Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2001-12-06
2004-04-20
Eley, Timothy V. (Department: 3724)
Abrading
Abrading process
Glass or stone abrading
C451S008000
Reexamination Certificate
active
06722954
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a wafer used for evaluating the ability of machining the peripheral portion of a wafer and a method of evaluating the ability of machining the peripheral portion of a wafer using said wafer for evaluating said ability.
TECHNICAL BACKGROUND
A semiconductor wafer is, in the process of machining the wafer or in the process of manufacturing devices using the wafer, exposed to frequent machining or handling operations such as automatic transfer using the peripheral portion of the wafer. When the peripheral portion of the disk-like wafer is in the state as cut and accordingly the perihery face is perpendicular to the surface of the wafer, its edges are easily chipped. As a result, the chips adhere to the main surface, etc. to effect as particles to reduce the yield in the succeeding process. Further, if the surface of the peripheral portion is coarse, the chemical substances used in an etching process, etc. is not entirely cleaned off, and the remained chemical substances affect the succeeding process. Still further, in the case of increasing the quality of a wafer by performing epitaxial growing process and the like on the main surface of the single crystal wafer, disadvantages such as the generation of a plurality of protrusions so-called nodules and crowns (jutting crystal growth) are resulted, according to the condition such as surface irregularity and defective crystal arrangement of peripheral portion. Accordingly, in the machining of a wafer, not only the machining of the main surface but also the machining of the peripheral position is important.
It is recently general that the peripheral position is mirror polished to make the highly neat surface of it for preventing chipping in addition to chamfering.
It is naturally necessary, in the process of machining the peripheral position of a wafer, to grasp quantitatively the machining ability to control the process. To be concrete, proper machining is performed through grasping grinding or polishing amount in a span of time. By the conventional evaluation method of the machining ability, the weight of the wafer is measured before and after the machining or at a time halfway through the machining to estimate the reduced thickness of the peripheral position. By this method only average stock removal is determined. The shape of the periphery in a cross section perpendicular to the main surface is not flat as the main surface but designed to have one of several kinds of contours which are generally of convex shape against the face of machining tool, so the contact attitude of the part to be machined to the machining tool surface is not constant. Accordingly, there is a strong tendency that the stock removal during a span of time, that is the machining ability, is different according to the region to be machined of the peripheral portion. In other words, the distribution of machining ability in the region to be machined in the cross section (hereafter referred to as distribution in peripheral surface) is difficult to evaluate. When the machining ability differs according to machined regions, the conventional evaluation of machining ability in average can not be said to be grasping the machining ability rightly.
In the conventional method, as the machining ability is adjusted to match that on the region where the machining speed is the slowest, the periphery is excessively machined as a whole resulting in increased machining time period, leading to reduced productivity and life of the polishing pad and increasing cost.
SUMMARY OF THE INVENTION
The present invention is to solve those problems of the prior art. It is therefore an object of this invention to provide a wafer for the evaluation of the ability of machining the peripheral portion thereof used to measure the distribution of the machining ability along the peripheral portion in the machining of the peripheral portion of the wafer.
Another object of the invention is to provide a method of evaluating the ability of machining the peripheral portion of a water using said wafer for evaluating said machining ability.
A further object of the present invention is to provide a wafer for the evaluation of the ability of machining the peripheral portion of a wafer and a method of measuring said distribution in the cross section to be used for the improvement of the machining process of the wafer peripheral portion, and thus to contribute to better uniformity of machining the peripheral portion.
Namely, the present invention is an evaluation wafer for evaluating the machining ability in the machining process of the peripheral portion of a wafer characterized by having a a reference position to be a boundary with respect to the direction of machining the surface layer of the wafer.
The evaluation of the ability of machining the main surface of a wafer is possible through measuring the change of thickness of the wafer in reference to the other surface of the wafer, but there have been no evaluation method for measuring in length the amount removed by machining because there is no reference position when machining the peripheral portion of the wafer, for the machining is done in the direction of thickness and diameter of the wafer.
This invention makes it possible to measure in length the amount removed by machining the peripheral portion by providing a reference position becoming a boundary with respect to the direction of machining the surface layer of the wafer.
The wafer for evaluation according to the present invention is provided with a reference position to become the boundary with respect to the direction of machining by covering a subtrate with a substance of which the machinability relative to that of the wafer to be machined in the process of machining the peripheral portion is apparent. By this method, the actual machining speed of the wafer is estimated from the machining speed of the evaluation wafer of this invention, which machining speed is of the covered substance, using the relative machinability of the covered substance in relation to the actual wafer to be machined.
The machining ability cited in this invention is defined as the quantity removed by grinding or polishing, or the thickness, or depth ground or polished of the wafer to be machined in a certain condition in unit time. For example, when the thickness of covered polysilicon is d
0
before machining and d
t
after machining during a time span of t, the machining ability PR is: PR=(d
0
−d
t
)/t. Here, the dimension of d
0
, d
t
is length and that of t is time.
According to the present invention, by measuring at a plurality of positions of the peripheral portion of the wafer, the distribution of machining ability in the surface of the peripheral portion is obtained. On the other hand, the conventional method evaluates the removed quantity by the change in weight. So, when the weight of the wafer is W
0
before machining and W
t
after machining during a time span of t, the machining ability PR is: PR=(W
0
−W
t
)/t. Here, the dimension of W
0
, W
t
is weight and that of t is time.
As only one value of each of W
0
and W
t
is obtained per wafer, the conventional method gives only average value of machining ability of a wafer.
It was a conscious choice to explain the machining ability here, for when the term ability is used in a production process, it means, unless particularly specified, the production capacity, that is, the output of the production article per unit time, or the process ability of controlling quality items in a certain value.
As mentioned above, by coating as surface layer a substance of which the relative machinability in relation to a wafer to be machined is known, precice evaluation of machined quantity, i.e. machining ability is possible. To be concrete, it is suitable to cover the single crystal silicon wafer with an oxide film or a polysilicon layer to obtain a wafer for evaluation. Specifically a layer of polysilicon is preferable.
In the case a wafer to be machined is a single crystal silicon wafer, by formi
Hashimoto Takahiro
Mizushima Kazutoshi
Crowell & Moring LLP
Eley Timothy V.
Shin-Etsu Handotai & Co., Ltd.
LandOfFree
Wafer for evaluating machinability of periphery of wafer and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Wafer for evaluating machinability of periphery of wafer and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wafer for evaluating machinability of periphery of wafer and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3272041