Etching a substrate: processes – Forming or treating an article whose final configuration has...
Reexamination Certificate
1998-11-19
2001-09-25
Gulakowski, Randy (Department: 1746)
Etching a substrate: processes
Forming or treating an article whose final configuration has...
C216S041000, C216S047000, C216S051000, C438S735000, C438S736000, C438S737000, C438S745000
Reexamination Certificate
active
06294099
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a method of circular patterning, and more particularly to a method of circular patterning which obtains a stable circular pattern or island without being affected by a difference in minute shapes of masks used for etching.
Prior art exposure devices such as mask aligners transfer a mask pattern to a photoresist layer on a substrate by contacting a chrome mask formed on glass (hereinafter referred to as a glass mask or simply a mask) with the substrate. The transferring process is commonly referred to as a photo fabrication process. Because of this, the shape of the mask is transferred to the photoresist layer with high accuracy.
For example, in
FIGS. 8
to
10
, the prior art etching processes are shown. Each of
FIGS. 8A
,
9
A, and
10
A shows a sectional view of the process and each of
FIGS. 8B
,
9
B, and
10
B shows a plane view thereof. As shown in
FIG. 8A
, silicon oxide film (SiO
2
)
22
is formed on a silicon substrate
20
by thermal oxidation or the like, and a photoresist film is applied thereon.
Next, resist masks
24
a
shown in
FIGS. 9A and 9B
are formed on the silicon oxide film
22
by transferring the mask patterns to the photoresist
24
by a photolithography technique using the above-mentioned exposure device such as a mask aligner. Here, circular and rectangle resist masks are formed as resist masks
24
a.
In
FIG. 10
, a desired pattern
22
a
is obtained by the silicon oxide film
22
using, for example, buffered hydrofluoric acid solution (BHF) or the like using the resist mask as an etching mask.
However, when the configuration of the circumference of the mask pattern itself is uneven and the shape thereof is distorted when comparing it with a plan diagram, the prior art etching process transfers a mask pattern including these problems because the mask pattern is transferred with high accuracy.
It is difficult to repair a defect at an end process in the prior art etching process.
In the above-mentioned mask, a reproduction of an original mask is generally used by producing an original mask by drawing on the mask after transformation of a coordinate system shape drawn by CAD or the like. Because of this, although high accuracy of transformation of the coordinate system is achievable for overcoming unevenness of the configuration of the circumference portion and the distorted shape of the above-mentioned mask pattern, transformation of the coordinate system can not entirely repair the defect and a high cost for the mask becomes inevitable.
As a defect in the mask pattern appears more often in a curved line pattern such as a circle than in a linear pattern such as a rectangle, a method of forming an accurate circular pattern is required.
Moreover, a defect in pattern shape sometimes appears due to a cause other than the mask shape, for example, because of dirt and dust infiltration during the fabrication process.
The present invention was made with regard to above-mentioned drawbacks of the prior art. An object of the present invention is to provide a method of processing a circular pattern enabling a desired circular pattern to be obtained even if there is pollution caused by dirt and/or dust or a defect in the mask pattern.
SUMMARY OF THE INVENTION
To achieve the above-mentioned object, a first aspect of the invention is characterized by obtaining a circular pattern comprising the steps of forming a circular etching mask on a semiconductor substrate, performing a first etching step to form a circular shape by etching the substrate, removing the etching mask after the first etching step, and performing a second etching step by isotropically etching the pattern obtained by the first etching step, wherein a circular pattern is obtained by etching an acute angle portion of an outline of the pattern obtained in the first etching step in the second etching step.
According to the invention, by removing a mask for etching after a first etching process and performing isotropic etching of the pattern at a second etching process, a smooth circular pattern can be obtained because an acute angle part is etched in the second etching process even if there is the acute angle portion at the circumference of the pattern obtained at the first etching process.
A second aspect of the present invention is characterized by the fact that the second etching process is divided into a plurality of etching processes in the method of forming a circular pattern according to the first aspect.
According to the invention, the second etching process can etch gradually plural times while confirming accuracy of dimension and state of repair of the acute angle portion without limiting etching times.
A third aspect of the present invention is characterized in that the thickness of the etched material and the diameter of the etching mask are set so that the thickness and diameter of the pattern obtained after the second etching process become the desired values in the method of processing of the first or the second aspects.
According to the invention, the pattern obtained finally become the desired dimensions if the thickness of the etched material and the diameter of the mask are determined in consideration of shrinkage because the pattern shape shrinks when the pattern is etched at the second etching process.
REFERENCES:
patent: 4496418 (1985-01-01), Ham
patent: 5317938 (1994-06-01), De Juan, Jr. et al.
patent: 5494179 (1996-02-01), Hori et al.
patent: 5853959 (1998-12-01), Brand et al.
patent: 5895582 (1999-04-01), Wilson et al.
Despont Michel
Ihcihara Susumu
Shirakawabe Yoshiharu
Takahashi Hiroshi
Adams & Wilks
Alanko Anita
Gulakowski Randy
Seiko Instruments Inc.
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