Abrading – Machine – Rotary tool
Reexamination Certificate
2001-09-28
2004-12-07
Rachuba, M. (Department: 3723)
Abrading
Machine
Rotary tool
C451S397000, C451S398000, C451S402000
Reexamination Certificate
active
06827638
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polishing apparatus and a polishing method capable of performing polishing of a work, for example, a silicon wafer (hereinafter may be simply referred to as “wafer”) or the like with high efficiency and high precision, a novel work holding plate for holding a work (for example, a wafer or the like) in a efficient way and a method for adhering a work onto the work holding plate.
BACKGROUND ART
Reflecting a tendency to prepare larger diameter silicon wafers and fabricate higher precision devices therewith, requirements for finish precision (thickness uniformity, flatness and smoothness) of a silicon wafer subjected to polishing finish (polished wafer) have been increasingly enhanced.
In order to satisfy such requirements, efforts have been made to attain a higher level in wafer polishing technique, and development and improvement of polishing apparatuses have been carried out.
As one example thereof, so-called single wafer polishing apparatuses have been newly developed for the purpose of polishing a large diameter wafer, especially 300 mm or more in diameter, and some of them have been practically used.
In the single wafer polishing method, however, there arise problems: for example, (1) requirements for reduction in wafer cost is hard to meet in terms of productivity, and (2) recent requirements for wafer flatness as far as an peripheral area adjacent to the wafer edge (within 2 mm) cannot be sufficiently satisfied.
Meanwhile, there has been widely used a batch type polishing apparatus in which a plurality of wafers are simultaneously polished. An outline of a configuration of a portion of the apparatus directly associated with polishing action is shown in FIG.
19
. In this polishing apparatus, one or more wafers W are held by means of such as adhesion on a lower surface of a work holding plate
13
rotated by a rotary shaft
18
; to-be-polished surfaces of the wafers W are pushed, for example, using a top weight
15
onto a surface of a polishing cloth
16
adhered on an upper surface of a polishing table
10
, which is rotated at a prescribed rotational speed by a rotary shaft
17
; and a polishing agent solution (hereinafter may be referred to “slurry”)
19
is simultaneously supplied at a prescribed rate onto the polishing cloth
16
through a polishing agent supply pipe
14
from a polishing agent supply device (not shown). In such a situation, polishing of the wafers W are performed while the to-be-polished surfaces of the wafers W are rubbed by the surface of the polishing cloth
16
in the presence of the polishing agent solution
19
therebetween.
In this batch type polishing apparatus, there is increasing difficulty in satisfying requirements for precision of finish surfaces of the wafers in a trend of transition to larger-sized apparatuses in company with larger diameter wafers for the following reasons: deflection of a polishing table and work holding plates by weights thereof and polishing pressure, and thermal deformation by heat generation in polishing action; and in addition thereto, deformation and displacement of the polishing table and the work holding plates caused by various kinds of mechanical deflections in rotation thereof.
In order to cope with such problems, various kinds of ingenious contrivances have been practiced about a structure and materials, and operating conditions of the polishing apparatus and other polishing conditions. For example, some of contrivances on the structure are as follows: (a) in order to prevent thermal deformation of a polishing table, as shown in
FIG. 20
, a separate lower table
23
on which multiple recesses
21
for circulating a cooling water H are formed is provided on a lower surface of an upper table
12
on an upper surface of which the polishing cloth
16
is adhered; further, ribs are provided on a lower surface of a polishing table to prevent deformation due to polishing pressure; and still further in order to effectively suppress thermal deformation, contrivances have been piled up about a structure of a polishing table and arrangement of flow paths of cooling water, as shown in JP-A-95-52034 and JP-A-98-296619.
In a prior art polishing table shown in
FIG. 20
, however, there is adopted a structure in which an upper table
12
made of SUS410 and a lower table 23 made of cast iron such as FC-30 provided with flow paths for cooling water are coupled to each other by fastening them with clamping members
11
or the like, and a temperature difference between the upper and lower surfaces of the upper table arising in the course of a prior art polishing operation is generally 3° C. or higher and, in higher cases, 5° C. or higher; therefore, a difference in height (deformation) at a highest or lowest point occurs inconveniently in places on the upper surface of the upper table amounting to 100 &mgr;m or more relative to the reference plane, namely the upper surface of the upper table with no temperature difference between the upper and lower surfaces thereof.
Furthermore, the following proposals have been made: (b) that a material with a low thermal expansion coefficient (8×10
−6
/° C.) is used as a material of a polishing table (WO94/13847), that a polishing table is of a one-piece structure made of ceramics in which a flow path for circulating cooling water is formed throughout almost all of the interior (JUM-A-84-151655), and the like techniques; and in addition, (c) that a temperature control fluid is likewise circulated in a work holding plate for the purpose of improving temperature uniformity across a wafer holding surface of the wafer holding plate (JP-A-97-29591).
Moreover, in order to suppress a temperature rise of a wafer and a polishing cloth due to heat generation accompanying polishing action, the following procedures have been performed: in addition to the cooling of the work holding plate and the polishing table described above, a cooling function is also given to a polishing agent solution (in usual case, a weak alkaline aqueous solution mixed with colloidal silica is used.) supplied directly onto a polishing action surface, an amount of the polishing agent solution exceeding a supply amount necessary for polishing action in a pure sense is supplied onto the polishing cloth, and the polishing agent solution discharged from a polishing site is recycled in order to reduce the cost.
In the construction of the prior art polishing apparatus and a cooling method as described above, a temperature on a polishing cloth surface during polishing gradually rises from the start of polishing and a value of the temperature at a portion where the polishing cloth is put in contact with a to-be-polished surface of the wafer rises usually to 10° C. or higher and a temperature at a corresponding upper surface portion of the polishing plate direct under the portion of the polishing cloth in the contact also rises by 3° C. or more.
On the other hand, changes in temperature on the lower surface of the polishing plate are restricted to 1° C. or less by virtue of an effect of suppression of a temperature rise by cooling water. Therefore, a temperature difference of at least 3° C. or more arises not only between the upper and lower surfaces of the polishing table, but also between a high temperature portion and a low temperature portion on the upper surface of the polishing table, which causes a portion of the upper surface of the polishing table with thermal deformation/displacement of 100 &mgr;m or more in a direction normal to the upper surface of the polishing table in comparison with that when no temperature difference exists.
Furthermore, a work holding plate has become larger in size in response to transition in diameter of a silicon wafer toward a larger value. For example, in case of a work holding plate for use in polishing of 8 inch wafers, a diameter of the work holding plate assumes about 600 mm and a weight thereof also increases as the diameter increases.
Accordingly, not only thermal deformation of a work holding plate caused by heat generation a
Hayashi Toshiyuki
Kiuchi Etsuo
Arent Fox
Rachuba M.
Shin-Etsu Handotai & Co., Ltd.
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