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Determination of the silicon etch rate of a number of n-and p-type doped epitaxial silicon wafers with different crystal orientations, dopant types, and dopant levels have been made. Oxidation behavior of the silicon in solution is found to be affected by the doping level of the arsenic doped wafer. Observed variation in the removal rate of the chemical mechanical polishing ͑CMP͒ process for these doped silicon wafers is correlated with the etch rates. The surface quality of these wafers following CMP and standard clean chemical treatment is found to impact the defect level and cleanliness of the post-CMP cleaning process. Resistance to oxidation and chemical dissolution of silicon is explained by the generation of surface charge, charge transfer mechanism, etching anisotropy, and activation energy for surface reaction caused by the dopant and crystal orientation. Information obtained thereof is useful to develop the wafer-manufacturing process, starting from silicon crystal to the final clean substrate or epi wafer with low surface defects.

Interaction between low-extractable polyvinyl chloride (PVC) pipe and high-purity water containing 50 ppb of dissolved ozone is investigated for a period of five weeks. Rinse water analysis from the pipe effluent showed an increased level of chloride ion following ozonation. A number of analytical investigations such as scanning electron microscopy, x-ray photoelectron spectroscopy, and static secondary ion mass spectroscopy revealed chemical interactions between the PVC pipe surface and the dissolved ozone. Organic solvent cement used for joining the pipe is also affected chemically by the action of ozone. Oxidative degradation of the PVC by dissolved ozone can be explained by dehydrochlorination mechanism.

Ultrapure water containing dissolved ozone is being increasingly considered for providing contamination-free environment required for advanced wet chemical processing of wafers, Fluoropolymers, including polyvinylidene fluoride, have become industry standard materials for the construction of piping and components used in the distribution of ozonated ultrahigh-purity water for the semiconductor industry. In order to determine the chemical stability of polyvinylidene fluoride in the presence of dissolved ozone, we used a number of complementary analytical techniques: scanning electron microscopy with energy dispersive spectroscopy, angle-resolved x-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectroscopy, and ion sputtering for chemical characterization of the polyvinylidene fluoride pipe surface. Both qualitative and quantitative information obtained from these analyses revealed a loss of fluorine with minor surface oxidation. This was found to be limited to several monolayers near the surface of the ozonetreated polyvinyldiene fluoride pipe. The loss of fluorine is explained via a dehydrofluorination mechanism which normally initiates via free radicals produced by interaction of ozone with polyvinylidene fluoride. Implications of such surface reactions for wet chemical cleaning of wafers for the semiconductor industry are discussed.

The behavior of nickel adsorption during caustic etching of boron-doped silicon wafer is investigated. Caustic solutions considered for investigation are sodium hydroxide (NaOH) and potassium hydroxide (KOH). In addition to the amount of nickel present in the caustic solution, the degree of nickel contamination of the wafer is also affected by the dopant concentration, temperature and nature of the caustic solutions used. Control of nickel contamination by various additives to the caustic solution is found to be effective and comparable to each other. The possible mechanism of nickel adsorption is explained by considering metal stability in specific caustic solution and the electro-chemical potential Wet etching of silicon by caustic solution is extensively used, because of its high anisotropic etch rate, in both silicon wafer manufacturing and device fabrication. Use of KOH in fabrication of microelectricalmechanical system (MEMS) is widespread.1 Strong dependence of silicon etch rate on crystal orientation (<100> vs. <111) and on silicon doping level is observed in caustic etching of silicon. This makes caustic etching a desirable candidate for manufacturing silicon structure requiring anisotropic etching. Numerous studies have been done to explain the etch rate, primarily in KOH solution, in terms of its dependence on temperature, dopant type and concentration, crystal orientation as a function of KOH concentration. 2-4In wafer manufacturing, silicon wafers are subjected to various processes such as lapping, grinding and edge profiling which generate surface defects caused by the stress induced from such processes. Subsequent caustic or acid etching is required to remove these defects. However, nickel contamination by adsorption is observed on the surface and in the bulk during the etching process. Continued reduction of overall metal contamination is proposed in technology roadmaps to improve device yield and performance.5 Deposition of metal ions during acid etching is explained based on the electrochemical potential of the ion compared to the semiconductor surface. In general, metal ions with a higher potential than the semiconductor are irreversibly adsorbed on the surface compared to one with lower electrochemical potential. 6 Higher etch rate, in addition to better flatness, back-side geometry, cost and operation safety is achieved in caustic etching of wafer compared to an acid etch process. 7Commercially available caustic solutions like sodium hydroxide and potassium hydroxide normally used as etchants typically contain a significant quantity of nickel, copper, and other metals. Some of these metals can diffuse easily into the bulk of the silicon wafer during the etching process. The caustic solutions namely NaOH and KOH are used for investigation of nickel adsorption on boron doped (<100>) silicon wafers with varying resistivity. The influence of caustic etchant type, wafer doping level and temperature on metal adsorption is discussed. A possible mechanism for nickel adsorption is discussed along wit...