Particles in C₂F₆-CHF₃and CF₄-CHF₃etching plasmas

Abstract

Particulate generation has been studied during reactive-ion etching of oxide wafers in C, F, -CHF, and CF. , +HF, plasmas using both a commercial etch tool and the GEC reference cell modified to resemble the commercial tool. Under certain discharge process conditions, copious amounts of submicrometresized particles are shown to form due to plasma interactions with the oxide substrate. In the commercial tool. particles were detected only by a downstream particle flux monitor, whereas in the reference cell, particles were observed by both in situ laser light scattering and downstream monitoring. in the commercial tool, wafers etched to end-point were shown by post-process surface analysis to be contaminated by submicrometre-sized columnar structures. Previous reports of similar such columnar structures formed during reactive-ion etching of oxide films have attributed the phenomenon to polymer micromasking. However, the results of this study clearly contradict this conclusion and suggest that the presence of columnar oxide etch residues Is ilnked to process-induced particulate contamination. Laser iight scattering measurements were made in the reference cell during reactive-Ion etching of blanket oxide wafers and used to help clarify the complex processes of parb'culate nucleation, growth and deposition during oxide etching. Polarization coagulation of spherical particles formed in the reference cell Is shown to occur, presumably in the high-field regions of the sheath, forming filamentous rod-like particle aggregates. The implications of this observation for wafer contamination are explored.

Study of particulate formation and its control by a radio frequency power modulation in the reactive ion etching process of SiO2 with CF4/H2 plasma

“…17,21,25 The formation of dome-shaped traps and ringshaped traps is generally reported by other authors. 12,20,21,25 In our reactor, two ring-shaped traps were observed, one near the grounded electrode and the other over the grounded shield that covers the edge and sidewall of the powered electrode as shown in Fig. 1.…”

“…The particulates are known to have negative charges due to the larger flux of electron impingement rather than ion impingement from the plasma. 15,16,[19][20][21] As a result of the balance between governing forces such as the ion drag force, 15 the electrostatic force, 16 the molecular drag force, 17 and the thermophoretic force, 21 a quasistatic particulate trap 12,20,25 can be formed in the plasma reactor. The location and the shape of the trap in the reactor differ with the mechanical structure, the electric field distribution, the gas flow geometry, and the temperature profile in the plasma reactor.…”

“…6 In this study, the effect of hydrogen addition on the particulate formation was examined in a RIE process of SiO 2 with a CF 4 /H 2 gas mixture. The particulate formation in plasma processes such as plasma enhanced chemical vapor deposition ͑PECVD͒, 7-9 etching, [10][11][12] and sputter deposition 13,14 has been widely studied by various groups from the viewpoint of the theoretical understanding of particulate transport, [15][16][17] the mechanism of formation in the plasma, 18,19 and suggestions to control the particulate contamination level. [20][21][22] The reduction of particulate formation level by the radio frequency ͑rf͒ power modulation method was reported by some groups [22][23][24] in the PECVD process of amorphous hydrogenated silicon with SiH 4 or SiH 4 /Ar plasmas.…”

Optimum inductively coupled plasma etching of fused silica to remove subsurface damage layer

“…So, the pits we observed are very likely to be plasma induced pitting damage: after metal contamination avoided, there is still a small amount of polymer deposition on etched surface. This polymer deposition takes the form of low density nucleated polymer particles [19] and causes the pitting damage. This is contrast to our understanding thus far that plasma induced pitting damage is high-density and accompanied by serious surface roughening [8][9][10][11].…”

Micro-Disperse Particles in Plasmas: From Disturbing Side Effects to New Applications

“…The generated particles can be analyzed by transmission electron microscopy (TEM). Examples for generation of particulates from the surrounding surfaces are Reactive Ion Etching (RIE) [40], [41], surface sputtering of targets [42,63], vacuum arc deposition [43]- [45], and in hollow cathode processes [46]. Formation of dust particles will be illustrated shortly for RIE processes with halogene containing species: An originally small roughness which might exist at the substrate surface can result in local deposition of polymer films.…”