Revolutionizing Thin Film Deposition: How KDF's ERPP Technology Achieves ±1% Uniformity
by Firas Mahyob
Summary
Meeting the uniformity and repeatability demands of modern microelectronics and optical device manufacturing requires more than incremental improvements to existing equipment. KDF Technologies developed the Enhanced Rotating Planetary Pallet (ERPP) to address this directly, combining planetary substrate motion with linear scanning to achieve metallic film uniformity better than ±1% and run-to-run repeatability exceeding ±0.5%. This article walks through the design rationale, process results, and practical implications of the ERPP for applications ranging from multilayer conductive barriers in integrated circuits to titanium tungsten coatings used in acoustic filter manufacturing.
Metallic coatings deposited using the KDF Enhanced Rotating Planetary Pallet (ERPP) show consistently high film uniformity and tight process repeatability. This performance comes from running planetary revolution and linear scanning simultaneously, where each motion compensates for limitations the other cannot address alone. KDF Technologies has developed both reactive and non-reactive sputtering processes for metallic, semi-metallic, semiconductor, and dielectric materials using this approach. Across a wide range of processes, the system achieves film uniformity better than ±1% across the pallet, with repeatability better than ±0.5% pallet to pallet. These results support high-performance processing of multilayer conductive barriers and contact materials for integrated circuits, as well as titanium tungsten films for adhesion and diffusion applications in microelectronics and decorative technologies. The programmability of the rotating motion also provides control over surface morphology, which is discussed in more detail below.
The KDF 900 series sputtering tools combine linear scanning with a sophisticated rotating substrate motion, shown schematically in Figure 1. The planetary motion ensures every area of the substrate sees sputtered material arriving from multiple angles, averaging out the angular distribution of sputtered atoms. The linear scan simultaneously compensates for non-uniform target erosion and variations in plasma density. Together, these two motions maximize exposure to the sputtered flux from all directions and reduce spatial non-uniformities in the sputtering plume. Pallet uniformity and run-to-run repeatability on the order of ±1% were demonstrated across several metallic deposition processes, including tungsten (W) and titanium tungsten (TiW). These capabilities support precise, repeatable processing of complex multilayer metallic coatings for optical devices and semiconductor components.
Process with Standard Deposition
On standard KDF sputtering tools, metallic films such as W and TiW are deposited onto a 12" x 12" pallet deposition zone, which scans across a 15" x 5" rectangular magnetron cathode. Deposition is performed via DC magnetron sputtering, either reactively using oxygen or nitrogen with elemental targets, or non-reactively from compound targets. The cathode is engineered to optimize uniformity for metallic films, achieving an average thickness variation of approximately ±2% across four 4" wafers mounted on a planetary rotating pallet. Figure 2 presents a 6" wafer configuration of KDF's Enhanced Rotating Planetary Pallet system.
Process with System Enhancement
In advanced microelectronic applications, tungsten films are commonly used as critical layers within frequency-selective components such as surface acoustic wave (SAW) and bulk acoustic wave (BAW) filters. For Solidly Mounted Resonator (SMR) configurations in BAW filters, multilayer silicon-based stacks require film uniformity and run-to-run thickness repeatability on the order of ±1%. Since resonant frequency is inversely proportional to the thickness of the constituent layers, including tungsten, precise thickness control is essential for accurate frequency tuning. KDF 900 series sputtering systems, equipped with three- or four-target configurations, precisely controlled scan speeds, and multistep recipe capabilities, handle these demanding deposition tasks well, offering fine resolution in film thickness across complex multilayer stacks.
To achieve stringent film uniformity targets without incorporating uniformity apertures, a new pallet design was introduced: the Enhanced Rotating Planetary Pallet. The ERPP maintains the linear translation characteristic of standard KDF systems.
On top of the pallet sits a rotating platform, referred to as the "sun," which can rotate continuously across a broad range of speeds. Mounted to this platform are four wafer holders, each accommodating a 4-inch-diameter wafer, referred to as "planets." Each planet rotates at a fixed gear ratio relative to the sun, generating a full planetary motion of the wafers within the deposition plane. This motion is superimposed onto the standard linear translation of the pallet underneath the target. By integrating both rotational and translational movement, the planetary architecture averages out spatial variations in deposition rate across the cathode, improving uniformity across all wafers and reducing edge-to-center thickness variation. Step coverage on 3D features is also expected to improve, as varying the incident angle of deposition during rotation should benefit coating of high-aspect-ratio structures. Figure 2 illustrates the schematic configuration of the Enhanced Rotating Planetary Pallet.
Results
Tungsten and titanium tungsten films were deposited non-reactively using elemental W and TiW targets. Figures 3 through 5 summarize the results obtained using the ERPP technique. Figure 3 shows a reduction in sheet resistance with increasing setpoint values under constant linear scanning conditions. Wafer rotation during sputtering was found to significantly improve thin-film uniformity by averaging out the spatial non-uniformities inherent in the sputtering process, stabilizing critical film properties such as sheet resistance.
Figure 4 presents the uniformity results for W and TiW films deposited with the ERPP-enabled KDF 900 system. The planetary scanning motion consistently achieved within-wafer uniformities better than ±1% and pallet-wide uniformities better than ±2%, confirming the system's capacity for high-precision film deposition. Table 1 summarizes the performance of planetary scanning for TiW depositions using a standard 15-inch cathode.
Figure 5 shows improvements in surface roughness alongside the uniformity gains. The relationship between wafer rotation and surface roughness is not straightforward. Depending on process parameters such as rotation speed, deposition pressure, and target power, surface roughness may increase or decrease. Careful optimization of sputtering conditions is therefore needed to achieve the desired film characteristics for each application.
Discussion
The planetary scanning substrate carrier demonstrated meaningful improvements in both film uniformity and run-to-run repeatability. Non-reactive metallic film uniformities were reduced from typical values of ±2% to less than ±1% across the pallet. This improvement came directly from combining planetary rotation with linear translation, where each motion addresses a different source of non-uniformity in the deposition process.
The technique shows potential for other film types as well. Investigations are currently underway into its advantages for optical films and features with high aspect ratios. The ERPP architecture is also compatible with integration of a Plasma Emission Monitoring system and DC Pulsing, which would expand the range of processes and control options available to the operator.
