Oxide Dual Damascene Trench Etch Profile Control

Abstract

A systematic study of trench profile evolution in a medium-density oxide etch reactor is presented. A Langmuir site balance model is developed in the limit of unity sticking coefficient which exhibits a flat etch front as is frequently required for dual damascene applications. The model indicates that it is desirable to operate in a neutral-limited ion-assisted etch regime. Physical sputtering is also shown to be necessary, but this etch contribution must be kept small with respect to the ion-assisted etch rate. The model also indicates how either microtrenching or bottom rounding may be controlled or avoided altogether. Model predictions are compared with experimental data obtained from a Lam Research 4520XLE medium density reactor. This work includes a study of the trench bottom rounding dependencies upon pressure, etch time, aspect ratio, and process gas flow for a fluorocarbon-based etch process. The model is shown to qualitatively capture experimentally observed process trends. In some regimes, good quantitative agreement with observed measurement is seen. It can thus serve as a useful guide for trench etch process development.

Review of trench and via plasma etch issues for copper dual damascene in undoped and fluorine-doped silicate glass oxide

“…67 Consequently, the ratio S 0 J n /a ia Y ia J i , which determines whether the etch regime is ion limited or neutral starved, and the maximum physical sputtering rate Y ps J i , which contributes to microtrenching, should both vary with pressure. 56. This behavior is illustrated in Fig.…”

“…Methods for achieving a controlled flat etch front have been identified, 56,57 and can be motivated by appealing to ion-assisted etch models derived from site-balance relationships determined by Langmuir adsorption kinetics. Any departure from this goal can only be in the direction of very slight bottom rounding.…”

“…68 This could be accomplished, for example, by exploiting the sidewall angle dependence on oxygen flow commonly seen in many etch processes. This profile can be ''fine tuned'' to achieve the desired square flat bottom by using various methods to enhance the physical sputtering component of the etch process.…”

Process Technology for Copper Interconnects

“…Microtrenching is caused by ion reflection from the sidewalls of features [48]. Microtrenching is caused by ion reflection from the sidewalls of features [48].…”

Mechanism of Microtrench Generation in Etching of Wiring Trench on SiO2 Layer: Proposal of Simulation Model using High-Pressure Etching Gas

“…It is reported that the reflection characteristic of ions from the sidewall or the charging effect of ions [1][2][3][4][5] mainly causes microtrenches, and that microtrenches are caused by the deposition effect of fluorocarbons formed in the etching gas under high pressure, and the reflection characteristic of ions from the bottom of the trench under low pressure. [6][7][8][9] These reports are based on experimental results and a common mechanism for microtrench generation has not been established yet. Moreover, although the trench etching process in the SiO 2 layer has been simulated, the mechanism of microtrench generation has not been considered.…”