Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2001-03-21
2003-12-09
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S270100, C430S313000, C430S314000, C430S317000, C430S329000, C430S942000, C430S296000, C430S030000
Reexamination Certificate
active
06660455
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-080093, filed Mar. 22, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a pattern formation material, pattern formation method, and exposure mask fabrication method and, more particularly, to a pattern formation material for electron beam lithography, a pattern formation method using the pattern formation material, and an exposure mask fabrication method using the pattern formation material.
Recently, chemically amplified resists are often used in the fabrication processes of semiconductor devices. These chemically amplified resists are roughly classified into positive resists and negative resists. Known examples of the positive chemically amplified resists are a ternary composition containing an alkali-soluble resin, dissolution inhibitor, and photoacid generator, and a binary composition containing an alkali-soluble resin to which a substituent (dissolution inhibiting group) having dissolution inhibiting capacity is introduced, and a photoacid generator.
When a positive chemically amplified resist is used, the dissolution of the alkali-soluble resin is inhibited in an unexposed state by the dissolution inhibitor or the dissolution inhibiting group. When this resist is irradiated with chemical radiation to generate an acid from the photoacid generator and the resultant resist is subjected to post-exposure baking (PEB), the dissolution inhibitor or the dissolution inhibiting group is decomposed by the generated acid to lose its dissolution inhibiting capacity. Since this makes an exposed portion of the positive chemically amplified resist soluble in alkali, the resist is selectively removed by development using an alkali developer.
In this chemically amplified resist, the acid generated when the photoacid generator is irradiated with chemical radiation functions as a catalyst. When this chemically amplified resist is used, therefore, a plurality of molecules can be reacted by one photon. That is, higher sensitivity than those of conventional resists can be obtained by the chemically amplified resist.
In a patterning process using the chemically amplified resist described above, a resist film is irradiated at once with ultraviolet radiation through a desired pattern, and a resist pattern obtained by developing the irradiated resist film is used as an etching mask to pattern a thin film. This resist pattern is required to decrease the pattern size and increase the shape accuracy. In effect, many proposals have been made to meet these requirements.
For example, Jpn. Pat. Appln. KOKAI Publication No. 8-262721 disclosed a binary chemically amplified resist composition containing, as alkali-soluble resins, polyhydroxystyrene in which 10 to 60 mol % of a hydroxyl group are substituted by a tert-butoxycarbonyloxy group (t-BOC group), and polyhydroxystyrene in which 10 to 60 mol % of a hydroxyl group are substituted by a residual group indicated by formula —OCR
1
R
2
OR
3
. Jpn. Pat. Appln. KOKAI Publication No. 8-262721 describes that this resist composition realizes high sensitivity, high resolution, and high heat resistance because the solubility of the alkali-soluble resins and the dissolution stopping power are well balanced by using the t-BOC group and the residual group indicated by formula —OCR
1
R
2
OR
3
(R
1
represents a hydrogen atom or methyl group, R
2
represents a methyl group or ethyl group, and R
3
represents a lower alkyl group) as dissolution inhibiting groups.
Jpn. Pat. Appln. KOKAI Publication No. 9-6002 describes that when the conventional chemically amplified resists are used, bridging occurs in the upper portion of an opening in the resist pattern because an acid generated by exposure is deactivated. This deactivation of the acid is brought about by ammonia or the like contained in the atmosphere in a clean room. As a solution to this problem, Jpn. Pat. Appln. KOKAI Publication No. 9-6002 disclosed a positive chemically amplified resist composition formed by further adding an organic carboxylic acid compound to the composition disclosed in Jpn. Pat. Appln. KOKAI Publication No. 8-262721. Note that Jpn. Pat. Appln. KOKAI Publication Nos. 9-6003, 9-22117, 9-127698, and 10-10738 also disclosed chemically amplified resist compositions similar to those disclosed in Jpn. Pat. Appln. KOKAI Publication Nos. 8-262721 and 9-6002.
Like Jpn. Pat. Appln. KOKAI Publication No. 9-6002, Jpn. Pat. Appln. KOKAI Publication No. 9-219355 describes that when the conventional chemically amplified resists are used, an acid generated by exposure is deactivated by ammonia or the like contained in the atmosphere in a clean room, and the section of the resist pattern assumes a T-top profile. As a method of solving this problem, Jpn. Pat. Appln. KOKAI Publication No. 9-219355 describes that the resist composition is so controlled that the film reduction amount is increased when the sectional shape of the resist pattern has a T-top profile, and that the film reduction amount is decreased when the sectional shape of the resist pattern has a sloping shoulders-like profile.
Any of the above Published Unexamined Patent Applications mainly describes that ultraviolet radiation is used to expose the chemically amplified resist disclosed in it. Recently, however, electron beam writing is beginning to be used in addition to ultraviolet exposure described above.
Theoretically, electron beam writing can increase the resolution to the beam diameter of an electron beam. That is, electron beam writing is more suitable for finer fabrication than ultraviolet exposure. Therefore, electron beam writing is used when ultrafine fabrication is necessary, such as in the fabrication of pattern formation masks, e.g., a general photomask, electron beam exposure mask, X-ray lithography mask, EUV (Extreme UltraViolet) lithography mask, and stencil mask.
Unfortunately, when an electron beam is used as chemical radiation, peculiar problems that cannot occur in ultraviolet exposure take place. For example, Jpn. Pat. Appln. KOKAI Publication No. 11-271965 describes that no resist patterns having good sectional shapes can be obtained when electron beam exposure is performed by using a chemically amplified resist containing a polymer having an acetal-type acid leaving group. Jpn. Pat. Appln. KOKAI Publication No. 11-27165 also describes that the cause of this defect is that the release reaction from a polymer having an acetal-type acid leaving group requires water, but the conventional methods cannot allow a resist film to absorb sufficient moisture. This lacking of water occurs because electron beam writing is performed in a vacuum, unlike ultraviolet exposure. As a method of solving this problem, Jpn. Pat. Appln. KOKAI Publication No. 11-271965 disclosed a method by which a resist film is allowed to absorb moisture as it is left to stand in the air between exposure and PEB.
The use of an electron beam as chemical radiation also poses other characteristic problems. When an electron beam is used as chemical radiation, exposure cannot be performed at once unlike when ultraviolet radiation is used. That is, writing must be gradually performed when an electron beam is used. Hence, in the fabrication of a pattern formation mask described above, writing of a resist film sometimes takes a long time of 10 hr or more. When this is the case, the diffused state of an acid generated by exposure of a chemically amplified resist differs in the writing end position largely from that in the writing start position.
At present, the dimensional accuracy required for electron beam writing used in the semiconductor device fabrication processes is on the nanometer order. However, some conventional technologies produce a dimensional difference of about 30 nm between the writing start and end positions. Such a dimensional difference obviously does not satisfy the above requirement and hence is a large ca
Itoh Masamitsu
Kondoh Takehiro
Baxter Janet
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Walke Amanda C.
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