Measurements of the Cl atom concentration in radio-frequency and microwave plasmas by two-photon laser-induced fluorescence: Relation to the etching of Si

Abstract

Articles you may be interested inAbsolute atomic hydrogen densities in a radio frequency discharge measured by two-photon laser induced fluorescence imaging J. Appl. Phys. 85, 696 (1999); 10.1063/1.369149Laserinduced dissociation of molecules during measurements of hydrogen atoms in processing plasmas using twophoton laserinduced fluorescence Atomic chlorine concentrations in Cl z plasmas have been measured by two-photon laser-induced fluorescence (LIF). Experiments were performed over a wide pressure range in rf, rfmagnetron, and microwave electron cyclotron resonance (ECR) discharges. Absolute calibration was achieved by generating CI atoms through UV photolysis of CCI 4 with the same laser radiation. The LIF measurements showed that in the respective discharges, the CI concentrations decreased and the corresponding CI fractions increased with decreasing pressure: the measured fractions ranged from 0.3% to 0.7% in rf discharges, from 0.8% to 8% in magnetron, and from I % to 2% in ECR. These results, together with electrical measurements of ion and electron energies and densities, demonstrated that the ratio of neutral CI flux to ion flux toward the substrate decreased from 400: 1 to 1: 1, almost linearly with decreasing pressure in the three discharges. These results of plasma diagnostics are compared with the etching characteristics of heavily P-doped polycrystalline Si obtained.

Numerical study of the etch anisotropy in low-pressure, high-density plasma etching

“…In typical LPHD Cl 2 plasmas, the neutral-to-ion flux ratio is ⌫ n /⌫ i ϳ 0.3-30 toward substrate surfaces at a gas pressure of 0.1-10 mTorr and a fixed ion current density of 10 mA/ cm 2 . 9,10 Figures 5͑a͒-5͑c͒ show etched profiles at a flux ratio of ⌫ n0 /⌫ i0 ϭ 100 toward the substrate for different R ϭ eV s /kT i values. Each curve represents the Si surface obtained every 10 time steps ⌬t/T ϭ 0.1.…”

“…In this study the incident ion energy was assumed to be E i ϳ 50 eV, which is a typical value in ECR plasma etching environments. 9,10 The etch yield was taken to be Y Si (0)ϭ0.4 from the experimental data at E i ϭ 50 eV for normal ion incident ͑⌽ϭ0͒, 22 where ⌽ is the incident ion angle from the surface normal. However, to the best of our knowledge no measurements of the angular dependence of Y Si have been made with the low-energy ͑ E i Շ 100 eV͒ ions of concern here, so its angular dependence was assumed to be Y Si (⌽)/Y Si (0) ϭ cos 0.5 ⌽, on the basis of the closest data at E i ϭ 400 eV of Mayer, Barker, and Whitman: 23 Y Si exhibits a fairly weak dependence on ⌽ with a maximum at ⌽ϳ0°.…”

“…24 Although atomic Cl is expected to have a larger sticking coefficient of ϳ1 on Si, it was reported that the degree of Cl 2 dissociation in the downstream region of an ECR reactor is ͓Cl͔/͓Cl 2 ] ϳ 1% at gas pressures of P 0 ϭ 1 -10 mTorr. 9,10 Thus, Cl 2 molecules may be more important in chlorinating bare Si sites than Cl atoms. In effect, Cheng et al 25 showed that Si surfaces during helical resonator Cl 2 plasma etching are chlorinated with a time constant of ϳ6 ms at P 0 ϭ 1mTorr and ϳ20 ms at P 0 ϭ 0.3 mTorr, using laserinduced thermal desorption spectroscopy.…”

“…[1][2][3][4][5][6][7][8] Electron cyclotron resonance ͑ECR͒ is one of such plasma sources giving high-density plasmas (10 11 -10 12 cm Ϫ3 )at low gas pressures (10 Ϫ3 -10 Ϫ4 Torr͒. [1][2][3][4]9,10 In such LPHD plasma etching, lower neutral-to-ion flux ratios (⌫ n /⌫ i Ͻ 10) are achieved onto substrate surfaces, along with lower sheath voltages or ion energies (E i Ͻ 100 eV͒, 9,10 leading to better etch anisotropy with higher selectivity and less damage. [1][2][3][4] Thus, the etch anisotropy may be largely limited by the ion temperature or their random motion in a plasma, because the sidewall etching resulting from spontaneous reactions of reactive neutrals and from obliquely incident ions scattered in a sheath is considerably reduced in LPHD plasmas.…”

Application of Techniques of Relaxation Oscillations to a System of Differential-Difference Equations From Ecology

“…Chlorine plasma has been diagnosed by several methods. In these studies, the chlorine atom density, 1) density of metastable chlorine ions (Cl + * ), drift velocity and temperature of Cl + * , [2][3][4][5] negative chlorine ion density, 6,7) chlorine molecular ion density, 8) and product species 9) have been investigated.…”