Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2002-07-23
2004-07-27
Huff, Mark F. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S914000, C522S035000
Reexamination Certificate
active
06767687
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a polymer for a chemically amplified resist and a resist composition comprising the same More particularly, the present invention relates to a novel polymer that can be used for a chemically amplified resist composition that can form finer patterns on a substrate in a micro-lithography process suitable for micro-processing of semiconductors, using a mono wavelength as the light source for light exposure, and which improves post exposure delay (PED) stability and has high resistance against the heat produced by dry etching, and a resist composition using the same.
(b) Description of the Related Art
The resist composition is generally used in the preparations of large size integrated circuits (LSI) or in high resolution lithography. Recently, resist compositions with high resolution and high sensitivity have been required due to the densification of large size integrated circuits. Such embodiments of microcircuits in semiconductor integrated circuits generally proceed using a lithography process through which process the microcircuit is constructed by coating resist on a substrate, transcribing patterns on the substrate using a prepared photo mask, and etching the substrate along the transcribed pattern.
Such lithography processes comprise the following steps: (a) a coating step comprising uniformly coating resist on the surface of a substrate, (b) a soft baking step comprising evaporating the solvent from the coated resist film to adhere the resist film to the surface of the substrate, (c) a light exposure step comprising light exposing the substrate while projecting the circuit pattern on the mask, repeatedly and sequentially using a light source such as ultraviolet light to transcribe the pattern of the mask onto the substrate, (d) a development step comprising selectively removing the part in which chemical properties such as solubility change by the exposure to the light source using development liquid, (e) a hard baking step for adhering more firmly the resist film that remains on the substrate after development, (f) an etching step comprising etching the predetermined part along the pattern on the developed substrate in order to impart the electric properties and (g) a stripping step comprising removing the resist that becomes unnecessary after said etching step.
The speed of high-integration of semiconductor integrated circuits has increased 4-fold for 3 years. Thus, at present, in the field of dynamic random access memory (DRAM), 64 mega bit DRAM and 256 mega bit DRAM are mass-produced, and the development of giga bit DRAM has started.
The conventional 16 mega DRAM used the technology of a 0.5 &mgr;m circuit line, while 64 mega DRAM uses the technology of a circuit line of 0.3 &mgr;m or less, and 256 mega DRAM and giga DRAM requires an ultra micro pattern of less than quarter micro, such as 0.20 &mgr;m, 0.18 &mgr;m, 0.15 &mgr;m depending on the design. In such micro-processing, the light-radiation wavelength moves to extreme ultraviolet. Therefore, there is a need for the development of a new resist that can effectively respond to extreme ultraviolet light.
The resist of the prior art comprising quinonediazide photoactive material and phenol novolac resin cannot satisfy the above-mentioned requirement, because, in such a resist system, there is a large absorption at the wavelength zone of 300 nm or less and thus, when mono wavelength light-exposure of 300 nm or less is conducted, pattern profile is significantly deteriorated. Therefore, there is a need for the embodiment of a stiff pattern in which the pattern profile does not flow.
In order to embody such a pattern profile, an aligner commonly called a stepper is generally used as a light-exposing apparatus. Such light-exposing apparatuses are divided into an apparatus using G line (wavelength 436 nm), I line (wavelength 365 nm) of mercury light, and an apparatus using an excimer laser of mono wavelength KrF (248 nm) and ArF (193 nm) according to the light source. For embodying micro-patterns on the substrate, the resolution value should be small The resolution value is expressed by the following Rayleigh diffraction limiting equation Theoretically, since the resolution value becomes smaller as the wavelength of the light source becomes shorter, it is preferable to use a shorter mono wavelength.
[Diffraction Limiting Equation]
R=&kgr;&lgr;/NA
Wherein, &kgr; is a constant, &lgr; is a wavelength of the light used, and NA is the number of the aperture of the lense.
In order to achieve high resolution of a quarter micron or less, the capacity of degradation of lithography should be improved. For this purpose, it is effective to use a mono wavelength light source having a short wavelength and to increase the aperture number (NA) of the optical lense of the exposing apparatus.
Accordingly, a resist composition that uses a high-output excimer laser light source so as to respond to the high-resolution tendency of semiconductor integrated circuits is commonly used. This composition is for a KrF and an ArF excimer laser, and high-sensitivity resist systems introducing the chemical amplification concept are suggested.
A chemically amplified resist produces acid by photolysis due to the irradiation of extreme ultraviolet light. The produced acid degrades the protective group which is partially protected with the aid of heat, and then it reacts with the acid labile polymer to initiate the chain reaction or act as a catalyst, and thus, one molecule of acid causes a number of bond formation or bond degradation reactions Therefore, a term “chemical amplification” means the phenomenon whereby active species produced by the action of one photon causes chemical chain reactions to rapidly amplify the yield of quantum. Due to this continuous reaction of acid, the concept of chemical amplification was introduced and used.
A chemically amplified resist is divided into a two-component system comprising an acid-labile polymer and a mineral acid producing agent and a three-component system comprising an acid-labile polymer, a mineral acid producing agent and a matrix resin. In the resist of the prior art, the degradation or the cross-reaction of a light sensitive material occurs directly at the light exposure part, and, when it is developed, a resist image pattern of a positive or negative form is obtained. However, in the chemically amplified resist, an acid labile polymer or compound is not directly reacted by light exposure, but an acid is produced from the mineral acid producing agent in the light-exposed part, and only a latent image is produced The produced acid acts as a catalyst for the acid labile polymer in the post-exposure bake (PEB) step, and thus, it causes the amplification of the reaction and the significant difference in solubility.
The first resist based upon the chemical amplification concept was a resist using a polyhydroxystyrene derivative poly[p-(t-butyloxycarbonyloxy)styrene] (PBOCSt) blocked with t-BOC (tertiary-butoxy carbonyl) group and onium salt as a mineral acid producing agent, and it is described in American Chemical Society, “Polymers in Electronics”, ACS Sym Series, No. 242 by Ito et al. The reason for using the polyhydroxystyrene derivative is as follows since the novolac phenol resin that was used in the resist of the prior art largely absorbs deep UV, UV light cannot sufficiently reach the contact surface of the resist substrate Thus, in the light-exposed part of the resist, chemical changes by light-exposure do not sufficiently occur in the membrane thickness direction, and thus the solubility of the developing liquid becomes irregular. This makes the shape of the section of the resist pattern formed after development triangular Thus when the obtained resist pattern is used as an inner etching mask for a substrate, the micro-circuit pattern to be aimed cannot be transcribed. In order to compensate for this, there is a need to change the base polymer, and a polyhydroxystyrene derivative having
Choi Yong-Joon
Chung Yoon-Sik
Kim Deog-Bae
Kim Hyun-Jin
Baker & Botts LLP
Dongjin Semichem Co., Ltd.
Huff Mark F.
Walke Amanda
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