Extrinsic Gettering of Copper in Silicon: Heterogeneous Precipitation on Near-Surface Dislocations
- PDF / 3,833,941 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 90 Downloads / 162 Views
EXTRINSIC GETTERING OF COPPER IN SILICON: HETEROGENEOUS PRECIPITATION ON NEAR-SURFACE DISLOCATIONS P.M. RICE, M.J. KIM, and R.W. CARPENTER Center for Solid State Science, Arizona State University, 85287-1704.
Tempe, Arizona
ABSTRACT Copper was precipitated on extrinsic near-surface dislocations in (100) Si wafers. Several types of precipitates were heterogeneously nucleated on low index planar arrays. Large crystalline precipitates with visible strain fields proved to be a silicide. Large weakly diffracting precipitates without strain fields proved to be voids. Small, thin, partially crystalline particles of unknown composition also precipitated on the arrays. Point defects played an important role in the precipitation reaction. INTRODUCTION Copper is an electrically active fast diffusing impurity in silicon likely to make its appearance at some stage of processing. The electrical behaviour depends on whether it is in solution or precipitated. It is known that under appropriate conditions copper will precipitate on dislocations in bulk silicon.[1,21 The interactions of copper with defects near free surfaces of Si wafers is of interest, since these regions are where copper and defects are most likely to occur, and the wafer surfaces are effective sinks for point defects, which are believed to be important during copper precipitation in bulk Si. In this paper we report microscopic observations of copper precipitation on dislocations introduced near (100) wafer surfaces. EXPERIMENTAL METHODS Dislocations were introduced into (100) Si wafers by light surface abrasion, and then a layer of Cu a few microns thick was applied to the surface of these wafers by evaporative deposition in a UHV apparatus. Immediately following Cu deposition, small specimens were sealed in quartz capsules under Ar atmosphere. The encapsulated specimens were heat treated at 1273 K for 24 hours with the heat treatment terminated by a mild water quench. After quenching cross section specimens for microscopy were made from epoxied multilayer composites of the heat treated specimens using dimple grinding and Ar ion beam thinning. Two microscopes were used in 100kV microscope (Philips) fitted loss/x-ray spectrometers was used instrument (JEOL) was used for spectroscopy.
this investigation. A field emission with a cold stage and parallel energy for most of the spectroscopy. A 200kV most of the imaging and some of the
RESULTS After copper deposition and heat treatment cross section electron microscopy examination of the near-surface defect array showed that heterogeneous precipitation had occurred on the defect array, shown at low magnification in Figure 1. The dislocation arrays on which precipitation occurred remain largely, but not completely, planar on low index planes. Three different morphological forms of precipitate occurred on the arrays: large three dimensional crystalline particles (50 to 100nm in size) easily visible in Fig. 1, thin discontinuous nearly planar precipitates resembling stacking faults and closely associated with the large
Data Loading...
