Laser-Induced Fluorescence Measurements in AN Electron-Cyclotron Resonance Plasma Etch Reactor
Abstract
Laser-induced fluorescence (LIF) and a variety of diagnostics have been used to investigate etch products and etching species in an electron-cyclotron resonance plasma etch reactor. Fluorine-based chemistries in SF _6/Ar plasmas was investigated. The ground state of SiF_2, X ^1A_1 (0,0,0), was detected using LIF to determine if ion bombardment stimulates desorption of SiF_2 from the wafer surface, increasing the etch rate and anisotropy. The A >=ts X band was excited near 220 m. Spatial profiles of the SiF_2 density indicate that the wafer surface is a strong source of SiF_2 and that measurements near the wafer surface are proportional to the surface desorption rate. The SiF_2 production rate was found to increase linearly with the average ion energy flux to the surface. The slope was independent of wafer temperature, but the y-intercept decreased with decreasing wafer temperature from 40^circC to -70^circC. The fraction of silicon leaving the wafer surface as SiF _2 was found to increase with increasing ion flux and energy. The SiF_2 X ^1A_1 (0,1,0) state desorption rate was found to follow the same trends as the ground state as ion flux and energy were varied. Densities were corrected for changes in the rotational temperature of SiF_2, which was found to vary from 600 to 1000 K and depend strongly on ion density. Measurements of the 3s ^4P _{5/2} metastable state of atomic fluorine were made to determine if densities in the ECR were high enough to impact the etch process. The absolute density was found to be less than 4 times 10^9 cm^ {-3} under all conditions examined. A model to predict the 3s ^4P _{5/2} density as a function of conditions indicates that the metastable flux to the surface is small compared to the ion flux under typical etching conditions. The lifetime of the 3s ^4P _{5/2} state was measured to be less than 5 musec. Finally, neutral temperatures were determined from measurements of the Doppler broadening of LIF excitation transitions. Metastable argon temperatures in a 1 mTorr argon plasma were measured to increase from 300 K to 800 K as the microwave power was increased. The temperature is attributed to heating by ion-neutral collisions.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1994
- Bibcode:
- 1994PhDT.......111Z
- Keywords:
-
- ETCHING;
- Physics: Fluid and Plasma; Engineering: Electronics and Electrical