Grinding surface roughness control method and system and grinding equipment

Abstract

The invention discloses a grinding surface roughness control method and system and grinding equipment. According to the method, when the expected target thickness is achieved through grinding, the grinding wheel is not directly lifted and reset at a relatively high speed, the grinding wheel continues to be ground for a period of time in situ, then is slowly lifted by a small distance, and then is moved downwards to the previous position to continue to be ground for a period of time; when the wafer is ground to an expected target thickness which is smaller than an actual target thickness, the wafer is rapidly reset after being slowly lifted to a higher height, so that the grinding wheel exerts small pressure on the wafer in the final stage, friction between the grinding wheel and the wafer can be effectively reduced, and smaller surface roughness can be obtained; therefore, the actual target thickness can be achieved through subsequent continuous grinding, and the problem that the final grinding quality is affected by abnormal grinding of the wafer and the grinding wheel due to molded surface change caused by rapid springback of the wafer bearing table due to rapid pressure unloading when the grinding wheel is directly lifted can be avoided.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor device processing, in particular to a grinding surface roughness control method, system and grinding equipment. Background Art

[0002] When semiconductor devices such as wafers are thinned, the surface roughness of the wafer after grinding needs to meet the requirements.

[0003] When wafer grinding is performed using a thinning device such as that disclosed in patent documents with application publication number CN116984975A ​​or authorization announcement number CN218639240U, the grinding wheel of the grinding mechanism will feed toward the wafer at a certain speed after contacting the wafer so that the grinding wheel applies a certain pressure to the wafer and grinds it; during the grinding process, the thickness of the wafer is detected in real time by a thickness detection component. When the thickness of the wafer measured by the thickness detection component reaches the target thickness, the grinding wheel of the grinding mechanism will be immediately lifted upward and reset.

[0004] In this processing method, the grinding wheel will exert greater pressure on the wafer during the final processing stage, which is not conducive to controlling the surface roughness of the wafer. Summary of the invention

[0005] The purpose of the present invention is to solve the above problems existing in the prior art and to provide a method, system and grinding equipment for controlling the roughness of a grinding surface.

[0006] The purpose of the present invention is achieved through the following technical solutions: The method for controlling the roughness of a grinding surface comprises the following steps: S1, when the grinding mechanism grinds the workpiece on the wafer stage to an expected target thickness, the main shaft of the grinding mechanism is maintained at the current height and continues grinding for a first time period; the expected target thickness is greater than the actual target thickness; S2, moving the spindle upward at a first speed and a first distance, and the grinding mechanism continues grinding during the upward movement; the first distance does not exceed 10 microns, and the first speed is not greater than the feed speed when the workpiece is ground to the expected target thickness; S3, moving the spindle downwards by the first distance at a second speed, and the spindle continues to grind during the downward movement; S4, allowing the spindle to continue grinding at the current height for a second time period; S5, moving the main shaft up a second distance at a third speed and then up to a waiting position at a fourth speed greater than the third speed, wherein the second distance is greater than the first distance.

[0007] Preferably, the first duration is between 8 and 13 seconds.

[0008] Preferably, the first distance is between 4 and 8 microns.

[0009] Preferably, the second speed and the third speed are not greater than the first speed.

[0010] Preferably, the second duration is between 4 and 6 seconds.

[0011] Preferably, the grinding mechanism grinds the workpiece to the expected target thickness in multiple stages, and the feed speed of each stage is different.

[0012] Preferably, before the spindle starts to move downward, the actual thickness of the workpiece on the wafer table is detected by a thickness measuring component, and the deceleration point height is determined based on the actual thickness and the standard thickness corresponding to the workpiece. When the spindle moves to the deceleration point height, the feed speed is reduced.

[0013] Preferably, before measuring the actual thickness of the workpiece on the wafer stage by the thickness measuring component, when grabbing the workpiece from the positioning mechanism by the transfer component, it is determined whether the actual thickness of the workpiece exceeds the measuring range of the thickness measuring component.

[0014] Grinding surface roughness control system, including: A first grinding unit is used to keep the main shaft of the grinding mechanism at a current height and continue grinding for a first time period when the grinding mechanism grinds the workpiece on the wafer stage to an expected target thickness; the expected target thickness is greater than the actual target thickness; a lifting unit, used to move the spindle upward at a first speed and a first distance, and the grinding mechanism continues grinding during the upward movement; the first distance does not exceed 10 microns, and the first speed is not greater than the feed speed when the workpiece is ground to the expected target thickness; A downward movement unit, used to move the spindle downward by the first distance at a second speed, and the spindle continues to grind during the downward movement; A second grinding unit, used to allow the spindle to continue grinding at the current height for a second time period; The reset unit is used to make the spindle move up a second distance at a third speed and then move up to a waiting position at a fourth speed greater than the third speed, wherein the second distance is greater than the first distance, and the waiting position is an initial state when the spindle has not started to move down.

[0015] A grinding device comprises a processor and a memory, wherein the memory stores a program executable by the processor, and when the program is executed, any of the above-mentioned grinding surface roughness control methods is implemented.

[0016] The advantages of the technical solution of the present invention are mainly reflected in: The present invention does not directly lift and reset the grinding wheel at a relatively fast speed when grinding reaches the expected target thickness, but makes the grinding wheel continue to grind in situ for a period of time and then slowly lift it a small distance, then move down to the previous position and continue grinding for a period of time, and then slowly lift it to a higher height before quickly resetting. In this way, in the final stage, the grinding wheel applies less pressure on the wafer during grinding, thereby effectively reducing the friction between the grinding wheel and the wafer, which is conducive to obtaining a smaller surface roughness. At the same time, since the wafer is first ground to an expected target thickness that is less than the actual target thickness, the actual target thickness can be reached through subsequent continued grinding. In this way, the problem of the wafer table quickly rebounding due to the rapid unloading of pressure when the grinding wheel is directly lifted, resulting in a change in the profile, causing abnormal grinding of the wafer and the grinding wheel and affecting the final grinding quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a process schematic diagram of the method of the present invention; Figure 2 The method of the present invention has a flow chart of a process of adjusting a deceleration point according to a thickness measured by a thickness measuring assembly; Figure 3 The method of the present invention has a flow chart of a process of adjusting the deceleration point according to the thickness measured by the thickness measuring component and the pressure sensor. DETAILED DESCRIPTION

[0018] The purpose, advantages and features of the present invention will be illustrated and explained by the non-limiting description of the following preferred embodiments. These embodiments are only typical examples of the application of the technical solution of the present invention, and any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection claimed by the present invention.

[0019] In the description of the scheme, it should be noted that the terms "center", "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience and simplification of description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0020] The grinding surface roughness control method disclosed by the present invention is described below in conjunction with the accompanying drawings. Figure 1 As shown, it includes the following steps: S1, when the grinding mechanism grinds the workpiece on the wafer stage to an expected target thickness, the main shaft of the grinding mechanism is maintained at the current height and continues grinding for a first time period; the expected target thickness is greater than the actual target thickness, and the actual target thickness is the thickness actually required to be achieved; S2, moving the spindle upward at a first speed and a first distance, and the grinding mechanism continues grinding during the upward movement; the first distance does not exceed 10 microns, and the first speed is not greater than the feed speed when the workpiece is ground to the expected target thickness; S3, moving the spindle downwards by the first distance at a second speed, and the spindle continues to grind during the downward movement; S4, allowing the spindle to continue grinding at the current height for a second time period; S5, moving the main shaft up a second distance at a third speed and then up to a waiting position at a fourth speed greater than the third speed, wherein the second distance is greater than the first distance.

[0021] In the S1, the specific process of grinding the workpiece on the wafer table to the expected target thickness by the grinding mechanism can adopt different processes according to the structure of different grinding equipment. For example, when the grinding equipment has only one grinding mechanism, it is only necessary to grind to the expected target thickness at the grinding structure according to the set process parameters. When the grinding equipment has two grinding mechanisms, and each workpiece needs to be moved to the two grinding mechanisms in turn for two-step grinding, it is necessary to grind the workpiece to the expected target thickness at the downstream grinding mechanism. During actual grinding, the grinding mechanism can use fixed process parameters for grinding from the beginning of grinding to grinding to the expected target thickness. More preferably, the grinding mechanism can grind the workpiece to the expected target thickness in multiple stages, and the feed speed of each stage is different. The process parameters of the grinding mechanism when grinding the workpiece, such as feed speed, spindle speed, wafer table speed, etc., can be adaptively designed according to different materials and processing requirements. It is not an innovation of the present invention and will not be repeated here.

[0022] The expected target thickness can be determined through experiments. Specifically, multiple samples can be ground according to the above-mentioned grinding surface roughness control method, and the final thickness of each sample after grinding according to the above-mentioned method is recorded, the difference between the final thickness and the expected target thickness is determined, and then the average value of all the differences is determined. Finally, the actual target thickness is added to the average value to obtain the expected target thickness. In this way, it can be ensured that the final thickness after grinding according to the above-mentioned control method is the same as or infinitely close to the actual target thickness.

[0023] The first time length is between 8 and 13 seconds, preferably about 10 seconds. At this time, since the pressure exerted by the grinding wheel on the wafer stage is reduced, the surface of the wafer stage will rebound upward so that the wafer and the grinding wheel maintain contact to achieve relatively gentle grinding.

[0024] Furthermore, in order to allow the wafer table to rebound and reset more fully, the spindle is slowly moved upward by a certain distance in S2, so that the wafer table has a larger rebound space. Correspondingly, the first distance is between 4-8 microns, preferably around 5 microns, and the first speed is preferably the same as the feed speed when the workpiece is ground to the expected target thickness, which is not elaborated here.

[0025] When the first height is further lowered, further grinding can be achieved with relatively greater pressure to achieve better grinding. Correspondingly, the second speed and the third speed during downward movement are not greater than the first speed, and preferably the two are the same. At the same time, after moving downward, the second time length is between 4 and 6 seconds, and preferably 5 seconds.

[0026] The third speed is the same as the first speed and the second speed mentioned above, the second distance is preferably 10-15 microns, and the fourth speed is the same as the upward movement speed when the main shaft is lifted directly after grinding in the prior art, and is not limited here.

[0027] As attached Figure 2 As shown, before the spindle starts to move downward, the actual thickness of the workpiece on the wafer table is detected by the thickness measuring component. Correspondingly, when the workpiece is located at the grinding mechanism, the two measuring rods of the thickness measuring component are controlled to move downward respectively to rest on the top surface of the workpiece and the top surface of the wafer table where the workpiece is located, so that the actual thickness of the workpiece can be measured. The specific structure of the thickness measuring component and the thickness measurement principle are known technologies, which are not the innovation of the present invention and will not be elaborated here.

[0028] Furthermore, in order to avoid errors in reading immediately after the measuring rod is loaded on the workpiece and the wafer table due to the instability of the measuring rod, when measuring the thickness of the workpiece by the thickness measuring assembly, multiple actual thicknesses measured by the thickness measuring assembly are read at intervals. For example, after the two measuring rods are lowered into place, multiple actual thicknesses are read at a certain time interval. The time interval and the number of readings can be determined as needed, for example, the time interval is 5 milliseconds, 10 milliseconds, 20 milliseconds, etc., and the number of readings is, for example, 3 times, 4 times, 5 times, etc., which are not limited here. When determining the actual thickness of the workpiece based on multiple actual thicknesses, the average of the multiple actual thicknesses can be taken, or the average value can be taken after removing the maximum and minimum values.

[0029] Then, the height of the deceleration point can be determined based on the actual thickness and the standard thickness corresponding to the workpiece, and the feed speed is reduced when the spindle moves to the deceleration point height. The reason for this operation is that when grinding starts, the spindle needs to move down from the waiting position at a faster downward speed to a certain deceleration point height, and then the spindle needs to reduce the downward speed to reduce the impact when the grinding wheel contacts the workpiece. The standard deceleration point height stored in the system is determined based on the standard thickness of the workpiece, but in actual production, the actual thickness of the workpiece is difficult to ensure consistency, that is, some workpieces are thicker and some are thinner. In this way, when the spindle reduces the downward speed according to the standard deceleration point height, it is easy to have safety hazards or efficiency losses.

[0030] When determining the height of the deceleration point, the adjustment is made based on the previously determined standard deceleration point height. The standard deceleration point height can be determined without reference to any point on the spindle, for example, based on the height of the top of the spindle. When the top of the spindle moves from the highest position to the deceleration point height, the feed speed of the spindle begins to decrease to a relatively low speed, and at this time, a predetermined gap is maintained between the grinding wheel at the lower end of the spindle and the workpiece of standard thickness on the wafer table.

[0031] Specifically, after determining the actual thickness of the workpiece, the difference between the actual thickness and the standard thickness can be determined. If the actual thickness is greater than the standard thickness, it means that when the workpiece is placed on the wafer table, its top surface is higher than the top surface of the standard workpiece when it is placed on the wafer table. If the spindle is controlled to reduce the feed speed according to the previously determined standard deceleration point height, the grinding wheel at the lower end of the spindle may have contacted the top surface of the workpiece at this time, which obviously poses a certain safety hazard. Therefore, the deceleration point height needs to be made higher, that is, the determined deceleration point height is the standard deceleration point height + (actual thickness - standard thickness). Conversely, if the actual thickness is less than the standard thickness, the determined deceleration point height is the standard deceleration point height - (actual thickness - standard thickness).

[0032] During subsequent grinding, when the spindle moves down to the determined deceleration point height, the feed speed of the spindle is reduced to a lower speed, and then grinding is performed according to the set grinding process.

[0033] Furthermore, since the thickness of the workpiece may vary greatly, and the thickness of the workpiece may even exceed the range of the thickness measurement component, the attached Figure 3 As shown, before the actual thickness of the workpiece on the wafer stage is measured by the thickness measuring component, when the workpiece is grabbed from the positioning mechanism by the transfer component, it is determined whether the actual thickness of the workpiece exceeds the measuring range of the thickness measuring component.

[0034] Specifically, before the workpiece is placed on the wafer table, the grinding equipment will first take the workpiece from the material box through the loading and unloading robot or the transfer component and place it on the placement table of the positioning mechanism. The positioning claws of the positioning mechanism gather toward the center to achieve the centering of the workpiece. After centering, the positioned workpiece is grasped by the transfer component and placed concentrically on the wafer table.

[0035] Among them, the specific structure of the transfer assembly is a known technology and will not be elaborated here. When it grabs the wafer on the positioning mechanism, the suction cup is moved to be coaxial with the wafer on the positioning mechanism by rotating the swing arm mechanism, and then the transfer assembly drives the rotating swing arm mechanism to move downward as a whole so that the suction cup moves down to the designated pickup position. At this time, the suction cup applies pressure to the workpiece at the positioning mechanism.

[0036] The present invention is improved on the basis of the existing positioning mechanism, that is, the present invention connects a pressure sensor for detecting the axial pressure on the top of the workpiece placing table below the workpiece placing table in the positioning mechanism. In addition, in order to improve the support, the diameter of the workpiece placing table can be made as large as possible, for example, equivalent to the diameter of a circle formed when a circle of positioning claws is expanded to the maximum position, and at the same time, a strip hole for the positioning claws to move is provided on the workpiece placing table.

[0037] When the transfer assembly grabs the workpiece, the pressure applied by the transfer assembly to the workpiece can be detected by the pressure sensor. Generally, when picking up materials at the same picking position, the greater the pressure detected by the pressure sensor, the greater the thickness of the workpiece. Therefore, the actual thickness of the workpiece can be calculated based on the picking pressure value measured by the pressure sensor when picking up materials.

[0038] Specifically, the calculation can be performed by determining a linear relationship between the material taking pressure value measured by the pressure sensor during material taking and the actual thickness of the workpiece.

[0039] For example, several samples of different thicknesses can be prepared and the actual thickness of each sample can be measured; After placing several samples one by one on the positioning mechanism and centering them, the transferring component grabs the centered samples according to the set program, and the suction cup of the transferring component moves to the designated pickup position each time. At the designated pickup position, the suction cup can apply pressure to the sample, so that the picking pressure value when the transferring component grabs each sample is measured by the pressure sensor. After obtaining the thickness of each sample and the corresponding picking pressure value, the linear relationship between the thickness and the picking pressure value can be calculated through feasible tools such as MATLAB. In subsequent calculations, the actual thickness of the workpiece can be calculated by substituting the picking pressure value measured each time the material is picked up into the linear relationship.

[0040] More preferably, after the workpiece is placed on the carrier, the workpiece pressure value measured by the pressure sensor is obtained (i.e., the pressure exerted by the workpiece on the carrier when no material is taken), and when determining the actual thickness of the workpiece based on the material taking pressure value, first subtract the workpiece pressure value from the material taking pressure value to obtain a pressure difference, and then substitute the pressure difference into the linear relationship between the pressure difference and the workpiece thickness to calculate the actual thickness of the workpiece.

[0041] The linear relationship between the pressure difference and the thickness of the workpiece is determined based on the process of measuring the material pressure value by grabbing the sample through the transfer component, that is, after each sample is placed on the carrier and centered, the workpiece pressure value measured by the pressure sensor at this time is first obtained, and then the material pressure value is measured when the transfer component grabs the sample, and the material pressure value is measured. The pressure difference corresponding to each sample is obtained by subtracting the workpiece pressure value measured when the sample is placed on the carrier from the material pressure value measured when the sample is grabbed. After obtaining the actual thickness of several samples and the corresponding pressure difference values, the linear relationship between the thickness and the pressure difference can be obtained based on the above data through feasible tools such as matlab, and then the actually measured pressure difference value can be substituted into it to calculate the actual thickness of the workpiece. The actual thickness obtained in this way is more accurate than the result calculated directly based on the pickup pressure value.

[0042] After determining the actual thickness of the workpiece, confirm whether the actual thickness exceeds the measuring range of the thickness measuring component of the thinning device. If so, an alarm is issued and the thinning process is exited; if not, execute S1.

[0043] Furthermore, before executing S1, it is also possible to determine whether the difference between the actual thickness determined by the workpiece thickness detection component and the actual thickness calculated according to the pressure sensor exceeds a threshold; if so, an alarm is issued and thinning is stopped; if not, the difference between the actual thickness determined by the workpiece thickness detection component and the actual thickness calculated according to the pressure sensor and the standard thickness is determined.

[0044] If it is determined that one of the actual thickness determined by the workpiece thickness detection component and the actual thickness calculated according to the pressure sensor is greater than the standard thickness, and the other is less than the standard thickness, an alarm is issued and thinning is stopped; If it is determined that the actual thickness determined by the workpiece thickness detection component and the actual thickness calculated according to the pressure sensor are both greater than the standard thickness, determine whether the actual thickness determined by the workpiece thickness detection component is greater than the actual thickness calculated according to the pressure sensor, if so, calculate the difference according to the actual thickness determined by the workpiece thickness detection component, otherwise, calculate the difference according to the actual thickness calculated according to the pressure sensor; If it is determined that the actual thickness determined by the workpiece thickness detection component and the actual thickness calculated according to the pressure sensor are both less than the standard thickness, determine whether the actual thickness determined by the workpiece thickness detection component is greater than the actual thickness calculated according to the pressure sensor. If so, calculate the error based on the actual thickness calculated according to the pressure sensor; otherwise, calculate the error based on the actual thickness measured by the workpiece thickness detection component.

[0045] Example 2 This embodiment discloses a grinding surface roughness control system, comprising: A first grinding unit is used to keep the main shaft of the grinding mechanism at a current height and continue grinding for a first time period when the grinding mechanism grinds the workpiece on the wafer stage to an expected target thickness; the expected target thickness is greater than the actual target thickness; a lifting unit, used to move the spindle upward at a first speed and a first distance, and the grinding mechanism continues grinding during the upward movement; the first distance does not exceed 10 microns, and the first speed is not greater than the feed speed when the workpiece is ground to the expected target thickness; A downward movement unit, used to move the spindle downward by the first distance at a second speed, and the spindle continues to grind during the downward movement; A second grinding unit, used to allow the spindle to continue grinding at the current height for a second time period; A reset unit is used to make the spindle move up a second distance at a third speed and then move up to a waiting position at a fourth speed greater than the third speed, wherein the second distance is greater than the first distance.

[0046] Example 3 This embodiment discloses a grinding device, including a processor and a memory, wherein the memory stores a program executable by the processor, and when the program is executed, the grinding surface roughness control method as described above is implemented.

[0047] There are many implementation methods of the present invention, and all technical solutions formed by equivalent transformation or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for controlling the roughness of a grinding surface, characterized in that: The steps include: S1, when the grinding mechanism grinds the workpiece on the wafer stage to the expected target thickness, the main shaft of the grinding mechanism is maintained at the current height and continues grinding for a first time period; The expected target thickness is greater than the actual target thickness; S2, moving the spindle upward at a first speed and a first distance, and the grinding mechanism continues grinding during the upward movement; the first distance does not exceed 10 microns, and the first speed is not greater than the feed speed when the workpiece is ground to the expected target thickness; S3, moving the spindle downwards by the first distance at a second speed, and the spindle continues to grind during the downward movement; S4, allowing the spindle to continue grinding at the current height for a second time period; S5, moving the main shaft up a second distance at a third speed and then up to a waiting position at a fourth speed greater than the third speed, wherein the second distance is greater than the first distance.

2. The grinding surface roughness control method according to claim 1, characterized in that: The first duration is between 8 and 13 seconds.

3. The grinding surface roughness control method according to claim 1, characterized in that: The first distance is between 4 and 8 micrometers.

4. The grinding surface roughness control method according to claim 1, characterized in that: The second speed and the third speed are not greater than the first speed.

5. The grinding surface roughness control method according to claim 1, characterized in that: The second duration is between 4-6 seconds.

6. The grinding surface roughness control method according to claim 1, characterized in that: The grinding mechanism grinds the workpiece to the expected target thickness in multiple stages, and the feed speed of each stage is different.

7. The method for controlling the grinding surface roughness according to any one of claims 1 to 6, characterized in that: Before the spindle starts to move downward, the actual thickness of the workpiece on the wafer table is detected by a thickness measuring component, and the deceleration point height is determined based on the actual thickness and the standard thickness corresponding to the workpiece. When the spindle moves to the deceleration point height, the feed speed is reduced.

8. The grinding surface roughness control method according to claim 7, characterized in that: Before measuring the actual thickness of the workpiece on the wafer stage by the thickness measuring component, when grabbing the workpiece from the positioning mechanism by the transfer component, it is determined whether the actual thickness of the workpiece exceeds the measuring range of the thickness measuring component.

9. A grinding surface roughness control system, characterized in that: include: The first grinding unit is used to keep the main shaft of the grinding mechanism at the current height and continue grinding for a first time period when the grinding mechanism grinds the workpiece on the wafer stage to an expected target thickness; The expected target thickness is greater than the actual target thickness; a lifting unit, used to move the spindle upward at a first speed and a first distance, and the grinding mechanism continues grinding during the upward movement; the first distance does not exceed 10 microns, and the first speed is not greater than the feed speed when the workpiece is ground to the expected target thickness; A downward movement unit, used to move the spindle downward by the first distance at a second speed, and the spindle continues to grind during the downward movement; A second grinding unit, used to allow the spindle to continue grinding at the current height for a second time period; A reset unit is used to make the spindle move up a second distance at a third speed and then move up to a waiting position at a fourth speed greater than the third speed, wherein the second distance is greater than the first distance.

10. A grinding device, comprising a processor and a memory, wherein the memory stores a program executable by the processor, characterized in that: When the program is executed, the grinding surface roughness control method as described in any one of claims 1 to 8 is implemented.

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