Research Of Epitaxy Technology On CoolMOS Products

In traditional power devices,the low-doped drift layers used to be voltage support layers.But in recent years,alternative PN structures have become popular in high-voltage MOSFET which we called CoolMOS with "super junction" structure.This kind of super-junction solves the contradiction between the RDSON and the BVDSS.The typical structure is to use the alternative PN structure as voltage support layers.In order to realize this kind of "super junction" structure,we have to use epitaxial technology.There are two kinds of epitaxial technology(Multi-EPI Technology and Trench-Fill Technology).Silicon epitaxial layer plays an important role in CoolMOS devices.Compared with the ordinary silicon epitaxial technology,this technology need higher requirements in dopant control,alignment mark control and temperature profile control.In this paper,the common silicon epitaxial process and equipment are described,and the requirements of epitaxial process and the quality characterization are described.Verification experiments of different epitaxial parameters are designed to study the key points of the two epitaxial methods.The experiments show that:(1)Photolithographic alignment mark distortion: the higher temperature,the lower growth rate,the smaller distortion.At the same time,the main hydrogen flow also has the effect,we suggest that it is better to use the hydrogen flow within 40slm/min to 60slm/min.(2)The uniformity of epitaxial resistivity and the failure rate of IDSS are directly related to the epitaxial temperature profile(the temperature profile within wafer should be controlled in5?).(3)The loss control for B dose: it is necessary to strictly control the epitaxial process(especially,the high temperature step)and the HCL gas etch using(the control of etch rate).(4)The BVDSS and EAS control: The experimental results show that when the PN concentration ratio reaches about 65%,the concentration equilibrium point is reached.At this time,BVDSS is the highest,but the EAS capacity increases linearly with the increase of PN concentration ratio.More boron concentration is needed to get better EAS capability.(5)Control of deep trench-fill: It is not the best to control the growth rate of epitaxial filling groove.It is necessary to strictly control the ratio of silicon source flow and HCL flow to achieve an optimal ratio.(6)Defect control of epitaxial process: the epitaxial lattice defects are largely damaged on the silicon surface after PW,which can be achieved by controlling the injection amount or by turning the high dose PW into epitaxial silicon.(7)Stability control of epitaxial resistivity: Because HCL is involved in the process reaction,the deep tank filling process needs to ensure the purity of the gas,so HCL must be purified.