| AVS 64th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Monday Sessions |
| Session PS+AS+SS-MoA |
| Session: | Plasma Surface Interactions |
| Presenter: | Yasufumi Miyoshi, Sony Semiconductor Solutions Corporation, Japan |
| Authors: | Y. Miyoshi, Sony Semiconductor Solutions Corporation, Japan M. Fukasawa, Sony Semiconductor Solutions Corporation, Japan K. Nagahata, Sony Semiconductor Solutions Corporation, Japan K. Ishikawa, Nagoya University, Japan M. Sekine, Nagoya University, Japan M. Hori, Nagoya University, Japan T. Tatsumi, Sony Semiconductor Solutions Corporation, Japan |
| Correspondent: | Click to Email |
It is important to reduce photon-induced interface defects, which degrade the performance of electric devices. Ishikawa et al. reported that using pulse-time-modulated plasma reduces UV photon-induced defects [1]. In this study, we investigated how temporal variation of the discharge affected these defects in pulse-modulated Ar/CF4/O2 inductively coupled plasma (ICP).
In this study, we varied the ICP source pulse frequency (0.5–20 kHz) and duty ratio (50–100%) as well as the gas ratio of Ar/CF4. To investigate the UV radiation damage, the interface-trap density (Dit) was measured by using on-wafer pallet for plasma evaluation (PAPE) [2]. We used Dit, which is proportional to the UV fluence from discharge, as an indicator of UV damage. Temporal changes in the optical emission spectroscopy (OES) intensity of pulsed plasma were also investigated.
The measured Dit was lower than that in the CW at lower frequencies but was higher at higher frequencies (> 10 KHz). Increasing the frequency increased Dit, which reached a maximum at 10 kHz for Ar/CF4 = 1, and then decreased Dit. Using a lower CF4 ratio shifted the maximum Dit to a lower frequency.
This frequency-dependent behavior comes from the transient behavior of the pulsed ICP. Time-resolved OES revealed an optical emission overshoot after ignition caused by the variation in the electron temperature and number density in the early ON phase. The number of overshoots increased with increasing frequency, increasing the UV fluence and Dit. At higher frequencies, the variation in the electron temperature and number density were suppressed due to stepwise ionization from residual long-lived metastable species in the early ON phase [3]. This behavior considerably decreased overshoot amplitude, in turn decreasing the UV fluence and Dit. At the lower CF4 ratio, quenching of the metastable species by CF4 decreased and the lifetime of the metastable species during the OFF phase likely increased. Therefore, we presume that, at the lower CF4 ratio, the overshoot amplitude began to decrease at a lower frequency than when Ar/CF4 = 1 and the maximum Dit consequently shifted to a lower frequency.
These results show that controlling the temporal variation of a pulse-modulated plasma is essential to reduce the photon-induced damage it causes during plasma processes.
[1] K. Ishikawa et al., J. Appl. Phys. 104 (2008) 063306.
[2] M. Fukasawa et al., Jpn. J. Appl. Phys. 52 (2013) 05ED01.
[3] S. K. Monfared et al., J. Phys. D: Appl. Phys. 46 (2013) 425201