Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2001-01-05
2003-12-16
Rachuba, M. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S063000, C451S287000, C451S288000, C451S307000, C451S398000
Reexamination Certificate
active
06663468
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for chemically and mechanically polishing and processing thin films formed on a surface of a substrate of a semiconductor device by using a polishing member.
PRIOR ART
In the manufacturing process of highly integrated semiconductor devices such as DRAMs (Dynamic Random Access Memories) or the like having a density of not less than 256 megabits, fine patterns of a minimum dimension of not more than 0.2 &mgr;m are often formed. In order to form such fine patterns at a high precision using photolithography, decrease in the wavelength of exposing light and increase in the number of apertures are required. Accordingly, the allowable focal depth of reduction projection exposure equipment used in the photolithographic process becomes shallow. In order to expose and transfer a fine circuit pattern onto a photosensitive film (photoresist film) on a thin film formed on the surface of a substrate at a high resolution using the photolithographic process, the flatness of the surface of the photosensitive film, which is the surface to be exposed, must be not more than 0.3 &mgr;m.
As a method for obtaining the flat property of the surface of a photosensitive film, JP-A-7-314298 specification discloses a reflow planarizing method, in which an insulating film used as the base to form a photosensitive film is softened by heating for allowing the insulating film to reflow. Furthermore, there are known such an etching method for melting and flattening a convex part of the insulating film and chemical mechanical polishing (CMP) method, in which insulating films are polished chemically and mechanically using slurry and a polishing pad, the slurry comprising a processing liquid in which powder or grinding grains are contained.
Also, a method in which when a wafer contacts a retainer, the entire retainer deforms in accordance with the change in shape of the wafer, is known, such as the method disclosed in JP-A-11-277417 specification.
Although conventional reflow planarizing or etching methods can locally planarize stepped portions, they have a problem in that flatness to satisfy the shallow allowable focal depth of exposure equipment throughout a wide area (not less than 30 mm in diameter) of a semiconductor substrate. On the other hand, conventional chemical and mechanical polishing gives better flatness than a reflow planarizing method. However, since the conventional chemical and mechanical polishing method polishes the surface of the substrate by pushing the surface of the thin film formed on the surface of a substrate against a flexible polishing cloth, which is a polishing member, (e.g. a polyurethane polishing pad of a modulus of longitudinal elasticity of not more than 1,000 kg/cm
2
), this method has a problem in that the polishing cloth is deformed non-uniformly by the pushing force of the surface of the substrate, and the flatness after processing is lowered. For example, as JP-A-9-267257 specification and JP-A-10-286758 specification disclose, the polishing cloth in the vicinity of the circumference of the substrate is caved or waved by the pushing force of the substrate, so that polishing properties of the circumferential surface of the substrate became non-uniform to thereby cause, so-called, edge sagging phenomenon.
The larger the pushing force of the substrate against the polishing member, that is, the higher the processing surface pressure, the worse the flatness of the surface of the substrate after processing. If the processing surface pressure is lowered to reduce the phenomenon of worsened flatness, the problem of the drop in polishing efficiency to thereby increase processing time and thus lower the throughput thereof was caused.
On the other hand, JP-A-9-232260 specification discloses a method for processing the surface of a substrate using a grinding stone which is manufactured by binding grinding grains for polishing with a resin (binded grinding grain disk), instead of using abrasives and abrasive cloth. Since the grinding stone is more rigid than abrasive cloth (e.g. the modulus of longitudinal elasticity of not less than 5,000 kg/cm
2
), the flatness of the surface of the substrate in non-uniform circuit pattern areas is improved, but non-uniform polishing properties of the outer circumferential surface of the substrate, that is, so-called edge sagging phenomenon could not have been solved.
Also, JP-A-6-155286 specification and JP-A-9-117860 specification disclose methods for preventing the wafer from approaching the polishing member side by providing an inclined surface on the structure body of the inner wall surface of the guide provided on the outer circumference of the wafer, or preventing the wafer from getting out of an inside of a guide and preventing the excessive polishing of the other circumferential end portion of the wafer. In these prior arts, however, the outer circumference end of the wafer goes up and down an inclined plane of the guide due to the variation of thrust applied thereto, and the excessive movement to the opposite side to the polishing member can not be prevented. Accordingly, since the ability of controlling the position and maintaining the contact of the outer circumference of the wafer is not satisfactory, non-uniform polishing properties of the outer circumferential surface of the substrate, that is, so-called edge sagging phenomenon could not have been solved, when grindstone that is more rigid than abrasive cloth is used as a polishing member.
Furthermore, JP-A-10-315125 specification discloses a method for aiming uniform polishing by changing load applied to the back surface of the wafer between the inner area and the outer area. In this method, since taking measures to meet against the thrust generated from the load and the friction coefficient cannot be performed, non-uniform polishing properties of the outer circumferential surface area of the substrate, that is, so-called edge sagging phenomenon could not have been solved, when rigid grindstone is used as a polishing member.
The inventors of the present invention had experimentally for the first time found a phenomenon that the deformation of grindstone as used for a polishing member does not occur when using the grindstone having a high-rigidity surface, but that the substrate is deformed when it is pushed against the guide of the carrier by the thrust generated in the direction of the substrate surface due to the load when polishing and friction. It was newly found that this phenomenon causes non-uniform polishing properties of the outer circumferential surface area of the substrate, that is,, so-called edge sagging phenomenon.
FIGS. 7 and 8
are schematic view showing prior art techniques for polishing substrates using grindstones.
FIG. 7
is a schematic view of a wafer
2
and a guide
83
pushed against the surface of a grindstone
1
, when viewed from above. In order to accommodate the dimensional tolerance of the outer diameter of the wafer
2
, and to facilitate attaching to or detaching from the carrier (not shown) in automatically conveying the wafer, the inner diameter of the guide
83
is normally made to be about 1 mm larger than the outer diameter of the wafer
2
. As a result, the gap
10
is produced between an inner wall of the guide
83
and the outer circumference of the wafer
2
. The grindstone surface
1
rotates in the direction of the arrow
4
, while the wafer
2
and the guide
83
rotate in the direction of the arrow
5
with they being integrated with the carrier. A friction force by polishing Fp is applied to the surface of the wafer
2
, due to two relative motions whose diameters and the centers of rotation are different from each other. The wafer
2
is held in the carrier by an elastic member (not shown) so as to generate a holding force Fc. The wafer
2
moves within an area defined by an inner wall of the guide
83
by the difference in force between the friction force by polishing Fp and the holding force Fc, and pushes the wafer
2
against the inner wall of the guide
83
so a
Harada Kunio
Katagiri Souichi
Kawamura Yoshio
Nagasawa Masayuki
Osabe Satoshi
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Rachuba M.
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