The Study On The Characterization And Deep Level Energy Of 4H-SiC Homoepitaxial Layers

As other semiconductor device, the quality of silicon carbide (SiC) material plays a very important role in the fabrication and performance of SiC device. The high quality SiC single crystal material is the base for achieving SiC devices with high performance, and making for the study and the further applications of SiC devices. At present; there are obviously progresses about the formation on the growth of 4H- SiC homoepitaxial layers. But many difficulties and problems are also existed on the characterization of the 4H-SiC homoepitaxial layers materials. It is necessary to systematically develop a series of characterization methods for characteristics of 4H-SiC homoepitaxial layers. Until now, there are still different opinions for the intrinsic deep energy level in unintentionally doped 4H-SiC. The results obtained from measurements are different for different samples. Also the origin of intrinsic deep energy level is not quite clear. However the related researches are just in beginning in mainland China.In this dissertation, the formation mechanism, technology, and characteristics on the 4H- SiC homoepitaxial layers are studied theoretically and experimentally. A series of test and characterization methods for characteristics of 4H-SiC homoepitaxial layers are presented. The intrinsic deep energy level in unintentionally doped 4H-SiC homoepitaxial layers, which has a great effect on the device performance, is comprehensively studied. The main studies and contributions of this dissertation are as follows.1. The key processes of growth are studied by experiments based on the theoretical analyse, and the major factors to affect the key processes are obtained. The trend of parameters and process are achieved.2. Several methods for the characterization of 4H-SiC homoepitaxial layers are investigated. A new simple method is presented according to the difference LOCP peak in Raman spectrum with different dopping concentrations. The quality of 4H-SiC homoepitaxial layers is evaluated and the depth is calculated using the intensity and frequency of interference fringes in FTIR spectrum. The resistivity mapping measurements reveal a good homogeneity of electrical properties in the main area of the wafer, with the maximum resistivity 0.3972Ω·cm and the minimun resistivity 0.3768Ω·cm. The maximum error of resistivity is only 1.04%.The FWHW of rocking curve is 36 second measured by X-ray diffraction (XRD), and another peak is found at the left, 41 second away from main peak. It is caused by the misorientation between the substrate and epilayer through mathematical analysis. The surface topography and element of 4H-SiC homoepitaxial layers are qualitatively and quantitatively analysed by SEM, AFM and XPS, and the concentration of heavy N-doping 4H-SiC and the doping of Al-doped sample are measured by secondary ion mass spectroscopy (SIMS). The thickness of different doping layers can also be obtained according to the concentration, which is used to verify the results from FTIR method.3. The intrinsic deep energy level in the bandgap of unintentionally doped 4H-SiC is investigated. An undoped 4H-SiC homoepitaxial layer grown by hot-wall chemical vapor deposition has been studied using photoluminescence (PL) technique with temperature varied from 10K to 240K. The broadband green luminescence has been observed. The broadband green luminescence may be composed of two Gauss-type spectra by using nonlinear optimization technique. It shows that the broadband green luminescence originates from the combination of two independent radiative transitions. The centers of two energy levels are located 0.942 eV and 1.190 eV below the conduction band, respectively. The ends of two energy levels are expanding and superimposed to each other. Vacancies of carbon (VC) are found by electron spin resonance (ESR) technique at 110K. The results strongly imply that vacancy of C and the extended defects are responsible for the green band luminescence.The The peak lambda and intensity of PL mapping indicated the intrinsic deep level energy exist in almost the whole wafer, and it is evenly distributed.4. In order to reduce vacancy of carbon, the theory and process design of 4H-SiC homoepitaxial layer implanted by carbon ion are studied. From the analysis of theory and process ion-implantation, the ion implantation range, location of peak concentration and longitudinal straggling of carbon are calculated with the Monte Carlo simulator TRIM. Then the process flow for removing deep energy level in undoped 4H-SiC homoepitaxial layer by three times carbon ion-implantation is proposed, including the design of implantation energy, dose, and depth of the SiO2 resist mask, annealing temperature, annealing time and annealing protection.5. The effect of carbon ion implantation and high C/Si ratio on deep energy level in the growth of 4H-SiC is investigated. The deep energy level in 4H-SiC material can be significantly improved by with implantation of carbon atoms into a shallow surface layer. The damage of crystal lattice can be repaired well, and the carbon ions are effectively actived after the 1600°C annealing. The vacancies of carbon and their related defects can be decreased by the process of carbon ion implantation and annealing.C/Si ratio to be suitable for the growth of 4H-SiC epilayer is discussed according to the quality of 4H-SiC epilyers and the experiment cost. C/Si=1.5 and C/Si=3 are selected to find the tendency of intrinsic deep energy level with the C/Si ratio increasing. The results indicate that the vacancies of canbon are suppressed and the density of deep energy level defects is decreaed in carbon rich growth conditions. But this method is limited by severl factors, such as quality of 4H-SiC epilyers and concentration of N dopping.