METHOD FOR DIFFUSION LIMITED MASS TRANSPORT

1328390 Depositing semi-conductors by reaction; apparatus INTERNATIONAL BUSINESS MACHINES CORP 22 Dec 1970 [2 Jan 1970] 60725/70 Heading C7F [Also in Division C1] A semi-conductor device is obtained by transferring a material between a vapour and a substrate of semi-conductor material, the process comprising passing the substrate along a predetermined path through a reaction zone and providing in said reaction zone a substantially laminar flow of the vapour over the substrate in a direction transverse to said path. The process may be applied to the reduction of silicon tetrachloride by hydrogen but other vapour transport reactions may be similarly formed such as disproportionation, decomposition, condensation and gas cracking. In the apparatus shown in Fig. 1 a process tube 10 generally rectangular in cross-section has entrance gate 12 at one and exit gate 14 at the other, the central portion of the process tube between the entrance and the exit gates comprises a continuously open chamber containing three process zones, the prebake, deposition and cooling zones. Gas inlet tubes 16 to 24 are provided to supply gas to these zones. Exhaust gases leave through tubes 26. Cooling water is circulated to a water jacket, via inlet tubes 28 and exit tubes 13. The substrates are mounted on carriers 32 which may be continuously passed through a process tube. 34 is a viewing port. Fig. 2 shows a plan view of an ideal deposition or vapour transport zone. The gaseous phase reactor material is passed through the transport zone and over the flat surface of a substrate 36 via a fritted quartz, or sintered stainless steel, filter tube 38, having a preferred pore size of 10 microns. Reactant gases are uniformly passed to the deposition zone along the entire length of the tube 38, the gases leaving the filter tube create a laminar flow through a deposition zone. After the reactant gases have passed to the surface of the substrate they meet an exhaust baffle 14, which allows for the uniform removal of gaseous reactant materials and deposition process by-products. The baffle 14 may be a perforated steel plate or a sintered stainless steel filter plate having sufficient porosity to provide a back pressure, a number of orders greater than the longitudinal pressure drop in the exhaust plenum 42. Preferably the exhaust baffle 40 is a perforated steel plate having one mil holes at 1, 000/in2.