Application of Fin Structure Factor to Reduce the Body Effect in 20 nm DRAM Cells

Tuesday, 30 May 2017
Grand Ballroom (Hilton New Orleans Riverside)
I. W. Jung (Sungkyunkwan University), H. S. Kim (Samsung Electronics Company), and B. D. Choi (Sungkyunkwan University)
Body effect is the key characteristic of DRAM cell transistor. In conventional planar transistor, length and width affect the body effect. But in recent buried channel structures, the fin structure affects the properties of transistor. In this paper, we investigated the effect of fin structure on the body effect in a DRAM cell. And we suggested a structure for reducing the body effect. In order to measure the body effect in DRAM cell, nondestructive measurement method was used. It uses a memory test system for fast, massive, nondestructive measurement. Newly developed method can measure 100,000 DRAM cell body effects in two minute, without sample damage. Since this method does not damage the sample during the measurement, there is no problem in making a TEM sample. After the measurement, we compared the body effect and the fin dimension. Fin height, fin width, fin top width, fin angle was measured to define the fin dimensions. Of the four dimensions, the fin height had a correlation with the body effect. The rate of change of the body effect according to the fin height was -10mV/V/nm. In the DRAM, the body bias is generated by a bias generator. And since this generator is affected by voltage and temperature, the body bias can vary depending on this environment. When the body bias changes, the threshold voltage of the DRAM cell changes. This result is bad for the characteristics of DRAM. So, we have to make the DRAM with a small body effect. In this paper, we propose to increase the fin height for a small body effect.