Andre P. Weill

Comparison of Dry Development Techniques using O2 and SO2/O2 Low-Pressure Plasmas

A parametric study of the pattern transfer step in a trilevel resist system using oxygen-based plasmas has been performed using a distributed electron cyclotron resonance reactor with independent rf biasing. In pure oxygen plasmas, critical dimension loss is always present. The mechanisms most likely to be responsible for these defects during the pattern transfer process are presented and discussed. A novel plasma etching process based on sidewall passivation by sulfur is proposed using SO2/O2 mixtures. Perfect anisotropy with negligiable critical dimension loss is obtained at room temperature.

New dry-development process of trilayer resist systems for advanced lithography

A parametric study of the pattern transfer step in a trilevel resist system using oxygen-based plasmas has been made using a distributed electron cyclotron resonance reactor with independent rf biasing. In pure oxygen plasmas, critical dimension loss is always present in the O2 pressure and ion bombardment energy ranges investigated. The mechanisms most likely to be responsible for these defects during the pattern transfer process are presented and discussed. Perfect anisotropy can only be obtained at substrate temperatures below -60 degree(s)C. A novel plasma etching process based on sidewall passivation by sulfur is proposed using SO2/O2 mixtures. Perfect anisotropy without critical dimension loss is obtained at room temperature by using an 80% SO2/20% O2 mixture and a moderate ion bombardment energy. The ultimate resolution using this new plasma process in conjunction with deep UV exposure and a phase-shift mask is presented.

The novolak calibration method applied to the GPC analysis of the UV photoresists

Abstract This paper first summarizes the influence of the molecular weight of the novolak-based photoresists on the different microlithographic steps: film deposition, soft bake, exposure, and hard bake. The second part deals with the use of gel permeation chromatography (GPC) for characterizing the photoresists. In order to convert elution curves into molecular weight distribution information, a calibration method is needed. The usual calibration techniques are poorly adapted to the analysis of photoresists. The proposed calibration method uses the first observable low molecular weight oligomers on the chromatogram as a standard. It is shown that experimental results are not dependent on the column set.

An industrial plasma process for avoiding charge effect

Insulating materials such as photoresists retain charges during electron or ion exposure. The ultimate performances of techniques such as scanning electron microscopy (SEM), trilayer e‐beam lithography, or plasma etching can be strongly affected by this phenomenon: observations of highly resolved resist patterns and the subsequent dimensional measurements by SEM are limited by significant charge effects; resist charge during trilayer electron‐beam exposure can produce considerable pattern placement errors; surface charging is also reported to damage etching profiles and to produce microloading effects during plasma etching. Techniques such as metal deposition, use of intrinsically conducting polymers, or Ar+ or H+ high energy implantation are mentioned among others for reducing the electrical resistance of the photoresist patterns. However, due to several major drawbacks (metallic contamination, nonavailability of materials, and global cost of the process), none of these methods has been accepted today at...

Plasma etching of silylated photoresist: a study of mechanisms

We have studied the relevant parameters involved in the dry development of silylated polymers. In particular the influence of substrate temperature, ion energy, and atomic oxygen concentration is investigated. Critical dimension loss is demonstrated to depend upon silylation angle, sputtering rate of the silylated polymer, and development time. Anisotropic etch profiles are argued to be due to a compromise between critical dimension loss and isotropic etching of the unsilylated polymer. Improvements of the process are suggested.

Dry development of silylated resist: influence of substrate temperature

During the last few years, silylation processes have been extensively studied. In particular, the mechanisms of silicon incorporation in the resist have been discussed. However, the importance of the dry etching step, which allows the image transfer in the resist, has often been neglected. In this paper it is shown that under standard dry etching conditions, the slight increase in the substrate temperature leads to the liquefaction of the silylated area which then flows down onto the sidewalls of the patterns.

The role of self diffusion in the dry development and plasma durability of polymers

Abstract The degradation of polymer layers during plasma etching is studied as a function of their viscoelastic properties. Above Tg, the mobility of polymer chains allows the extension of surface degradation to the entire thickness in a self diffusion mechanism. This effect is particularly important in the case of low molecular weight polymers such as novalaks. The same effect can affect silicon transport during silylation processes.

Dry development and plasma durability of resists: melt viscosity and self-diffusion effects

The degradation mechanisms of novolaks and high molecular weight polymers during plasma etching are investigated. The mechanical effects of ion bombardment are shown to generate surface degradation whereas the thermal effects allow the extension of the degradation to the bulk through self diffusion of chains. The various experiments clearly demonstrate the role of chain mobility and viscoelastic properties in the bulk degradation of polymers. If self diffusion, and this degradation, can easily occur with low molecular weight polymers, chain scission in high molecular weight polymers can lead to the same result. Degradation can be avoided by crosslinking polymer chains before or during plasma etching. Experiments with several commercial resist are given as an example.

Concept Of Buried Mask And Its Realisation

A new method for fabricating photomasks is proposed. The mask is prepared by burying the absorbent patterns inside the transparent photoplate instead of depositing them on the surface of the photoplate. After imaging and etching trenches into the glass substrate, an absorbent material is set into them. Two different ways of filling in these holes are considered: planarisation and lift-off. Various advantages of this technique are expected, namely high resolution. This paper presents results obtained by vacuum contact printing of positive and negative novolak based photoresists exposed through buried masks.

Characterization of commercial dyes for PMMA bilayer systems

The absorption properties of the well-known coumarin dyes are evaluated at the 436 nm g line for PMMA bilayer systems. Their properties are compared with those of other commercial products. The main requirements to be met are : good solubility in PMMA solutions, an absorption spectrum adapted to bilayer processes and thermal stability. Several azo dyes have been selected from among a large number of compounds and are proposed as an advantageous alternative to coumarin dyes. The implementation of one of these selected dyes in a bilayer process is given as an example. A good dimensional control is obtained for 1 μm lines over critical topographies.