Thin Film Diamond Detectors for Industrial Applications
in Next Generation 157nm Lithography and High power Excimer Laser Beam
Diagnostics
Michael D Whitfield1,
Nadeem Rizvi1, Robert D McKeag2, Stuart P Lansley3,
Olivier Gaudin3 and Richard B Jackman3
1Exitech Ltd. Hanborough Business Park, Long Hanborough, Witney OX29 8SL. U.K.
2Centronic, Croydon. U.K.
3Departement of Electronics & Electrical Engineering, University College London, Torrington Place, London WC1E 7JE. U.K.
ABSTRACT
The next generation of photolithography stepper tools will operate at 157nm allowing the routine fabrication of sub-100 nm device features. For efficient commercial operation these machines will require robust solid-state UV detectors for direct beam monitoring and photoresist exposure dosimetry. Currently, no commercially available detectors can fully meet the all the specifications required for these applications. Silicon detectors, for example, suffer from rapid performance degradation and unacceptably high attenuation in the surface metallisation and passivation layers. This paper examines the role of CVD diamond as a detector material solution for use in 157nm research and future production steppers and in other high power excimer laser micro-machining applications. The authors discuss the fabrication of simple inter-digital surface point source detectors including the passivation and smoothing steps needed to realies high performance detector structures. The results of a detailed study of detector performance under industrial conditions on the world’s first commercially available 157nm micro-stepper tool are presented. To improve device sensitivity and transient response times it is necessary to carry out gaseous thermal passivation treatments to modify the defect structure of the near surface layer forming the active layer in these detectors. Spectral and pulse response characteristics have been evaluated by steady state and transient photoconductivity methods. Device sensitivity was studied over the laser fluence range 0.05-1.5 mJcm-2. Device gain was found to be liner with applied bias over a 3-order range. Long-term operational performance was studied up to a total of 107 laser pulses. Charge sensitive deep level transient spectroscopy and transient photoconductivity has been used to relate the observed device performance to the electrical defect structure of the CVD diamond material.
Many laser micro-machining applications would benefit from a device structure that would enable direct beam imaging for beam shaping and monitoring purposes at the work-piece. The paper will present results from performance studies on a 1-D array CVD diamond deep UV detector that has been used to image 193nm excimer laser beams and will discuss the design, fabrication and testing of a prototype 2-D array that is currently being built by the authors.