AVS 49th International Symposium
    Manufacturing Science and Technology Monday Sessions
       Session MS-MoA

Paper MS-MoA6
Monitoring and Control of Binary Gas Mixtures from Solid Phase MOCVD Sources using an Acoustic Sensor

Monday, November 4, 2002, 3:40 pm, Room C-109

Session: Control Issues in Electronics Manufacturing
Presenter: L. Henn-Lecordier, University of Maryland
Authors: L. Henn-Lecordier, University of Maryland
J.N. Kidder, University of Maryland
G.W. Rubloff, University of Maryland
Correspondent: Click to Email
In-line acoustic sensors have been used for several years in MOCVD source delivery systems to monitor and control the upstream composition of binary gas mixtures obtained from temperature- and pressure-controlled "bubbler" vessels. Since the vapor pressures of some commonly used MOCVD solid sources is low, extending into the sub-Torr range, it becomes difficult to maintain a constant - but minute - concentration of reagent in a high flow of carrier gas. In this study, an Inficon Composer acoustic sensor was implemented to measure and control the concentration obtained from two solid phase sources using H2 as a carrier gas, including (1) trimethylindium (TMI), which is used to grow GaInAs III-V compound semiconductors for optoelectronics, and (2) bis(cyclopentadienyl) magnesium (Cp2Mg) which is used in part as a p-type doping element in nitride-based compound semiconductors for blue LED’s. Both sources are crystalline solids with low vapor pressures (2.5 and 0.04 Torr at 25°C respectively for TMI and Cp2Mg), which causes unstable sublimation/delivery rates and associated variability in composition and lattice mismatch. Using the acoustic sensor, reagent levels as low as 1.E-4 mol % in H2 were monitored and found in close correlation with the expected concentrations over a broad range of total pressure from 500 down to 60 Torr. This sensitivity suggests that source delivery control may be achievable to control (i.e., compensate for) variations in source delivery rate, e.g., adjusting the flow of the carrier gas through the source, diluting the binary mixture downstream of the source, or adjusting the gas density in the source.