Chemical and Biological Engineering ETDs

Karla Waters

Publication Date

4-17-2000

Abstract

The etching characteristics of oxide and photoresist thin films in C4F8 discharges in an inductively coupled GEC Reference cell have been determined. Infrared diode laser absorption spectroscopy (IR-DLAS) measured absolute concentrations of CFx radicals in C4F8 discharges and correlated their behavior to the oxide etch process. Additionally, Langmuir probe and OES data were collected to aid in characterizing the plasma and the oxide/photoresist etch processes.

A central composite design of experiment was employed. The factors were source power, chuck bias power, and total pressure. The source power varied from 200 to 500 W, the chuck bias power varied from 20 to 150 W, and the total pressure varied from 5 to 25 mTorr. Etch rate, gas phase radical concentrations, and plasma characteristics were examined.

Oxide thin films etched at approximately 6000 A/min under high bias (148 W) conditions, but at low bias (70 W) there was net polymer deposition. IR-DLAS revealed that CF2 was consumed during oxide etching and that CF2 concentrations showed an inverse correlation with high bias. This suggests that CF2 is participating in the oxide etch process and may be the principle source of carbon and fluorine for oxide etching. CF did not appear to have any significant role in the process. Photoresist films also etched under high bias conditions, but there was no correlation between CF or CF2 concentrations and photoresist etch rates.

Absolute concentrations of CF and CF2 over blanket oxide wafers were in the range of 1x1013 to 1.33x1014 cm-3, but >50% (~2.7 mTorr) of the CF2 present under polymer deposition conditions appeared to be consumed under the high bias oxide etching conditions. This information, along with plasma properties obtained from Langmuir probe and OES are used to help develop models for oxide and photoresist thin film surface etching. This information is also critically important to global plasma modeling programs ongoing at SEMATECH and elsewhere. Simulation results from two such global plasma models are examined to determine whether these models are predicting the correct trends observed experimentally in this work.

Sponsors

SEMATECH for their funding of this project

Document Type

Thesis

Language

English

Degree Name

Chemical Engineering

Level of Degree

Masters

Department Name

Chemical and Biological Engineering

First Committee Member (Chair)

Harold M. Anderson

Second Committee Member

Timothy L. Ward

Third Committee Member

Charles B. Fleddermann

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