Electron-enhanced atomic layer deposition of silicon thin films at room temperature

Abstract

Silicon thin films were deposited at room temperature with electron-enhanced atomic layer deposition (EE-ALD) using sequential exposures of disilane (Si2H6) and electrons. EE-ALD promotes silicon film growth through hydrogen electron stimulated desorption (ESD) that creates reactive dangling bonds and facilitates Si2H6 adsorption at low temperatures. Without hydrogen ESD, silicon growth relies on thermal pathways for H2 desorption and dangling bond formation at much higher temperatures. An electron flood gun was utilized to deposit Si films over areas of ∼1 cm2 on oxide-capped Si(111) substrates. The silicon film thickness was monitored in situ with a multiwavelength ellipsometer. A threshold electron energy of ∼25 eV was observed for the Si film growth. A maximum growth rate of ∼0.3 Å/cycle was measured at electron energies of 100–150 eV. This growth rate is close to the anticipated growth rate assuming dissociative Si2H6 adsorption on dangling bonds on representative single-crystal silicon surfaces. The Si growth rate also displayed self-limiting behavior as expected for an ALD process. The silicon growth rate was self-limiting at larger Si2H6 pressures for a fixed exposure time and at longer electron exposure times. The silicon growth rate versus electron exposure time yielded a hydrogen ESD cross section of σ = 5.8 × 10−17 cm2. Ex situ spectroscopic ellipsometry showed good conformality in thickness across the ∼1 cm2 area of the Si film. Si EE-ALD should be useful for a variety of applications.