Nanoscale-controlled Plasma CVD of Metal-doped Semiconducting DLC Films

以甲烷、氢气和一种有机金属化合物为气源，采用射频等离子体增强化学气相沉积法（PECVD）制备了金属掺杂类金刚石碳（DLC）薄膜。首先，我们使用四甲基锡（TMT）作为掺杂源，并研究了锡掺杂DLC膜的膜特性。X射线光电子能谱证实了薄膜中形成了锡碳直接键。薄膜中的锡浓度可以通过TMT分压比R（=（P_<TMT>/P_<Total>）× 100 [%]）来控制。当R大于0.2%时，在沉积膜中形成具有随机取向的纳米尺寸的β-锡相团簇。为了避免团簇的形成和原子尺寸的掺杂，R值应小于0.2%，这导致薄膜中Sn/C的最大浓度比为0.1。掺锡类金刚石薄膜的电阻率为-10^3 Ω·cm，远低于纯类金刚石薄膜的电阻率（-10^7 Ω·cm）。其次，我们采用射频等离子体化学气相沉积（PECVD）和射频溅射相结合的方法制备了掺金或掺铜的类金刚石薄膜。在掺金类金刚石薄膜中，金只以金属团簇的形式存在。没有形成金碳直接键。另一方面，少量的铜-碳键被发现在铜掺杂的薄膜。掺杂剂金属的浓度可以通过位于射频电极上的金属尖端的数量来控制。随着金属浓度的增加，电阻率从10^7 Ω·cm急剧下降到1 Ω·cm。通过掺杂金属元素可以使DLC膜的电阻率在8个数量级的范围内变化，这意味着掺杂金属可以使DLC膜的电学性质从绝缘变为半导体。该研究揭示了DLC膜在有源电子器件中的可能应用。

We synthesized metal-doped diamond like carbon (DLC) films by rf plasma-enhanced chemical vapor deposition (PECVD) using methane, hydrogen and an organometallic compound as gas sources. First, we used tetramethyltin (TMT) as a dopant source and investigated the film properties of tin-doped DLC films. Tin-carbon direct bonds are formed in the films, which is confirmed with X-ray photoelectron spectroscopy. The tin concentration in the films can be controlled by TMT partial pressure ratio, R (= (P_<TMT>/P_<Total>)*100 [%]). When R is over 0.2%, nanometer-size clusters of beta-tin phase are formed in the deposited films with random orientation. To avoid the formation of the clusters and dope tin at atomic size, the R value should be less than 0.2%, which led to the maximum Sn/C concentration ratio of 0.1 in the films. The electrical resistivity of the tin-doped DLC films is-10^3OMEGAcm, much lower than that of pure DLC films (-10^7OMEGAcm). Higher R value causes lower transmittance in infrared region.Next, we prepared gold-or copper-doped DLC films by a hybrid process of rf PECVD and rf sputtering. In the gold-doped DLC films, gold exists only in the state of metallic cluster. Gold-carbon direct bonds are not formed. On the other hand, small amount of copper-carbon bonds are found in the copper-doped films. The concentration of the dopant metal can be controlled by the number of metal tips located on an rf electrode. The electrical resistivity decreased drastically from 10^7OMEGAcm up to 1OMEGAcm with the increase in the metal concentration. We can vary the electrical resistivity of DLC films over a wide range of 8 order by doping a metallic element.These results mean that the doped metal can change the electrical properties of DLC films from insulating to semiconducting. This study reveals the possible application of DLC films to active electronic devices.