Preparation Of Diamond Film By MW-PCVD Method, And Its IR Transmittance And Stress Properties

Diamond is an excellent material for many applications dueto its unique optical, electrical, thermal and mechanical properties.However, natural diamond is rare and expensive, which prohibitsits extensive usage, the method of fabricating diamond is of greatinterest. So far, the two developed main methods of fabricatingdiamond are High Pressure High Temperature method (HPHT)and low-pressure Chemical Vapor Deposition (CVD) method.Because of the small size of HPHP diamond synthesized byHPHT, its application in many fields is limited. CVD methodshows the ability to fabricate large size and high qualitativediamond films which makes diamond application possible inmany fields. But the quality of diamond films synthesized byCVD method different from the natural diamond, many studiesshould be done. Lots of regularities about diamond depositionhave been revealed. But the research work should be done toenlarge size, make quality better and put down the cost. Amongseveral methods, microwave PCVD method is one of the mostsuitable methods in synthesizing high qualitative CVD diamondfilms. Because of its low contaminated and stable plasmadischarge, microwave PCVD method is considered as thebest method for fabricating high quality transparent diamondfilms. There are many studies in microwave PCVD diamond filmsduring the past years, but the study is still not enough onproperties and fabricating high quality diamond films. So in thispaper, the diamond films are fabricated by microwave PCVD, theproperties and the stresses of diamond films are studied. Thecontent of this study contains three parts as follows:(1) In the MW-PCVD diamond film deposition, the methaneconcentration, microwave power and oxygen are the mostimportant parameters which affect the quality of diamond films.Choosing suitable parameters is important for the fabrication ofhigh quality diamond films stable and speedy. With the increasingof the methane concentration, the diamond film growth rateincreases while it's quality get worse;at the same time, highmethane concentration make the figure of surface grains augment.The film quality is good but the film growth rate is low when themethane concentration is 2%;when the growth rate goes to 3%,the film growth rate increases and the film quality is as the sameas the film deposited in 2% methane concentration, so weconclude that 3% methane concentration is the perfect conditionin synthesizing high quality diamond film fabrication. With theincrease of microwave power, the quality of diamond films ispromoted and the Graphite element decreases. So high microwavepower is favorable to the deposition growth rate and it is alsogood for getting high quality sample. A small quantity of oxygenadded in the reaction will make good effects on the deposition ofdiamond film well.(2) The property of high quality transparent diamond film bymicrowave PCVD method is studied. The transmission ofdiamond films dealt with polishing by MW-PCVD in infraredregion is near 60%, which is close to the theoretic transmission ofdiamond 71%. The UV (ultraviolet) spectrum shows that thetransmission of diamond film in UV region is also good, absorbedpeak was not found. We find that the diamond films byMW-PCVD have high thermal conductivity and the facturestrength of diamond film is also good, which means it can be usedin many applications.(3) The stress in diamond films was studied. The parameterslargely affect the macro-stress in free standard diamond films. Ithas been found that the stress in diamond films deposited at lowmethane flow rate is tensile, and it decreases and graduallybecomes compressive with the increase of methane flow rate orair pressure.