Coating apparatus – With means to centrifuge work
Reexamination Certificate
2000-01-14
2002-04-16
Crispino, Richard (Department: 1734)
Coating apparatus
With means to centrifuge work
C118S059000, C118S066000, C454S187000, C432S202000
Reexamination Certificate
active
06372042
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photo process system for use in the manufacturing of semiconductor wafers. More particularly, the present invention relates to a photo process system for forming a high quality photoresist film on a semiconductor wafer.
2. Description of the Related Art
The fabrication of semiconductor devices includes a photo process comprising steps of forming a photoresist film on a wafer, exposing the photoresist film to define a predetermined pattern thereon, and developing the exposed photoresist to form a film of the predetermined pattern on the wafer.
In clustered systems whose use has been increasing as of recent, all of the units of equipment for performing the photo process, for example, a coating unit, a developing unit, a baking unit, and the like, are clustered in one place. Therefore, the distance between the units, and hence, the time required to move a wafer from one unit to the next, is relatively short. Thus, the photo process can be performed efficiently by such equipment.
FIG. 1
is a schematic of the layout of a conventional clustered photo process system.
As shown in
FIG. 1
, a robot
110
for transferring a wafer is installed at the center of a housing
100
. The robot
110
is surrounded by a coating unit
120
, a developing unit
130
, a baking unit
140
, a loading/unloading unit
150
, and a controller
160
.
The coating unit
120
executes a spin coating method in which the wafer is rotated at a predetermined speed, and the rotating wafer is coated with a photoresist. The photoresist is dispersed uniformly over the surface of the wafer due to the centrifugal force of the rotating the wafer.
The developing unit
130
develops a pattern formed on the photoresist film in the exposure step, and the baking unit
140
bakes the wafer at a predetermined temperature between the above-described steps.
The loading/unloading unit
150
both loads the wafer into the system and unloads a completely processed wafer from the system. The loading/unloading unit
150
is designed to support several wafer carriers at a time.
The controller
160
includes a computer system for controlling the units of photo processing system. The robot
110
has a support
111
fixed to the bottom surface of the housing
100
, and an arm
112
which is integrated with the support
111
and can move freely. The arm
112
moves a wafer between the units within the housing
100
.
The steps of the photo process performed by the conventional photo process system will now be described generally.
In a pre-baking step (
1
), a wafer is introduced via a wafer carrier into the loading/unloading unit
150
. From there, the wafer is transferred to the baking unit
140
by the robot
110
. In the baking unit
140
, the wafer is heated to a predetermined temperature which causes organic material or foreign material to evaporate from the surface of the wafer.
In a photoresist (PR) coating step (
2
), the resultant wafer is transferred to the coating unit
120
. A photoresist film is formed on the surface of the wafer by the coating unit
120
.
In a soft baking step (
3
), the wafer is transferred back to the baking unit
140
where the wafer is heated for a predetermined amount of time. In this step, the photoresist is dried so that it attaches firmly to the surface of the wafer.
In an exposure step (
4
), the wafer is transferred to an exposure unit, such as a stepper or scanner. The photoresist film is photo-sensitized by the exposure unit to define a pattern thereon.
In a post-exposure baking (PEB) step (
5
), the exposed wafer is transferred back to the baking unit
140
. The wafer is again heated for a predetermined amount of time by the baking unit
140
.
In a developing step (
6
), the wafer is cooled to a temperature within a predetermined range. Subsequently, the photoresist pattern is developed by the developing unit
130
.
In a hard baking step (
7
), the wafer is heated so that the photoresist pattern will be even more firmly attached to the surface of the wafer.
The above-described steps are performed in a clean environment in which the temperature and humidity are controlled, and in which dust or other foreign materials have been eliminated. Thus, the photo process system is installed within a clean room provided with an air conditioner.
In the PEB step, optically-decomposed resins are rearranged due to thermal diffusion by heating the exposed photoresist at a predetermined temperature, thus cleaning the profile boundary (cross section) between exposed patterns. This PEB step is performed to prevent abnormalities from being produced in the profile of the patterns and non-uniformity of the critical dimension of the patterns when the patterns are irradiated with ultraviolet (UV) or deep ultraviolet (DUV) light during the exposure process. Because light irradiating the exposed portion diffracts and produces interference according to the reflectivity and refractivity of the wafer and the optical absorption level of the photoresist, the diffraction and interference of the light would create the above-mentioned abnormalities and non-uniformity in the exposed portion if the resins were not rearranged by being heated prior to exposure.
The problems posed by these optical phenomena of diffraction and interference can alternatively be solved by coating the photoresist film with an anti-reflection film prior to exposure. However, the PEB process is used more often.
When the exposure light in the photo process is a DUV light, a chemically-amplified resist is used as the photoresist. A portion of the chemically-amplified resist, which is exposed by thermal treatment, changes into an acid which is soluble in a developing solution. Also, the alteration of the chemically-amplified resist occurs due to a chain reaction, so that the balance of heat applied to the entire wafer in the PEB step has the greatest effect on the uniformity of the critical dimension of a pattern.
FIG. 2
is a schematic diagram of a conventional photo process system installed in a clean room.
Referring to
FIG. 2
, the clean room typically has a passageway
10
and an equipment installation zone
20
. The photo process system is located in the equipment installation zone
20
, adjacent to the passageway
10
. The upper portion of the clean room is provided with an upper plenum
30
through which clean air enters the room, and the lower portion of the clean room is provided with a lower plenum
40
through which air is discharged from the room. Filters
31
are installed between the upper plenum
30
and the equipment installation zone
20
and passageway
10
of the clean room. The photo process system has a housing
100
, a coating unit
120
disposed in the housing
100
at one side thereof, and baking unit shelves
140
a
disposed in the housing
100
at the other side thereof. A plurality of baking units
140
are installed in multiple stages on the baking unit shelves
140
a
. A robot
110
is installed at the center of the housing
100
.
The air conditioner of the photo process system includes a blower
171
, blast pipes
172
, and an air filter
173
. The blower
171
is installed within the lower plenum
40
, the air filter
173
is installed in the upper portion of the housing
100
, and the blast pipes
172
extend from the blower
171
to the upper portion of the housing
100
in which the air filter
173
is provided. The blower
171
typically includes a chemical filter for removing NH
3
from the air.
In the clean room, dust in the equipment installation zone
20
is a prevented from entering the housing
100
, and different pressures are maintained in different areas of the clean room to prevent fumes or the like from diffusing from one area to another. For example, the pressure in the passageway
10
is about 0.17 to 0.18 mmH
2
O greater than that in the upper area of the housing
100
. The pressure in the passageway
10
is about 0.07 to 0.08 mmH
2
O greater than that in the housing
100
. The pressure in the housing
100
is about 0.09 to
Han Sam-soon
Nam Jeong-lim
Oh Chang-wook
Sung Woo-dong
Crispino Richard
Samsung Electronics Co,. Ltd.
Shortsle Kevin P.
Volentine & Francos, PLLC
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