.

Claims

1. A method for rapid etching of silicon dioxide at the back edge of a polishing sheet, characterized in that: The following steps are involved: (1) adding hydrofluoric acid into a liquid tank, the liquid tank being provided with an air inlet pipe for introducing high-purity nitrogen below the liquid level of the hydrofluoric acid; and an air outlet pipe, one end of which is located above the liquid level and the other end of which is introduced into the etching tank of the suction cup type edge removal machine; (2) Place the suction cup with the wafer into the suction cup edge removal machine, rotate the shaft to make the suction cup pause on the etching tank, and then adjust the point to place the wafer at the specified position in the etching tank; (3) The liquid tank is sealed, and then high-purity nitrogen is introduced into the liquid tank. The nitrogen carries the HF gas from another pipeline and is transported to the etching tank to react with the silicon dioxide at the edge of the wafer; (4) After the reaction is completed, the rotating shaft is rotated to drive the suction cup into the designated cleaning agent for cleaning; (5) After cleaning, take out the wafer and place it in a spin dryer to dry it.

2. The method for rapid etching of silicon dioxide at the back edge of a polishing sheet according to claim 1, wherein: In the step (1), 2L±0.5L of hydrofluoric acid is added into the liquid tank, and the purity of the hydrofluoric acid is ≥49%, UP grade.

3. The method for rapid etching of silicon dioxide at the back edge of a polishing sheet according to claim 1, characterized in that: The MFC flow rate of nitrogen was maintained at 3000±100, and the acid exhaust was controlled at 0.1±0.05kPa.

4. The method for rapid etching of silicon dioxide at the back edge of a polishing sheet according to claim 1, characterized in that: In the step (3), the reaction time is controlled to be 30s±5s, and the vacuum pressure of the suction cup is controlled to be -20±5kPa.

5. The method for rapid etching of silicon dioxide at the back edge of a polishing sheet according to claim 1, characterized in that: In the step (4), the cleaning agent is a mixed solution of ammonia water, hydrogen peroxide and water, the volume ratio of ammonia water, hydrogen peroxide and water is 1:1-2:15, and the working temperature range is 25-35°C.

6. The method for rapid etching of silicon dioxide at the back edge of a polishing sheet according to claim 1, characterized in that: In the step (5), a hot air flow is introduced into the drying barrel, the temperature is controlled to be 25-30°C, and the drying speed is controlled to be 1000r for 30s, 1200r for 20s, and 1400r for 20s.

7. The method for rapid etching of silicon dioxide at the back edge of a polishing sheet according to any one of claims 1 to 6, characterized in that: After processing every 400 pieces, the hydrofluoric acid in the liquid tank is replaced.

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