Silicon Nanocluster Formation by a Pulse-type Gas Feeding Technique in the LPCVD System for the Nonvolatile Memory Appli
- PDF / 305,382 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 64 Downloads / 141 Views
0997-I03-04
Silicon Nanocluster Formation by a Pulse-type Gas Feeding Technique in the LPCVD System for the Nonvolatile Memory Applications Kyongmin Kim1, Eunkyeom Kim1, Myeongwook Bae2, Daeho Son1, Juhyung Lee1, Moonsup Han2, Junghyun Sok1, and Kyoungwan Park1 1 Department of Nano Science & Technology, University of Seoul, Seoul, 130-743, Korea, Republic of 2 Department of Physics, University of Seoul, Seoul, 130-743, Korea, Republic of ABSTRACT We developed a pulse-type gas-feeding technique in low pressure chemical vapor deposition system in order to grow Si nanoclusters with high density and uniform size. The maximum density and average size of the Si nanoclusters were 7 x 1011/cm2 and 7 nm, respectively. Floating gate memory devices containing the storage node of the Si nanoclusters were fabricated. The memory window was 4.5 V when the writing and erasing voltages were +14 V and -18 V, respectively. The writing and erasing times were measured to be 1 ms and 200 ms, respectively. The retention time of Si nanocluster nonvolatile memory was estimated about 10 years.
INTRODUCTION The Si nanocluster (Si-nc) nonvolatile memory has been widely investigated, because it is expected to show several advantages in the nonvolatile memory properties, such as long charge retention, the low power consumption, and a fast writing/erasing time [1-7]. However, it has difficulties in the device application, for example, low threshold voltage shift and nonuniformity in the electrical characteristics, which are due to the low Si-nc density and the spread of its size. Therefore, the formation of Si-nc with high density and uniform size became a critical issue in the Si-nc nonvolatile memory technology. In order to obtain Si-ncs with high density and uniform size, we suggested a pulse-type gas-feeding technique in low pressure chemical vapor deposition (LPCVD).
EXPERIMENT In the device fabrication we used the general Si device processing techniques [8]. Active silicon region of p-type Silicon-on-Insulator (SOI) substrate, which will be the channel and source/drain, was fabricated by photolithography and plasma reactive ion etching processes. Then, a 7 nm thick SiO2 was thermally grown in a dry oxidation furnace to prepare the tunneling oxide layer in the Si-nc floating gate memory structure. Si-ncs were deposited on the tunneling oxide layer by using the pulse-type gas-feeding method in LPCVD. Pure disilane ( Si2H6, 99.99% ) was used as the reactant gas source in order to obtain high density Si-ncs. Figure 1 shows the definition of gas-pulses which were used in this work. Pressure variation in the LPCVD reactor tube was modified by the gas-feeding time. The flow rate was set at 100sccm in all different feeding times.
Figure 1. Pressure variations in the LPCVD reactor tube along the transient time for several gasfeeding times. The gas-feeding times were shown in the right-upper corner. The shorter gas-feeding time in the Si-nc formation was applied, the lower maximum pressure and the shorter duration of the gas-pulse were obtained.
Data Loading...
