Enhancement of Mask Selectivity in SiO₂ Etching with a Phase-Controlled Pulsed Inductively Coupled Plasma

Abstract

We developed a new method to enhace the photoresist selectivity in SiO2 etching by modulating both the source and bias powers and by controlling the phase difference between the modulation functions. Enhancement of mask selectivity was observed in the pulse plasma, especially in the out-phase condition. To understand the heavy polymerization in the out-phase pulse plasma, we analyzed the ion energy distributions of CF x +(x=1, 2, 3) ions using the energy-spectroscopic quadrupole mass spectrometer (QMS) and measured the waveforms of the bias power with a high-voltage probe which was connected directly to the wafer. Two distinct plasma potential distributions were obtained in the pulse plasma and the dc bias voltage (V DC) was maximum in the out-phase condition. The heavy polymerization in the out-phase condition was explained as a result of high V DC. We also investigated the emission intensity of the C2 (516.5 nm) line, and found that C2 species were precursors of the polymerization and contributed to the heavy polymerization in the out-phase condition.

Pulsed plasma etching for semiconductor manufacturing

“…More recent studies have shown reduced damage to the Si substrate during gate etching [17]. Furthermore, pulsed plasmas offer other important advantages (compared to CW plasmas) including (a) improved etch selectivity by, for example, modifying the concentration of chemical species present in the plasma [18][19][20], (b) improved etch or deposition rate [21,22], (c) reduced dust generation [23][24][25][26] and (d) improved etch or deposition uniformity [22,27,28]. A review of pulsed plasmas, focusing on high density reactors, has been presented by Banna et al [29].…”

“…Shin and co-workers [20] did experiments on etching of SiO 2 in C 4 F 8 /Ar ICPs by pulsing both the source and bias power (synchronous pulsing), varying the phase between them. They observed heavy polymerization in the out-ofphase condition, which enhanced selectivity of SiO 2 etching compared to the photoresist mask.…”

Time-resolved electrostatic probe studies of a pulsed inductively-coupled plasma

“…An example of such additional capabilities for control can be found in the work of Samukawa [1], who reported an increased selectivity of CHF 3 for etching SiO 2 over Si, by choosing an optimized pulsed-power repetition frequency in an ECR plasma source. Shin et al [2] showed an enhancement of mask selectivity in SiO 2 etching with a pulsed ICP (inductively-coupled plasma) source. These sources can also reduce process-induced damage, such as that caused by electron shading [3,4].…”

Factors influencing ion energy distributions in pulsed inductively coupled argon plasmas

“…With the shrink of semiconductor device dimensions, pulsed plasmas have emerged as promising candidates to address the formidable plasma etching challenges in sub 10 nm region [1,2]. Compared to continuous wave (CW) plasmas, pulsed plasmas can improve etch uniformity [3][4][5], etch selectivity [6] and etch rate [5], minimize the surface damage [7,8]. Pulsed plasmas can also improve unwanted micro-features in etching processes, such as notching, bowing, micro-trenching and aspect ratio dependent etching [1,2,9,10].…”