HF溶液中硅基质的铜污染机理

As the dimensions of semiconductor devices are  downsized, aiming at manufacturing VLSI and ULSI  circuits, the cleaning of the silicon surfaces is one  of the most critical operations in the fabrication of  integrated circuits. The gate oxide electrical characteristics being very sensitive to contaminants, it is  essential to study the contamination of Si wafers together with the resulting corrosion process occurring during wet treatment. .

Torcheux et al., and more recently Teerlinck  have shown that the rate of elemental copper deposition is approximately proportionnal to the  ion-concentration in solution, but decreases slightly  with time, the effect being attributed to a diffusion  rate determining step. The experiments by Chyan  allow the determination of the kinetics of  copper deposition from AFM microscopy evaluation.  More recently, Parks [14] proposed an electrochemical approach of the process. This idea was elaborated  by Chyan [15], who experimentaly demonstrated that  electrochemical parameters could be very sensitive  to trace amounts of noble metals present in DHF solutions.

In the present work we have undertaken electrochemical and radioactivity measurements to study the  mechanism of copper deposition on p and n-type silicon surfaces from DHF solutions containing traces  of copper in the range of a few tens of ppb. In order  to derive fundamental parameters describing the contamination mechanisms, we have limited the study to  systems constituted by electronic grade silicon in contact with high purity deoxygenated DHF solutions, in  the dark.  

Fig1

T h e addition of trace amounts of copper contaminant was observed to result in a sudden shift of the potential towards positive values, as shown in Figs. 1 (a)  and 1(b). Immediately upon copper ion addition the  rest potential increased at a rate nearly proportional to  the coppe r concentration, and then tended rapidly to  a stable limiting value. The reference experimental curve, resulting from the addition of pure deoxygenated DH F under the same conditions, was nearly  flat. So, we think that rest potential is characteristic of  the silicon surface reactivity modified by the reduction  of copper ions, whethe r the silicon substrates were p  or n-type doped. According to the usual models for  mixed potentials, this variation should be ascribed to  a steep increase of the ratio ic / za corresponding to  cathodic and anodic site exchange current.

hodic and anodic site exchange current.  To explain mor e precisely the shape of these rest  potential curves, we have recorded, on each silicon  sample, the voltamperometric characteristics, presented in Figure 2. Whe n the current intensity is zero,  the curve gives the open-circuit potential which is  identical to the final values indicated in Figs. 1(a) and  1(b). This experiment reveals the anodic and cathodic  electrode behavior, showing very clearly that the cathodic current is amplified while the anodic current  remains nearly unchanged.