Highly conformal TiN by atomic layer deposition: growth and characterization

Electrically conductive conformal thin films are needed in a variety of applications, e.g. in supercapacitors [1]. This abstract reports the first results of highly conformal TiN films grown by thermal atomic layer deposition (ALD) process from TiCl₄ and NH₃. The TiN films were characterized by several methods: i) the thickness and density by X-ray reflectometry, ii) the composition by time-of-flight elastic recoil detection, iii) the resistivity by four-point probe measurements, iv) the residual stress by wafer curvature measurement and Stoney's equation, and v) the conformality by the "PillarHall" microscopic lateral high-aspectratio (LHAR) structures [2]. The "stop flow" (SF) option available in the Picosun reactor at VTT was used to increase the thin film conformality. The SF was tested on oxidized 150 mm silicon wafers, LHAR test structures and porous silicon samples. The process was investigated in a temperature window of 300 to 500^oC and the typical layer thicknesses were from 10 to 20 nm. Density of up to 5.0 g/cm3 was obtained by XRR. According to ToF ERDA, the main impurity was oxygen. Resistivity, measured after chamber conditioning (initial 500 cycles of AlTiCN and additional 6000 cycles of TiN), decreased with increasing ALD temperature, being <200 µOhm cm for films grown at 450^oC. Films were all under tensile stress. The residual stress decreased with increasing deposition temperature, from about 2000 MPa at 350^oC to about 1000 MPa at 450^oC after which the stress saturated (Figure 1a). For a 200 nm gap LHAR sample an aspect ratio of 2500:1 was achieved using the SF option (cycle time was 36 s; Figure 1b).