Electrical Properties of Solid Phase Crystallized Silicon Films
- PDF / 93,653 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 7 Downloads / 287 Views
ELECTRICAL PROPERTIES OF SOLID PHASE CRYSTALLIZED SILICON FILMS Tadashi Watanabe, Hajime Watakabe and Toshiyuki Sameshima Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan ABSTRACT
In this study, the carrier mobility and density for solid phase crystallized (SPC) silicon films fabricated at 600 ºC for 48 hours are analyzed by free carrier optical absorption. The carrier mobility is 40 cm2/Vs for SPC films doped with 6×1019-cm-3-phosphorus atoms. This analysis suggests the SPC films have fine crystalline grains closed to single crystalline silicon. In addition, initial carrier density was 3×1019 cm-3, which increased to 6×1019 cm-3 by XeCl excimer laser irradiation of 500mJ/cm2. The inactivated regions in SPC films are reduced by laser irradiation. However, the electrical conductivity after laser irradiation for SPC films doped with 6×1018-cm-3-phosphorus atoms decreased from 3.3 to 0.018 S/cm as laser energy density increased to 500mJ/cm2. On the other hand, the electrical conductivity increased from 14.7 to 31.3 S/cm with similar increase of laser energy density after H2O vapor heat treatment at 260ºC for 3 hours with 1.3 MPa. Furthermore, the characteristics of n-channel TFTs fabricated with initial SPC films as well as SPC films which was irradiated by laser at 425mJ/cm2 are also researched. The threshold voltage is decreased from 3.8 to 2.0 V by laser irradiation. Threshold voltages of both cases are decreased from 3.8 to 2.4 V for no-laser irradiation and from 2.0 to 0.8 V for laser irradiation, after H2O vapor heat treatment at 310ºC for 1 hour with 9.0MPa. Based on the above trial, the defect reduction method combining laser irradiation and H2O vapor heat treatment has proved to be very effective for SPC films and SPC TFTs.
INTRODUCTION
The solid phase crystallized (SPC) silicon films have been widely used for device applications such as MOS transistor, bipolar transistor and interconnect materials [1-3]. The carrier transport properties are influenced by grain boundaries around the crystalline grains. Therefore, an improvement issue for such property is to reduce the number of grain boundaries. The solid phase crystallization is a fabrication method of poly crystalline silicon films, which have large average grain size. It should be noted that the SPC films have about 0.5µm grain size [1-3]. In this paper, the electrical properties of SPC films is investigated. The carrier transport properties in SPC films are also investigated with electrical measurement and transistor characteristics. Furthermore, the electrical properties of crystalline grains are taken into account with analysis of free carrier optical absorption [4-10]. For improvement of electrical properties, XeCl excimer laser irradiation [6, 11] and H2O vapor heat treatment are also carried out [12-14].
EXPERIMENTAL DETAILS A6.3.1
50nm thick amorphous silicon films are formed on quartz substrate by low-pressure chemical vapor deposition (LPCVD). Heat treatment for the solid phase crystallizatio
Data Loading...
