Manipulation of space charge in silicon by intentional thermal donor activation
(1.Helsinki Institute of Physics, University of Helsinki, Finland 000142.Department of Mechanical Engineering, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki 214-8571, Japan)
Abstract: A quantitative study about the thermal activation of thermal donors (TD) in high resistivity magnetic Czochralski (MCz) silicon was carried out. The samples are p+/p/n+ diodes (active area 0.25 cm2, thickness 300 μm) made of <100> MCz p-type Si wafers with the resistivity of about 2 kΩ？cm. The concentration of interstitial oxygen (Oi) in this material was measured by the Fourier transformation infrared (FTIR) spectroscopy method and it is 4.9×1017 cm？3. The TD activation was performed through an isochronal thermal treatment at 430 ℃ up to a total time of 120 min. The space charge density after each annealing step was extracted from capacitance-voltage (CV) measurements. The TD generation can be utilized in processing of silicon detectors (pixel, strip and drift detectors) that are used e.g. in space applications, high-energy physics experiments, and several visual imaging applications. If the starting material is boron-doped p-type high-resistivity Cz-Si, the TD generation process can be utilized in order to produce p+/n-/n+ detectors. The last thermal process step, i.e. the sintering of aluminum, is intentionally carried out at the temperature where TD’s are created. Due to the generated donors, the p-type bulk will eventually be compensated to n-type bulk. Moreover, the full depletion voltage of detectors (Vfd) could be tailored between a wide range from 30 V up to almost 1 000 V by changing heat treatment duration at 400？450 ℃ from 20 to 120 min.
Key words: thermal donor; silicon; particle detector; radiation defect