Surface shape precision prediction and control method for ultra-precision grinding of semiconductor wafer

Abstract

The invention provides a surface shape precision prediction and control method for ultra-precision grinding of a semiconductor wafer. The method comprises the following steps that 1, the grinding force F of the whole grinding wheel is calculated according to the grinding force F0 of a single abrasive particle and the number N of effective abrasive particles participating in grinding in the grinding wheel; step 2, simplifying the stress on the grinding wheel into a uniformly distributed load q distributed in a grinding contact area, and establishing a grinding wheel load distribution model; 3, the grinding wheel installed on the main shaft is simplified into a disc, and a grinding wheel flexural deformation model is established according to the flexural deformation principle that the disc is subjected to evenly-distributed loads; and 4, calculating the wafer TTV increment delta TTV caused by the deformation of the grinding wheel to obtain a TTV prediction model of wafer grinding. According to the method, the surface shape precision TTV model is established through mechanics and kinematics principles, and the influence of grinding process parameters on the surface shape precision is emphatically considered. Before grinding, according to the TTV value solved by the TTV model, the inclination angles of the grinding wheel and the vacuum suction cup are reversely adjusted so as to achieve surface shape precision control.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor wafer processing, and in particular, to a method for predicting and controlling the surface form accuracy of ultra-precision grinding of semiconductor wafers. Background Art

[0002] In the manufacturing process of semiconductor wafers, ultra-precision grinding based on the principle of workpiece rotation is one of the common finishing processes. In semiconductor applications, extremely high requirements are placed on the surface form accuracy of wafers, and usually, the surface form accuracy needs to be controlled at the grinding stage. Total thickness variation (TTV) is an important indicator for evaluating surface form accuracy. How to predict and control the TTV of the wafer after grinding is the key to improving surface form accuracy.

[0003] Currently, research on methods for predicting and controlling the TTV of ground semiconductor wafers believes that for workpiece rotation grinding, the semi-contact grinding state is the key to controlling TTV. Semi-contact grinding requires the grinding wheel to be parallel to one side of the dressed vacuum chuck. If other factors such as machining deformation are not considered, theoretically, the TTV of the processed wafer = 0. However, in actual grinding processes, different process parameters will cause changes in grinding forces, and the grinding wheel will inevitably deform due to grinding forces, especially for ultra-hard wafers, the influence of this deformation is more obvious. Currently, only a small amount of experimental research has explored the influence law of grinding process parameters on TTV. For example, in "A study of the total thickness variation in the grinding of ultra-precision substrates" published by Tso et al. (pages 182 - 188, volume 116, 2001, Journal of Materials Processing Technology), the influence law of grinding process parameters such as workpiece speed ratio and grinding wheel feed speed on the surface form accuracy of silicon wafers was analyzed through grinding experiments. There have been few relevant research reports in recent years.

[0004] In summary, there is an urgent need to carry out research on the influence mechanism of grinding process parameters on the surface form accuracy of semiconductor wafers, and based on this, develop a surface form accuracy control method considering the influence of grinding process parameters. Summary of the Invention

[0005] In response to the above-mentioned technical problems, the present invention proposes a method for predicting and controlling the surface form accuracy of ultra-precision grinding of semiconductor wafers. By considering the influence of grinding process parameters on grinding forces and the deformation of the grinding wheel caused by grinding forces, a more accurate TTV prediction model for surface form accuracy is established, and the relative inclination angle between the grinding wheel and the vacuum chuck is adjusted reversely to achieve the control of TTV.

[0006] The technical means adopted by the present invention are as follows:

[0007] A method for predicting and controlling the surface shape accuracy of ultra-precision grinding of semiconductor wafers, comprising the following steps:

[0008] Step 1: Calculate the overall grinding force F of the grinding wheel according to the grinding force F0 of a single abrasive grain and the number N of effective abrasive grains participating in grinding in the grinding wheel;

[0009] Step 2: Simplify the force on the grinding wheel into a uniformly distributed load q distributed in the grinding contact area, and establish a grinding wheel load distribution model;

[0010] Step 3: Simplify the grinding wheel installed on the main shaft into a disc, and establish a grinding wheel deflection deformation model according to the principle of deflection deformation of the disc under uniformly distributed load;

[0011] Step 4: Calculate the wafer TTV increment ΔTTV caused by the deformation of the grinding wheel, and obtain the TTV prediction model for wafer grinding.

[0012] Furthermore, considering the interference of other external factors, determine TTV0 caused by other factors through experimental fitting, and finally obtain the TTV prediction model for wafer grinding:

[0013] TTV = TTV0 + ΔTTV.

[0014] Furthermore, after step 4, the following steps are further included:

[0015] Based on the model in step 7, analyze the influence law of grinding process parameters on surface roughness;

[0016] After determining the grinding process parameters, calculate the TTV value and the grinding wheel deformation angle after grinding based on the prediction result of the TTV model, and inversely adjust the inclination angle between the grinding wheel and the vacuum chuck for reverse compensation, so as to achieve the control of TTV.

[0017] Furthermore, the overall grinding force F of the grinding wheel in step 1 is obtained based on the following formula:

[0018]

[0019] where f is the feed speed of the grinding wheel, n w is the workpiece rotation speed, n s is the grinding wheel rotation speed, r1 is the distance from the center on the wafer, θ is the semi-cone angle of the abrasive grain, and H is the wafer hardness.

[0020] Furthermore, in step 2, the grinding wheel load distribution model is established as:

[0021]

[0022] where R is the wafer radius.

[0023] Further, in Step 3, the established grinding wheel deflection deformation model is as follows:

[0024]

[0025] where D is the grinding wheel diameter, ν s is the Poisson's ratio of the grinding wheel, E s is the elastic modulus of the grinding wheel, and t is the thickness of the grinding wheel.

[0026] Further, in Step 4, the TTV increment ΔTTV of the wafer caused by the deformation of the grinding wheel is:

[0027]

[0028] Further, the semiconductor materials mentioned above include but are not limited to common semiconductor materials such as single-crystal silicon, silicon carbide, gallium nitride, gallium arsenide, aluminum nitride, etc.

[0029] Further, the TTV increment in Step 4 establishes an analytical model related to the grinding process parameters.

[0030] Further, the inclination compensation in Step 6 is determined by substituting different grinding process parameters into the TTV grinding calculation to obtain the TTV value.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] 1. The present invention establishes a surface form accuracy TTV model through mechanical and kinematic principles, and focuses on the influence of grinding process parameters on the surface form accuracy.

[0033] 2. The TTV model established by the present invention only requires one grinding test, and obtaining a set of TTV data fitting can predict the TTV under any other grinding parameters.

[0034] 3. The present invention inversely adjusts the inclination angles of the grinding wheel and the vacuum chuck according to the TTV value solved by the TTV model before grinding to achieve surface form accuracy control. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is a schematic diagram of the prediction and control process of the grinding surface form accuracy of the semiconductor materials involved in the present invention.

[0037] Figure 2This is the control effect diagram of the surface shape accuracy after grinding a certain semiconductor wafer in the present invention. Detailed implementation manners

[0038] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0039] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0040] As Figure 1 shown, the embodiments of the present invention disclose a method for predicting and controlling the surface shape accuracy of ultra-precision grinding of semiconductor wafers, including the following steps:

[0041] Step 1: Calculate the overall grinding force F of the grinding wheel according to the grinding force F0 of a single abrasive grain and the number N of effective abrasive grains participating in grinding in the grinding wheel.

[0042] Step 2: Simplify the force on the grinding wheel into a uniformly distributed load q distributed in the grinding contact area, and establish a grinding wheel load distribution model.

[0043] Step 3: Simplify the grinding wheel installed on the spindle into a disk, and establish a grinding wheel deflection deformation model according to the deflection deformation principle of the disk under uniformly distributed load.

[0044] Step 4: Calculate the wafer TTV increment ΔTTV caused by the deformation of the grinding wheel, and obtain the TTV prediction model for wafer grinding.

[0045] Furthermore, since TTV is also affected by other external factors such as machine tool stiffness and spindle runout, determine TTV0 caused by other factors through experimental fitting, and finally obtain the TTV prediction model for wafer grinding:

[0046] TTV = TTV0 + ΔTTV.

[0047] Further, after step 4, the following steps are also included:

[0048] Based on the model in step 7, analyze the influence law of grinding process parameters on surface roughness;

[0049] After determining the grinding process parameters, calculate the TTV value after grinding and the wheel deformation angle based on the prediction result of the TTV model, and inversely adjust the inclination angle between the grinding wheel and the vacuum chuck for reverse compensation, so as to realize the control of TTV.

[0050] Further, in step 1, the grinding force F of the whole grinding wheel is calculated based on the following formula:

[0051]

[0052] where f is the feed speed of the grinding wheel, n w is the workpiece rotation speed, n s is the grinding wheel rotation speed, r1 is the distance from the center on the wafer, θ is the half-cone angle of the abrasive grain, and H is the wafer hardness.

[0053] Further, in step 2, the grinding wheel load distribution model is established as:

[0054]

[0055] where R is the wafer radius.

[0056] Further, in step 3, the grinding wheel flexure deformation model established is:

[0057]

[0058] where D is the grinding wheel diameter, ν s is the Poisson's ratio of the grinding wheel, E s is the elastic modulus of the grinding wheel, and t is the thickness of the grinding wheel.

[0059] Further, in step 4, assuming that the wheel deformation angle is completely replicated to the wafer surface, the TTV increment ΔTTV of the wafer caused by the wheel deformation is calculated according to the geometric relationship as:

[0060]

[0061] Further, the semiconductor materials include, but are not limited to, common semiconductor materials such as single crystal silicon, silicon carbide, gallium nitride, gallium arsenide, aluminum nitride, etc.

[0062] Further, the TTV increment in step four establishes an analytical model related to the grinding process parameters.

[0063] Further, the inclination compensation described in Step 6 is determined by substituting different grinding process parameters into the TTV grinding calculation to obtain the TTV value.

[0064] In summary, the present invention combines the grinding process parameters to calculate the overall grinding force of the grinding wheel; then, based on the force condition in the grinding contact area, a load distribution model of the grinding wheel is established, the grinding force is simplified into a uniformly distributed load form, and a deflection deformation model of the grinding wheel under the action of the load is further derived. The deflection of the grinding wheel is calculated by the disk theory; then, assuming that the deformation of the grinding wheel is completely transmitted to the wafer surface, the total thickness variation (TTV) increment of the wafer caused by the deformation of the grinding wheel is calculated through geometric relations; on this basis, considering the influence of other external factors (such as machine tool stiffness and spindle runout) on TTV, the compensation error term is fitted through experiments, and finally a complete TTV prediction model is established; next, based on the prediction model and the grinding process parameters, the TTV value after grinding is calculated, and the deformation angle of the grinding wheel is calculated according to the model prediction result, and the inclination angle between the grinding wheel and the vacuum chuck is adjusted in the reverse direction to achieve the compensation control of TTV, so that the surface shape accuracy can be optimized before grinding; among them, the inclination compensation determines the compensation angle by substituting different grinding process parameters and combining the prediction model; finally, the TTV of the wafer after grinding is optimized by using this method, as Figure 2 described. This method can obtain the fitting parameters only through one grinding experiment, significantly improving the model prediction accuracy and grinding efficiency, and providing a scientific basis for the surface shape accuracy control in ultra-precision machining.

[0065] In the above embodiments of the present invention, the descriptions of each embodiment have their own emphases. For the parts not detailed in a certain embodiment, reference may be made to the relevant descriptions of other embodiments.

[0066] In several embodiments provided by the present application, it should be understood that the disclosed technical content can be implemented in other ways. Among them, the device embodiments described above are only illustrative. For example, the division of the units can be a logical function division. In actual implementation, there can be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point, the displayed or discussed mutual coupling or direct coupling or communication connection can be through some interfaces. The indirect coupling or communication connection of units or modules can be in an electrical or other form.

[0067] The units described as separate components may or may not be physically separated. The components displayed as units may or may not be physical units, that is, they can be located in one place, or can be distributed to multiple units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0068] In addition, in each embodiment of the present invention, each functional unit can be integrated into a processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of a software functional unit.

[0069] If the above-mentioned integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in each embodiment of the present invention. The aforementioned storage medium includes: various media such as USB flash drives, read-only memories (ROMs), random access memories (RAMs), mobile hard disks, magnetic disks, or optical discs that can store program codes.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of each embodiment of the present invention.

Claims

1. A method for predicting and controlling the surface form accuracy of ultra-precision grinding of semiconductor wafers, characterized in that, It includes the following steps: Step 1: Calculate the overall grinding force F of the grinding wheel according to the grinding force F0 of a single abrasive grain and the number N of effective abrasive grains participating in grinding in the grinding wheel. Step 2: Simplify the force on the grinding wheel into a uniformly distributed load q distributed in the grinding contact area, and establish a grinding wheel load distribution model. Step 3: Simplify the grinding wheel installed on the spindle into a disc, and establish a grinding wheel deflection deformation model according to the principle of deflection deformation of the disc under uniformly distributed load. Step 4: Calculate the increment ΔTTV of the wafer TTV caused by the deformation of the grinding wheel, and obtain the TTV prediction model for wafer grinding.

2. The method for predicting and controlling the surface form accuracy of ultra-precision grinding of semiconductor wafers according to claim 1, wherein, Considering the interference of other external factors, determine TTV0 caused by other factors through experimental fitting, and finally obtain the TTV prediction model for wafer grinding: TTV = TTV0 + ΔTTV.

3. The surface roughness prediction and control method for ultra-precision grinding of semiconductor wafers according to claim 1, characterized in that, After Step 4, the following steps are further included: Based on the model in Step 7, analyze the influence law of grinding process parameters on the surface roughness. After determining the grinding process parameters, calculate the TTV value after grinding and the deformation angle of the grinding wheel based on the prediction result of the TTV model, and inversely adjust the inclination angle between the grinding wheel and the vacuum chuck for reverse compensation, so as to achieve the control of TTV.

4. The surface roughness prediction and control method for ultra-precision grinding of semiconductor wafers according to claim 3, characterized in that, In Step 1, the overall grinding force F of the grinding wheel is calculated based on the following formula: where f is the feed rate of the grinding wheel, n w is the rotational speed of the workpiece, n s is the rotational speed of the grinding wheel, r1 is the distance from the center on the wafer, θ is the half-cone angle of the abrasive grain, and H is the hardness of the wafer.

5. The method for predicting and controlling the surface roughness of ultra-precision grinding of semiconductor wafers according to claim 4, characterized in that In Step 2, the established grinding wheel load distribution model is: where R is the radius of the wafer.

6. The surface roughness prediction and control method for ultra-precision grinding of semiconductor wafers according to claim 5, characterized in that, In Step 3, the established grinding wheel deflection deformation model is: where D is the diameter of the grinding wheel, ν s is the Poisson's ratio of the grinding wheel, E s is the elastic modulus of the grinding wheel, and t is the thickness of the grinding wheel.

7. The surface roughness prediction and control method for ultra-precision grinding of semiconductor wafers according to claim 6, characterized in that In Step 4, the increment ΔTTV of the wafer TTV caused by the deformation of the grinding wheel is:

8. The surface roughness prediction and control method for ultra-precision grinding of semiconductor wafers according to claim 1, characterized in that The materials of the semiconductor wafer include but are not limited to single crystal silicon, silicon carbide, gallium nitride, gallium arsenide, aluminum nitride.

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