H_(2)对HfO_(2)衬底上等离子体增强化学气相沉积石墨烯的影响

Effect of H_(2)on Plasma Enhanced Chemical Vapor Deposition of Graphene on HfO_(2)Substrate

HfO_(2)薄膜和石墨烯是用于制作石墨烯场效应晶体管的主要材料,而采用PECVD(等离子体增强化学气相沉积法)在HfO_(2)衬底上原位生长石墨烯是极具潜力的一种石墨烯制备方法,这种方法有助于降低石墨烯转移过程对石墨烯质量的影响,从而提高石墨烯场效应晶体管的性能。使用真空电子束蒸镀方法在重掺杂单抛硅片衬底上分别于50、150、250℃下沉积了100 nm厚的HfO_(2)薄膜样品;随后选用最优质量的HfO_(2)薄膜作为生长石墨烯的衬底,采用PECVD方法在温度为600℃、CH4流速为4 sccm的条件下,以不同的H2流速(0、5、10、15、20 sccm)原位生成石墨烯薄膜。结果显示,150℃下蒸镀的HfO_(2)薄膜粗糙度最低,表面最平整,同时也拥有最佳的介电性能。当H2流速为10 sccm时,可获得少层石墨烯薄膜,此时的石墨烯薄膜缺陷最小,表面平整且连续性好。通过对HfO_(2)衬底上石墨烯的生长机理进行分析发现,HfO_(2)衬底的低表面能导致含碳物种难以吸附到衬底上,石墨烯不易生长,但适当的H2参与可以有效降低CH4裂解反应的活化能,促进CH4的裂解,有利于生长出大面积的连续型石墨烯薄膜。

HfO_(2)thin film and graphene are the main materials used in the fabrication of graphene field-effect transistors.Employing plasma enhanced chemical vapor deposition(PECVD)for the in-situ growth of graphene on HfO_(2)substrate represents a highly promising method for graphene synthesis,which mitigates the impact of the graphene transfer process on graphene quality to consequently improve the performance of graphene field-effect transistors.HfO_(2)thin film samples with a thickness of 100 nm were deposited on heavily doped single-side polished silicon substrates using vacuum electron beam evaporation at temperatures of 50℃,150℃and 250℃.Subsequently,the HfO_(2)thin film with the best quality was used as the substrate for the growth of graphene.Graphene thin films were synthesized in-situ by PECVD at a tempe-rature of 600℃and CH_4 flow rate of 4 sccm with varying H_(2)flow rates(0 sccm,5 sccm,10 sccm,15 sccm and 20 sccm).The results indicate that the HfO_(2)thin film evaporated at 150℃exhibits the lowest roughness,smoothest surface,and optimal dielectric properties.Graphene thin films with few layers can be obtained at the H_(2)flow rate of 10 sccm with minimal defects,smooth surface,and good continuity.Analysis of the growth mechanism of graphene on the HfO_(2)substrate reveals that the low surface energy of HfO_(2)substrate hinders the adsorption of carbon species onto the substrate,making it challenging for graphene to grow.However,the appropriate involvement of H_(2)effectively reduces the activation energy for CH_(4)decomposition,facilitating CH_4 cleavage and favoring the growth of large-area continuous graphene thin films.