Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1999-01-15
2001-01-09
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S323000, C430S330000, C430S331000
Reexamination Certificate
active
06171761
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a method of forming a resist pattern, and more particularly to an improved method of forming a resist pattern permitting control of a resist profile of a chemically amplified-type resist. The present invention also relates to a method of forming semiconductor device using the resist pattern.
2. Description of the Background Art
In the field of photolithography, a chemically amplified-type resist is currently proposed as a resist having high sensitivity as well as high resolution. This resist has a feature that it is baked after exposure to light, and this post exposure bake (hereinafter referred to as “PEB”) accelerates pattern forming reaction with an acid generated during the exposure as a catalyst, and thus pattern imaging is completed.
FIGS.
15
-
18
are cross sectional views of a semiconductor device at successive steps of a conventional method of forming a fine resist pattern using a chemically amplified-type resist.
Referring to
FIG. 15
, a substrate
1
is coated with a chemically amplified-type resist
2
. Note that the surface of substrate
1
has been processed with HMDS (hexamethyldisilane) or the like before coating with the resist, to ensure close contact between substrate
1
and resist
2
.
Resist
2
is formed of poly (p-t-butyl oxy-carbonyl oxy-styrene) with t-butyl oxy-carbonyl (hereinafter referred to as “t-BOC”) coupled to poly-phydroxy styrene, as shown, for example, in FIG.
19
A. This composition is only by way of example, and other compositions may also be used. In
FIG. 19A
, n is a natural number representing a degree of polymerization. Resist
12
includes an acid generating agent, i.e., triphenyl sulfonium trifluoro methane sulfonate, as shown in FIG.
19
B.
Once substrate
1
has been coated with resist
2
, it is pre-baked to remove a solvent or the like included in resist
2
.
An acid film
3
is formed on resist
2
, which is made, for example, of water-soluble polymer such as polyvinylpyrrolidone or polyacrylic acid. Acid film
3
selves for preventing intra-film multiple reflections. Another function expected of the film here will be described later. Thereafter, baking is conducted again to remove a solvent in acid film
3
.
With reference to
FIG. 16
, resist
2
is selectively exposed to light using a mask
4
, to form an exposed portion
5
and an unexposed portion
6
.
At the exposed portion, the acid generating agent is irradiated with light, and thus generates a protonic acid, as shown in FIG.
20
.
Referring to
FIG. 17
, resist
2
is subjected to PEB. At this time, the protonic acid causes t-BOC groups to leave from poly (p-t-butyl oxy-carbonyl oxy-styrene), so that hydroxyl groups (phenol groups) are generated. Thus generated poly-p-hydroxy styrene is soluble in alkali.
Next, how the t-BOC groups leave from the base resin will be described in more detail with reference to FIG.
22
.
With reference to FIG.
22
(
a
), resist
2
is irradiated with light. Accordingly, the acid generating agent in the resist decomposes to generate a protonic acid (H
+
) (see FIG.
22
(
b
)). As shown in FIG.
22
(
c
), subsequent baking of resist
2
causes the t-BOC groups to leave from poly (p-t-butyl oxy-carbonyl oxy-styrene), thereby generating hydroxyl groups. As the baking is continued, more t-BOC groups are generated (
FIG. 22
(
d
)). Ultimately, as seen in FIG.
22
(
e
), the base resin is converted to polyvinylphenol, that is soluble in an alkaline developer solution.
Generally, a chemically amplified-type resist is susceptible to acid and base existing within the resist or entering from the outside. An acid film
3
is thus formed on the resist
2
as a protective film. Since this protective film is an acid film, however, acid is fed from acid film
3
to the surface of resist
2
at the unexposed portion
6
. The reference numeral
7
in
FIG. 17
shows a portion which has been supplied with the acid and thus become soluble in alkali.
With reference to
FIG. 18
, when developed with an alkaline solution with 2.38% tetramethylammonium hydroxide (TMAH)
2
, the alkali-soluble portion is removed to form a fine resist pattern. Using this resist pattern, a bit line or the like is patterned.
As described above, in a conventional method of forming a fine resist pattern using a chemically amplified-type resist, acid is supplied from acid film
3
to resist
2
even at the unexposed portion, as shown in
FIGS. 17 and 18
. Accordingly, resist pattern
8
obtained after the development has a rounded top portion. That is, a rectangular resist profile can not be attained as desired.
If acid film
3
is not formed on resist
2
, amine (ammonia etc.) will penetrate into resist
2
from the outside, and as shown in
FIG. 23
, the top portion of resist pattern
8
will expand in the horizontal direction, resulting in a so-called T-shaped resist pattern. Either in this case, a desirable, rectangular resist cannot be attained.
SUMMARY OF THE INVENTION
The present invention is made to solve the above-described problems. One of its objects is to provide an improved method of forming a resist pattern allowing a rectangular resist profile to be obtained as desired.
Another object of the invention is to provide an improved resist pattern forming method capable of avoiding an adverse effect of amine from the outside.
A further object of the invention is to provide an improved resist pattern forming method permitting control of a resist profile of a chemically amplified-type resist.
A still further object of the invention is to provide an improved resist pattern forming method allowing a desirable resist profile to be obtained even when rays of light are defocused and some of them undesirably enter the unexposed portion of the resist from its periphery.
A still further object of the invention is to provide an improved method of forming a semiconductor device.
In the resist pattern forming method according to a first aspect of the present invention, a chemically amplified-type resist is first formed on a substrate, and is exposed to light using a mask. After the exposure, the resist is baked at a first temperature, and then developed halfway. The resist developed halfway is then baked at a second temperature which is lower than the first temperature. Thereafter, it is fully developed and a resist pattern is obtained.
According to this aspect, the resist is not fully developed at the first developing step, and an alkali-insoluble layer with acid inactivated by alkali is thus formed on the surface of the resist pattern at the unexposed portion. The second developing step is conducted thereafter. Accordingly, a rectangular resist pattern can be obtained as desired.
In the resist pattern forming method according to a second aspect, a positive resist is employed as a chemically amplified-type resist, and thus a positive resist pattern is obtained.
In the method according to a third aspect, the first temperature is set in the range of 30 to 150° C. The post exposure bake at a temperature in this range allows an acid generating agent in the exposed portion to generate acid smooth.
In the method according to a fourth aspect, the difference between the first and second temperatures is set to be 10° C. or larger. This prevents an alkali-insoluble portion formed on the surface of the resist pattern at the unexposed portion from dissolving into an alkaline developer solution.
In the method according to a fifth aspect, the step of developing the resist halfway is performed until 10 to 80% of the resist at the exposed portion is removed. In other words, the first developing step is performed incompletely.
In the method according to a sixth aspect, an acid film is formed on the chemically amplified-type resist prior to the exposure. This prevents penetration of amine from the outside into the resist.
In the method according to a seventh aspect, the resist pattern is adapted to form an interconnection pattern of 0.20-0.22 &mgr;m L/S (Line and Space). Accordingly, the present inven
Ishibashi Takeo
Minamide Ayumi
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
Young Christopher G.
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