Prebake Temperature Research Articles

The formation of resist profile by TMSDEA-treatment and dry development based on oxygen-helium RIE

Silylation and dry development are the key processes of DESIRE technique. In the present work, the silylation of resist has been investigated as a function of prebake temperature and TMSDEA concentration. The effect of neutral scatterer, He, on anisotropy of resist profile in dry development has been studied by using optical emission spectroscopy. The dependences of anisotropy and etch rate on RF power and pressure are also described.

Multilayer resists with variable layer parameters for submicron lithography

Abstract The properties of methyl acrylate-methacrylic acid copolymer used as a resist in submicron lithography have been investigated. Besides high sensitivity, contrast and resolution, the resist exhibits the nonmonotonic dependence of sensitivity, contrast and resolution the resist exhibits nonmonotonic dependence of sensitivity on the prebake temperature. This allows fabrication of multilayer resist films with different ratios of layer sensitivity and so permits control of resist structure profiles.

Towards an optimized image reversal process for half micron lithography

A 0.5 μm process was developed based on image reversal technology, using AZ5214-E, followed by l-line exposure, post exposure bake, flood exposure and track development. Starting with a prebake temperature of 90 °C, several problems were encountered. One problem was that only 0.6 μm lines and spaces could be resolved. Another problem was distortion at the line ends, which was accompanied by a relatively large corner radius in larger features. However, using a prebake of 130 °C, 0.5 μm lines and spaces were resolved with good latitudes for dose, post exposure bake temperature and develop time. The focus latitude for 0.5 μm features is acceptable. Moreover, both the distortion at the line ends is diminished and the corner radius is reduced. Patterns in the range 0.5–2.0 μm can be reproduced without using a mask bias. The results are interpreted in terms of the physical chemistry of the process.

ステンレス鋼の放出ガス速度の低減 ベーキング温度，履歴の効果

Reduction of outgassing from stainless steels by baking is examined as a function of baking temperature and previous baking history. The effect of baking and prebaking temperature and subsequent air exposure on the outgassing reduction is discussed in terms of the changes in the surface compositions determined by Auger electron spectroscopy and in the desorption characteristics of adsorbed gases by thermal desorption spectra.The significance of the surface change in the outgassing reduction is pointed out. The surface compositional changes cannot fully explain the ougassing reduction and the changes in the structure and thickness of the surface oxide layer must be taken into account. This surface oxide layer is suggested to play a critical role in determining the desorption characteristics of adsorbed gases from the surface.This surface oxide layer also contributes to the outgassing reduction during the repeated air exposure/baking cycles. Full characterization of the surface oxide layer may result in more effective process of outgassing reduction leading to the establishment of extreme high vacuum technique.

Characterization of electron-beam exposed optical resist

The behavior of Hitachi RD‐2000N negative resist under electron‐beam exposure at high‐beam current density on the AEBLE‐150 has been characterized and modeled through dissolution measurement on the Perkin–Elmer development rate monitor (DRM) and SAMPLE simulation. A three parameter quantitative dissolution rate versus deposited energy model has been established. This model when combined with SAMPLE, can accurately predict the resist thickness versus log dose data and simulate resist profile development. The high‐beam current density exposure available with AEBLE‐150 give a noticeable increase of resist thickness top loss and rough resist surface topography at 25 Å/cm2. This change in development behavior is consistent with thermal heating of the top of the resist during exposure. Initial data on the AEBLE‐150 showed lower contrast (γ) and higher sensitivity than has been reported previously. A factorial experiment of developer type, developer temperature, and prebake temperature showed that they are not the main contributing factors for the discrepancy observed. A combination of process factors especially freshness of developer and time between exposure and development appears to account for this difference. Comparison of simulation and scanning electron micrographs of developed resist profiles gives generally good agreement.

Deep UV Photoresist Containing Ortho‐Nitrobenzylsilylether Structure in the Main Chain

Photoresist containing Si, which works as a positive resist, was developed. The photoresist consists of an ortho‐nitrobenzylether group and silyl moiety. Six polymers were newly synthesized and characterized. Quantum yields for model compounds of these polymers were around 0.2 and varied, depending on the ortho‐nitrobenzylether structure. After exposure, the photoresist was developed with tetramethylammonium hydroxide solution in alcohol or in alcohol. Sensitivity depended on the structure of the polymers, prebake temperature, and developers. reactive ion etching durabilities for these polymers were about five to ten times greater than conventional cresol novolak resin resist.

Relationship between electron sensitivity and chemical structures of polymers as EB resists: Poly(lactam thioether) as new positive EB resists

AbstractPoly(lactam thioether) was synthesized from tetrahydro‐1,4‐thiazepine‐5(4H)‐one by a ring opening reaction under various conditions and was evaluated as positive electron beam(EB) resist. It was found that poly(lactam thioether) was easily decomposed by EB irradiation. The decomposition by EB exposure may be attributed to cleavage of CS bonds in the polymer chains. The sensitivity of poly(lactam thioether) was influenced by prebake temperature, molecular weight, and developer, a high sensitivity of 5.3 × 10−6 coulomb/cm2 was observed with a good resolution of less than 1 μm. Poly(lactam thioether) showed a high sensitivity and a high resolution, and is suitable as a positive EB resist.

High performance positive photoresists

An attempt was made to improve the sensitivity and heat resistance of positive photoresist applicable to very large‐scale integrated (VLSI) semiconductor processing. It was found out that, in general, when the lithographic sensitivity of resist was made higher, film thickness retention and heat resistance were lowered. A study was made on how to raise sensitivity without decrease in film thickness retention and heat resistance. It was necessary to design a new type of novolac resin that has a molecular structure and a molecular weight different from the existing materials. Many kinds of cresol‐formaldehyde type novolac resins were synthesized and evaluated. Such items as the isomeric structure of cresol, the position of the methylene bond, and the influence of molecular weight were investigated. As a result of the optimization of these items, a number of different resist materials that exhibit improved characteristics in sensitivity, film thickness retention, and/or heat resistance were obtained. It is also remarkable that the introduction of the new polymer design enabled to make the allowance of the operating conditions much wider at various points of resist work, including prebaking temperature, light exposure time, developing time, and developing temperature, compared to the present commercially available products. This new material not only makes it possible to raise the throughput of the stepper exposure machine and developing machine, but the wider allowance of processing conditions assures higher yield of the circuits.

Characterization of diazo-type photoresists using e-beam exposure and metal–ion-free developers

The performance characteristics of diazo‐type positive photoresists are explored using e‐beam exposure and metal–ion‐free developers. For Tokyo Ohka OFPR1000, resist profiles with straight sidewalls are obtained while maintaining sufficient resist thickness. The effects of prebake and developer temperature on the solubility rate of OFPR1000 are investigated. A higher contrast is obtained with the resist prebaked at 65 °C and developed at 23 °C. Higher prebake temperatures and lower or higher developer temperatures result in a lower contrast. Submicron resolution can be obtained.

Analytical model of positive resist development applied to linewidth control in optical lithography

A new analytical model is described for positive resist development. Using the model, the linewidth that will be obtained at any development time is calculated directly from the incident image. The accuracy of the analytical model is verified by comparison to a numerical simulation of positive resist development (SAMPLE). The analytical model is used to obtain expressions for the rate of change of linewidth with respect to both process parameters and resist parameters. Some of the process parameters that are considered are developer time and temperature, prebake time and temperature, and exposure dose. Some of the resist parameters that are considered include sensitivity, contrast, absorption, and developer concentration.

Autodoping in Silicon Epitaxy

Vertical and lateral autodoping in silicon epitaxy deposited in a vertical pancake‐type reactor were examined as a function of pre‐epitaxial bake cycle, dopant type, source gas, and growth parameters. Boron, phosphorus, arsenic, and antimony were used as dopant elements to form a localized buried layer at the center of substrates. Silane, dichlorosilane, and silicon tetrachloride were used as the silicon source for epitaxial growth. The results show that higher prebaking temperature produces more lateral autodoping for boron and phosphorus, while the opposite holds for arsenic and antimony. Autodoping in both vertical and lateral directions decreases with increasing prebake time. A continual decrease in lateral autodoping is found with increasing growth rate for phosphorus; for arsenic, only a slight difference is noticed in the growth‐rate range studied. Phosphorus and arsenic show a similar trend at the deposition temperature of lateral autodoping, i.e., autodoping decreases at first, then increases with increasing temperature. For all the dopants studied, vertical and lateral autodoping decrease with increasing number of chlorine atoms in the source gases.

Evaluation of poly(allyl methacrylate)‐co‐(hydroxyethyl methacrylate) as negative electron‐beam resist

AbstractPoly(allyl methacrylate)‐co‐(hydroxyethyl methacrylate) has been evaluated as a high‐sensitivity, high‐resolution, high temperature‐resistant negative electron resist. The effects of molecular weight and polydispersity of the copolymer on its lithographic performance as an E‐beam resist were studied. The sensitivity of the copolymer is nearly constant in the weight‐average‐molecular‐weight range of 50,000 to 75,000, and it gradually decreases with a decrease in molecular weight. As expected for a negative resist, the resist contrast increases as the polydispersity is decreased. The sensitivity curve shape of the polymer was independent of the prebake temperature, which varied from 70 to 110°C, and of the various developers used. The exposed coating requires vacuum curing for image optimization. Resolution of 0.5 μm line/space pairs was obtained from a 0.6 μm thick resist by exposing the resist to 10 keV electrons with either a raster‐scan‐type or vector‐scan‐type electron‐beam exposure machine. After postbaking at 170°C, the resist had good resistance to both chemical etching and dry etching. The plasma‐etch resistance was about twice that of PMMA.