Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1997-06-25
2001-02-20
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S330000
Reexamination Certificate
active
06190837
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to a method for forming a photoresist film pattern on a wafer substrate by a lithography process and, more particularly, to the use of a silylation photoresist film in forming a fine pattern.
2. Description of the Prior Art
Necessary to form a pattern in a semiconductor device is a lithography process, which generally comprises coating a photoresist film on a layer to be patterned, exposing and developing the photoresist film through a patterned mask to form a photoresist film pattern, and etching the layer with the photoresist film pattern serving as a mask.
To produce 4 G or 16 G DRAM semiconductor devices, a fine pattern as small as 0.18 &mgr;m or less in size is required. However, the wet development process in current use has a difficultly in solving the problems of the breaking down of patterns and the allowance for the depth of focus on a practical topology. For this reason, a dry development process in combination with a silylation technique was developed and used in a masking process for 4 G and 16 G DRAM semiconductor devices.
In order to better understand the background of the invention, a description will be given of a conventional method for forming a photoresist film pattern through a silylation technique, in connection with some drawings.
First, a light beam is irradiated through a mask to a photoresist film
2
underlain by a layer
2
upon a semiconductor substrate
100
, as shown in FIG.
1
. The layer
2
is to be etched and consists of a photoresist material and a novolak resin.
FIG. 2
is a schematic view after the photoresist film
2
is subjected to a baking process, to make the irradiated regions
5
of the photoresist film
2
thermally cured whereas the regions which are not exposed to the light beam remain as they are.
FIG. 3
shows a silylation process in which a silylation agent, containing N—Si bond, such as hexamethyl disilazane or tetramethyldisilazane, is injected into the regions
5
exposed to the light beam. N—Si bond is so weak that it may be readily broken and react with R—O—H of the resin to form R—O—Si—(CH
3
)
3
(trimethylsilicon).
FIG. 4
shows a dry developing process utilizing O
2
plasma, by which a silicon oxide 6 is formed in the trimethyl silicon bonded with the resin of the exposed regions whereas the unexposed regions of the photoresist film
2
are etched to form a photoresist film pattern
2
′.
FIG. 5
is a schematic view after the layer
1
is etched to create a pattern
1
′, with the photoresist film pattern
2
′ serving as a mask.
As illustrated, this conventional method by which the exposed regions remain as a photoresist film pattern whereas the unexposed regions are removed, forms a pattern such as that of the general negative photoresist film.
The photoresist film pattern formed via the conventional silylation process is poor in profile because the boundaries between the exposed regions and the unexposed regions are not clear. In addition, light diffracts into the regions which are determined not to be exposed, generating a swelling phenomenon.
Typically, KrF (248 nm) or ArF (193 nm) is used as a light source. The photo acid compound (PAC) contained in the convention photoresist film depends on and varies with the light source.
SUMMARY OF THE INVENTION
Therefore, it is an objective of the present invention to overcome the above-mentioned problems encountered in prior arts and to provide a method for forming a fine pattern on a wafer substrate though a silylation process, by which one photoresist film can be used irrespective of light sources including KrF (248 nm) and ArF (193 nm) and a positive pattern with a positive pattern as small as 0.18 &mgr;m in size can be obtained.
In accordance with the present invention, there is provided a method for forming a fine photoresist film pattern, comprising the steps of: coating a photoresist film on a layer to be etched and exposing a certain depth of the photoresist film through a mask to a light beam, said photoresist film comprising a resin, a photoacid generator and a base; subjecting the photoresist film to post-exposure bake, to remove the base of the exposed region through the reaction of acid and base; silylating the photoresist film with a material containing H—Si bond, to create a Si—O-resin bond in the unexposed region with the aid of a catalytic action of the base which remains therein but no Si—O-resin bond in the exposed region; and etching the exposed region of the photoresist film by use of O
2
plasma, said Si—O-resin contained in the unexposed region of the photoresist film combining with oxygen to form a silicon oxide which serves as an etch barrier.
REFERENCES:
patent: 5312717 (1994-05-01), Sachdev
patent: 5384220 (1995-01-01), Sezi
Jung Jae Chang
Kim Hyang Gi
Duda Kathleen
Hyundai Electronics Industries Co,. Ltd.
Nath Gary M.
Nath & Associates
Novick Harold L.
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