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Bias-controlled hot filament chemical vapor deposition (HFCVD) system has been set up for the synthesis of diamond films. Silicon wafer was chosen as substrate to study the processing parameters of the system. Five commercial hard films was chosen as buffer layers to evaluate the feasibility of depositing diamond films on high speed steels.
Hot filament plays a vital role in HFCVD system. Variations in electrical resistivity and los of mechanical integrity due to the carburization process during depositions are main concerns for choosing the candidate filament materials. In this study, the Ta wires turn out to be more stable and durable than W wires in supporting the HFCVD process. The high temperature reistivity data of Ta and W were measured and calculated to complement the design specification of a production HFCVD system for diamond film synthesis in the furture.
Among various deposition parameters, the substrste temperature showed significant effects on the film quality. An optimum substrate temperature based on thermalcouple measurements was identified as 750℃. Lower temperatures bring down both deposition kinetics and film quality. On the other hand, poor crystallinity and morphology start to develop at higher substrate temperatures. Substrate biasing affects the electron distributinand plasma behavior. Excessive electron bombardment on substrates was induced by the forward biasing and resulted in improvement in nucleation density. However, at large forward biasing potential, degradation of film quality occurred due to the local shift of methyl/hydrogen ratio as a result of additional excitation of reactive species within the boundary layer. For reverse biasing, microcrystalline structure tends to develop at higher biasing current.
Chromium nitride of 4 um showed the most promising result in improving the film adhesion between the diamond film and high speed steel substrates. In addition, a non-crystalline glassy carbon film, which may contribute to the improved film adhesion was found between the diamond film and the CrN buffer layer. There existed significant intrinsic stress within the diamond films grown on CrN. The internal stress based on the calculation from the Raman peak shift is about 1.2*1011 dyn/cm2.
Preliminary results showed a promising potential for depositing high purity diamond films on the CrN-coated high speed steels.
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