Application of in-situ spectroscopic ellipsometry to the study of organometallic vapor phase epitaxy.

摘要

The ever increasing demands on reproducibility and economy of semiconductor processing suggest the use of appropriate in-situ monitoring tools to obtain information about the process and, if possible, make the required corrections. The scope of this thesis was to study the application of in-situ spectroscopic ellipsometry to the monitoring of organometallic vapor phase epitaxy, using the growth of {dollar}rm Hgsb{lcub}1-x{rcub}Cdsb{lcub}x{rcub}Te,{dollar} CdTe and ZnTe on GaAs as a suitable vehicle.; The optical constant library of {dollar}rm Hgsb{lcub}1-x{rcub}Cdsb{lcub}x{rcub}Te{dollar} at the growth temperature of {dollar}rm 350spcirc C{dollar} was first determined. Real-time composition control was performed during {dollar}rm Hgsb{lcub}1-x{rcub}Cdsb{lcub}x{rcub}Te{dollar} growth on GaAs, using the Cd precursor flow as the actuator. The system was able to attain the required setpoints as well as compensate for a disturbance such as temperature fluctuation.; The nucleation behavior of CdTe and ZnTe on vicinal GaAs (100) substrates was also investigated. The Bruggeman Effective Medium Approximation was used to quantify the nucleation behavior in terms of the variation of the layer volume fraction with thickness. Experimental results for CdTe and ZnTe growth on vicinal GaAs (100) indicated the presence of Stranski-Krastonov nucleation mode. A physical model of this mode was proposed, assuming hemicylindrical islands nucleating along the ledges spaced uniformly in the misorientation direction. The model agreed quite well with the experimental data and indicated that the growth was of CdTe was highly 3-dimensional in nature whereas that of ZnTe was more 2-dimensional in nature. This difference can help explain the suitability of ZnTe as a buffer for the growth of CdTe on GaAs (100).; Atomic layer epitaxy of CdTe was carried out over the range of {dollar}rm 300{lcub}-{rcub}325spcirc C.{dollar} It was observed that the growth occurred almost completely in the Cd cycle at {dollar}rm 300spcirc C,{dollar} indicating a surface catalyzed decomposition of di-isopropyltelluride (DIPTe). The extent of the 1 monolayer/cycle growth window as a function of DMCd and DIPTe partial pressures was also investigated. Increasing the DIPTe flushing time at different temperatures indicated a growth mechanism involving competing reaction/desorption. A model incorporating this mechanism was used to fit the observed data, yielding an activation energy of 16.2kcal/mol for the reaction rate.