Selective Dry Etching of Tungsten for VLSI Metallization

Abstract

Recently, refractory metals such as tungsten have attracted considerable attention as materials suitable for high density, high speed VLSI interconnect structures. Producing submicron tungsten structures requires an etching process with high anisotropy and selectivity, such as can be achieved in RF glow discharge reactors. In this work, we compare three plasma chemistries, namely, CF4/O2/normalHe , CClF3/O2/normalHe , and CBrF3/O2/normalHe , for the etching of photoresist‐patterned tungsten over SiO2 . Optical emission spectroscopy of reactive fragments and nonreactive additives (Ar, Xe, N2 ) is used to identify plasma species suitable for use as endpoint monitors in each case. Of these three freons, the CBrF3 provides an etch process least dependent on oxygen concentration, with the best anisotropy and selectivity. Etch rates, optical emission intensities, Auger and XPS surface analyses are used to interpret differences in reaction mechanism among these plasmas. It is concluded that anisotropy is promoted by the deposition on the tungsten sidewalls of a polymer film, which is more substantial in CBrF3 than in CClF3 .

Fabrication of high aspect ratio tungsten nanostructures on ultrathin c-Si membranes for extreme UV applications

“…However, the isotropic etching resulting from the interaction of neutral fluorine plasma species with W causes severe undercutting [16]. This can be avoided either by etching at substrate temperatures below −50 °C [16], or by protecting the sidewall with compounds generated from fluorocarbon gases (CBrF 3 , CClF 3 , CHF 3, CF 4 or C 4 F 8 ) [17][18][19][20][21] or inhibitor gases such as H 2 , O 2 , N 2 [22][23][24][25]. The best results have been achieved with SF 6 /O 2 gas mixture [25] under cryogenic temperature conditions.…”

Plasma‐Enhanced Etching of Tungsten and Tungsten Silicide in Chlorine‐Containing Discharges

“…(10)(11)(12)] and (ii) reaction of the Si substrate surface under high (HV) or ultrahigh (UHV) vacuum conditions at a hydrocarbon partial pressure corresponding to molecular (free) flow 4 [Ref. (13)(14)(15)(16)(17)(18)]. A brief review of those studies most pertinent to our research is presented below.…”

“…By comparison, only a few studies have been reported that deal with the etching of tungsten or tungsten silicide in plasmas containing chlorine. Tungsten etching was investigated in CC1F.,/OJHe discharges at 160 mtorr (15). The etch rate continued to increase with oxygen additions up to 46%.…”