Which of the following statements is correct?<br/> A、Ultra high purity films can be obtained by thermal evaporation.<br/> B、E-beam evaporation cannot be used to deposit films on wafers with MOS devices already made on their surfaces.<br/> C、The thicknesses of deposited films can be well controlled during evaporation deposition. <br/> D、It is not possible to deposit refractory materials by vacuum evaporation.