Real Time Stress Measurements During Growth of Aluminum Nitride on Si(111) and Si(001)

  • PDF / 777,564 Bytes
  • 6 Pages / 414.72 x 648 pts Page_size
  • 93 Downloads / 257 Views

DOWNLOAD

REPORT


REAL TIME STRESS MEASUREMENTS DURING GROWTH OF ALUMINUM NITRIDE ON SI(111) AND SI(001) W. J. Meng, J. A. Sell, G. L. Eesley, T. A. Perry Physics Department, General Motors Research and Development Center Warren, Michigan 48090

ABSTRACT We have performed real time measurements of intrinsic stresses during growth by reactive dc magnetron sputtering of aluminum nitride (AIN) thin films on silicon substrates in an UHV growth chamber. An experimental setup based on laser beam reflection is constructed such that substrate curvature as well as film thickness can be continuously monitored as growth proceeds. On Si(111) substrates, stress measurements were carried out during growth of both polycrystalline and epitaxial AIN films as a function of deposition pressure. This is the first such comparative study to our knowledge for the A1N/Si system. Our room temperature measurements on polycrystalline films corroborates previous post-growth measurements. Our high temperature measurements provide evidence of large intrinsic stresses and negligible stress relaxation during epitaxial growth of AIN on Si(111). We further compared stress behavior during both room temperature and high temperature growth of AIN films on Si(111) and Si(001) substrates. Our observations indicate while intrinsic stresses during room temperature growth can be compressive or tensile depending on plasma conditions, it is tensile during late stage growth at high temperatures. INTRODUCTION Heteroepitaxial growth of III-V nitride thin films are being pursued intensely for possible electronic applications[1]. The commonly used saphire and silicon substrates poses large lattice mismatches with AIN, leading to island growth, high dislocation density, and rough film surfaces[2]. Because of the refractory nature of the III-V nitrides, dislocation motion is expected to be difficult at the common growth temperatures. The nature of intrinsic stress and stress relaxation during growth is thus of fundamental interest to growth of this class of materials. EXPERIMENTAL We have constructed a scanning laser reflection setup to measure the Si substrate curvature as well as the growing film thickness continuously during growth of AIN films in an UHV chamber. Further details on the experimental setup can be found elsewhere[3]. In all experiments, the N2 and Ar gases used for sputtering were introduced at a fixed ratio of 1.3:1, and the total deposition pressure was varied by varying the pumping speed. The Al target bias was - 300 V, and was relatively stable during deposition. With the initial wafer curvature measured prior to growth (at the growth temperature), our measurements yielded wafer curvature as well as film thickness as a function of growth time. Using the Stoney formulation, the integrated stress (force per unit width fpw) of the AIN film is obtained from change in wafer curvature (1/R)[4],

fpw(t) =

(t)

t oh )),

(1)

where h is the wafer thickness and (E/(1 - v))si is the biaxial moduli of the silicon sub-

strates (2.290x10" N/in 2 and 1.805x10" N/m2 for Si (

Data Loading...