We investigated the effects of chemical treatments for removing native oxide layers on InAlN surfaces by X-ray photoelectron spectroscopy (XPS). The untreated surface of the air exposed InAlN layer was covered with the native oxide layer mainly composed of hydroxides. Hydrochloric acid treatment and ammonium hydroxide treatment were not efficient for removing the native oxide layer even after immersion for 15 min, while hydrofluoric acid (HF) treatment led to a removal in a short treatment time of 1 min. After the HF treatment, the surface was prevented from reoxidation in air for 1 h. We also found that the 5-min buffered HF treatment had almost the same effect as the 1-min HF treatment. Finally, an attempt was made to apply the HF-based treatment to the metal-InAlN contact to confirm the XPS results.

The growth behavior of copper particle on crystalline and amorphous silicon surfaces has been investigated. The study reveals that the growth behavior of copper particle depends on the substrate condition. When samples are intentionally contaminated in ultrapure water, both crystalline and amorphous silicon surfaces show no difference in their contamination levels. However, copper particles were not observed on an amorphous silicon surface except dipping in dilute CuCl2 solution. The copper concentration on an amorphous silicon surface after dipping in a 0.5% HF solution is similar to the level after contaminating in ultrapure water. The copper contamination level on a crystalline silicon surface, except from CuCl2 solution, decreased two orders of magnitude as compared with ultrapure water. The copper impurity level on crystalline silicon surface was reduced by two orders by cleaning in a sulfuric acid-hydrogen peroxide mixture. The sulfuric acid-hydrogen peroxide mixture cleaning was not effective on an amorphous silicon surface. When native oxide pre-existed on an amorphous silicon surface before contamination, however, the sulfuric acid-hydrogen peroxide mixture cleaning was effective for removing copper impurity. Our results suggest that copper contamination on an amorphous silicon surface have the characteristics of bonding directly with silicon and/or existing in the native oxide, in contrast with the situation on crystalline silicon surface. After contamination with 1000 ppm copper in CuF2 solution, the etch rate of an amorphous silicon film in a 0.5% HF solution was approximately one order of magnitude faster than that of crystalline silicon. This is attributed to the difference in crystalline structure between crystalline silicon and amorphous silicon.

High-performance ULSI devices require ultraclean silicon surfaces, the complete removal of native oxides, and atomic level flatness and stabilization of the cleaned surfaces against molecular contaminants. Dry cleaning techniques are an attractive alternative to conventional wet processing for future ULSI production using cluster chambers or multi-process cham-bers. Organic contaminants, including photoresist polymers, are effectively removed by photo-excited ozone cleaning. We have found photo-excited halogen radicals to be useful for removing trace metals and native oxides from silicon surfaces without damaging on silicon and silicon-dioxide surfaces. We success-fully terminated hydrogen on (100) silicon surfaces by annealing in pure hydrogen ambient. A dry cleaning system with these sequential processes will be useful in constructing fully-integrated mass-production lines of high-performance ULSI devices.

Chemical structures of native oxides formed during wet chemical treatments of silicon surfaces were investigated using X-ray Photoelectron Spectroscopy (XPS) and Fourier Transformed Infrared. Attenuated Total Reflection (FT-IR-ATR). It was found that the amounts of Si-H bonds in native oxide and at native oxide/ silicon interface are negligibly small in the case of native oxides formed in H2SO4-H2O2 solution. Based on this discovery, it was found that native oxides can be characterized by the amount of Si-H bonds in the native oxide and the combination of various wet chemical treatments with the treatment in NH4OH-H2O2-H2O solution results in the drastic decrease in the amount of Si-H bonds in the native oxides.