Method for grinding semiconductor wafers

Abstract

The present invention relates to a method for grinding a semiconductor wafer, wherein the semiconductor wafer is machined for material removal by a grinding tool including grinding teeth having a height h, a cooling medium is supplied to the contact area between the semiconductor wafer and the grinding tool, and at any time during grinding, a rinsing liquid is applied by a nozzle to an area on one side of the semiconductor wafer, the distance between this area and the center of the semiconductor wafer being 2 mm or more and 10 mm or less.

Description

[Technical field]

[0001] The subject of the present invention is a method for grinding a wafer made of semiconductor material, comprising: It is based on an optimal distribution of fluid around the grinding tool for processing semiconductor wafers to remove material from both sides simultaneously. [Background technology]

[0002] The electronics, microelectronics and microelectromechanics fields require as starting material semiconductor wafers (substrates) that have extreme requirements in terms of global and local flatness, one-sided local flatness (nanotopology), roughness and cleanliness. Semiconductor wafers are wafers made of semiconductor materials, in particular compound semiconductors such as gallium arsenide or elemental semiconductors such as silicon and germanium.

[0003] According to the prior art, semiconductor wafers are manufactured in a number of successive process steps. The following production sequences are commonly used: - Producing single crystal semiconductor rods (crystal growth); - dividing the semiconductor rod into individual rod pieces; -Splitting the rod into individual wafers (inner diameter or wire sawing), -Mechanical processing of the wafer (lapping, grinding), - chemically treating the wafer (alkaline or acid etching), - chemically and mechanically treating (polishing) the wafer, - optional further coating steps (e.g. epitaxy, temperature treatment).

[0004] The mechanical processing of the semiconductor wafer serves to remove the waviness caused by sawing, to remove surface layers that have been damaged in terms of their crystalline structure by the rougher sawing process or contaminated by the sawing wire, and mainly to globally planarize the semiconductor wafer. Furthermore, the mechanical processing of the semiconductor wafer serves to produce a uniform thickness distribution, i.e. the wafer has a uniform thickness.

[0005] Known methods for mechanically processing semiconductor wafers include lapping and surface grinding (single-sided and double-sided).

[0006] The technique of simultaneous double-sided lapping for several semiconductor wafers has been known for some time and is described, for example, in EP 547894 A1. In double-sided lapping, the semiconductor wafer is moved under pressure while a suspension containing an abrasive substance is fed between the upper and lower working disks of a lapping disk, which is usually made of steel and provided with channels for improved distribution of the suspension, thereby removing material. The semiconductor wafer is guided by a carrier having a notch for receiving the semiconductor wafer during lapping, the semiconductor wafer is held on a geometric path by the carrier, and the carrier is set in rotation by inner and outer drive sprockets.

[0007] In single-sided grinding, the semiconductor wafer is held on its backside on a chuck and flattened on its front side by a cup grinding wheel, while the chuck and the grinding wheel rotate and undergo slow axial and radial feed. Methods and devices for single-sided grinding of semiconductor wafers are known, for example, from US 2008 021 40 94 A1 or EP 0 955 126 A2.

[0008] In simultaneous double-sided grinding (sDDG), the semiconductor wafer is processed simultaneously on both sides in a freely floating manner between two grinding disks mounted on opposing collinear spindles, and in the process is guided axially between water cushions (hydrostatic principle) or air cushions (aerostatic principle) acting largely free from binding forces on the front or rear side, and is held radially floating and fixed by thin, loosely surrounding guide rings or individual radial spokes. Methods and devices for simultaneous double-sided grinding of semiconductor wafers are known, for example, from EP 0 755 751 A1, EP 0 971 398 A1, DE 10 2004 011 996 A1 and DE 10 2006 032 455 A1.

[0009] However, due to kinematic characteristics, double-sided grinding (DDG) of semiconductor wafers as a rule leads to greater material removal in the center of the semiconductor wafer ("grinding center point"). In order to obtain a semiconductor wafer with the best possible geometry after grinding, the two grinding spindles on which the grinding disks are mounted must be aligned exactly in the same line, since radial and / or axial deviations have a negative effect on the shape and nanotopology of the ground wafer. German application DE 10 2007 049 810 A1 teaches, for example, a method for correcting the grinding spindle position in a double-sided grinding machine.

[0010] In the grinding process - and this applies to both single-sided and double-sided grinding methods - it is necessary to cool the grinding tool and / or the processed semiconductor wafer. Water or deionized water is usually used as the coolant. In double-sided grinders, the coolant usually leaves the center of the grinding tool and is transferred or projected by centrifugal force to the grinding teeth arranged in a circle on the outer edge of the grinding disk. The coolant throughput, i.e. the amount of coolant that leaves in a defined time, may be controlled electronically or mechanically.

[0011] Document DE 10 2007 030 958 A1 teaches a method for grinding semiconductor wafers, in which the semiconductor wafers are treated by at least one grinding tool to remove material on one or both sides while being supplied with a coolant. In order to ensure constant cooling during grinding, the coolant flow is reduced as the height of the grinding teeth decreases, since if the coolant flow is kept high and unchanged, this would inevitably lead to hydroplaning.

[0012] The invention of document DE 10 2017 215 705 A1 is based on an optimal distribution of a fluid in a grinding tool for processing semiconductor wafers so as to simultaneously remove material from both sides, which is achieved using an optimized sliding plate, where it is taught that an uneven distribution of the fluid has a negative effect on the grinding result.

[0013] Patent document US2019 / 134782 A1 discloses a specific design of a grinding disk that can be used for double-sided grinding. It also teaches the use of water applied onto the semiconductor wafer by a nozzle.

[0014] Document DE 10 2007 030958 A1 presents a method for grinding semiconductor wafers, in which the amount of grinding water is supplied to the process as a function of the tooth height. Summary of the Invention [Problem to be solved by the invention]

[0015] Problem description All of the above-mentioned prior art documents have the common drawback that the removal of material is greater at the center of the semiconductor wafer than at its edge, which leads to deterioration of the geometric parameters of the semiconductor wafer in this processing step, which deviations are not corrected or are not sufficiently corrected in subsequent processing steps.

[0016] Purpose Description The object of the present invention is to provide a method which does not present the above mentioned drawbacks. [Means for solving the problem]

[0017] Explanation of achievement of objectives This object is achieved by a method of grinding semiconductor wafers, in which the semiconductor wafer is treated to remove material by a grinding tool comprising grinding teeth having a height h, and a coolant is supplied to the contact area between the semiconductor wafer and the grinding tool, and at any point in the grinding, Rinse Solution is applied through a nozzle onto an area on one side of a semiconductor wafer.

[0018] Both sides of a semiconductor wafer are processed to remove material; Rinse Solution It has proven to be particularly advantageous if the is applied to areas on both sides of the semiconductor wafer.

[0019] In this case, it is particularly preferred to reduce the amount of coolant per hour as the height h of the grinding teeth of the grinding tool decreases.

[0020] Amount of coolant per hour and Rinse Solution Advantageously, the sum of the amounts of is kept constant during grinding.

[0021] Measured with the nozzle used Rinse Solution The excess pressure is preferably greater than or equal to 0.1 bar, particularly preferably less than or equal to 0.5 bar.

[0022] Preferably, per hour Rinse Solution It should be ensured that the amount is greater than or equal to 0.1 l / min and less than or equal to 1 l / min.

[0023] In particular, during grinding Rinse Solution Attention should be paid to the area on the semiconductor wafer to which the flow is directed, preferably at a distance of 2 mm or more, preferably 4 mm or more and 10 mm or less, preferably 6 mm or less, from the center of the semiconductor wafer.

[0024] The surface area of ​​the nozzle used in this case is 1.5 mm 2 Less than or equal to 0.1 mm2 More preferably, it is equal to or greater than this.

[0025] per hour Rinse Solution It is particularly preferred that the amount of is kept constant throughout the grinding process. [Brief description of the drawings]

[0026] [Figure 1] The results of two series of tests on the shape in the center of a semiconductor wafer are shown. The vertical axis in this case shows the deviation of the geometric shape (G) from the ideal geometric shape in the central area of ​​the semiconductor wafer. The semiconductor wafers in group B (prior art) in this case have, on average, a larger deviation from the desired shape than the semiconductor wafers in group A (according to the invention). It also holds true that the statistical distribution of the measured deviations for the method according to the invention (group A) results in a narrower distribution than for the semiconductor wafers processed according to the prior art (group B). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS ACCORDING TO THE PRESENT PRESENT EMBODIMENT A crystal piece of silicon with a nominal diameter of 300 mm, obtained from a crystal rod pulled by the Czochralski method, was cut into semiconductor wafers by a wire saw. The semiconductor wafers thus obtained were divided into two groups A and B, with every second semiconductor wafer assigned to group A and the remaining semiconductor wafers assigned to group B.

[0028] Both Group A and Group B semiconductor wafers were ground on a Koyo DSGX320 grinding system, which in this case was equipped with a commercially available grinding wheel, type #3000-OVH, from ALMT.

[0029] The semiconductor wafers of group B were in this case ground according to the prior art. According to the prior art, the amount of grinding water is supplied to the process in a controlled manner depending on the tooth height (according to DE 10 2007 030 958 A1), which ensures that there is no floating of the tool on the wafer being processed (corresponding to hydroplaning) when an excessive amount of grinding water is forced out of the interior of the tool onto the path during the process, and that there is no overheating, corresponding to grinding burnout of the wafer being processed, and damage to the grinding wheel, if too little grinding water is available during the process.

[0030] Group A semiconductor wafers, in contrast, use a coolant during the grinding process in addition to the coolant used during grinding to cool the semiconductor wafer. Rinse Solution was added using the grinding method. Here, Rinse Solution It was guaranteed that the flow would always have a noticeable current.

[0031] In this case, a significant flow is to be understood as a flow of 0.01 l / min. Rinse Solution It has been preferred to use water, however, it is contemplated that additional additives may be used.

[0032] Like this Rinse Solution The addition of the SiO2 nanoparticles significantly improved the shape of the center of the wafer. However, during the grinding process, Rinse Solution If the flow is interrupted, this again deteriorates the geometry of the center of the semiconductor wafer.

[0033] According to the present invention, Rinse Solution is directed towards a region substantially around the centre of the semiconductor wafer, which region, according to the invention, is at a distance of 2 mm or more, preferably 4 mm or more and 10 mm or less, preferably 6 mm or less, from the centre of the semiconductor wafer during grinding.

[0034] The effect is, Rinse Solution It appears to be particularly good when the flow rate is greater than 0.1 l / min and up to 1 l / min.

[0035] The inventors have 2~1.5mm 2 It has been determined that using a nozzle with a minimum nozzle cross section of 0.1 mm has a particularly advantageous influence on this effect.

[0036] Furthermore, the inventors have confirmed that the set pressure also clearly plays a role in the improvement: thus, an excess pressure set at the nozzle of 0.1 bar to 0.5 bar has a particularly positive effect.

[0037] Both groups of semiconductor wafers "A" and "B" were measured with respect to the geometry achieved after grinding, where the respective deviation of the measured geometry at the center of the semiconductor wafer was compared with the ideal geometry and the difference was given as a measurement value.

[0038] FIG. 1 shows a comparison of semiconductor wafers of Group A (according to the present invention) with semiconductor wafers of Group B (prior art).

[0039] In this case, the semiconductor wafers of group B (prior art) have, on average, a larger deviation from the desired shape than the semiconductor wafers of group A (according to the invention). Thus, the method according to the invention improves the geometric shape in the center of the semiconductor wafer compared to the method according to the prior art.

[0040] Furthermore, the statistical distribution of the measured deviations for the method according to the invention (group A) results in a narrower distribution than for the semiconductor wafers processed according to the prior art (group B), which means that the method according to the invention also offers further advantages regarding the statistical distribution of the geometrical feature values ​​in the center of the semiconductor wafer.

[0041] The inventors have determined that a relatively small amount of the abrasive that is not applied to the direct active area of ​​the grinding wheel is Rinse Solution However, we were surprised by the fact that it achieved a significant effect in terms of improving the geometric shape.

[0042] So far it has been possible to speculate about the corresponding relationships and causes, but they are not clear to the inventors.

[0043] The above description of the exemplary embodiments should be understood as examples. The disclosure made thereby, on the one hand, enables a person skilled in the art to understand the present invention and its related advantages, and on the other hand, also includes changes and modifications to the described structures and methods that are obvious within the understanding of a person skilled in the art. Therefore, all such alternatives and modifications and equivalents are also intended to be encompassed in the scope of protection of the claims.

Claims

1. 1. A method of grinding a semiconductor wafer, the method comprising: processing the semiconductor wafer to remove material with a grinding tool including grinding teeth having a height h; a coolant is supplied to a contact area between the semiconductor wafer and the grinding tool; and at any point during grinding, a rinsing liquid is applied through a nozzle onto a single-sided area of ​​the semiconductor wafer being processed.

2. 10. The method of claim 1, wherein both sides of the semiconductor wafer are simultaneously processed to remove material, and the rinsing solution is applied to areas on both sides of the semiconductor wafer.

3. The method of claim 1 or claim 2, wherein the amount of coolant per time is reduced as the height h decreases.

4. 4. The method according to claim 1, wherein the sum of the amount of coolant per hour and the amount of rinsing liquid per hour is constant.

5. 5. The method of claim 1, wherein the pressure of the rinsing liquid measured at the nozzle is greater than or equal to 0.1 bar.

6. 6. The method of claim 1, wherein the pressure of the rinsing liquid measured at the nozzle is less than or equal to 1.0 bar.

7. The method according to any one of claims 1 to 6, wherein the amount of the rinsing liquid per hour is between 0.01 L / min and 1 L / min.

8. 8. The method according to claim 1, wherein the area to which the rinsing liquid is applied is at a distance of 2 mm to 10 mm from the center of the semiconductor wafer.

9. The surface area of ​​the nozzle is 1.5 mm ２ 0.1mm or less ２ The method according to any one of claims 1 to 8.

10. 10. The method according to claim 1, wherein the amount of rinsing liquid per time is constant during grinding.

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