JP3658851B2 - Thin plate surface grinding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thin plate workpiece surface grinding method and apparatus therefor having a waviness component, and more particularly to a thin plate workpiece surface grinding method and apparatus suitable for surface grinding on a wafer immediately after slice cutting (hereinafter referred to as an as-cut wafer).
[0002]
[Prior art]
In general, a semiconductor wafer is a slicing process in which a silicon rod pulled up by the CZ method or the like is cut into a thin disk using a circular inner peripheral blade or a wire saw, and chamfering, lapping, and etching of an as-cut wafer obtained by slicing. It is manufactured through processing steps in the order of surface polishing and cleaning.
The etching is for dissolving and removing a processing strain layer generated by mechanical processing such as lapping and finishing it to a smooth surface, or removing dirt on the surface to obtain a clean crystal surface.
Now, the as-cut wafer immediately after slicing has a corrugated or S-shaped warp with a long period and a undulation that repeats irregularities with a small period of about 0.5 to 30 mm.
[0003]
These occur because the cutting edge does not necessarily move straight due to a slight difference in the cutting resistance of the cutting edge during slicing, and when the wire saw and the circular inner peripheral edge are used as the cutting edge, the waviness and warpage are In particular, when a wire saw is used, undulation is likely to occur. In recent years, with the increase in diameter of wafers, wire saws tend to be used instead of circular inner peripheral blades.
The swell could be improved by the subsequent lapping process. However, with regard to longer-period warping, the wafer easily elastically deformed, and correction was difficult.
In recent years, as the degree of integration of semiconductor devices increases, a semiconductor wafer serving as a substrate is required to have a small thickness variation, that is, a higher level of flatness.
[0004]
In order to obtain this high level of flatness, it is necessary to incorporate surface grinding.
When incorporating this surface grinding, a processing method such as [slicing step-surface grinding step-chamfering step-polishing step] or [slicing step-chamfering step-lapping step-surface grinding step-chamfering step-polishing step] Applies.
In such a surface grinding apparatus, the wafer supporting and fixing method employs a supporting method in which the back side of the wafer to be ground to a hard chuck table such as a porous ceramic plate is vacuum-adsorbed.
[0005]
However, when the vacuum suction method is applied to a thin plate workpiece such as a semiconductor wafer, as shown in FIG. 4 (A), the uneven surface shape of the wafer back surface 1b is formed with high flatness by the vacuum suction force. When surface grinding is performed in a state of being elastically deformed in accordance with the flat shape on the two sides, the ground wafer surface 1a has a so-called high flatness with a small thickness variation in the adsorbed state. When the force is released, the elastically deformed portion returns to its original shape, and the unevenness on the wafer back surface 1b side is transferred to the ground wafer surface 1a side. As a result, the grinding can remove or reduce the waviness. I can't.
That is, in a process using a wire saw in the slicing process and using surface grinding without using a lapping, waviness becomes a very serious problem.
[0006]
In order to solve the above problem, in the unknown Japanese Patent Application No. 6-227291 previously filed by the present applicant, in order to eliminate the waviness, the surface of the base plate 2 that supports the wafer 1 and the wafer rear surface 1b by suction. Proposals have been made to absorb waviness on the wafer rear surface 1b side by interposing an adhesive material 3 such as wax therebetween.
[0007]
That is, as shown in FIG. 4B, when the wafer back surface 1b is fixed to the upper surface of the base plate 2 via the adhesive 3, the unevenness of the wafer back 1b is held in the adhesive 3 in a absorbed state. In other words, the surface of the wafer 1 can be ground without causing elastic deformation because the adhesive 3 is an absorbent material even when the wafer back surface 1b is uneven. As a result, the surface grinding can be performed. Even if the suction is released, not only waviness but also longer-period warping can be removed from the surface ground wafer 1a.
[0008]
That is, a gap due to the warpage and waviness that occurs when a thin plate workpiece such as a wafer is placed on the base plate 2 is filled to prevent transfer to the workpiece surface.
The adhesive 3 is configured to use molten wax, hot melt adhesive, gypsum, ice or the like.
[0009]
By the way, the prior application technique has an advantage that not only waviness but also warpage can be removed or reduced. However, the adhesive 3 filling the space between the wafer 1 and the base plate 2 is mixed with bubbles during filling. If this is the case, deformation will occur at the time of grinding, so it is essential to prevent bubbles from being mixed in. Therefore, specially prepared adhesive filling equipment is required, especially when using molten wax or hot melt adhesive Further requires a melt adhesive supply device.
[0010]
Further, in the prior application technique, the wafer 1 is bonded and fixed to the base plate 2 via the adhesive 3, the wafer is removed from the base plate 2, and the adhesive 3 applied to the wafer back surface 1 b and the base plate 2 is removed. Such a complicated pre-processing and post-processing steps are required, which has a large negative effect in terms of manufacturing cost and manufacturing time.
[0011]
[Problems to be solved by the invention]
Therefore, the inventions according to claims 1 and 2 of the present invention are the surface grinding of a thin plate work having a waviness component which will be a problem particularly when a wire saw is used in the future without substantially transferring the waviness to the work surface side. The object of the present invention is to provide a surface grinding method for thin plate workpieces that can be used.
[0012]
Further, the invention described in claim 3 is to provide a thin plate workpiece surface grinding method which can be suitably applied to the surface grinding of a semiconductor wafer, particularly an as-cut wafer.
[0013]
According to a fourth aspect of the present invention, there is provided a surface grinding apparatus capable of effectively implementing the thin plate workpiece surface grinding method.
[0014]
Further, the invention described in claims 5 and 6 is to provide a surface grinding apparatus that can be suitably applied as a surface grinding apparatus for a semiconductor wafer, particularly an as-cut wafer.
[0015]
[Means for Solving the Problems]
As described above, in order to enable high flatness grinding without transferring waviness with a period of about 0.5 to 30 mm to the workpiece surface side, elastic deformation occurs when a thin plate such as a wafer is adsorbed to the base plate. Therefore, it is only necessary to perform surface grinding.
For this reason, in the surface grinding method in which the surface side of the thin plate workpiece having the swell component is adsorbed and fixed by negative pressure (hereinafter referred to as adsorption pressure), the surface pressure side of the surface workpiece is substantially undulated. What is necessary is just to set to such an extent that the elastic deformation which erase | eliminates does not arise. Longer-term warping is apparently lost due to elastic deformation caused only by the weight of the wafer, so that correction is difficult as with lap.
[0016]
However, reducing the adsorption pressure decreases the work holding force, and the fine movement of the work is lost against the feed pressure of the grindstone, so that surface grinding cannot be achieved effectively.
That is, as shown in FIG. 1, at the initial stage of grinding, as shown in FIG. 1A, grinding is performed while holding the workpiece 1 with an adsorption pressure close to a normal vacuum. If the adsorption pressure is reduced to such an extent that the holding force can be maintained as shown in (B) at the end of the non-existing processing, the elastic deformation force of the workpiece 1 is substantially released while the holding force is maintained. Grinding can be performed, and even if the adsorption is released, the surface-grinded waviness or reduced shape is maintained.
[0017]
That is, the present invention is characterized in that grinding is carried out by reducing the adsorption pressure at the time of sparking when the feed pressure of the grindstone at the end of grinding is reduced .
Specifically, the adsorption pressure is preferably reduced at the time of so-called spark-out at the time of zero-cut grinding in which the feed pressure of the grindstone decreases (including the case where there is substantially no grinding pressure).
The present invention is not particularly limited as long as it is a thin plate workpiece. For example, even in the case of a semiconductor wafer, a surface grinding process in a semiconductor wafer immediately after slice cutting, or a surface grinding process performed after a slicing process, a chamfering process, and a lapping process. It can be applied to either case.
In the case of a surface grinding method in which the thin plate workpiece is an as-cut wafer immediately after slice cutting, the reduced adsorption pressure is preferably about −100 to −50 mmHg.
[0018]
The apply to surface grinding apparatus capable of suitably implementing the previous SL invention, for example, it provided the pressure switching means for switching the suction pressure between the workpiece 1 and the suction cup (base plate 2) during grinding, the grinding wheel feed What is necessary is just to comprise so that at the time of the spark-out where a pressure falls, the adsorption pressure is switched by the pressure switching means, and the adsorption pressure is reduced to perform grinding at the spark-out.
In this case, in the surface grinding apparatus for an as-cut wafer, the pressure switching means may be switching means for switching between two negative pressures of approximately −600 mmHg to −760 mmHg and −100 to −50 mmHg.
Further, the thin plate workpiece surface grinding apparatus of the present invention is suitably applied to a vertical axis rotary table type grinding machine, preferably an infeed type grinding machine using a cup type grindstone.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the form of the Example of this invention is demonstrated with the example of illustration. However, unless otherwise specified, the dimensions, shapes, relative positions, and the like of the components described in this embodiment are merely illustrative examples, and are not intended to limit the scope of the present invention. Absent.
FIG. 2 is an infeed surface grinder of a vertical axis rotary table type according to an embodiment of the present invention. The grindstone 12 uses a so-called cup type, and the rotary axis is a vertical type that can be moved up and down (grind feed / escape). High-efficiency in-feed type that can receive high-precision machining as it receives the normal grinding resistance during grinding in the thrust direction, has a small amount of deflection, and has high rigidity, and can be continuously ground by the rotary table 11 It is.
[0020]
More specifically, the grindstone 12 is composed of a ring-shaped grindstone main body 121 and a holding member 122 having a concave shape with a downward flattened cross section for holding the grindstone main body, and a DC rotary motor 15 on the center line of the upper surface of the holding body 122. The rotating shaft 14 is attached so as to be able to rotate with high accuracy.
Further, the grindstone 12 or the rotary shaft 14 including the grindstone is configured to be moved up and down (grind feed / escape) 13 by a grinding feed means (not shown).
[0021]
On the other hand, the rotary table 11 side is configured to be accurately rotated by a DC rotary motor 17 or the like via a rotary shaft 16, and an adsorption base plate 2 made of a porous ceramic body is provided on the upper surface side on which the wafer 1 is placed. At the same time, the suction pipe 21 is connected to the lower surface side of the adsorption base plate 2, and the high vacuum negative pressure source 23 of −600 to −760 mmHg and the low negative pressure source 24 of −100 to −50 mmHg are switched by the switching operation of the switching valve 22. The two negative pressure sources can be selectively sucked.
[0022]
The surface grinding process of the present embodiment is applied as a wafer machining process consisting of [slicing process-surface grinding process-chamfering process-polishing process], that is, as a grinding process in place of lapping and etching of the as-cut wafer 1 immediately after slicing. In particular, it is possible to remove the warp of the as-cut wafer 1 that cannot be removed by conventional lapping and etching, in addition to the removal of waviness of a short period.
[0023]
In general, in a grinding wheel cutting method in grinding, a grinding cycle is formed by rapid feed, rough grinding feed, fine grinding feed, spark-out, and fast escape.
In this embodiment, too, the grindstone position is fast-forwarded to the wafer thickness position, and then the rough grinding is performed at the primary feed speed to perform the predetermined thickness grinding, and then the grinding wheel cutting speed is lowered to shift to the fine grinding by the secondary grinding feed. Then, after shifting to the spark-out in which the grinding operation is performed in a state where the cutting of the grindstone is stopped to improve the roughness and flatness of the grinding surface, the grinding is released by quick escape. An example of this sequence is shown in FIG.
[0024]
In this embodiment, the wafer 1 is sucked and held at a high vacuum negative pressure of −600 to −760 mmHg until fine grinding, and the low negative pressure source 24 of −100 to −50 mmHg is used for the switching operation of the switching valve 22 at the time of the spark-out transition. It was configured to perform low negative pressure adsorption.
[0025]
As a result, until the fine grinding process in which the grinding wheel is cut, the workpiece is held with a strong suction pressure close to a normal vacuum (with the elastic deformation force of the wafer 1 generated). Since the suction pressure has been reduced to such an extent that the holding force of the wafer 1 can be maintained after the wheel feed pressure is reduced or the spark-out transition is almost absent, the elastic deformation force of the wafer 1 until the fine grinding is processed. Surface grinding can be performed in a state in which the surface is substantially released, undulations that could not be removed by the elastic deformation are removed, and even if the adsorption is released, there is no undulations that are surface-ground or less wafer shape Is maintained.
[0026]
【Example】
In the sequence shown in FIG. 3, rough grinding to fine grinding are performed in the state where the suction pressure is maintained at −600 mmHg until coarse grinding feed rate = 150 mm / min, fine grinding feed rate = 70 mm / min, and then compared. In Example 1, the adsorption pressure was maintained at −600 mmHg, and in Comparative Example 2, the pressure was reduced to −400 mmHg. In the example, the pressure was reduced to −100 mmHg, and the sparkout time was 20 to 50 seconds. It was confirmed from FIG. 5 that the swell was reduced in the case of 100 mmHg.
[0027]
FIG. 5 shows image maps of Comparative Example 1 (−600 mmHg), Comparative Example 2 (−400 mmHg), and Example (−100 mmHg) using ORP based on the magic mirror principle. It was confirmed that it did not occur.
[0028]
【The invention's effect】
As described above, according to the present invention, there is no need for particularly large capital investment, and there is no need for special raw materials or complicated work. Flatness polishing is possible without substantially transferring the undulation to the workpiece surface side.
In particular, when applied to the surface grinding of an as-cut wafer, it is possible to manufacture high-quality semiconductor silicon with low undulations that does not require conventional lapping and, in some cases, etching.
[Brief description of the drawings]
FIG. 1 is an operation diagram showing a basic configuration of the present invention.
2A and 2B are schematic views showing a schematic configuration of a surface grinding apparatus according to an embodiment of the present invention, in which FIG. 2A is a schematic sectional view and FIG. 2B is a schematic perspective view.
FIG. 3 is a sequence diagram showing an overview of a thin plate workpiece surface grinding method according to an example of the present invention and Comparative Examples 1 and 2;
FIG. 4 is an operation diagram showing a basic configuration of a conventionally known technique (A) and a prior application technique (B).
FIG. 5 is an image mapping using ORP based on the magic mirror principle of each wafer ground according to the working procedure of the embodiment of FIG. 3 and Comparative Examples 1 and 2;
[Explanation of symbols]
1 Work (Wafer)
2 Base plate (Suction plate)
DESCRIPTION OF SYMBOLS 11 Rotary table 12 Grinding wheel 15, 17 Rotary motor 14, 16 Rotary shaft 22 Switching valve 23 High vacuum negative pressure source 24 Low negative pressure source

Claims (2)

In the surface grinding method of surface grinding the surface side in a state where the back surface of the thin plate workpiece having a swell component is adsorbed and fixed by negative pressure,
A thin plate work surface grinding method characterized in that grinding is performed by reducing a negative pressure (hereinafter referred to as an adsorption pressure) for adsorbing and fixing the thin plate workpiece at the time of sparking when the feed pressure of the grindstone is reduced.   2. The thin plate workpiece surface grinding method according to claim 1, wherein the thin plate workpiece is a semiconductor wafer, wherein the reduced adsorption pressure is set to about -100 to -50 mmHg.

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