The slips on a silicon wafer edge which normally occur during rapid thermal process have been eliminated by forming an oxide ring on the wafer-back surface, thereby reducing the light reflectance from the silicon wafer edge. A simple model which gives the optimum ring oxide thickness and width has been proposed. From the model and experimental results, it has been found that about 3000Å thickness of ring oxide gives the best thermal compensation effect. The effect of nonuniform irradiation on the wafer has been incorporated in the model by introducing light power uniformity(LU) factor. In the case of 3300Å-thick, 7㎜-wide ring oxide and 0.86$\sim$0.88 of LU, the temperature variation on a 3inch wafer is within±4℃ at 1137℃, and the slip is completely eliminated.
Two-step rapid thermal diffusion (RTD) of phosphorus using a solid diffusion source has been described. Phosphorus profiles in silicon, measured by SIMS, show two distinct regions which are i) constant concentration region near the surface where the phosphorus concentration exceeds the solid solubility and ii) exponentally decaying region forming the diffusion tail. For the quantative analysis of the RTD process, two correction terms for the diffusion time have been introduced. The first correction term incorporates the temperature transient cycle, and the second term is due to the point defect life time during the cooling. From the Boltzmann-Matano analysis, we have found that the correction term due to the supersaturated point defects during the cooling ($t_{def}$) is about 3 sec. A simple mathmatical modeling shows that one can regard $t_{def}$) as the life time of point defects. In the case of the boron diffusion, the correction term in the effective diffusion time has a strong dependence on temperature. And the maximum value of $t_{def}$ for boron diffusion has been found to be less than phosphorus diffusion case. The introduction of the additional correction terms to the effective diffusion time makes it possible to treat the RTD process similar to the normal diffusion. Also, concentration dependent diffusivity of phosphorus in RTD has been extracted. The diffusivity at low concentrations is similar to the conventional furnace diffusion, but the diffusivity at high concentrations is much higher than the furnace diffusion case. The solid solubility and precipitation of P-Si binary system have been discussed. It has been found that the chemical concentration exceeds solid solubility near the surface in the predeposition process due to the codiffusion of phosphorus and oxygen. The high diffusivity in the high concentration region in the RTD has been explained as the precipitation enhanced diffusion.
Characteristics of NMOS transistors with phosphorus source/drain junctions formed by RTD process have been investigated. In the case of 1100℃, 10 sec RTD of P, the specific contact of $n^+Si$-Al was $2.4\times10^{-7}\Omega\cdot$㎠, which is 1/5 of the As junction. The comparision of P junction devices formed by RTD and conventional As junction devices shows that both short channel effect and hot carrier effect of P junction devices are smaller than those of As junction devices when the devices have same junction depths. P junction device has maximum of 0.4 times lower $I_{sub}/I_d$ than As junction device. Characteristics of P junctions formed by several different RTD conditions have been compared and 1000℃ RTD sample showed the smallest hot carrier generation. Also, it has been shown that the hot carrier generation can be futher reduced by forming the P junctions by 3-step RTD which has RTO-drive-in process additionally.
