SBIR-STTR Award

II-VI semiconductors, especially HgCdTe, are used extensively in infrared imaging and night vision electronics. These semiconductors have soft surfaces; growth of device quality material is difficult; device yields are low, and costs are high. There is thus a great need for non-invasive process control. Recently our company has developed in situ spectroscopic ellipsometry for the monitor of Al(x)GA(1-x). As crystal growth by MBE. In ellipsometry linearly polarized light is incident on the material of interest and the polarization state of the reflected light is determined. Our in situ work to date has been reasonably successful using rotating analyzer, fixed polarizer ellipsometry; however, considerable further progress must be made before ellipsometry can be adopted for in situ Control of HgCdTe crystal growth. Faster data acquisition and analysis methods need to be adopted. For this purpose we propose using a solid state optical multidetector array, as well as very fast computers and more efficient software. In addition, the optical constants of Hg(1-x)Cd(x)Te need to be measured at elevated temperatures and for various x values. Thus in Phase I we will build and test a fast prototype spectroscopic ellipsometer and gain experience making measurements at growth temperatures. Emphasis will be on monitoring growth; however, we will implement a simple demonstration of process control in Phase I. In Phase II we will further perfect the technique for control of MBE growth of HgCdTe and gain considerable experience on an actual Army growth chamber. An operating and well documented spectroscopic ellipsometer system will be deliverable as part of the Phase II contract.

Benefits:
This work will lead to development of a fast non-invasive technique for in situ diagnostics and control of the growth of II-VI semiconductor multilayer materials to be used in Army night vision optoelectronics.

Keywords:
spectroscopic ellipsometry in situ control HgCdTe crystal growth

Hg1-xCdxTe is a II-VI semiconductor used extensively in infrared imaging and night vision electronics. These materials have soft surfaces, and growth of reproducible values is extremely important but difficult. Device yields are low and costs are high. Thus there is a great need for non-destructive, non-invasive process control. Spectroscopic ellipsometry is capable of measuring, and thus controlling, the x value to very high accuracy. Layer thickness control during etching is also possible by ellipsometry with atomic scale resolution. In Phase I we demonstrated the effectiveness of an ellipsometer which measures at 12 wavelengths simultaneously and with sufficient speeds that accurate control of x value during growth should be possible. In both growth and etching the surface roughness can be measured in real time. Our goals in Phase II are to build, install, and test an ellipsometer on the Army Night Vision Laboratory MBE chamber which will lead to accurate control of mercury content as well as monitor roughness during MCT growth. This technology will then also be available for other DoD MCT contractor laboratory use.