Description of the Prior Art The need for constant reduction in critical dimensions (CD) of integrated circuits has been the driving force for next generation lithography. If the semiconductor industry continues at its historical pace of packing more information on a chip, lithography using shorter wavelength (193 nm) will need to be introduced in production.

As a result, integrated circuit manufacturers and equipment vendors are currently in the process of qualifying materials and processes for this type of technology.

Lithography using 193 nm wavelengths faces numerous challenges, including the problem of photoresist pattern collapse at sub-90 nm feature sizes. Several material and process solutions have been proposed to suppress the collapse of patterns including adding surfactants to photoresist developers and post-develop rinse liquids (like de- ionized water) to reduce surface tension and therefore reduce the capillary forces acting on the resist feature, freeze drying after the develop and rinse steps, adding modulus- enhancing materials to 193 nm photoresist compositions, and reducing the resist thickness. However, these methods assist in reducing collapse but do not completely prevent it. Furthermore, reducing the resist thickness results in very little resist being available after the bottom anti-reflective coating open etch process which is undesirable.

Hexamethyl disilazane (HMDS) is a commonly used adhesion promoting layer in the semiconductor industry. Typically, an HMDS vapor is generated and then deposited on bare silicon or other substrate to form a continuous film. Bottom anti-

reflective coatings are widely used as underlayers for the photoresist in order to eliminate problems associated with reflective substrates like silicon, polysilicon, etc., and planarize topography in order to achieve tighter CD control. Bottom anti-reflective coatings have somewhat eliminated the use of HMDS since bottom anti-reflective coating layers can also act as adhesion layers besides primarily acting as anti-reflective layers.

The silicon surface is a high energy, hydrophilic surface, and conventional photoresists have difficulties adhering to silicon. As demonstrated in Scheme A, HMDS reacts with the moisture present on the surface to form covalent bonds (Si-O- Si). However, even with the HMDS layer, it has still been necessary to coat the silicon substrate with a bottom anti-reflective coating layer to reduce problems associated with reflective substrates. fizz 2-Si-OH + N-H3 C3 silicon silicon surface treated with HMDS Thus, there is a need for anti-reflective coating compositions having improved adhesion between the photoresist and the anti-reflective coating film so that collapse of the photoresist patterns is substantially reduced and more preferably prevented.

SUMMARY OF THE INVENTION The present invention overcomes the problems of the prior art by broadly providing new anti-reflective coating compositions which have improved adhesion to photoresists. The compositions comprise polymers which include pendant silicon atoms in the polymer side chains, thus improving adhesion of photoresists to the bottom anti-reflective coating film and preventing collapse of photoresist patterns.

In more detail, the inventive compositions comprise a polymer dispersed in a solvent system. The polymer comprises recurring monomers having the formula

polymer backbone , t l Z z where Z has the formula wherein: each R' is individually selected from the group consisting of alkyls (preferably C1-C8, and more preferably Cl-C3), alkoxys (preferablyCl-C8, and more preferablyCl-C3), esters, and ethers; n is 0-4; and each R"is individually selected from the group consisting of alkyls (preferably Cl-C8, and more preferably Cl-C3), alkoxys (preferably Cl-C8, and more preferably C1-C3), halogens, substituted and unsubstituted phenyl groups, and-OSi (R"') !")., where: m is 1-3; and each R"'is individually selected from the group consisting of alkyls (preferably C1-C8, and more preferably Cl-C3) and alkoxys (preferably C1-C8, and more preferably C1-C3).

Particularlypreferred R'groups include-CH2CH2CH2-,-CH2-, and -CH2CH2O-.

Particularly preferred R" groups include -OCH3, -CH3, -OCH2CH3, -CH2CH3, -Cl, -OSiOCH3,-OSi (CH3) 3,-OSiCH2CH3, and-OSiOCH2CH3.

In another embodiment, the polymer includes light attenuating compounds (i. e., dyes or chromophores) bonded thereto, with the light attenuating compounds including at least one Si atom.

In one embodiment, preferred recurring monomers have the formula where Z is as described above. Preferred examples of monomers having this formula are

Regardless which of the foregoing monomers is utilized, it should be present in the polymer at a level of from about 5-50% by weight, and preferably from about 5-20% by weight, based upon the total weight of the polymer taken as 100% by weight.

Finally, while can include any polymer, preferred polymers are those selected from the group consisting of acrylic polymers (e. g. , acrylates, methacrylates), vinyl polymers, and mixtures thereof. It is preferred that the polymer include crosslinkable hydroxy (-OH) groups, amine (-NEI2) groups, amide (-NHCO) groups, epoxy groups, and carboxylic (-COOH) groups.

It is also preferred that the average molecular weight of the polymer be from about 500-100,000 Daltons, and more preferably from about 5,000-50, 000 Daltons.

The polymers are commercially available, or they can be formed by polymerizing the desired monomers according to known polymerization techniques or grafting (i. e., chemically attaching) a compound comprising the desired groups to a polymer.

These polymers can then be utilized to make compositions (e. g. , anti-reflective coatings) for use in microlithographic processes. The compositions are formed by simply dispersing or dissolving the polymer (s) in a suitable solvent system, preferably at ambient conditions and for a sufficient amount of time to form a substantially homogeneous dispersion. Preferred compositions comprise from about 0.5-20% by weight of the polymer solids, and preferably from about 1-5 % by weight of the polymer solids, based upon the total weight of the composition taken as 100% by weight.

The solvent systems can include any solvent suitable for use in the microelectronic manufacturing environment. Preferred solvent systems include a solvent selected from the group consisting of propylene glycol monomethyl ether (PGME), propylene glycol monomethyl ether acetate (PGMEA), ethyl lactate, propylene glycol, n-propyl ether (PnP), cyclohexanone, y-butyrolactone, and mixtures thereof. Preferably, the solvent system has a boiling point of from about 50-150°C.

Any additional ingredients are also preferably dispersed in the solvent system along with the polymer. Examples of suitable additional ingredients include

crosslinking agents, catalysts, and surfactants. Preferred crosslinking agents include aminoplasts (e. g., POVTDERLRW 1174, Cymel products), multifunctional epoxy resins (e. g., MY720, CY179MA, DENACOL), anhydrides, and mixtures thereof. The crosslinking agent should be present in the composition at a level of from about 0.2-2% by weight, and preferably from about 0. 5-1. 0% by weight, based upon the total weight of the composition taken as 100% by weight. Thus, the compositions of the invention should crosslink at a temperature of from about 100-250°C, and more preferably from about 100-180°C.

Examples of preferred catalysts include sulfonic acids (e. g., p-toluenesulfonic acid, styrene sulfonic acid), thermal acid generators (e. g. , pyridinium tosylate), carboxylic acids (e. g. , trichloroacetic acid, benzene tetracsarboxylic acid), and mixtures thereof. The catalyst should be present in the composition at a level of from about 0.01-0. 10% by weight, and preferably from about 0.02-0. 05% by weight, based upon the total weight of the composition taken as 100% by weight.

The method of applying the inventive anti-reflective compositions to a substrate (e. g. , Si, Al, W, WSi, GaAs, SiGe, Ta, and TaN wafers) simply comprises applying a quantity of a composition hereof to the substrate surface (either a planar surface or one comprising vias or holes formed therein) by any conventional application method, including spin-coating. The layer should then be heated to at least about the crosslinking temperature of the composition (e. g. , about 100-200°C) so as to cure the layer having a thickness of anywhere from about 250-2000 A where the thickness is defined as the average of 5 measurements taken by an ellipsometer. A photoresist can then be applied to the cured material, followed by exposing, developing, and etching the photoresist.

Anti-reflective coatings according to the invention have high etch rates. Thus, the cured anti-reflective coatings have an etch selectivity to resist (i. e. , the anti- reflective coating layer etch rate divided by the photoresist etch rate) of at least about 0.8, and preferably from about 1.0-1. 6 when HBr/02 (60/40) is used as the etchant and a 193 nm photoresist is used. Additionally, at about 193 nm a cured layer formed from the inventive composition and having a thickness of about 300 A will have a k value (i. e. , the imaginary component of the complex index of refraction) of at least about 0.2,

and preferably at least about 0.6. Finally, the coatings can be used to obtain a dense line space resolution of about 90 nm with 193 nm photoresists.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 depicts a scanning electron microscope (SEM) photograph showing cross-sectional views of a prior art silicon wafer which has experienced photoresist collapse; and Fig. 2 shows an SEM photograph depicting cross-sectional views of a silicon wafer coated with an anti-reflective coating composition according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES The following example sets forth preferred methods in accordance with the invention. It is to be understood, however, that this example is provided by way of illustration and nothing therein should be taken as a limitation upon the overall scope of the invention.

1. Preparation of Polymer Mother Liquor In this procedure, 15.0 g (85% by mol. wt. ) of an acrylate monomer (2-hydroxy 3-phenoxypropyl acrylate ; obtained from Toagesei Chemical Co. , Japan), 2.95 g (15% by mol. wt. ) of a silane functional methacrylate monomer (methacyloxy propyltrimethoxy silane; obtained from Gelest, Inc.), and 0.1795 g of an initiator (azodiisobutyronitrile; obtained from Aldrich Chemical Co. ) were dissolved in 72.51 g of PGME. The monomer solution was approximately 20% by weight solids and was stirred at 70°C for 24 hours.

2. Formulation of the Anti-reflective Coatirag An anti-reflective coating was formulated by mixing 10.0 g of the polymer mother liquor prepared in Part 1 of this example with 1.264 g of a crosslinker (POWDERLINK 1174) and 0.051 g of a catalyst (p-toluenesulfonic acid) in 153.94 g of a 10: 90 PGME: PGMEA solvent mixture.

3. Film Properties The product was spincoated (2500 rpm/60 sec) onto silicon wafers followed by baking at 205°C for 60 sec using a vacuum hotplate. Film thickness measurements were taken using an ellipsometer while the optical properties of the film were determined using a J. A. Woollam VASETM (variable angle spectroscopic ellipsometer).

The n value of the film was 1.74, and the k value was 0.52 4. Photolithography For comparison purposes, Fig. 1 shows the photoresist collapse experienced with prior art anti-reflective coating compositions. With the inventive composition of this example, photolithography was carried out using an ArF photoresist with a target critical dimension of 90 nanometers for lines and spaces. As shown in Fig. 2, the imaging performance was excellent, and all of the lines were standing with no collapse observed. This was due to the enhanced adhesion between the anti-reflective coating and the photoresist.