Monitoring Silicon Quality From Diffusion Furnaces Using In-Line Measurements
- PDF / 1,035,239 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 77 Downloads / 203 Views
developed for measuring minority carrier lifetimes in the silicon. These lifetime measurements have been shown to reflect the levels of defects and impurities in the silicon and are amenable to in-line wafer analysis 2. Some of the lifetime measurement techniques include photo-conductive decay with microwave reflection (jiPCD), photo current collected by silicon-electrolyte contact (ELYMAT), and the surface photo-voltage method (SPV) 3. Typically, these methods measure the recombination lifetimes, which reflect the rate at which excess carriers are destroyed through recombination. This paper investigates a technique which uses a corona oxide semiconductor (COS) to measure minority carrier lifetimes in the silicon. The COS technique is a fast, extremely sensitive, non-contact technique that requires no additional processing beyond growth or deposition of a dielectric film. In addition this technique is capable of measuring both recombination and generation lifetimes. An advantage of the generation lifetime measurement is that the depth of the measurement can be controlled4 . The COS technique is very sensitive to metal contaminants such as iron, nickel, chromium, copper and cobalt. These contaminants act as recombination and generation centers by providing energy states in the Si band gap. This reduction in carrier lifetimes can decrease device performance and reliability5 . One method for reducing the effects of metal contaminants in Si is the high-temperature denude process. This multi-step process involves out-diffusion of oxygen from the near-surface 219 Mat. Res. Soc. Symp. Proc. Vol. 591 0 2000 Materials Research Society
region and subsequent nucleation and precipitation of oxygen impurities deeper in the silicon6 . During high temperature processing, these oxygen precipitates deep in the silicon act as traps, gettering heavy metal impurities away from the surface. This results in a high-quality nearsurface region of silicon that is relatively free of impurities, called the denuded zone7 ". The depth and quality of the denuded zone can be controlled by the temperature and time of the various denude process steps. In this study we used the COS technique to monitor the formation and quality of this denuded zone for several sets of process conditions. We also used the COS technique to detect metal contamination in a diffusion furnace after a quartz tube change and the subsequent removal of these impurities after several high temperature steam and HCI cleans. EXPERIMENT COS Lifetime Measurements A KLA-Tencor Quantox COS system was used for all of the silicon measurements presented in this work. Prior to the measurements an oxide layer was grown on the surface of the silicon. The Quantox system uses three components in various combinations to make measurements in silicon as shown in Figure 19. 1. A small amount of charge is deposited on the oxide surface by ionizing moisture and CO 2 above the wafer. 2. A vibrating Kelvin probe is then used to measure the resulting surface voltage (V.) response. 3. A light source
Data Loading...
