Monitoring Epiready Semiconductor Wafers
OXFORD UNIV (UNITED KINGDOM) DEPT OF PHYSICS
Pagination or Media Count:
Gallium Arsenide GaAs wafers are often sold by the manufacturer as epiready, meaning the substrates can be used with no further treatment. However, there is no clear agreement on what epiready means, although one manufacturer recommends that they be used within 3 months of purchase. However, many growers find they are unable to obtain good growth results from their processes with untreated wafers and have to resort to long-established etching procedures. With the increase in multi-wafer molecular beam epitaxy MBE and metalorganic vapor phase epitaxy MOVPE reactors, this approach is no longer viable. This paper investigates the aging of GaAs wafers stored under a variety of conditions e.g. temperatures of 200 degrees Centigrade, room temperature, and -20 degrees Centigrade and assessed by atomic force microscopy AFM after various procedures had been performed, including annealing in molecular hydrogen using a MOVPE reactor. The primary source of aging for an epiready GaAs wafer has been found to be the transfer oxidation from the native As2O3 present at time 0 to Ga2O3 present after 24 hours, 3 months, and 2 years. respectively, at the storage temperatures mentioned above. This transfer oxidation does not occur across the whole surface but in discrete areas that may be associated with the step edges on the substrate surface. This is the cause of deterioration of an epiready substrate, but it can be slowed by storing the GaAs wafers at -20 degrees Centigrade. Storage in a domestic freezer has allowed even 2-year-old GaAs wafers to be used without any further preparation. 2 tables, 11 figures, 8 refs.
- Solid State Physics