New Ellipsometer Focuses on Ultrathin Gate Measurement

17-Sep-2001

Our PQ Ruby Sub''tomic Laser ellipsometer/reflectometer measures ultra-thin gate oxide (UTGO) layer thicknesses with an accuracy and repeatability better than 0.025 Ångström. That is less than 1/100th the thickness of a SiO2 mono-layer, which already pushes the performance of the instrument ahead of today''s requirements in the International Technology Roadmap for semiconductors. Designed principally for in-line process control in IC production, the Sub''tomic determines the thicknesses, optical refractive indices, absorption constants and reflectivities of thin films The Sub''tomic is the first of a range of optimized Application-Specific metrology tools currently being developed from our standard product families. By dedicating existing technologies to specific applications, we aim to optimize performance and eliminate metrology-related bottlenecks from the semiconductor production process. The Sub''tomic focuses on (transparent) dielectric films, while our PQ Emerald opto-acoustic tool characterizes opaque metal layers. Characterizing ultra-thin gate oxide layers is becoming a major challenge as the semiconductor industry continues to scale device dimensions. Channel lengths below 180 nm have corresponding gate dielectric thicknesses of 20 Ångström and less. Measuring films with thicknesses of a few atomic dimensions demands sub-atomic repeatability. With a typical repeatability of 0.04 to 0.06 Ångström, the standard PQ Ruby targets thick films and multi-layer stacks. Improving this figure to 0.025 Ångström optimizes the Sub''tomic for UTGOs and high-k film analysis. Laser ellipsometers already give the highest available resolution for film thickness measurements but we have been able to tune the PQ Ruby Sub''tomic to UTGOs by optimizing the optical path and related electronics and hardware. The instrument uses an ultra-stable 633 nm HeNe laser to measure films between 0 and 3000 Ångström, and a UV/VIS-reflectometer to measure films between 500 Ångström and 30µm. This allows it to combine two roles to form a truly optimized UTGO metrology tool that retains the versatility of the PQ Ruby. Besides its specialized UTGO measurement function, the Sub''tomic can thus perform all the functions of the standard PQ Ruby. So, it can act as a backup for other thin film metrology equipment. It shares the same user-friendly features as the Ruby, including cassette-to-cassette loading with single or dual load port, small footprint, high throughput (greater than 120 wafers/hour) and easy-to-use SEMI E95-0200 compliant PQ Diamond software. Typical applications Ultra-thin gate oxides Alongside all the other demands, measuring equipment has to cope with inherent statistical atomic variations of UTGOs. High-k dielectrics Laser ellipsometry is the most precise optical method for measuring the high-k dielectrics that are increasingly being used in advanced MOS devices

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