Silicon Carbide CVD Approaches Industrial Needs
- PDF / 4,941,738 Bytes
- 11 Pages / 414.72 x 648 pts Page_size
- 39 Downloads / 228 Views
configuration: the not satisfying homogeneity in doping and thickness of the layer along the main flow direction. Furthermore it is very difficult to avoid gas recirculation in the reactor, preventing the use of this reactor type without a fully SiC-coated susceptor. This usually causes a very thick unintentional deposition of SiC on the back of the wafer. Similar arguments hold for the hot wall configuration as well, but the SiC deposition on the backside is less, due to the very small temperature gradients perpendicular to the wafer surface. By using this reactor type the highest breakdown voltage value (4500 V, [13]) and minority carrier lifetime (2 us) has been reported up to today, which makes this reactor concept very promising for the future, if the doping homogeneity can be improved and the reactor concept can be transferred to multi-wafer processing. Hydrogen Fig. 1: Sketch of the principal design of Silane. . Nitrogen the CVD reactor chamber: Propane(1) double-walled water cooled reactor chamber 2 (2) gas diffuser
I I I I I
-
-
-
-(3)
SiC-wafer
(4)substrate holder
(5)rf pancake coil
(6) bell-jar-like graphite susceptor
laminar gas flow
3 _4 -5 6
> to pump
In a different approach, the type 3 reactor which is in use at the authors location is based on a long tradition of VPE reactors in the III-V epilayer growth. A high speed rotation of the substrate holder and a reduction of pressure are employed to adjust a stationary flow without recirculation. With this method good homogeneity and reproducibility together with low background doping should be achievable even without SiC coating of all graphite parts. The following chapters will introduce this type of a SiC-CVD reactor in detail and give an overview of the results attained in the last two years. EXPERIMENTAL CVD-system The CVD-system was built by EMCORE Corp. (New Jersey) following their experience with III-V epi-equipment. A palladium cell is used to provide high purity hydrogen to the process and a loadlock equipped with a turbo pump is attached to the process chamber for fast batch processing. A pressure control system with a big roughing pump allows accurate pressure adjustment in the growth chamber, even at high flow rates. The process control and data acquisition for all relevant parameters is computer based, a precondition of good reproducibility. The special needs of SiC-CVD, e. g. very high temperature capability, are taken into account for the construction of the growth chamber which is displayed schematically in fig. 1. The reactor allows processing of 254
single wafers with diameters up to 2 ΒΌ".The rf-heated bell-jar-like susceptor and the substrate holder (aid for transferring the wafer from the loadlock into the reactor) are made of high purity graphite. A SiC-coating of the susceptor was not used in order to avoid the above mentioned unintentional SiC-deposition on the back of the wafer during growth. This is not only an advantage for the setup of vertical devices but also allows an easy determination of the thickness of the
Data Loading...
