A resist exposed to a micron or sub-micron pattern of highly absorbed ion beams forms a highly crosslinked barrier layer in the exposed regions of the resist surface. The complementary surface regions are silylated in a silicon-containing reagent, and the exposed regions are then removed by a plasma etch. Pattern definition is enhanced by limiting the exposure and the silylation to the surface of the resist. The process allows feature definition below 1000 Angstroms using a relatively inexpensive single element low energy ion source.

Positive resist pattern formation through focused ion beam exposure and surface barrier silylation

A phenolic resist without photoadditives achieves enhanced sensitivity when exposed to patterned short wavelength radiation to form a highly crosslinked barrier layer in the exposed regions of the resist surface. The complementary surface regions are silylated in a silicon-containing reagent, and the exposed regions are readily removed by a oxygen RIE plasma. The laser exposure is a reciprocal process allowing precise control. Pattern definition is enhanced by limiting the exposure and the silylation to the surface of the resist.

Method of patterning a phenolic polymer film without photoactive additive through exposure to high energy radiation below 225 nm with subsequent organometallic treatment and the associated imaged article

5 – Plasma Etching of Organic Polymers

The kinetics of rise and decay of ground‐state atomic oxygen was investigated in a low‐pressure O2 radio‐frequency discharge. The ground state of O was monitored using laser‐induced‐fluorescence spectroscopy. The discharge was operated in two modes: a continuous mode and a pulsed mode. Typical discharge settings are rf power of 100 W, a pressure of 10 Pa, and a gas flow of 10 sccm. Using a pulsed mode the behavior of the O density was determined in a pure O2 discharge with no reaction products, and in a discharge during etching of organic polymers. Production and loss mechanisms for O in a pure O2 discharge are discussed. For an O2 discharge during etching of resist it is found that under the given experimental conditions atomic oxygen does not play a significant role in the chemical etch mechanisms involved.

On the role of atomic oxygen in the etching of organic polymers in a radio‐frequency oxygen discharge

The authors have studied the etching of novolac‐based photoresist, polyimide, and polymethylmethacrylate in oxygen and argon rf plasmas at pressures between 0.3 and 10 Pa in a reactive‐ion‐etching (RIE) reactor. Energy‐flux density measurements on the powered electrode were performed under experimental conditions identical to those used during the etch experiments. In both plasmas the etch rate of these polymers depends proportionally on the energy‐flux density of the impinging energetic particles, which are the ions and the energetic neutrals formed by elastic and charge‐exchange collisions between ions and neutral gas particles in the sheath. In oxygen and argon plasmas under RIE conditions the etch mechanism of these polymers is ion induced. Average values of the overall carbon yield were determined as a function of the average energy of the impinging energetic particles between 50 and 650 eV and as a function of the angle of incidence. The results obtained in oxygen plasmas were compared with those ob...

Ion‐induced etching of organic polymers in argon and oxygen radio‐frequency plasmas

In this paper various single level resist systems are presented that combine gas phase silylation with dry development. For novolak-diazoquinone type resists it is shown that the photoselectivity of the silylation process is determined, to a large extent, by the presence of hydrogen bonds between the resin and the un-exposed sensitizer. Upon irradiation these physical crosslinks are replaced by weaker hydrogen bonds between the resin and the indene-carboxylic acid. The effect of the presilylation bake temperature and decarboxylation are discussed. Also the influence of decomposition of the photoactive compound on the selectivity is shown. Other systems presented in this paper are based on chemical crosslinking of the resist. SUPER (SUbmicron Positive dry Etch Resist) is based on the combination of acid-catalyzed crosslinking and gas phase silylation. Because of the chemistry that is used, SUPER can be an interesting candidate for DUV-lithography. Crosslinking of, novolak-diazoquinone type photoresists is another possibility to create a selectivity for the silylation process. A system based on electron beam lithography is presented. Sub-half-micron features, without problems with the proximity effect, are shown.

Single Level Dry Developable Resist Systems, Based On Gas Phase Silylation

The silylation from the gas phase of photoresists based on diazoquinone and novolac or polyvinylphenol, which can be used in dry developable systems has been investigated. It is shown that the phenolic hydroxyl groups are almost completely silylated. The kinetics of the reaction have been followed by gravimetry, IR spectroscopy and Rutherford backscattering spectrometry. During the reaction a completely silylated, swollen layer is formed with a sharp front separating it from the unreacted resin. The rate control-ling processes are the relaxation of the polymer and the diffusion of the reagent. When the relaxation is slow with respect to diffusion, linear reaction kinetics as in Case II diffusion are observed. When the relaxation is fast the reaction proceeds with the square root of time. The increase of the reaction rate with UV exposure of the resist is attributed to an increase in the relaxation rate of the resist. A model explains the higher photoselectivity of the reaction at elevated temperatures. Results with a number of model resists indicate that some diazoquinones can act as physical crosslinks between polymer chains via the formation of hydrogen bonds whereas the corresponding in-denecarboxylic acids cannot. Due to the high content of silicon after the treatment these resists become highly etch-resistant towards oxygen plasmas.

Mechanism and kinetics of silylation of resist layers from the gas phase

Super: A submicron positive dry etch resist; a candidate for DUV-lithography

The reaction of silicon-containing vapour with a photoresist layer, as used in dry developable lithographic processes, was studied with Rutherford backscattering spectrometry (RBS). Degradation of the polymer layer was observed, but the total amount of incorporated Si was found to be constant during the measurement. Si-depth profiles were found to be independent of dose and in agreement with profiles obtained with secondary ion mass spectrometry (SIMS). The detection of hydrogen by elastic recoil detection (ERD) was used to study the degradation in detail. The decrease in hydrogen countrate from a layer of polystyrene on Si in combination with the shift of the Si-substrate edge in the corresponding RBS spectra was used for a model description. Only one degradation cross-section for hydrogen and one for carbon, both independent of beam current and dose, were required for a successful fit of the experimental data.

Degradation effects and Si-depth profiling in photoresists using ion beam analysis

The reaction of a silicon-containing vapor with a photoresist layer, as used in some dry developable lithographic processes, was studied with Rutherford backscattering spectrometry. Degradation of the polymer layer under ion beam irradiation was observed, but it was found that this had no influence on the shape of the Si-depth profile and the total areal density. The RBS measurements were also verified with secondary ion mass spectrometry measurements. To describe the degradation process that occurs in polymeric layers upon ion beam exposure, elastic recoil detection measurements were carried out on polystyrene layers. Only one dose-independent cross section for carbon and only one for hydrogen were needed to describe the degradation behavior.

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Jack P. W. Schellekens

Papers

Single Level Dry Developable Resist Systems, Based On Gas Phase Silylation

Mechanism and kinetics of silylation of resist layers from the gas phase

Super: A submicron positive dry etch resist; a candidate for DUV-lithography

Degradation effects and Si-depth profiling in photoresists using ion beam analysis

Si-depth profiling with Rutherford backscattering in photoresist layers; a study on the effects of degradation