Hot Water Etching of Silicon Surfaces: New Insights of Mechanistic understanding and Implications to Device Fabrication
- PDF / 1,104,097 Bytes
- 10 Pages / 414.72 x 648 pts Page_size
- 9 Downloads / 212 Views
Over the recent years, many new approaches in wafer cleaning have utilized hot water rinsing. Benefits of hot water rinsing are (1) it aids the removal of residual chemicals and (2) it improves the performance of the dry, e.g. TREBOR hydrodry. However, there have been a number of significant disadvantages documented with regard to device performance. Earlier work done at this laboratory showed that the use of DI rinse water at elevated temperatures can cause etching of the Si surface producing unwanted surface topography and microroughness. The surface erosion
created under these conditions had a negative device impact which led to product yield loss. In this paper, we provide a fundamental understanding of the mechanism by which Si is etched during hot water rinsing. To this end, we have explored the interaction of dissolved oxygen concentration, water temperature, and rinse time as it relates to the attack/dissolution of H-terminated silicon. Contact angle measurements, surface roughness measurements, and etch rate data from TEM measurements as a function of water temperature, rinse time, and dissolved oxygen concentration have been made. The etch rate data strongly correlates with the rinse water temperature, however little dependence was observed with dissolved oxygen concentration. A mechanism to explain the etching will be discussed. INTRODUCTION
As the device featuie; continue to decrease for future ULSI technologies, the product yield and performance become more dependent on the wafer cleaning technology. For many years, HF-last and RCA cleaning have been the main approaches for producing an ultraclean surface. After an HF step, the silicon surface has been found to be completely hydrogen terminated (1) and has a high stability against reoxidation in air (2,3). However, the H-terminated surface has been shown to
181
Mat. Res. Soc. Symp. Proc. Vol. 477 0 1997 Materials Research Society
be readily attacked by oxidants such as OH- (4). When deionized water at elevated temperatures comes in contact with an HF-treated surface, dissolution of the Si substrate occurs(5) even though DI water has long been thought to be completely benign to the Si surface. Etching by hot DI water rinsing was first reported by Higashi et. al. who found that the Si(100) surface etched anisotropically causing unwanted surface topography(5). These earlier studies demonstrated the impact on device yield when high levels of dissolved oxygen are present in hot DI rinse water. The results showed that there was a synergistic effect coupled to dissolved oxygen concentration and water temperature. Test structures fabricated under these conditions exhibited a depression in the FN tunneling voltage when the dissolved oxygen in the DI rinse water was high. TEM evaluations revealed etching with a high degree of surface micro-roughness in the gate region. A mechanism was proposed which involved sequential back-bond attack; first by the dissolved oxygen and then by OH - on the hydrogen terminated surface. More recent studies by IMEC showed tha
Data Loading...
