Preparation and Structural Investigation of Ultra-Uniform Mo Films on a Si/SiO₂ Wafer by the Direct-Current Magnetron Sputtering Method

Abstract

As a kind of important strategic resource, molybdenum (Mo) and its alloys are widely applied in solar cells and 5G radio frequency filters. In order to improve the yield of industrial production, it is important to reduce the nonuniformity of thin-film thickness. We prepared Mo films on CMOS compatible Si/SiO2 wafers through a magnetron sputtering method and systematically investigated the effect of tuning of several process parameters on film thickness nonuniformity and other structural properties, including crystallite size (D), microstrain (ε), and dislocation density (δ). At optimized sputtering power (80 W), chamber pressure (0.4 Pa), argon flow rate (90 sccm), substrate temperature (350 °C), and target–substrate distance (9 cm), the deposited 200 nm-thick Mo films show a unified <110> preferred orientation, and the film thickness nonuniformity reaches an excellent value of 0.46%, with a surface roughness of 0.83 nm and the full width at half maximum (FWHM) of X-ray diffraction (XRD) (110) rocking curve as low as 0.47°. Our results provide efficient reference for the preparation of uniform metal films, which have potential for improving the quality and yield in filter device manufacturing.

Realizing Ultrauniform Films at Wafer Scale through the Magnetron Sputtering Method

“…Then, the thickness ( t ) at 18 evenly distributed points along the step edge was measured using a step profiler (Dektak XT, Bruker Nano Inc.). These measurements were further used to calculate the average thickness ( t̅ ), standard deviation (σ), and thickness nonuniformity (η) as η = σ / t̅ …”

“…As a result, the film thickness nonuniformity reached an exceptional level of 0.46%. 6 In order to further improve the thickness uniformity of magnetron-sputtered films, an accurate theoretical model, prediction, and design are required. However, existing research in this field is insufficient.…”

“…4,5 Generally, the nonuniformity of film thickness is a critical factor in highprecision electrical and optical applications, 6 such as gravitational wave detection reflectors, 7 optical filters, 8,9 thermochromic glass, 10 optical components in microscopy, 11 and the electrode layer in resonators. 6,12 Moreover, the fabrication of large-sized multilayer mirrors for extreme ultraviolet, soft Xray, and X-ray applications typically requires ultrauniform films. 13 To improve the thickness uniformity of sputtered films, researchers have conducted numerous experimental efforts, such as adjusting the arrangement of magnetic circuits, 14 designing the shape of baffle plates, 15 regulating the relative position of the target and the substrate, 16 reforming the motion mode of the substrate, 17,18 and optimizing the process parameters.…”

“…As an important deposition technique, magnetron sputtering (MS) has been widely applied for the preparation of various films. − It owns several advantages, including compatibility with the complementary metal-oxide-semiconductor transistor (CMOS) process, high deposition rate, excellent quality, good controllability, and environmental friendliness. , Generally, the nonuniformity of film thickness is a critical factor in high-precision electrical and optical applications, such as gravitational wave detection reflectors, optical filters, , thermochromic glass, optical components in microscopy, and the electrode layer in resonators. , Moreover, the fabrication of large-sized multilayer mirrors for extreme ultraviolet, soft X-ray, and X-ray applications typically requires ultrauniform films …”

“…Recently, we successfully achieved ultrauniform Mo films on wafer-scale Si/SiO 2 substrates by systematically optimizing the process parameters, including sputtering power, chamber pressure, argon flow rate, substrate temperature, and target-substrate distance. As a result, the film thickness nonuniformity reached an exceptional level of 0.46% …”