Process for using bilayer photoresist

Details Process for using bilayer photoresist Process for using bilayer photoresist

2001-06-28

2003-10-21

Ashton, Rosemary (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Forming nonplanar surface

C430S273100, C430S156000, C430S166000, C430S323000, C430S270100, C430S905000, C430S910000

Reissue Patent

active

RE038282

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an improved bilayer photoresist and process for its use in lithography for manufacturing semiconductor devices.
BACKGROUND OF THE INVENTION
There is a desire in the industry for higher circuit density in microelectronic devices made using lithographic techniques. One method of achieving higher area density is to improve the resolution of circuit patterns in resist films. It is known in the art that increasing the numerical aperture (NA) of the lens system of the lithographic imaging tool increases the resolution at a given wavelength. However, increasing the NA results in a decrease in the depth of focus (DOF) of the imaging radiation, thereby requiring a reduction in the thickness of the imaging resist film. Further, the industry-wide shift to shorter wavelength exposure systems also results in a decrease in the DOF. A decrease in the resist film thickness can lead to problems in subsequent processing steps (e.g., ion implantation and etching).
In order to overcome these problems, bilayer resists have been developed. Bilayer resists generally comprise a top thin film imaging layer coated on a thick organic underlayer. The resist is patterned by: (i) imagewise exposure and development of the top layer, and then (ii) anisotropically transferring the developed pattern in the top layer through the thick underlayer to the substrate. Suitably, the top layer contains precursors to refractory oxides such as silicon, boron, or germanium which enable the use of oxygen-reactive ion etching (RIE) in the image transfer step. However, the incorporation of silicon into the photoresist film often leads to the degradation of resolution and imaging performance.
Bilayer resists are known in the art. However, these resists were generally developed before the advent of deep U.V. lithography (e.g., 248 nm and 193 nm) and are of little utility for high-resolution imaging. For example, in the review article “Polymeric Silicon-containing Resist Materials”, Advanced Material for Optics and Electronics, Vol. 4, pp. 95-127 (1994), there is disclosed on page 112 a positive bilayer resist having a top layer comprising the copolymer poly(co-trimethylsilylmethyl methacrylate and monooximido &agr; diketone). The top layer is imaged by radiation chain scission and the image is transferred with oxygen R.I.E. However, the resist is not commercially viable due to slow photospeed and other resist performance problems. Therefore, there still is a need in the art for a bilayer photoresist suitable for commercial use.
It is therefore an object of the present invention to provide an improved bilayer photoresist.
Other objects and advantages will become apparent from the following disclosure.
SUMMARY OF THE INVENTION
The present invention relates to a process for forming bilayer resist images on a substrate with a chemically-amplified, radiation-sensitive bilayer resist. The bilayer resist is disposed on a substrate and comprises (i) a top imaging layer comprising a radiation-sensitive acid generator and a vinyl polymer or copolymer formed by the polymerization of monomers, including one or more monomers selected from acrylate, methacrylate, hydroxystyrene (optionally substituted with C
1-6
alkyl), and C
5-20
cyclic olefin monomers, where preferably the polymer has an acid-cleavable silylethoxy group; and (ii) an organic underlayer. The present invention relates to the process for using the bilayer resist to make resist images in a film in the manufacture of integrated circuits.
A more thorough disclosure of the present invention is presented in the detailed description which follows.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention relates to a positive tone, chemically-amplified, radiation-sensitive bilayer resist. The bilayer resist comprises (a) a top imaging layer comprising (i) a radiation-sensitive acid generator; (ii) a vinyl polymer or copolymer formed by the polymerization of one or more monomers, including a monomer selected from acrylate, methacrylate, hydroxystyrene (optionally substituted with C
1-6
alkyl), and C
5-20
cyclic olefin monomers (preferably C
7-15
, e.g., norbornene and tetracyclododecane); and (iii) a compound having a silylethoxy acid-cleavable group; and (b) a polymeric organic underlayer. The ethoxy portion of the silylethoxy group is optionally substituted with C
1-6
alkyl, phenyl, or benzyl. The vinyl polymer may optionally comprises other types of monomers known to those skilled in the art. Preferably, the silicon-containing, acid-cleavable group is bonded to the vinyl polymer.
The resist is chemically amplified in that the proton produced in the photoreaction of the radiation-sensitive acid generator initiates catalytic cleavage reactions of the acid-cleavable group independent of the radiation, thereby increasing the effective quantum yield to values above 1.
The silicon-containing, acid-cleavable group consists of silicon atoms, carbon atoms, hydrogen atoms, and one oxygen atom. Suitable acid-cleavable silylethoxy groups have the formula R
1
R
2
R
3
Si (CR′
2
)
2
O, where each R′ is independently hydrido, C
1-6
alkyl (e.g., methyl), phenyl, or benzyl optionally substituted with C
1-6
alkyl and R
1
, R
2
, and R
3
are each independently hydrido, alkyl preferably lower (C
1-6
) alkyl or (R
4
)
3
Si, where each R
4
is independently hydrido or lower alkyl. Preferred silicon-containing, acid-cleavable groups are C
1-6
alkyl silylethoxy; mono, bis, tris (C
1-6
alkyl silyl) silylethoxy. The bridging alkylene (CR
2
′)
2
group is important in that it enables nonhydrolytic, solid state, acid-catalyzed cleavable of the acid-cleavable group which is believed to occur through the formation of a beta silyl carbocation as a cleaving group. The top imaging layer of the present invention is not crosslinked (uncrosslinked) and has a high silicon content to give enhanced stability against reactive ion etching. The top imaging layer is also hydrolytically stable and the top layer composition has enhanced shelf stability.
In one embodiment of the present invention, the top imaging layer comprises a radiation-sensitive acid generator and an acrylate or methacrylate polymer having an acid-cleavable, silicon-containing group (e.g., silylethoxy) attached to the carbonyl of the acrylate or methacrylate.
The silicon-containing acrylate or methacrylate can be used as a homopolymer or can be a copolymer. Suitable comonomers include (i) acrylate or methacrylate monomers with lower alkyl ester groups, (ii) acrylic acid or methacrylic acid monomers, (iii) methacrylate or acrylate monomers with other types of acid labile ester groups such as tertiary alkyl esters (t-butyl esters), or (iv) hydroxystyrene.
In an alternative embodiment, the polymer in the top imaging layer can be an alicyclic polymer having an alicyclic backbone (e.g., formed from cyclic olefin monomer) where the silicon-containing, acid-cleavable group (e.g., silylethoxy) is preferably bonded to a carbonyl group attached to the cycloalkyl ring. Suitable monomers include functionalized norbornene and tetracyclododecane.
In another alternative embodiment, the top imaging layer comprises a vinyl polymer, an acid generator, and a compound having a silicon-containing, acid-cleavable group. Suitable compounds are bisphenol A and steroids (e.g., substituted androstane as disclosed in Allen et al., U.S. Pat. No. 5,580,694, issued Dec. 3, 1996, the disclosure of which is incorporated herein by reference for all purposes). Other suitable compounds will be known to those skilled in the art.
In another alternative embodiment, the polymer in the top imaging layer is polyhydroxystyrene where the silicon-containing, acid-cleavable group (e.g., silylethoxy) is bonded directly to the aromatic ring (e.g., as a protected hydroxy substituent).
The second component of the top imaging layer is the radiation-sensitive acid generator. Upon exposure to radiation, the radiation-sensitive acid generator generates an acid. Suitable acid generators include triflates (e.g., trip

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