Abrading – Precision device or process - or with condition responsive... – Controlling temperature
Reexamination Certificate
2000-09-11
2003-11-25
Rose, Robert A. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Controlling temperature
C125S016020
Reexamination Certificate
active
06652356
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wire saw for cutting out many wafers from a work such as a columnar semiconductor ingot, ceramics, glass or the like, and a cutting method using it.
2. Description of the Related Art
Recently, wafers have been required to be large, and highly flat. In order to cope with the large wafer, a wire saw have been mainly used for cutting of an ingot.
A wire saw is an apparatus for cutting many wafers at the same time by a grinding action comprising pressing the work against wires provided with a predetermined pitch, and moving the wire and the work relatively with pouring a cutting fluid containing abrasive grains.
Advantages of the wire saw are that it can cut many wafers at the same time, and thus productivity is high, and that it can produce cut wafers having the approximately same shape owing to simultaneous cutting.
Disadvantage of the wire saw is that a warp (sori) of the cut wafer is large. As a conventional method to solve the problem, there has been adopted a method comprising controlling a temperature of a bearing part of a grooved roller on which the wire is wound to suppress thermal expansion of the roller due to frictional heat during cutting or the like, and thereby the problem of the warp has been solved to some extent.
More specifically, in wire saw frictional heat is generated when the work is pressed against the wire, so that the temperature not only of the work, but also of the working room is increased. If the temperature gets high during cutting, not only the work, but also a part of an apparatus such as a working table is also thermally expanded. As a result, relative position of the work and the apparatus are shifted, and the shape thereof is transcribed to the work as a warp of the wafer.
The conventional method for solving the problem comprises decreasing an influence of increased temperature by applying a cooling medium to a main part of the apparatus such as a bearing, housing or the like. However, there is no means against heat at a part where the work is processed, which is a source of generation of heat, As a result, change in temperature during processing cannot be controlled.
The heat generated during cutting process depends on length of the arc vertical to the direction of cutting (length of the wire that is in contact with the work; cutting length). The change in the length of the arc is large against the direction of cutting. Accordingly, the temperature is significantly changed for a short time after initiation of the cutting, and thus relative shift of the position of the work and the apparatus gets large. The same phenomenon also occurs just before the end of the cutting. Accordingly, the shape having locally large warp formed at the early stage and the terminating stage of the cutting of the wafer (see FIG.
5
).
The warp formed during cutting cannot be corrected in the following steps such as lapping, etching or the like, and kept to the end. It has been confirmed that such a warp that is locally large affects flatness during a polishing step.
SUMMARY OF THE INVENTION
The present invention has been accomplished to solve the above-mentioned problems, and a main object of the present invention is to provide a method of cutting an ingot and an apparatus therefor wherein a relative shift of the work and the wire is suppressed, a level of a warp of a wafer and a local warp can be improved, and flatness in a polishing step can be improved.
To solve the above-mentioned problems, the present invention is a cutting method comprising winding a wire around plural grooved rollers, and pressing the wire against the work with running it, to cut the work, wherein the work is cut with controlling temperature of the work by supplying a cutting fluid containing abrasive grains to the grooved rollers, and supplying a temperature controlling medium to the work.
As described above, when the work is cut with supplying a cutting fluid containing abrasive grains to the grooved rollers, and supplying a temperature controlling medium to the work, increase of temperature of the work due to the heat generated during cutting of the work can be suppressed to be slow, and the temperature can be kept at a desired value or lower. Accordingly, a level of a warp on the section of the work, a local warp, waviness of all over the work can be improved, and flatness in the following polishing process can be significantly improved. Thereby, productivity and yield of a semiconductor silicon wafer can be improved, and cost performance can also be improved.
The present invention is also a cutting method comprising winding a wire around plural grooved rollers, and pressing the wire against the work with running it, to cut the work, wherein a temperature of the work is previously defined at a predetermined value, and the work is cut with supplying a cutting fluid containing abrasive grains to the grooved rollers.
The method comprises preheating the work to a predetermined temperature before cutting of the work, and then initiating the cutting to cut the work with supplying a cutting fluid containing abrasive grains to the grooved rollers. Thereby, change in temperature of the work, especially at the early stage of the cutting can be made gentle, a level of the warp of the cut surface and a local warp can be significantly improved. If the temperature of the work is increased as described above, it is also advantageous for the reason that the work is hardly affected by external temperature such as room temperature, temperature of the mechanical part of the apparatus or the like.
A method for preheating the work to the predetermined temperature is, for example, a method of preheating the work outside the apparatus, for example using an oven or the like before the work is set in the wire saw, and then set the work therein. Alternatively, there can be adopted the method comprising installing a heater to a plate for holding a work, and heating the work set therein, the method of supplying a temperature controlling medium such as a cutting fluid or air, or the like, controlled in a predetermined temperature to the work and preheating it before cutting.
The present invention is also a cutting method comprising winding a wire around plural grooved rollers, and pressing the wire against the work with running it, to cut the work wherein a temperature of the work is previously defined at a predetermined temperature, and the work is cut with controlling a temperature of the work by supplying a cutting fluid to the grooved rollers, and supplying a temperature controlling medium to the work.
Thereby, the change in temperature of the work in the early stage can be suppressed to be gentle, and increase in the temperature of the work in a period from the middle to the terminating stages of the cutting process can be further suppressed. Accordingly, a local warp generated in the early stages or terminating stages of the cutting process can be made small, and waviness of the whole work and flatness thereof after polishing can be improved significantly.
In that case, change in temperature of the work in a period from the beginning of the cutting process to the time when a cutting length reaches 60% of a diameter of the work and/or in a period from the time when a cutting length reaches 60% of a diameter of the work to the end of the cutting process in the latter half of the cutting is controlled to be 10° C. or less.
For example, in the case that the work having a diameter of 8 inches is cut, and the temperature of the work before cutting is about 25° C., the cutting length reaches 60% of a diameter when the cutting length in a direction of the diameter is 20 mm after cutting is initiated. Accordingly, the change in temperature of the work in the period should be controlled to be 10° C. or less. Namely, the temperature of the wafer at the early stages of the cutting process should be controlled to be 35° C. or lower. As described above, when the change in temperature of the work is controlled so as not to be large, espec
Rose Robert A.
Shin-Etsu Handotai & Co., Ltd.
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