Takehiko Orii

Insights into Watermark Formation and Control

Introduction Watermarks have long been known to occur when hydrophobic silicon is exposed after HF wet processing, particularly where patterns include hydrophilic and hydrophobic regions [1-3]. Historically these defects have been associated with an inadequate drying process, and were a driving factor in the semiconductor industry’s transition from spin to IPA-based drying in FEOL batch systems. Silicon is oxidized by oxygen dissolved in DI water during rinsing, and this oxide is dissolved into the water. Upon thinning of a water layer or droplet on the wafer, dissolved silica and/or silicic acid precipitate on the wafer. Avoiding oxygen in the water and evaporation during drying have been identified as key factors in preventing watermark formation. We systematically studied mechanisms of formation of such defects after dilute HF processing in a single wafer wet cleaning chamber. As a result, different types of defects were identified that are distinct from previously reported watermarks. Subsequently the conditions under which these defects can be formed were found, so that they may be prevented.

Evaluation of the Plasmaless Gaseous Etching Process

Introduction The precise control of the etching of various films on device surfaces is becoming increasingly important because slight changes in device structures can cause serious deterioration of their electrical properties. For example, a depression that is called a divot, in the CVD oxide of a shallow trench isolation (STI) results in increased leakage current, especially in advanced devices. The cause of the divot formation is considered to be the successive etching of the CVD oxide in the STI with hydrofluoric-based chemicals. The purpose of this successive etching is to remove the oxide on the device. The CVD oxide film has a poor structure, so the wet etch rate of the CVD oxide is greater than that of the thermal oxide. In this paper, we report a plasmaless, gaseous etching process technology that achieves a larger reduction of the etch rate of the CVD oxide than that of the conventional wet etching process. We discuss the mechanism of the reaction of this process and apply this technology to the STI formation process.