Direct current superposed dual-frequency capacitively coupled plasmas in selective etching of SiOCH over SiC

Abstract

Superpositioning of negative dc bias in dual-frequency capacitively coupled plasmas (dc-superposed (DS)-CCP) was realized for the selective etching of carbon-doped silicon oxide (SiOCH) films over carbon-doped amorphous silicon (SiC) films, while the dc bias exceeded about −800 V. When a dc bias of −1200 V was superposed on 60 MHz VHF power on the top electrode opposed to a wafer on the bottom electrode biased with 13.56 MHz power, a selectivity of above 50 for SiOCH over SiC was obtained. From characterization of the plasma density and various chemical species in the gaseous phase, such as CF2, CF and atomic N, the density of CF2 significantly decreased with the application of dc bias ranging from −800 to −1200 V. This indicated that CF2 radicals were consumed at the surface of the counter electrode which was made of silicon. The bulk densities of the species including CF2 were decreased, especially due to excess surface loss caused by the bombardment of highly energetic ions accelerated by the superposed dc bias, as well as the rf sheath for the superposition of the negative dc bias. The DS-CCP technology is thus concluded to be indispensable for yielding highly selective etching of SiOCH over SiC.

Heating mode transition in a hybrid direct current/dual-frequency capacitively coupled CF4 discharge

“…11. The peak value of the calculated electron density first increases when adding a small dc bias (up to À200 V), then it decreases for slightly higher negative dc bias values (up to À400 V), and finally it increases again at high enough negative dc voltages (between À400 and À600 V).…”

“…27,28 Figure 2 shows the calculated time-averaged electron density profiles for various dc voltages, in comparison to experimental data, obtained from Ref. 11. These experiments were carried out using a DF-CCRF reactor in which the HF (60 MHz) source and a negative dc source were simultaneously applied to one electrode, and the LF (13.56 MHz) source was applied at the other electrode.…”

“…The low frequency (LF) component usually operates with large voltage amplitude to control the ion energy and angular distributions, whereas the high frequency (HF) component with small voltage amplitude is typically used to determine the plasma density and ion flux. Lai et al 9 and Yamaguchi et al 10,11 have experimentally shown that the plasma density and the etch rate can be increased by introducing an extra negative direct current (dc) potential to the RF discharge. Yamaguchi et al also pointed out that the superposed negative dc bias can significantly improve the selectivity of the etching of SiOCH over SiC in a DF CF 4 discharge.…”

“…Therefore, this kind of hybrid dc/RF plasma source has received increased attention recently in both industrial and academic fields. [11][12][13][14][15][16][17][18][19][20] When a negative dc voltage is applied to the electrode, the sheath structure is determined by the superposition of a dc sheath and an RF sheath. 12,13 Under the effect of the large potential drop in the dc/RF sheath, ions are attracted to bombard the dc electrode continuously, and abundant secondary electrons are thus emitted and accelerated toward the plasma.…”

Trench and hole patterning with EUV resists using dual frequency capacitively coupled plasma (CCP)

“…This mandates etch selectivity of TL: EUV PR > 5:1 to achieve reasonable pattern transfer fidelity. Direct current super position [DCS] technology is a feature on TEL CCP Etchers and has been described previously 11,12 . Application of a DC potential to the upper electrode creates a thicker top sheath, changing the radial distribution of the plasma and increasing plasma density.…”