Method for improving morphology of wafer obtained by cutting single crystal by using structural steel wire through single crystal multi-wire cutting machine

Abstract

The invention discloses a method for improving the morphology of a wafer obtained by cutting a single crystal by using a structural steel wire through a single crystal multi-wire cutting machine, and belongs to the technical field of silicon single crystal multi-wire cutting. Comprising the following steps that (1) a single crystal multi-wire cutting machine presets a constant cutting fluid temperature for cutting, and the correlation between the cutting fluid temperature change rule after cutting when different positions of a wafer are cut and the morphology of the obtained wafer is determined; and (2) a cutting fluid temperature change curve is formulated, and the temperature change of the cutting fluid participating in cutting in the whole cutting process is gentle by adjusting the temperature of the cutting fluid when the cutting fluid is cut to different positions of the wafer, so that a relatively flat wafer morphology is obtained. According to the method provided by the invention, the temperature change of the cutting environment in a complete cutting process is more stable, and finally a relatively flat, regular and symmetrical wafer morphology is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of single crystal multi-wire cutting, and particularly relates to a method for improving the wafer morphology obtained by cutting single crystal with structural steel wire by using a single crystal multi-wire cutting machine. BACKGROUND

[0002] With the increasing demand for 300mm wafers in the global market, the requirements for the quality of wafers are becoming more and more stringent. As the first step of wafer manufacturing, the cutting process of turning a crystal bar into a wafer lays the foundation for the basic quality of the wafer. The current mainstream slicing processing uses a multi-wire slurry cutting machine with stable performance. The device uniformly winds steel wire at a certain interval on two driven main rollers for reciprocating motion and carries a suspension containing silicon carbide sand to make material removal action on the crystal bar under the relative force of the cutting machine processing table and the wire mesh, and finally turns the crystal bar into several thin slices of a certain thickness.

[0003] In order to pursue as flat as possible wafers, the cutting machine processing table speed, main roller rotation speed, steel wire usage, cutting reciprocating cycle, wire mesh tension and other parameters can be adjusted. In the prior art, patent document CN116572410A discloses a method for controlling the morphology of cut silicon wafers by multi-wire cutting, and patent document CN116638640A discloses a process method for controlling the morphology of cut silicon wafers. Both of these two patent documents disclose that the frame and the main roller of the multi-wire cutting machine have thermal expansion during the cutting process, which causes a large deformation of the silicon wafer during the cutting process. By controlling the expansion amount of the frame and the main roller, the overall wafer warpage value is reduced and the area is flattened.

[0004] When cutting single crystal with structural wire, the uneven morphology of the wafer at the in-out knife position is a common phenomenon in the structural wire cutting process. The uneven morphology of the wafer at the in-out knife position will cause the overall wafer warpage value to be large, which is not conducive to the processing of the subsequent process. Therefore, in order to pursue a more flat wafer, we start to improve this phenomenon by controlling the temperature change of the cutting fluid involved in the cutting process. This time, we focus on improving the morphology of the wafer at the in-knife position. SUMMARY

[0005] The inventors found that the temperature change of the cutting fluid during the cutting process is related to the morphology change of the wafer from the in-knife to the out-knife direction. By controlling the temperature change of the cutting fluid during the cutting process to control the cutting environment temperature, it is of practical significance to adjust the morphology of the wafer from the in-knife to the out-knife direction.

[0006] Therefore, the present application aims to provide a method for improving the appearance of a wafer cut by a single crystal multi-wire saw by controlling the temperature variation of the cutting fluid to neutralize the heat generated during cutting, thereby making the heat variation of the crystal bar during cutting close to stable, reducing the thermal deformation amplitude, and improving the appearance of the wafer from the cutting-in direction to the cutting-out direction.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: A method for improving the appearance of a wafer cut by a single crystal multi-wire saw, comprising the following steps: (1) Pre-setting a constant cutting fluid temperature for cutting by a single crystal multi-wire saw, and determining the correlation between the temperature variation of the cutting fluid after participating in the cutting at different positions of the wafer and the appearance of the obtained wafer; (2) Formulating a temperature variation curve of the cutting fluid by adjusting the temperature of the cutting fluid at different positions of the wafer during cutting, so that the temperature variation of the cutting fluid after participating in the cutting during the entire cutting process is gentle, thereby obtaining a relatively flat wafer appearance.

[0008] As an embodiment of the present application, in the step (1), the temperature variation function of the cutting fluid during cutting is closed, the pre-set constant cutting fluid inlet temperature (the temperature of the cutting fluid entering the cutting environment) is a first predetermined temperature, and the first predetermined temperature remains unchanged during cutting (i.e., the temperature of the cutting fluid entering the cutting environment remains unchanged); the cutting fluid outlet temperature (the temperature recorded when the cutting fluid after participating in the wafer cutting flows out of the equipment) during cutting is captured to obtain a cutting fluid outlet temperature variation curve, and the appearance fluctuation of the obtained wafer from the cutting-in position to the cutting-out position (the direction from the start cutting position to the end cutting position) is observed after cutting is completed; the obtained cutting fluid outlet temperature variation curve is compared with the appearance of the wafer from the cutting-in position to the cutting-out position measured to obtain the correlation between the cutting fluid outlet temperature variation curve and the appearance curve of the wafer from the cutting-in position to the cutting-out position.

[0009] Further, in the step (1), the first fixed pre-set temperature is 18-24°C.

[0010] Further, in the step (2), a reverse temperature control curve is formulated according to the cutting fluid outlet temperature variation curve monitored after cutting is completed under the constant cutting fluid temperature, and the temperature variation at each position is formulated according to the cutting area variation at each position, so that the difference between the maximum value and the minimum value of the cutting fluid outlet temperature curve after participating in the cutting is less than the difference between the maximum value and the minimum value of the temperature variation curve of the cutting fluid under the constant cutting fluid temperature.

[0011] As another embodiment of the present application, in the step (1), the cutting fluid outlet temperature change curve in the cutting machine log is captured, and the wafer morphology from the in-cut position to the out-cut position is detected by the wafer detection device after cutting, and the two are compared to obtain the correlation between the cutting fluid outlet temperature change curve and the wafer morphology from the in-cut position to the out-cut position.

[0012] Further, in the step (2), a reverse curve is formulated according to the cutting fluid outlet temperature change curve in the cutting machine log after constant cutting fluid temperature cutting, and the temperature change rule at each position is formulated according to the cutting area change at each position, so that the difference between the maximum value and the minimum value in the cutting fluid outlet temperature curve finally participating in cutting is less than the difference between the maximum value and the minimum value in the temperature change curve of the constant cutting fluid temperature cutting.

[0013] Compared with the prior art, the present application has the following beneficial effects: The present application verifies the correlation between the cutting fluid temperature change after participating in cutting and the wafer morphology by constant cutting fluid temperature cutting experiment in advance, formulates a relevant cutting fluid temperature change curve according to the heat change trend of the cutting environment during cutting, sets different cutting fluid temperatures when cutting different positions of the wafer, neutralizes the cutting fluid temperature and the heat generated by cutting, so that the cutting fluid temperature change after participating in cutting is as smooth as possible during the entire cutting process, that is, the cutting environment temperature change is more stable during a complete cutting process, thereby causing smaller deformation of the wafer, and finally obtaining a more flat, regular and symmetrical wafer morphology. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 Wafer morphology of the first wafer of the single crystal head obtained by constant temperature cutting experiment (the left side is the in-cut, and the right side is the out-cut).

[0015] Figure 2 Cutting fluid outlet temperature change curve in the cutting log (the horizontal coordinate is the cutting time point record, and the unit is min; the vertical coordinate is the real-time temperature feedback).

[0016] Figure 3 Comparison diagram of the wafer morphology of the first wafer slice of the single crystal head obtained by constant temperature cutting experiment and the cutting fluid outlet temperature change curve in the cutting log.

[0017] Figure 4 Wafer morphology of the first wafer slice of the single crystal head obtained by variable temperature cutting experiment.

[0018] Figure 5 Comparison diagram of the wafer morphology of the first wafer slice of the single crystal head obtained by variable temperature cutting experiment and the wafer morphology of the first wafer slice of the single crystal head obtained by constant temperature cutting experiment. DETAILED DESCRIPTION

[0019] In order to further illustrate the technical means adopted by the present application to achieve the predetermined inventive purpose and effects, the specific embodiments and effects according to the present application are described in detail below in combination with the drawings and preferred embodiments.

[0020] The present application adjusts wafer entry position topography and reduces warpage by controlling cutting fluid inlet temperature variation, specifically, the method of the present application comprises the following steps: S1: The correlation between the cutting fluid temperature variation after participating in cutting and the wafer topography obtained is verified in advance by constant temperature cutting experiment of cutting fluid, specifically comprising the following operation steps: First step: Turn off the cutting fluid temperature variation function during cutting, and preset the cutting fluid temperature as a first predetermined temperature; Second step: According to the wafer topography map corresponding to the cutting fluid temperature variation curve after participating in cutting during the cutting process, determine the correlation between the cutting fluid temperature variation after participating in cutting and the wafer topography; S2: Improve the wafer entry position topography and reduce warpage by controlling the cutting fluid temperature variation during cutting, specifically comprising the following operation steps: First step: Add the cutting fluid inlet temperature variation curve, control the cutting fluid supply temperature variation during cutting, and control the cutting fluid outlet temperature variation amplitude after participating in cutting in real time by adjusting the cutting fluid supply temperature at different cutting positions; Second step: Obtain the product topography and warpage value after cutting; Third step: Compare the product topography and warpage obtained in the second step with the constant temperature cutting experiment results.

[0021] In the above S1 and S2, a silicon single crystal rod with a diameter of 300 mm and a length of 350 mm to 420 mm is selected, and a cutting steel, a cutting fluid and a cutting equipment are used to complete the machining process.

[0022] The cutting steel wire has a structure with a wire diameter of 0.12 mm to 0.14 mm.

[0023] The cutting fluid is a mixture of silicon carbide sand and suspending agent with a ratio of 1 kg of silicon carbide sand to 1 L of suspending agent, and the mixture is stirred for more than 10 hours. The final use of the cutting fluid has a density of 1.545 kg / L to 1.585 kg / L, the silicon carbide sand has a specification of 1100 mesh to 1300 mesh, and the D50 is 10.3 pm ± 0.5 pm. The suspending agent is a water-based suspending agent, and the main components are water, dihydric alcohol and organic hydrochloric acid.

[0024] The cutting device processing parameters mainly include: processing table speed 0.310 mm ± 0.05 mm / min, steel wire speed 11 m-14 m / s, forward and return wire ratio 1:0.75 ± 0.01, wire usage 150 km-200 km, steel wire tension 24 N-26 N, guide wheel temperature 22℃-24℃, rack temperature 22℃-24℃, clamping temperature 22℃-24℃, cutting fluid temperature 22℃-24℃.

[0025] Embodiment A silicon single crystal rod with a diameter of 300 mm and a length of 400 mm is selected, and a cutting steel and a cutting fluid are used to complete the cutting device processing.

[0026] The cutting steel is a structure cutting steel with a wire diameter of 0.13 mm.

[0027] The cutting fluid is a mixture of silicon carbide sand and a suspending agent, with a ratio of 1 kg of silicon carbide sand to 1 L ± 0.2 L of suspending agent, and the mixture is stirred for more than 10 hours. The final cutting fluid density is 1.545 kg / L-1.585 kg / L, the silicon carbide sand specification is 1200 mesh, and the D50 is 10.3 μm ± 0.5 μm. The suspending agent is a water-based suspending agent, and the main components are water, dihydric alcohol, and organic hydrochloric acid.

[0028] The cutting device processing parameters are: processing table speed 0.310 mm / min, steel wire speed 13 m / s, forward and return wire ratio 1:0.75, wire usage 168 km, steel wire tension 25 N, guide wheel temperature 23℃, rack temperature 23℃, clamping temperature 23℃, cutting fluid temperature 23℃.

[0029] In S1, the correlation between the cutting fluid temperature change after participating in the cutting and the appearance of the wafer from the cutting-in to the cutting-out direction is verified by a cutting fluid constant temperature cutting experiment. The cutting fluid temperature change function during the cutting process is closed, the preset cutting fluid inlet temperature is 23℃, and the constant temperature cutting is carried out. After the cutting fluid constant temperature cutting experiment is completed, the morphology of the first slice of the single crystal head is obtained, and the cutting log is compared with the cutting fluid temperature change curve after participating in the cutting.

[0030] The morphology of the first product of the single crystal head obtained by the capacitive measurement principle detection equipment (LBW-3020R BX-726) is measured, and the image from the cutting-in to the cutting-out direction is intercepted, as shown in Figure 1 .

[0031] The cutting fluid outlet temperature change curve obtained from the cutting log is shown in Figure 2 .

[0032] As shown in Figure 3As shown, after the experimental cutting was completed, the image of the morphology of the first slice of the single crystal head from the cutting direction to the cutting direction was compared with the cutting fluid outlet temperature change curve in the cutting log. It can be seen that the morphology of the slice from the cutting direction to the cutting direction is positively correlated with the cutting fluid temperature change curve after cutting.

[0033] In S2, another identical silicon single crystal rod is taken, and the same processing technology is used to add a cutting fluid temperature change curve.

[0034] The method for formulating the cutting fluid temperature change curve is as follows: As shown in Table 1, the 300mm diameter wafer is divided into 20 blocks of different areas by dividing it into 15mm sections from the entry to the exit position. The actual area of ​​each part is calculated according to the integral formula (1). The area of ​​the kth horizontal strip is: (1) Among them, y k =−150+15k, k=0,1,2,…,20) (y k This represents the y-coordinate of the lower boundary of the k-th horizontal strip.

[0035] As shown in Table 1, the area of ​​the first strip (the topmost strip) is approximately 1321 mm². The area of ​​subsequent strips gradually increases until it reaches the vicinity of the center, where it decreases again. It can be seen that the change in area of ​​each segmented strip increases with increasing area and decreases with decreasing area. Based on this pattern, the cutting fluid temperature variation curve shown in Table 2 is established. From the area changes at different locations in Table 1, it can be seen that the area change of each strip decreases progressively from the edge to the center, rather than decreasing by a constant amount. Therefore, the same pattern should be followed when setting the cutting fluid temperature variation curve; the temperature change at each location from the edge of the cut wafer to the center should decrease progressively, rather than decreasing by a fixed value at each location.

[0036] As shown in Table 2, the first 1.6% of the “Experimental Position (%)” represents the guide strip at the edge of the single crystal, which does not touch the single crystal and therefore the temperature does not change. The last 1.3% represents the resin strip at the edge of the single crystal, which does not touch the single crystal and therefore the temperature does not change. For the remaining parts, the temperature is changed every 5% of the cut to determine the temperature variation node. The temperature variation range between 25% and 75% is small, so no cutting fluid temperature control is performed, and the cutting is done at a fixed temperature.

[0037] Table 1 shows the area of ​​each 300mm diameter wafer divided into 20 blocks of different areas, with each block being diced every 15mm from the entry to the exit point. Table 2 Cutting fluid temperature variation curves The morphology of the first slice of the single crystal head after the cutting is completed is obtained, as shown in Figure 4 The morphology of the first slice of the single crystal head after the cutting is completed is obtained, as shown in

[0038] As shown in Figure 5 The morphology of the first slice of the single crystal head after the cutting is completed is obtained, as shown in

[0039] As shown in Table 3, the wafer warpage value in S2 is obviously lower than that in S1.

[0040] As shown in Table 4, the difference between the maximum value and the minimum value of the outlet temperature in the processing process in S2 is obviously lower than that in S1, indicating that the variation range of the cutting fluid temperature in the processing process in S2 is smaller.

[0041] Table 3 Comparison of wafer warpage values in cutting fluid variable-temperature cutting experiment and cutting fluid constant-temperature cutting experiment Table 4 Comparison of the maximum value and the minimum value of the cutting fluid outlet temperature and the difference between the maximum value and the minimum value in the processing process in the cutting fluid variable-temperature cutting experiment and the cutting fluid constant-temperature cutting experiment As can be seen from the above, by controlling the variation of the cutting fluid temperature in the cutting process, the morphology of the slice cutting position can be effectively improved, and the warpage can be reduced.

Claims

1. A method for improving the morphology of wafers obtained by cutting single crystals using structural steel wire in a single crystal multi-wire dicing machine, characterized in that, It comprises the following steps: (1) A single crystal multi-wire saw is preset with a constant cutting fluid temperature for cutting, and the correlation between the temperature variation of the cutting fluid after participating in the cutting at different positions of the wafer and the appearance of the obtained wafer is determined; (2) A cutting fluid temperature variation curve is formulated, the temperature of the cutting fluid at different positions of the wafer is adjusted, the temperature variation of the cutting fluid after participating in the cutting in the whole cutting process is gentle, and a relatively flat wafer appearance is obtained.

2. The method of claim 1, wherein, In the step (1), the cutting fluid temperature variation function in the cutting process is closed, the preset constant cutting fluid inlet temperature is a first predetermined temperature, and the first predetermined temperature remains unchanged in the cutting process; The cutting fluid outlet temperature in the cutting process is captured, the cutting fluid outlet temperature variation curve is obtained, the appearance of the obtained wafer from the cutting-in position to the cutting-out position is observed after the cutting is completed, the cutting fluid outlet temperature variation curve is compared with the appearance of the obtained wafer from the cutting-in position to the cutting-out position, and the correlation between the cutting fluid outlet temperature variation curve and the appearance curve of the obtained wafer from the cutting-in position to the cutting-out position is obtained.

3. The method of claim 2, wherein, In the step (1), the first fixed preset temperature is 18-24℃.

4. The method according to claim 2 or 3, characterized in that, In the step (2), a reverse temperature control curve is formulated according to the cutting fluid outlet temperature variation curve monitored after the cutting is completed under the constant cutting fluid temperature, and the temperature variation at each position is determined according to the cutting area variation at each position, so that the difference between the maximum value and the minimum value in the cutting fluid outlet temperature curve finally participating in the cutting is less than the difference between the maximum value and the minimum value in the temperature variation curve of the cutting under the constant cutting fluid temperature.

5. The method of claim 1, wherein, In the step (1), the cutting fluid outlet temperature variation curve in the cutting machine log is captured, the appearance of the obtained wafer from the cutting-in position to the cutting-out position is detected by a wafer detection device after the cutting is completed, and the two are compared to obtain the correlation between the cutting fluid outlet temperature variation curve and the appearance variation of the obtained wafer from the cutting-in position to the cutting-out position.

6. The method of claim 5, wherein, In the step (2), a reverse curve is formulated according to the cutting fluid outlet temperature variation curve in the cutting machine processing log after the cutting is completed under the constant cutting fluid temperature, and the temperature variation at each position is determined according to the cutting area variation at each position, so that the difference between the maximum value and the minimum value in the cutting fluid outlet temperature curve finally participating in the cutting is less than the difference between the maximum value and the minimum value in the temperature variation curve of the cutting under the constant cutting fluid temperature.

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