JP4034560B2 - Polishing method of semiconductor wafer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for polishing a semiconductor wafer.
[0002]
[Prior art]
A semiconductor wafer having a plurality of semiconductor chips such as IC and LSI formed on the front surface is ground to have a thickness of 100 μm or less, preferably 50 μm or less, thereby reducing the weight of electric devices such as mobile phones, notebook computers and smart cards. , Enabling miniaturization. However, when a semiconductor chip such as an IC or LSI is ground thinly to 100 μm or less, the bending strength (breaking strength) is remarkably lowered by the grinding strain layer on the surface thereof. This ground strain layer remains in a region about 1 μm deep from the ground surface. Therefore, in order to remove the grinding strain layer, etching removal using an etching solution containing nitric acid and hydrofluoric acid, or dry etching removal using hydrofluoric acid and oxygen as plasma is performed.
[0003]
[Problems to be solved by the invention]
However, the removal of the grinding strain layer of the semiconductor wafer by this chemical etching requires a large-scale facility, and there are problems such as a large amount of etching processing liquid and processing gas being generated as industrial waste. is doing.
[0004]
The present invention has been made in view of the above-mentioned facts, and its technical problem is to provide a grinding strain layer of a semiconductor wafer without providing a large-scale facility and without generating a large amount of a material to be treated as industrial waste. It is to provide a method that can be removed.
[0005]
[Means for Solving the Problems]
As a result of intensive studies and experiments, the present inventor has developed a method for polishing a semiconductor wafer that can uniformly remove the grinding strain layer of the semiconductor wafer with a polishing grindstone having a polishing layer.
[0006]
That is, according to the present invention, as a method of removing the grinding strain layer of the semiconductor wafer that solves the above technical problem, the grinding strain layer of the semiconductor wafer is removed by polishing, which is disposed on the turntable. Each surface to be polished of a disk-shaped semiconductor wafer held and rotated by a plurality of chuck tables is positioned in a concentric polishing process and an eccentric polishing process by intermittently rotating the turntable, and has a diameter larger than that of the semiconductor wafer. the abrasive grinding wheel having an abrasive layer formed by impregnating the abrasive grains, and the concentric polishing step of polishing is rotated in the rotation center and the same center of rotation of the semiconductor wafer, the rotation center of the polishing layer of the polishing layer The above-mentioned eccentric polishing step of polishing with the outer peripheral edge positioned at a position passing through the rotation center of the semiconductor wafer is performed, and the polishing margin is 0.5 μm to 2. and [mu] m, with respect to the polishing surface of the first polished semiconductor wafer by concentric polishing process or eccentric polishing process performs the remaining polishing step by the maximum grinding depth formed same polishing allowance on the polished surface, that A semiconductor wafer polishing method is provided.
[0007]
Then, the grinding strain layer is uniformly removed by a combination of the concentric polishing step and the eccentric polishing step. Therefore, according to this method, it is possible to remove the grinding strain layer without providing a large-scale facility like chemical etching and without generating a large amount of a material to be treated as industrial waste.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings.
[0010]
FIG. 1 shows an embodiment of a polishing apparatus for polishing a ground back surface, which is a surface to be polished of a semiconductor wafer. The polishing apparatus generally indicated by numeral 2 has a pair of polishing units 10 and a pair extending in the same manner on a vertical wall 6 standing on one end of the apparatus housing 4 via a pair of guide rails 8 and 8 extending in the vertical direction. A polishing unit 14 is provided via the guide rails 12 and 12. A turntable 18 having four chuck tables 16 arranged at a predetermined interval is provided on the upper surface of the apparatus housing 4. Each of the chuck tables 16 has a mounting surface made of a circular porous ceramic plate for adsorbing and holding a semiconductor wafer on the upper surface, and is rotatably provided. The turntable 18 is provided so as to be freely rotatable in a counterclockwise direction indicated by an arrow T. Due to the intermittent rotation, the chuck table 16 is moved and positioned to a position G1 that is an installation position of the polishing unit 10 where the concentric polishing process is performed and a position G2 that is an installation position of the polishing unit 14 where the eccentric polishing process is performed.
[0011]
The method for polishing a semiconductor wafer according to the present invention is performed by the above-described concentric polishing step and eccentric polishing step. In this embodiment, the concentric polishing step is performed first, and then the eccentric polishing step is performed. .
[0012]
The grinding unit 10 includes a disc-shaped polishing stone 20 at the lower end of a rotating shaft that is driven to rotate by an electric motor around an axis 11 extending in the vertical direction. Similarly, the polishing unit 14 includes a polishing grindstone 20 at the lower end of a rotating shaft that is driven to rotate by an electric motor about an axis 15 extending in the vertical direction. Although the polishing unit 10 and the polishing unit 14 is formed on the same, each is mounted offset dimension L position relative the upright wall 6 is in the turntable 18 direction. This difference in dimension L, the polishing unit 10 is disposed to one Itasa the axis 11 of the rotation center and the polishing unit 10 of the chuck table 16 at a position G1 where concentric polishing process is performed, the polishing unit 14 is eccentric polishing At the position G2 where the process is performed, the center of rotation of the chuck table 16 and the axis 15 of the polishing unit 14 are eccentrically arranged (relationship between dimension L, concentric polishing process, eccentric polishing process, eccentric position, etc.) Will be detailed later).
[0013]
The grinding wheel 20 will be described with reference to FIG. 2 and FIG. 3 which shows FIG. 2 in an inverted state. The polishing grindstone 20 includes a support plate 22 attached to the flanges at the lower ends of the respective rotating shafts of the polishing units 10 and 14, and a polishing layer 24 joined to the support plate 22. The support plate 22 is made of an appropriate metal such as aluminum and has a disk-like bottom surface that is a flat circular support surface. The support plate 22 includes a plurality of blind screw holes 22a extending downward from the upper surface thereof (four in the illustrated case) at intervals in the circumferential direction, and a set screw (not shown) is attached to the blind screw hole 22a on the flange of the rotary shaft. Not) are screwed together. The polishing layer 24 is also disk-shaped, and its outer diameter is substantially the same as the outer diameter of the support plate 22. The disc shape of the polishing layer 24 is formed to have a larger diameter than the disc-shaped semiconductor wafer.
[0014]
According to the examination and experiment by the present inventors, the polishing layer 24 for polishing the grinding strain layer of the semiconductor wafer by the polishing method according to the present invention is a felt formed by impregnating a felt with abrasive grains and solidifying it with a bonding agent. It is convenient to use a grindstone. As the felt, well-known synthetic fibers such as wool, polyester and nylon, natural fibers such as cotton and hemp are used. As the abrasive, a known material such as silica or diamond having a particle diameter of 0.01 μm to 100 μm is used. The abrasive is impregnated into the felt and bonded into the felt with a phenolic resin adhesive. The polishing layer 24 is bonded to the lower surface of the support plate 22 with an appropriate adhesive such as an epoxy resin adhesive.
[0015]
FIG. 4 is an explanatory view showing the arrangement positional relationship of the polishing unit 10 that performs the above-described concentric polishing process and the polishing unit 14 that performs the eccentric polishing process as seen from the direction of the semiconductor wafer from the polishing wheel side. To explain.
(1) At the concentric polishing step position indicated by G1, the polishing layer 24 (polishing unit 10) indicated by a two-dot chain line has its axis 11 aligned with the rotation center 17 of the semiconductor wafer W (chuck table 16) indicated by a solid line. Arranged.
(2) At the eccentric polishing step position indicated by G2, the polishing layer 24 (polishing unit 14) indicated by a two-dot chain line has its axis 15 with respect to the rotation center 17 of the semiconductor wafer W (chuck table 16). The outer peripheral edge 24 is arranged at a position passing through the rotation center 17 of the semiconductor wafer W and is eccentric with the dimension L described above.
[0016]
According to the examination and experiment of the present inventors, in order to polish the grinding strain layer of the semiconductor wafer, the relationship between the polishing layer 24 and the semiconductor wafer W is positioned as described above, and the rotation direction of the semiconductor wafer W (chuck table 16). The polishing layer 24 (polishing grindstone 20) is rotated in the opposite direction (indicated by arrow V) (indicated by arrow S), the rotation speed of the chuck table 16 is set to 100 RPM to 300 RPM, and the rotation speed of the polishing grindstone 20 is increased. It may be set to 4000 RPM to 7000 RPM.
[0017]
With reference to FIG. 1 again, the flow of the semiconductor wafer W in the polishing apparatus 2 will be described. The semiconductor wafer before polishing is accommodated in the cassette 26. The semiconductor wafer in the cassette 26 is conveyed to the center alignment table 30 by the loading / unloading means 28 and center alignment is performed. Next, the semiconductor wafer is attracted by the conveying means 32 having the swivel arm, conveyed to the chuck table 16 positioned at the receiving position Q, sucked and held on the mounting surface, and intermittently rotated in the direction indicated by the arrow T of the turntable 18. It is positioned at the disposition position G1 of the polishing unit 10 for performing the concentric polishing process. At this time, the four chuck tables 16 on the turntable 18 are located at the position G2 where the chuck table 16 at the concentric polishing process position G1 is located at the position G2 where the polishing unit 14 for performing the eccentric polishing process is located. 16 are positioned at the delivery position R, respectively. The polished semiconductor wafer W positioned at the delivery position R is released from the suction and holding of the mounting surface of the chuck table 16 and is adsorbed by the conveying means 34 having a turning arm and conveyed to the spinner cleaning means 36. After cleaning and drying, the cassette is accommodated in the cassette 38 by the carry-in / out means 28.
[0018]
Next, the polishing state of the semiconductor wafer W in each of the concentric polishing step by the polishing unit 10 and the eccentric polishing step by the polishing unit 14 will be described with reference to FIG. 5 that exaggerated the polishing state together with FIG.
[0019]
(1) Concentric polishing process, FIG. 5 (a):
In the concentric polishing process, the disk-shaped semiconductor wafer W is increased in the circumferential direction with the disk-shaped polishing layer 24 rotated concentrically as the outer edge moves from the rotation center 17 to the outer edge side. Is easily polished and is polished into a convex shape having a maximum polishing depth δ at the outer edge. This maximum polishing depth δ is defined as 0.5 μm to 2.0 μm according to the thickness of the grinding strain layer removed by polishing of the semiconductor wafer W.
[0020]
(2) Eccentric polishing process, FIG. 5 (b):
In the eccentric polishing process with respect to the state of the polished semiconductor wafer W (indicated by the two-dot chain line) in concentric polishing process is polished at its maximum grinding depth [delta] and the same size of the grinding allowance [delta]. In the eccentric polishing step, since the outer peripheral edge of the polishing layer 24 passes through the portion of the rotation center 17 of the semiconductor wafer W, the semiconductor wafer W is easily polished on the side of the rotation center 17 and polished into a concave shape with a recessed central portion. Is done.
[0021]
(3) End of polishing, FIG. 5 (c):
Thus, on the semiconductor wafer W that has been subjected to the concentric polishing step and the eccentric polishing step, a substantially uniform and flat polishing surface from which the grinding strain layer has been removed is formed as shown in FIG.
[0022]
The operation of the semiconductor wafer polishing method as described above will be described.
[0023]
(1) Equipment and industrial waste:
The removal of the grinding distortion layer on the grinding surface of the semiconductor wafer is mechanically performed with a polishing wheel, so that no large-scale equipment is provided as in the case of removal by conventional chemical etching, and as industrial waste Does not produce a large amount of material to be processed. Further, in a known grinding apparatus for grinding the back surface of a semiconductor wafer, a polishing grindstone is attached in place of the grinding grindstone, and the position of the rotation axis is changed, whereby the polishing apparatus for performing the polishing method of the present invention can be easily performed. Can be prepared.
[0024]
(2) Strain layer removal surface:
The surface of the semiconductor wafer polished by the polishing method of the present invention is polished into a concave shape in which the rotation center portion is concaved into a basin shape in the eccentric polishing step after the rotation center portion is polished into a convex shape having a mountain shape by the concentric polishing process. Therefore, a high-quality polished surface from which the grinding distortion layer is uniformly removed is formed by the projections and depressions.
[0025]
As described above, the present invention has been described in detail based on the embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications or corrections may be made within the scope of the present invention, for example, as described below. It is something that can be done.
[0028]
In the embodiment of the present invention, the eccentric polishing process is performed after the concentric polishing process, but the order of the polishing processes may be reversed.
[0029]
【The invention's effect】
According to the method for polishing a semiconductor wafer configured according to the present invention, a material to be treated as industrial waste can be obtained from a ground back surface of a semiconductor wafer without providing large-scale equipment, such as a method by chemical etching. The grinding strain layer can be removed without producing a large amount.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of a polishing apparatus for performing a method for polishing a semiconductor wafer according to the present invention.
FIG. 2 is a perspective view of a preferred embodiment of a polishing grindstone used in a semiconductor wafer polishing method according to the present invention.
3 is a perspective view showing the grinding wheel of FIG. 2 in an inverted state.
FIG. 4 is an explanatory view showing the positional relationship of a concentric polishing process and an eccentric polishing process according to the present invention as viewed from the side of the polishing wheel viewed from below the semiconductor wafer to be polished.
FIG. 5 is an explanatory view showing an enlarged and exaggerated cross section of a semiconductor wafer polished by the semiconductor wafer polishing method according to the present invention. The cross-section hatching is omitted to avoid the figure from becoming complicated.
(A) is the state which performed the concentric grinding | polishing process.
(B) is the state which performed the eccentric polishing process after performing the concentric polishing process.
(C) is a state after polishing after the end of the eccentric polishing step.
[Explanation of symbols]
2: Polishing apparatus 10: Polishing unit 11: Axis 14: Polishing unit 15: Axis 16: Chuck table 18: Turntable 20: Polishing wheel 24: Polishing layer W: Semiconductor wafer G1: Concentric polishing process position G2: Eccentric polishing process position

Claims (1)

A method for removing a grinding strain layer of a semiconductor wafer by polishing,
Each surface to be polished of a disk-shaped semiconductor wafer held and rotated by a plurality of chuck tables disposed on the turntable is positioned in a concentric polishing step and an eccentric polishing step by intermittently rotating the turntable.
The abrasive grinding wheel having an abrasive layer formed by impregnating the abrasive grains are larger in diameter felt than the semiconductor wafer, and the concentric polishing step of polishing is rotated in the rotation center and the same center of rotation of the semiconductor wafer Performing the above-described eccentric polishing step in which the polishing center is polished at a position where the outer peripheral edge of the polishing layer passes through the rotation center of the semiconductor wafer.
The stock removal and 0.5Myuemu～2.0Myuemu, to the polishing surface of the first polished semiconductor wafer by concentric polishing process or eccentric polishing step, the remaining by the maximum grinding depth and the same polishing allowance formed in the polishing surface A method for polishing a semiconductor wafer, comprising performing the polishing step.

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