Graft polymers and use thereof

Details Graft polymers and use thereof Graft polymers and use thereof

1999-07-12

2001-03-06

Baxter, Janet (Department: 1752)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S360000, C524S379000, C524S391000, C524S504000

Reexamination Certificate

active

06197896

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to certain solutions of graft polymers which can be used as photoresists and which exhibit enhanced resistance to plasma and especially to Cl/O plasma used in reactive ion etching. The present invention is concerned with the compositions as well as their use in lithography. For instance, the materials of the present invention are suitable for use in device fabrication on all optical, e-beam, x-ray and ion-beam lithography tools.
The present invention is also concerned with certain graft polymers that exhibit increased hydrophobicity or increased hydrophilicity depending upon the characteristics of the moiety grafted onto the polymer. Moreover, graft polymers of the present invention can be grafted so as to create a permanent graft of a dye thereon.
BACKGROUND OF INVENTION
In the manufacture of patterned devices and especially microelectric devices, the processes of etching different layers which constitute the finished product are among the most crucial steps involved. One method widely employed in the etching process is to overlay the surface to be etched with a suitable mask.
The mask is typically created by imagewise forming a pattern of photoresist material over those areas of the substrate to be shielded from the etching. The photoresist is normally formed of a polymeric organic material. The pattern is formed by imagewise exposing the photoresist material to irradiation by photolithographic techniques. The irradiation employed is usually x-ray, UV radiation, or electron beam radiation.
Photosensitive materials and/or compositions are either positive-acting (i.e. photosolubilizable) or negative-acting (i.e. photoinsolubilizable or photocrosslinkable). Positive-working (photo)sensitive compositions are rendered soluble (or developable) by actinic radiation (deep-near UV, x-ray or electron-beam) and can be removed using selective developing solutions leaving unexposed areas intact. Negative-working (photosensitive compositions are those which become insoluble upon exposure to actinic radiation. Selected solutions can dissolve and remove the unexposed areas of the composition while leaving the exposed portions intact. Development of such exposed materials yields negative tone images.
Concerning positive working resists, it is well known in the art that the photochemical formation of carboxylic acids, be it by amplified means such as a catalytic acidic-decomposition of a tertiary butyl ester, or as in the case of the photochemical decomposition of 1,2-naphthoquinone diazides, can be employed to produce high resolution and high efficiency resists. This type of reaction is being relied upon extensively in the production of positive working resists.
The manufacture of integrated circuits and other patterned devices relies primarily on resist materials that enable the formation of high resolution patterns. In the search for materials and methods for formation of patterns below 0.25 microns, it is recognized that such patterns require exposure sources based on UV radiation below 248 nm, or on x-ray, or on e-beams. Likewise, it is essential to employ resist materials suitable for use with short wavelengths sources. In the case of UV radiation, it might be convenient to use excimer laser sources that produce radiation at 193 nm.
U.S. patent application Ser. No. 08/700,348 discloses certain polymer compositions that when exposed to actinic light such as UV radiation below 240 nm, or soft rays, x-ray or e-beam, undergo a photochemical reaction that leads to the formation of pendant carboxylic acid groups, which are base soluble. This photochemical reaction is very efficient and can be used for high resolution positive resists.
In particular, the resists are non-amplified polymers having pendant recurring groups selected from the group consisting of
—COO—CH
2
—CH(OH)—(CH
2
)
x
—H, wherein x is 0-20;
—COO—CH
2
—CH(OH)—(CH
2
)
y
—HE—(CH
2
)
z
—H; and mixtures thereof,
wherein HE is O or S, and each y and z individually is 1-18, and mixtures thereof.
U.S. patent application Ser. No. 08/717,644 discloses using certain copolymers for minimizing possible water absorption of the non-irradiated regions of the resist film. These copolymers are from monomers consisting essentially of:
1) CH
2
CHCOOCH
2
CHOH(CH
2
)
n
H and/or CH
2
C(CH
3
) CHOOCH
2
CHOH(CH
2
)
n
H, wherein n=0 to 10; and
2) CH
2
CHCOO(CH
2
)
n
H and or
CH
2
C(CH
3
) COO(CH
2
)
n
H, wherein n=1 to 10. The amount of 1) is about 75 to about 95, preferably about 80 to about 90, and most preferably about 84 to about 87 wt. % and the amount of 2) is about 5 to about 25, preferably about 10 to about 20 and most preferably about 13 to about 16 wt. %. These weight percents are based upon the total weight of 1) and 2).
The entire disclosures of U.S. patent applications Ser. No. 08/700,348 and 08/717,644 are incorporated herein by reference.
After the photoresist is developed forming the desired mask, the substrate and mask can be immersed in a chemical solution which attacks the substrate to be etched while leaving the mask intact. These wet chemical processes suffer from the difficulty of achieving well-defined edges on the etched surfaces. This is due to the chemicals undercutting the mask and the formation of an isotropic image. In other words, conventional chemical wet processes do not provide the selectivity of direction (anisotropy) considered necessary to achieve optimum dimensional consistent with current processing requirements.
Moreover, such wet etching processes are undesirable because of the environmental and safety concerns associated therewith.
Accordingly, various so-called “dry processes” have been suggested to improve the process from an environmental viewpoint, as well as to reduce the relative cost of the etching. Furthermore, these “dry processes” have the potential advantage of greater process control and higher aspect ratio images. Also, when fabricating patterns having feature sizes below 350 nm, dry etching processes are necessary.
Such “dry processes” generally involve passing a gas through a container and creating a plasma in this gas. The species in this gas are then used to etch a substrate placed in the chamber or container. Typical examples of such “dry processes” are plasma etching, sputter etching, and reactive ion etching.
Reactive ion etching provides well-defined, vertically etched sidewalls.
However, a crucial challenge posed by the reactive ion etching relates to providing photoresist compositions that are sensitive to the radiation employed in its imaging procedure but resistant to the reactive ion etching. A particularly harsh environment for the resist material involves those RIE processes using Cl/O plasma. Most resist materials do not survive long enough in this environment to provide proper protection. The manufacture of optical masks requires a chromium etch step which can be done preferentially by RIE etching. This step requires Cl/O plasma.
However, although the above discussed non-chemically amplified resists based upon the polymers disclosed in U.S. Ser. No. 08/700,348 and 08/717,644 perform quite well lithographically, their resistance to withstand plasma environments and especially Cl/O plasma is not satisfactory.
It has also been found that the available commercial e-beam resists offer little protection in this plasma environment.
In co-pending application U.S. Ser. No. (YO998-421) titanates, zirconium and/or hafnium are added to polymers having hydroxy groups to import improved resistance to reactive ion etching. The addition of these compounds also enhances the development with TMAH, an industry standard, which improves film Tg and hardness.
Furthermore, organic tetra alkyl titanates and titanate chelates such as the series of DuPont products available under the tradename TYZOR® promote crosslinking of polymers that contain active hydrogen groups such as hydroxy, amino, amido, carboxyl and thio groups. The reaction produces resins with improved hardness, solvent resistance and new electrical properties.
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