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Outgassing methodology development, set-up and outgassing measurement results

Outgassing has been found to be a very serious topic for current and upcoming lithography nodes such as 193nm and especially for 157nm. Since the photon energy at these wavelengths is high enough to cleave chemical bonds, photoresist materials generate volatile organic products under exposure conditions. These compounds can deposit on the surface of the front lens of the exposure tool, causing severe and irreversible lens damage especially under high volume productive conditions.

Goal of this project was to develop and introduce a reliable and quick methodology for resist outgassing behaviour under exposure. This methodology and the regular resist benchmarking can be seen as two complementary methods for resist selection for the MSVII (and later on also planned for the AT1600).

Two methodologies for outgassing detection have been developed and setup in the Infineon R&D cleanroom facilities in Erlangen. The studies in an early learning phase have been done with the “established” and in-house available 193nm wavelength and concentrated on the evaluation of the potential of the methodologies.

The On-line MS methodology has been setup and tested with respect to detection capability, reproducibility, and quantification. Several resist model systems and competitive resists have been investigated with the technique. The typical and partially from literature known behaviour of the resist have been observed and the major part of the data has been assigned giving a rather high confidence in the detection capability. MS data are highly reproducible and quantification relative to a baseline resist is possible. Despite the fact that the technique employs vacuum conditions the received results are a good basis to identify possible contaminants outgassing from a resist at the target wavelength of 157nm. Its clear advantage is the speed of analysis of a resist sample.

As second technique we developed and evaluated a proof plate methodology, a technique that is “closer” to the reality. It simulates an optical system and collects the total remaining outgassing residues on a transparent proof plate under atmospheric conditions. The residues are analysed after exposure with X-ray photoelectron spectroscopy (XPS). The PPM is the key to identify the outgassing elements and concentrates on the outgassing material, which remains in “the optical system”. On-line MS and PPM have to be seen in close conjunction and to further confirm outputs of each methodology.

After assessment of the different methodologies, on-line mass spectroscopy was selected as standard technique due to its simplicity and reliability. It has been shown that with this special setup clear differences of the outgassing behaviour at 193nm could be seen.

Since the lithography mainstream changed towards 193nm immersion over the last turn of the year it was necessary to adapt the planning and outgassing efforts to the new situation. As result we decided to skip the transfer of PPM to 157nm and concentrate only on On-line MS. Despite this reduction to one technique the results gave valuable input to the 157nm resist technology development.

Several commercial resist samples from 4 resist vendors (AZ Electronic Materials, JSR Corporation, Rohm & Haas, and Tokyo Ohka Kogyo (TOK)) as well as in-house formulations and model compounds have been characterized first at 193nm and then at 157nm wavelength. The resists have been ranked with respect to the total observed outgassing. The samples have been treated in exactly the same way to make the mass spectroscopic data comparable. Several common but also different outgassing fragments and molecules have been observed and identified. Each sample has been characterized by its specific “fingerprint”. However, a real comparison was not possible due to intellectual property issues of the resist vendors. Therefore the total amount of outgassing has been used to compare the resist samples neglecting the chemical and physical properties of the outgassing material.

As a major outcome, a sample that is representative for the single layer prototype resist (AZ® EXP FX 2000P) was identified as the resist with the lowest total amount of outgassing and therefore should be suitable for 157nm full field exposures.

More information on the UV2LITHO project can be found at:

Reported by

Infineon Technologies AG, R&D
Paul-Gossen-Str. 100
91052 Erlangen
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