Organic Contamination Control in Silicon Surface Processing

Abstract

Introduction As semiconductor devices continue to be highly integrated and their geometry also continues to shrink, not only metallic and particulate contamination but also trace chemical contamination, particularly organics, adsorbed on the surface of silicon wafers has an increasingly detrimental impact on the performance and yield of semiconductor devices [1-4]. The adsorption of airborne organic volatiles onto the surface of silicon wafers leads to unintentional hydrophobization (or wettability changes) and haze generation. Time dependent haze on silicon surfaces is generated by the interaction of organic volatiles on the silicon surfaces with moisture [5]. The haze on silicon surfaces is widely known to prevent the effective removal of metallic contaminants from the silicon surface, as well as to prevent the uniform etching of silicon surfaces and insulator films during aqueous chemical treatment [6]. Airborne organic volatiles also cause degradation haze on the lenses and mirrors of wafer steppers/scanners in photolithography [7], where high energy photons in a short wavelength of light stand a better chance of breaking the bonds of several organic species commonly present in cleanrooms, ultimately transforming them into reactive species that stick to optical surfaces. The resultant haze on the optical surfaces causes a transmission loss of light, resulting in a reduction in image uniformity. Trace organic volatiles on silicon surfaces can also cause an accelerated oxidation rate due to the presence of moisture generated by the decomposition of organic compounds during the rapid thermal oxidation of silicon wafers due to the incomplete combustion of organic volatiles before the start of rapid thermal oxidation. Furthermore, trace organic volatiles have an increasingly detrimental impact on the performance, yield, and reliability of ever smaller semiconductor devices. It has been shown that such organic contaminants have deleterious effects on the gate oxide integrity (GOI) in MOS transistors during wafer transport/storage before the oxidation process [1, 2], as well as after the gate oxidation process prior to polycrystalline silicon deposition [8]. Figure 1 shows the degradation of the time-dependent dielectric breakdown (TDDB) characteristics of gate oxide films for MOS capacitors contaminated by organic volatiles. As alternative gate insulating film, such as HfO2 and Al2O3 are introduced for low-power CMOS applications, organic contaminants residing at the interface between gate electrode and gate insulation films can degrade the gate dielectrics. In addition, trace organic volatiles on silicon surfaces cause a lot-to-lot deviation of the film thickness due to variable incubation times in chemical vapor deposition (CVD), as shown in Fig. 2 [9]. They can also cause the locally abnormal growth of CVD films. Especially in low temperature deposition, such as the selective epitaxial growth of Si or SiGe in the source drain region, organic contaminants or residual carbon contaminants can generate defects in the deposited film [10].