Cleaning Process Optimization in a Gate Oxide Cluster Tool Using an in-Line XPS Module
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I. INTRODUCTION The state-of-the-art process monitoring in IC fabs relies on metrology tools physically separated from production equipment. This off-line concept suffers from major limitations, i.e., time consuming transportations and logistics, the need for monitor wafers, and a lack of direct feedback to equipment control. Recent R&D efforts aim at the integration of measurement tools into process equipment, cluster tools, or work cells [1]. This integration, also anticipated by the published roadmaps [2], is mostly driven by the need to enhance productivity, namely to save costly monitor wafers and to reduce the amount of batches misprocessed before the yield problem is detected. As film thickness decreases, Si/Si0 2 interface properties play a more significant role with respect to gate dielectric processing and integrity. Thus, pre-gate surface preparation becomes one of the most critical steps in future device technologies. The commonly used wet cleaning prior to gate oxide growth is not only expensive, but also environmentally detrimental, since large quantities of ultrapure liquids are manufactured and have to be treated properly after use. Wet cleaning is not compatible with multichamber process systems (cluster tools), which are increasingly considered as a key equipment in many technological process sequences in advanced manufacturing e.g. for gate oxidation [3, 4, 5]. 371 1997 Materials Research Society Mat. Res. Soc. Symp. Proc. Vol. 477 ©
Using cluster tools for gate stacks the wafer transfer is performed under controlled environment. In combination with a Vapor Phase Cleaning module (VPC) such a cluster tool can lead to particle free surfaces without native oxide and carbonaceous contamination, which enhance the quality and integrity of thin gate dielectric films. II. EXPERIMENTAL To investigate the properties of silicon surfaces after cleaning, an in-line X-Ray Photoelectron Spectroscopy module (XPS) was integrated into a gate oxide cluster consisting of a Vapor Phase Cleaning module (VPC) and a Rapid Thermal Oxidation module (RTO), as shown in Fig. 1.
XPS Module
Rapid Thermal Oxidation Module
Fig. 1: Schematic of the Cluster Tool Vanor Phase Cleaning Module The cleaning process was carried out in a STEAG AST Vapor Phase Cleaning module (VPC) integrated in a state-of-the-art cluster tool also consisting of a STEAG AST Rapid Thermal Oxidation module (RTO). The VPC process chamber (Fig.2) is made of HastalloyTM to avoid contamination during the cleaning process. All parts of the reactor were kept at a temperature of 40'C. The VPC chamber wall was heated by an integrated, temperature controlled water circuit, whereas the quartz-window was heated by a hot air blower. Anhydrous HF (AHF) (99.9%), contained in a nickel cylinder at 40'C, was fed at cylinder pressure through a heated gas line into a temperature controlled mass flow controller. The nitrogen bubbler, filled with methanol was kept at 20'C. All tubes in contact with either methanol or HF were heated to prevent condensation. Ozone at a conce
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