Wafer processing method

Abstract

To provide a wafer processing method which can reduce the nano topography and dispersion of post-grinding wafers even by not repeating a plurality of surface-grinding processes accompanied by resin sticking.SOLUTION: This invention relates to a wafer processing method which has a resin sticking process for resin-sticking a first principal plane of a wafer having the first principal plane and a second principal plane, a first grinding process for surface-grinding the second principal plane by sucking the first principal plane side subjected to resin sticking in the resin sticking process, and a second grinding process for surface-grinding the first principal plane by sucking the second principal plane side. The wafer processing method has a waviness component evaluation process before the resin sticking process, measures the shape of both principal planes of a wafer in the waviness component evaluation process, evaluates the waviness components of both the principal planes, respectively, on the basis of measurement results, and specifies the principal plane with the smaller waviness component on the basis of evaluation, so as to make the first principal plane of the principal plane with the smaller waviness component in the resin sticking process.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a wafer processing method. [Background technology]

[0002] Conventionally, semiconductor wafers require flattening of their surfaces in order to fabricate fine patterns using photolithography. In particular, a technology called nanotopography has been proposed to improve the flatness of semiconductor wafers by reducing surface waviness.

[0003] For example, Patent Document 1 discloses a technique in which one surface of a workpiece is fixed to the upper surface of a base plate via an adhesive material and the other surface is surface-ground. Patent Document 2 discloses a resin coating method in which one surface of a wafer is coated with resin in order to grind the wafer flat. Patent Document 3 also discloses a wafer grinding method using resin bonding, which includes a step of resin bonding one surface of the wafer and single-sided grinding the other surface, and a step of resin bonding the other surface and single-sided grinding the one surface. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-66850 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-148866 [Patent Document 3] Japanese Patent Application Publication No. 2023-172169 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the method of grinding with resin attachment (hereinafter sometimes referred to as "resin attachment grinding") described in Patent Documents 1 and 2 has the problem that nanotopography and warp deteriorate when the wafer shape after slicing is large.

[0006] To address this issue, Patent Document 3 discloses a technique for simultaneously improving nanotopography and warp level by repeating resin-attached grinding twice, but this technique has the problem of varying nanotopography levels depending on the wafer being processed.

[0007] The present invention has been made to solve the above problems, and has an object to provide a wafer processing method that can reduce the nanotopography of the wafer after grinding and reduce the variation. [Means for solving the problem]

[0008] The present invention has been made to achieve the above-mentioned object, and provides a wafer processing method comprising: a resin bonding step of resin bonding the first main surface of a wafer having a first main surface and a second main surface; a first grinding step of suctioning the first main surface side resin-bonded in the resin bonding step and surface grinding the second main surface; and a second grinding step of suctioning the second main surface side and surface grinding the first main surface, wherein the wafer processing method comprises a waviness component evaluation step prior to the resin bonding step, in which the shapes of both main surfaces of the wafer are measured in the waviness component evaluation step, and the waviness components of both main surfaces are evaluated based on the measurement results, and the main surface with the smaller waviness component is identified based on the evaluation, and in the resin bonding step, the main surface with the smaller waviness component is used as the first main surface.

[0009] This wafer processing method can reduce the nanotopography of the wafer after grinding and minimize variations in the nanotopography. It also eliminates the need for repeated surface grinding involving resin lamination, improving productivity and reducing costs.

[0010] In this case, in the waviness component evaluation step, a laser or capacitance type shape measuring device is used to acquire shape profiles of both main surfaces of the wafer, and a waviness profile is extracted by subjecting the shape profile to bandpass filtering processing with a wavelength of 1 mm or more and 50 mm or less, and the difference between the maximum value and the minimum value of the waviness profile can be taken as the waviness component.

[0011] This makes it possible to more accurately evaluate the irregularities on both main surfaces of the wafer and more accurately identify the main surface with the smaller waviness component.

[0012] In this case, the wafers may be obtained by slicing an ingot.

[0013] The wafer processing method of the present invention is suitable for wafers obtained by slicing an ingot, since the front and back surfaces have different shapes. [Effects of the Invention]

[0014] As described above, the wafer processing method of the present invention can reduce the nanotopography of the wafer after grinding and minimize variation. Furthermore, the technique of repeating resin-attached grinding twice, as in Patent Document 3, improves the level of warp and nanotopography, but has the problem of reduced productivity compared to a method of performing resin-attached grinding once. Therefore, the wafer processing method of the present invention can omit the need to repeat surface grinding with resin attachment multiple times, thereby improving productivity and reducing costs. [Brief explanation of the drawings]

[0015] [Figure 1] 1 shows a flow diagram of an example of a wafer processing method according to the present invention. [Figure 2] 1 is a schematic diagram showing an example of a conventional method for grinding a resin-coated wafer. [Figure 3] 1 shows a schematic diagram of a state (cross section) during cutting processing of a wafer with a wire saw. [Figure 4]1 shows a schematic diagram of an example of a method for measuring the shape of a wafer (cross section). DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below, but the present invention is not limited thereto.

[0017] As described above, there has been a demand for a wafer processing method that can reduce the nanotopography of the wafer after grinding and reduce the variation.

[0018] After extensive research, the inventors have found that although conventional resin-attached grinding is a technology that can improve waviness in slices, it cannot completely eliminate the effects of shape changes on the wafer surface.

[0019] Furthermore, when the waviness components on the front and back sides of the raw material wafer were evaluated, it was found that when resin was first applied to the side with the larger waviness component and this side was chucked and surface grinding was performed, the nanotopography after processing was worse than when resin was first applied to the side with the smaller waviness component and this side was chucked and surface grinding was performed.

[0020] A schematic diagram of an example of a conventional method for grinding resin-coated wafers is shown in Figure 2. As shown in Figure 2, an example is shown in which the unevenness (waviness component) on the front surface 1 of the raw wafer (hereinafter simply referred to as "wafer") W after chamfering is larger than the waviness component on the back surface 2.

[0021] In the flow shown in the upper diagram of Figure 2, first, a resin is applied to the front surface 1 of the raw material wafer W and the wafer is adsorbed to a chuck table 7, and then the back surface 2, which has no resin layer, is single-sidedly ground (first grinding) with a grinding wheel 6. Thereafter, the resin layer on the first main surface is peeled off, and the first main surface is single-sidedly ground (second grinding). In the flow shown in the lower diagram of Figure 2, the same wafer is used, but first, a resin is applied to the back surface 2 of the raw material wafer W and then ground. Resin application is performed, for example, by placing an optically transparent film 4 on a surface plate (lower surface plate) 5, supplying resin 3 on top of that, placing the wafer W on the resin 3, and pressing the wafer W.

[0022] When the shapes of the front and back surfaces are different in this way, it was found that even for wafers of the same shape, the shape after surface grinding can vary greatly depending on which surface is used as the base surface for surface grinding first. In the example of Figure 2, when first resin is attached to front surface 1 and then chucked and ground, the waviness after processing was worse than when resin is attached to back surface 2 and then chucked and ground first.

[0023] Conventional resin-attached grinding involves a mixture of the cases shown in the upper and lower figures in Figure 2, resulting in variations in the nanotopography level of the wafer after grinding.

[0024] As a result of extensive research into the above-mentioned problems, the present inventors have come up with a method for processing a wafer, the method comprising: a resin bonding step of bonding a resin to a first main surface of a wafer having a first main surface and a second main surface; a first grinding step of suction-holding the first main surface side that has been resin-bonded in the resin bonding step and surface-grinding the second main surface; and a second grinding step of suction-holding the second main surface side and surface-grinding the first main surface, the method comprising: a waviness component evaluation step prior to the resin bonding step; The present inventors have found that a wafer processing method characterized by measuring the shape, evaluating the waviness components of both main surfaces based on the measurement results, identifying the main surface with the smaller waviness component based on the evaluation, and using the main surface with the smaller waviness component as the first main surface in the resin lamination process can reduce the nanotopography of the wafer after grinding and its variation, and can also omit the need to repeat surface grinding involving resin lamination multiple times, thereby improving productivity and reducing costs, and have completed the present invention.

[0025] A flow diagram of an example of a wafer processing method according to the present invention is shown in Figure 1. As shown in Figure 1, the wafer processing method according to the present invention includes a resin bonding step of resin bonding the first main surface of a wafer having first and second main surfaces, a first grinding step of sucking the first main surface side resin-bonded in the resin bonding step and surface grinding the second main surface, and a second grinding step of sucking the second main surface side and surface grinding the first main surface, and includes a waviness component evaluation step before the resin bonding step.

[0026] The wafers used in the wafer processing method according to the present invention may be wafers obtained by slicing an ingot. After slicing the wafers, chamfering may be performed, and the wafers may be polished after the second grinding step.

[0027] The wafers can be sliced ​​and chamfered by a conventional method, for example, by using a wire saw to slice the ingot into a plurality of wafers.

[0028] A schematic diagram of the state during cutting processing in which a wafer is cut with a wire saw is shown in Figure 3. In Figure 3, the left side (one side) of the sliced ​​wafer (sliced ​​wafer) SW is expressed as the front side 8, and the right side (the other side) is expressed as the back side 9.

[0029] The shape of the sliced ​​wafer SW affects the movement trajectory of the wire 10, but when viewed from the perspective of a certain wire 10, the shape of the back surface 9 is formed for the wafer on the left side, and the shape of the front surface 8 is formed for the wafer on the right side. As such, the conditions for creating the front and back surfaces are prone to change during the slicing process, which can lead to variations in the shapes of the front and back surfaces. In particular, unevenness known as wire marks is generated on the front and back surfaces after slicing due to the reciprocating motion of the wire 10, and the undulation components of these marks also differ. Furthermore, variations in thickness and the adhesion of dirt that occur during slicing also cause differences in the shapes (unevenness) of the front and back surfaces.

[0030] Since the wafers obtained by slicing the ingot have different shapes on the front and back sides, the wafer processing method of the present invention is suitable.

[0031] [Waviness component evaluation process] In the waviness component evaluation step, the shapes of both main surfaces of the raw material wafer are measured, the waviness components of both main surfaces are evaluated based on the measurement results, and the main surface with the smaller waviness component is identified based on the evaluation.

[0032] In the present invention, the "waviness component" refers not only to the overall shape such as bow or warp, but also to shape changes in a narrower area that affect quality, such as waviness or nanotopography.

[0033] The device used to measure the shape of the wafer is not particularly limited as long as it is a device that can evaluate the surface shape of the wafer, but it is preferable to use a laser or capacitance type displacement meter (shape measuring device) 11, as shown in Fig. 4, to measure the shapes of both main surfaces of the wafer W. A one-dimensional type laser type displacement meter may be used, but a two-dimensional type laser type displacement meter is more preferable.

[0034] The measurement method is not particularly limited, and measurements can be made by scanning a displacement meter or a wafer, and measurements can be made on one side at a time or on both main surfaces simultaneously.

[0035] For one-dimensional displacement meters, the probe diameter should be 6 mm or less, and more preferably 1 mm or less. For two-dimensional laser displacement meters, the probe width in the scanning direction should be 1 mm or less.

[0036] The distance between adjacent measurement points should preferably be 1 mm or less.

[0037] It is also preferable to measure four or more diameter-direction shape profiles evenly distributed radially, and more preferably to measure the entire surface.

[0038] The shape profiles of both main surfaces of the wafer obtained as described above are subjected to bandpass filtering processing with a wavelength of 1 mm or more and 50 mm or less to extract a waviness profile, and the difference between the maximum and minimum values ​​of the waviness profile is taken as the waviness component value of the target surface, thereby making it possible to derive the waviness component.

[0039] By performing the evaluation in this manner, the irregularities on both main surfaces of the wafer can be evaluated more accurately, and the main surface with the smaller waviness component can be identified more accurately.

[0040] [Resin pasting process] The principal surface with the smaller waviness component identified in the waviness component evaluation step is designated as the first principal surface, and resin is applied to the first principal surface.

[0041] The method and device for applying the resin are not particularly limited. As shown in the lower diagram of Figure 2, a light-transmitting film 4 is laid on a surface plate (lower surface plate) 5 having a flat surface, and a plasticized, for example, liquid resin 3 is applied thereon. A wafer W is then placed on the resin 3, and a surface plate (upper surface plate) is used to press the film with a predetermined load so that the surface of the film is flat. Then, a curing process is performed according to the type of resin used.

[0042] [First grinding process] The first principal surface to which the resin has been applied is used as a chuck surface (reference surface), the first principal surface side is vacuum-adsorbed to a chuck table 7, and the principal surface opposite the first principal surface (second principal surface) is ground with a grinding wheel 6. There are no particular limitations on the grinding method or device, but it is preferable that the chuck table 7 be made of porous ceramic and capable of holding the wafer by vacuum adsorption.

[0043] The coating applied to the first main surface can be removed from the wafer after the first grinding step. In the present invention, a wafer with good nanotopography can be obtained even if resin bonding to the second main surface is omitted, but resin bonding to the second main surface is not excluded.

[0044] [Second grinding process] The second main surface side is vacuum-sucked to the chuck table 7, and the first main surface is ground with the grinding wheel 6 using the same method as in the first grinding step.

[0045] As described above, in the present invention, it is important to judge the surface to be first resin-attached based on the waviness component evaluated by the evaluation method of the present invention, and resin removal and grinding may be performed in the same manner as in the past. Note that resin-attachment grinding may be further repeated after the second grinding step.

[0046] Polishing can be performed after the second grinding step. The polishing device and conditions are not particularly limited, and polishing can be performed using commonly used polishing devices and conditions such as double-side polishing, mirror chamfering, and CMP polishing (finish polishing).

[0047] As described above, by first determining the surface to be resin-bonded in resin-bonded grinding of a wafer, a wafer processing method can be achieved in which the nanotopography after grinding is small and has little variation. Furthermore, it is possible to omit the need to repeat multiple rounds of surface grinding involving resin bonding, thereby improving productivity and reducing costs. Even when resin bonding is performed multiple times, by first determining the surface to be resin-bonded as in the present invention, nanotopography variation can be reduced compared to conventional techniques. [Example]

[0048] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0049] (Example) The raw wafers used were 300 mm diameter P-type Si single crystal wafers that had been chamfered after slicing. 25 wafers were processed consecutively under the following conditions.

[0050] The shape of both main surfaces of the wafer was measured using a one-dimensional capacitance displacement sensor. The interval between adjacent measurement points was 1 mm, and four diameter direction shape profiles were measured evenly in a radial pattern.

[0051] The shape profiles of both main surfaces of the wafer obtained by measuring the shape were subjected to bandpass filtering with wavelengths of 1 mm to 50 mm, and the waviness profile was extracted. The difference between the maximum and minimum values ​​of the waviness profile was taken as the waviness component of the target surface.

[0052] The magnitude of the waviness component (waviness component value) on both main surfaces of the same wafer was compared, and the main surface with the smaller waviness component was identified for each wafer.

[0053] A PET film was placed on a flat glass surface plate (lower surface plate), and 10 ml of UV-curable resin was dropped onto the PET film.

[0054] The principal surface with the smaller waviness component was designated the first principal surface in the wafer processing method according to the present invention, and the second principal surface (the principal surface opposite the first principal surface) was held by vacuum suction on a ceramic surface plate (upper surface plate), and the first principal surface was pressed against the resin to bond it. The pressing force was controlled by a servo motor that held the ceramic surface plate, and pressure was applied until a predetermined load was detected. The resin was irradiated with UV-LED light with a wavelength of 365 nm to harden it (resin bonding process).

[0055] After the first resin lamination process, the first main surface was vacuum-attached to a chuck table, and the second main surface was subjected to surface grinding (first grinding process). A grinding wheel with diamond abrasive grains was used for the grinding process. The axis angle of the chuck table was also adjusted to keep the wafer thickness variation to 1 μm or less.

[0056] Next, the coating on the first main surface was peeled off, the wafer was turned over, and the first main surface was subjected to surface grinding in the same procedure as in the first grinding step (second grinding step).

[0057] Thereafter, both main surfaces of the wafer were mirror-polished using a commonly used polishing device under commonly used polishing conditions.

[0058] The nanotopography of the wafers after polishing was measured. For the measurements, an optical interference type flatness and nanotopography measuring device (KLA: WaferSight2+) was used. As an index of nanotopography, an SQMM 10mm x 10mm was used. The average value of the nanotopography of 25 wafers was calculated and used as the "average nanotopography value after polishing."

[0059] (Comparative Example 1) In the resin lamination process of the example, the wafer was processed and evaluated in the same manner as in the example, except that the front surface of the wafer was designated as the first main surface regardless of the result of identifying the main surface with the smaller waviness component.

[0060] (Comparative Example 2) In the resin lamination process of the example, the wafer was processed and evaluated in the same manner as in the example, except that the back surface of the wafer was used as the first main surface regardless of the result of identifying the main surface with the smaller waviness component.

[0061] In Comparative Examples 1 and 2, the front side refers to one side shown in the schematic diagram of the state (cross section) of the wafer during cutting processing in Fig. 3, and the back side refers to the other side. After slicing, the wafer was processed without being turned over.

[0062] The results of Example, Comparative Example 1, and Comparative Example 2 are shown in Table 1. The average values ​​of the nanotopography after polishing in Table 1 are values ​​normalized with the value of Comparative Example 1 as the standard.

[0063] [Table 1]

[0064] In the Example, the average value of the nanotopography after polishing was better than in Comparative Examples 1 and 2. This is because the waviness component was evaluated after chamfering, and resin was first applied to the main surface with the smaller waviness component, and surface grinding was performed using this as the reference surface (chuck surface).

[0065] As described above, according to the embodiment of the present invention, the shape of both main surfaces of the wafer was measured, the waviness component was evaluated, and first a resin was applied to the main surface with the smaller waviness component and the other main surface was flat-ground using it as a reference surface (chuck surface), and then the other main surface with the smaller waviness component was flat-ground using the other main surface as the reference surface (chuck surface). This made it possible to improve the nanotopography after processing compared to Comparative Examples 1 and 2, in which the first main surface was fixed to either the front or back surface and ground with a resin.

[0066] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0067] 1...surface, 2...back surface, 3...resin, 4...light-transmitting film, 5...Surface plate (lower surface plate), 6...Grinding wheel, 7...Chuck table, 8...surface (one side), 9...back side (other side), 10...wire, 11...Displacement meter (shape measuring device), W...raw material wafer (wafer), SW...Sliced ​​wafer.

Claims

1. a resin bonding step of bonding a resin to the first main surface of a wafer having a first main surface and a second main surface; a first grinding step of surface-grinding the second main surface by suctioning the first main surface side to which the resin has been attached in the resin attaching step; a second grinding step of surface grinding the first main surface by suctioning the second main surface side, The wafer processing method includes a waviness component evaluation step before the resin bonding step, In the waviness component evaluation step, the shapes of both main surfaces of the wafer are measured, the waviness components of both main surfaces are evaluated based on the measurement results, and the main surface having the smaller waviness component is identified based on the evaluation; A wafer processing method, characterized in that in the resin laminating step, the main surface having the smaller waviness component is used as the first main surface.

2. In the wavy component evaluation step, obtaining shape profiles of both main surfaces of the wafer using a laser or capacitance shape measuring device; A waviness profile is extracted by subjecting the shape profile to bandpass filtering with a wavelength of 1 mm or more and 50 mm or less.

2. The wafer processing method according to claim 1, wherein the waviness component is a difference between a maximum value and a minimum value of the waviness profile.

3. 3. The wafer processing method according to claim 1, wherein the wafers are obtained by slicing an ingot.

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