A novel approach for negative ion analysis using 160 GHz microwave interferometry and laser photodetachment in oxygen cc-rf plasmas

Abstract

Microwave interferometry at 160.28 GHz with Gaussian beam propagation (beam waist: 5 mm) and laser photodetachment were combined for the analysis of negative atomic oxygen ions in the bulk plasma of an asymmetric capacitively coupled 13.56 MHz discharge (cc-rf). The line-integrated negative oxygen ion density amounts to between 2.5 × 10 14 and 10 15 m −2 depending on the oxygen pressure and rf power. Furthermore, the measured decay of the detachment signal reveals two modes of rf oxygen plasma characterized by different electronegativities. High electronegativity, α > 2, is associated with a low decay time constant of only a few microseconds, whereas in oxygen plasmas with low electronegativity, α < 1, the relaxation of electron density needs much longer with typical decay time constants of up to about 100 µs. The transition between the two modes shows a step-like characteristic and was observed at a specific rf power depending on the oxygen pressure. In the case of high electronegativity the electron density relaxation can be described by a simple 0D-attachment-detachment model, taking into consideration a constant density for positive ions and neutral oxygen species. Using the appropriate rate coefficients from the literature and the experimentally determined effective rate coefficients of first order kinetics, the evaluation of the attachment and detachment rates indicates the significant role of O 2 (a 1 g ) in the formation and loss of negative atomic oxygen ions.

The influence of surface properties on the plasma dynamics in radio-frequency driven oxygen plasmas: Measurements and simulations

“…Since the electron density remains almost unaffected, while the charged heavy particle densities increase, the electronegativity of the system increases correspondingly. The global electronegativity values are found to be in good agreement with independent measurements 12,19,20 in view of the differences in discharge design and operational parameters.…”

Control of plasma properties in capacitively coupled oxygen discharges via the electrical asymmetry effect

“…This is caused by the rather long mean free path of the electrons (λ mf p ≈ 7 mm L b ≈ 10 mm at 10 Pa). Therefore, fast electrons, which are accelerated in the sheath regions [36,[52][53][54][55][65][66][67][68][69][70][71][72][73][74][75][76][77], ionize the background gas within the entire plasma bulk region and the common diffusion profiles are obtained for the positive ions. The negative ions are confined within this region; due to their low kinetic energy, they cannot penetrate into the sheath regions, where the time averaged potential is much lower than the plasma potential in the bulk.…”

“…Electron heating at the powered and grounded electrode sheath [52][53][54][55][65][66][67][68][69][70][71][72][73][74][75][76][77] leads to a negative and positive current, respectively. Figure 8 (a) shows the measured discharge current as a function of time within one low frequency period at 100 Pa.…”

“…This has been our motivation of conducting a combined experimental, numerical and analytical investigation of CCRF discharges in pure oxygen. Oxygen discharges, being one of the simplest electronegative plasma system, provide an interesting scenario for theoretical modeling (see for example [41][42][43][44][45][46][47][48][49][50]52] and references therein) and experimental diagnostics [49,50,[52][53][54][55][56][57] of electronegative plasmas. In contrast to the previous work of the EAE in oxygen discharges with only numerical simulation [36], our complementary approach here certainly promises a more comprehensive description of the discharge properties.…”

Isolation Trench Etch Process Using Pulsed RF Bias Power in HBr/CF4/O2 Plasma

“…Pulsed plasma dry etch is known to have increased selectivity to masks, enlarging windows of loading control as well. Other advantageous aspects of pulsed power process include such factors as charge pile-up reduction and negative ions utilization, plasma damage reduction at high power levels, as reported by authors [1][2][3][4][5]. Although pulsed RF power had been devised decades ago, it is rather recent to practically implement in manufacturing processes.…”