Cubic　boron　nitride　(c-BN)　thin　films　have　been　deposited　on　Si　substrates　by　radio　frequency　sputter.　Sputtering　target　was　hot　pressed　hexagonal　boron　nitride　of　4N　purity.　Sputtering　gas　was　the　mixture　of　nitrogen　and　argon.　During　depositing　c-BN　thin　films,　substrates　were　biased　by　dc　voltage　negatively　with　respect　to　ground.　By　optimizing　the　deposition　conditions,　the　boron　nitride　(BN)　films　containing　a　large　amount　of　cubic　phase　were　obtained.　The　samples　were　characterized　with　Fourier　transformation　infrared　spectroscopy　(FTIR),　X-ray　photoelectron　spectroscopy　(XPS),　and　atomic　force　microscopy　(AFM).　According　to　FTIR,　the　cubic　phase　content　of　the　c-BN　thin　films　was　evaluated　to　be　92.　The　B/N　ratio　was　estimated　to　be　approximately　1　from　XPS.　The　AFM　shows　that　the　c-BN　thin　films　delaminated　from　Si　substrates　obviously.