Two approaches that control the overflow of silylated material that can occur subsequent to surface imaging of acid-hardened resists are introduced. Treatment of the resist surface with a cross-linking agent [bis(dimethylamino)dimethylsilane] prior to silylation can produce a surface layer with the physical integrity to constrain silylated material. Alternatively, the unexposed areas of the resist may be partially removed by development with a basic solution. The surface depressions thus produced allow volume expansion to occur during silylation without causing overflow.
KEYWORDS: Silicon, Photoresist processing, Semiconducting wafers, Scanning electron microscopy, Reactive ion etching, Etching, Manufacturing, Image processing, Very large scale integration, Deep ultraviolet
Many approaches to surface imaging rely upon selective incorporation of silicon into an already imaged resist layer. SAHRTM (silylated acid hardened resist) obtains its selectivity by a lower rate of silicon incorporation into exposed and crosslinked areas, providing a positive tone image after RIE development. Two difficulties with the practical implementation of this approach have been the overflow of silylated material onto crosslinked areas, and reduced silicon incorporation in small openings. We have found that surface treatment with a bifunctional silylation agent (the `two gas process') can prevent overflow, and that removing part of the resist layer with dilute tetramethyl ammonium hydroxide (TMAH) (the `presilylation develop process') minimizes overflow and improves silicon incorporation in small features. With a predevelop step, feature size linearity is obtained below k1 equals 0.7, with uniformity and repeatability consistent with VLSI manufacturing practices.
A variety of analytical and process control techniques have been employed during process development activities for a 0.5 micrometers deep UV positive tone surface imaging process. Examples of applications of these methods for identification of primary positive tone surface imaging issues and process optimization for enhancement of ultimate resolution are described. Advantages and limitations for each technique are discussed.
A new i-line negative resist has been developed which exploits acid-catalyzed cross-linking chemistry in combination with a sensitizing chromophore and a light absorbing dye. During exposure acid is generated by excitation energy transfer from the sensitizer to a halogen- containing compound. Concurrently, the highly absorbing dye is bleached. The optical component of this resist can be modeled as follows: the imaginary part of the complex refractive index is proportional to A1M1 + A2M2 + B, where M1 is the bleachable dye concentration, M2 is the sensitizer concentration, B is the fixed absorption and A1 and A2 are the corresponding Dill coefficients for bleachable absorbance. The kinetics of the bleachable dye and sensitizer decays are given by (delta) Mi/(delta) t equals -CiMiI. The final acid concentration is a nonlinear function of these concentrations and can be expressed as H equals [(1-M2) + (kappa) (1-M1)]/(1 + (kappa) ) with (kappa) determined experimentally. The exposure is computed by our spectral element numerical method. As exposure terminates, post exposure baking (PEB) takes place, similar in form to the crosslinking of the deep-UV product MegapositR SNRTM 248 Series photoresist. This step is modeled via reaction diffusion equations, producing a nonsoluble monolith due to cross-linking of the polymers. The final profiles are obtained by solution of a system of reaction-diffusion equations and are described graphically using a novel dynamic triangulation algorithm. A comparison between simulated and actual micrographs is given and process latitude and CD control discussed.
G- and i-line diazonaphthoquinone/novolak photoresist films are surface imaged with g-line, i-line and deep-UV steppers. Following optical exposure, the resist film is treated with aqueous solutions which deposit a catalyst for electroless metal deposition. Wet development of the exposed and catalyzed photoresist results in selective removal of catalyst along with the exposed portion of the underlying photoresist. Upon immersion in an aqueous electroless plating solution, metal is selectively deposited on the unexposed photoresist which is still bearing catalyst to yield a positive-tone plasma etch mask. Oxygen magnetron-enhanced reactive ion etching (O2 MERIE) provides high polymer etch rates (approximately equals 1 micrometers /min) with excellent selectivity (> 300:1) to 70-170 angstrom Ni films. In addition, large ion fluxes produce highly anisotropic etch profiles for faithful pattern transfer. The process has achieved 0.30 micrometers resolution with a 6:1 aspect ratio at 248 nm (0.35 NA). Printing of 0.40 micrometers lines and spaces has been achieved at i-line (0.45 NA) over Al steps.
This paper describes the evaluation of several phenothiazine and benzophenothiazine derivatives which
are useful as i-line and g-line photosensitizers for a class of chemically amplified crosslinked resists. Data
supporting an electron transfer mechanism of sensitization from the excited state of the sensitizer to the
acid generator are provided. Initial lithographic screening demonstrates the potential for both high
sensitivity and submicron resolution in these systems.
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