Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
1999-08-10
2001-07-17
Letscher, Geraldine (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S327000, C430S330000
Reexamination Certificate
active
06261744
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a baking apparatus and a baking method for baking a resist film coated on a substrate such as a semiconductor wafer and an LCD substrate.
When a semiconductor device is manufactured, photolithgraphic technique is usually employed. In the manufacturing step using the photolithgraphic technique, the surface of a semiconductor wafer is coated with a photoresist, exposed to light together with a predetermined pattern, and developed. In this manner, a resist film having a predetermined pattern is formed on the wafer. If the resist film is further subjected to etching and film-formation steps, a circuit with a predetermined pattern can be formed. The aforementioned series of resist processing steps are usually performed in the coating/developing system, for example, disclosed in U.S. Pat. No. 5,664,254 publication. The series of resist processing steps include various baking processes performed for different purposes. Prebake is made to stabilize the resist. Post exposure bake (PEB) is carried out after the resist is exposed to light. After the resist is developed, post bake is performed.
With an increase in bit number from 64M to 256M in recent years, the line width of a DRAM circuit has been reduced to the sub micron order, e.g., 0.3 &mgr;m or less. With this tendency, the requirement for the quality of a resist film has become extremely stringent. To form such an ultra-fine pattern, highly sensitive, chemically amplified resists have been developed and put in wide use.
Since the light exposed portion of the chemically amplified resists initiates a chemical reaction in a post exposure baking step performed after the light exposure. Therefore, an ultra-fine pattern can be formed even by the radiation of a low energy laser such as a krypton fluoride eximer laser (wavelength: 248 nm). However, when the chemically amplified resist is subjected to the PEB using a conventional baking apparatus, it tends to be difficult to obtain the wiring with a constant width. As a result, a predetermined pattern cannot be formed and thus the yield of the semiconductor device decreases.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a baking apparatus and a baking method capable of forming a pattern having a line width in the order of sub micron. More specifically, the present invention is intended to provide a baking apparatus and baking method capable of forming an ultra fine pattern uniform in line width on a chemically amplified resist film.
The baking apparatus of the present invention comprises:
a casing surrounding a substrate having a pattern-exposed resist film;
a hot plate for heating the substrate in the casing; and
a gas supply mechanism for supplying a H
2
O component containing humidity gas into the casing,
in which the H
2
O component included in the humidity gas is allowed to react with the resist film by introducing the humidity gas in the casing while the substrate is being heated by the hot plate, thereby rendering either an irradiated portion or a non-irradiated portion of the resist film soluble in alkali.
It is preferable that the apparatus of the present invention further comprise a cover provided closely the substrate in the casing for forming a process space for baking the resist film between the cover and the substrate, and an elevator mechanism for elevating the cover. If such a small process space is formed between the cover and the substrate, H
2
O component contained in the humidity gas can be efficiently reacted with the resist film, with the result that a quality of the resist film is improved, increasing the throughput of the baking process.
The cover has a gas inlet at the center thereof and a gas outlet in the periphery thereof. It is preferable that the humidity gas be introduced through the gas inlet into the process space and exhausted through the gas outlet from the process space.
Furthermore, it is preferable that the baking apparatus have a plurality of lift pins for lifting the substrate above the hot plate.
It is preferable that the gas supply mechanism have a gas source and a humidifier for humidifying the gas supplied from the gas source and sending the gas to the casing.
It is further preferable that the humidifier have a pot for storing water, a cover provided over the pot, a first gas supply pipe inserted in the pot through the cover and connected to the gas source, and a second gas supply pipe inserted in the pot through the cover and connected to the casing.
It is yet preferable that the gas supply mechanism comprise a temperature controlling means for controlling temperature of the gas.
It is still preferable that the temperature controlling means have a first temperature controller provided upstream of the humidifier and a second temperature controller provided downstream of the humidifier, a temperature sensor provided downstream of the second temperature controller, and a controller for controlling the first and second temperature controllers separately on the basis of temperature detection signals sent from the temperature sensor. Furthermore, it is preferable that the humidifier have a fan for introducing a gas from the gas source, a chiller for removing humidity from the introduced gas by exchanging heat with a coolant, a heater for heating the humidity-removed gas by the chiller, and an evaporation plate for adding steam to the humidity-removed gas by the chiller.
A baking method according to the present invention comprises the steps of:
(a) forming a space around the substrate, for processing a substrate having a pattern-exposed resist film so as to isolate the substrate from the outside,
(b) generating a H
2
O component containing humidity gas by adding steam to gas, and
(c) heating the substrate while the humidity gas is being introduced into the space for processing to react the H
2
O component contained in the humidity gas with the resist film, thereby rendering either an irradiated portion or a non-irradiated portion of the resist film, soluble in alkali.
It is desirable that the substrate be heated to a temperature within the range of 80° C. to 170° C. and for 70 to 150 seconds.
It is further desirable that the humidity containing gas be generated by adding water vapor to an air or an inert gas such as a nitrogen gas, argon gas, or helium gas.
In the step (c), it is preferable that a relative humidity of the space for processing be controlled within the range of 30 to 50% by controlling an amount of the humidity gas.
In step (b), it is preferable that temperature of the humidity gas be controlled.
It should be noted that the resist film is formed of a chemically amplified resist containing an alkali-insoluble resin as a main component.
Now, we will explain the chemical reaction which takes place when the resist film is subjected to the PEB with reference to the formulas 1-1, 1-2, 2-1 and 2-2.
When a photoresist is exposed to light, H
+
is generated from a photoacid generator contained in the photoresist. Thereafter, when the wafer W is subjected to PEB, H
+
present at an irradiated portion cuts out an acetal group and isolated from polyhydroxystyrene (PHS). The polyhydroxystyrene (PHS) is soluble in alkali. On the other hand, the isolated acetal group presents in the form of a carbocation represented by a resonance structure (1) or (2). Since the carbocations (1) and (2) are labile intermediate products, they readily decompose and freshly generate H
+
. The generated H
+
decomposes the carbocations. H
+
is thus consecutively generated in a chain reaction manner. As described, when the chemically amplified resist is subjected to PEB, H
+
is produced one after another. Therefore, even if the film is exposed to even low energy eximer laser, the resultant pattern is obtained with high sensitivity.
When the chemically amplified resist is subjected to the PEB process under the humidified atmosphere, H
2
O works actively to decompose the carbocation (1) or (2) as shown in the formulas 1-2 and 2-2. To explain more spe
Letscher Geraldine
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tokyo Electron Limited
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