Stoyan Nihtianov

Pure boron-doped photodiodes: A solution for radiation detection in EUV lithography

A pure boron chemical vapor deposition (CVD) technology, which forms delta-doped boron surface layers during diborane B2H6 exposure at 700degC, has been successfully used to fabricate silicon-based p+n photodiodes for radiation detection in the extreme-ultra-violet (EUV) spectral range. Outstanding electrical and optical performance has been achieved in terms of extremely low dark current (< 50 pA at reverse bias of 10 V), near theoretical responsivity (0.266 A/W at 13.5 nm wavelength), and excellent stability to high radiation doses (< 1% responsivity degradation after 0.2 MJ/cm2 exposure). Therefore, the diodes are suitable candidates for photon detection functions in the next-generation EUV lithography systems.

Power-Efficient High-Speed and High-Resolution Capacitive-Sensor Interface for Subnanometer Displacement Measurements

This paper presents a power-efficient capacitive-sensor interface solution for high-speed and high-resolution subnanometer displacement measurement systems. The proposed solution utilizes a zoom-in capacitance-to-voltage converter stage to remove the offset posed by the large nominal sensor capacitance, which would otherwise dominate the dynamic range. The realized zoom-in factor is 100. The designed circuit uses a correlated-double-sampling technique to cancel both the amplifier offset and the reset noise. First, a printed-circuit-board solution was realized to verify the principle of operation and its limitations. Then, an integrated circuit was designed, fabricated, and tested. Measurement results show that the achievable capacitance resolution is better than 30 aF, from a sensor with a nominal capacitance of 10 pF, which translates into a dynamic range of 18 b. The measurement latency is only 5 μs. This performance is achieved with only 2.4-mW power consumption.

An interface circuit for R-C impedance sensors with a relaxation oscillator

A simple interface circuit for impedance sensors based on a relaxation oscillator is presented. The measurement strategy and the principle of operation are discussed. The circuit is intended for measuring impedance, which can be represented as a capacitor and a resistor in series. By means of a four-signal measurement technique, continuous self-calibration is achieved. The output signals for both components of the unknown impedance are time periods, and for calculating their values only one reference capacitor is needed. A measurement set-up is presented with which the new method was tested. The experimental results prove that with this new technique, very high resolution for both components of the measured impedance can be achieved-better than 0.1 /spl Omega/ for R. and better than 0.1 pF for C/sub x/.

Surface-Charge-Collection-Enhanced High-Sensitivity High-Stability Silicon Photodiodes for DUV and VUV Spectral Ranges

The electrical and optical performance of silicon pure-boron (Pure-B) diode is investigated in relationship to the thermal processing used after formation of the PureB chemical-vapor-deposition layer that creates otherwise extremely ultrashallow p+-n junctions. The measured responsivity of PureB diodes is high and stable in the deep ultraviolet (UV) and vacuum UV spectral ranges, covering the spectrum from 220 down to 50 nm. Results are presented, showing that a very high surface charge collection efficiency can be obtained owing to a strong surface electric field resulting from a doping profile that is steep and without roll-off right up to the Si surface.

Electrical and Optical Performance Investigation of Si-Based Ultrashallow-Junction

Recently, a silicon-based ultrashallow-junction photodiode (B-layer diode) has been reported, with very high and very stable sensitivity in the vacuum-ultraviolet and extreme-ultraviolet spectral ranges. However, the ultrashallow nature of the junction leads to a high series resistance of the photodiode if no conductive capping layers are used. In a recent paper by Shi , a study on the relation between the sensitivity and the series resistance of the B-layer diodes, which can be large due to the shallow-junction depth, was presented. In this paper, an extensive analysis of the photodiode electrical and optical performance parameters and their interrelation is given. The influence of the series resistance on the response time of the photodiode for different illumination patterns is studied theoretically and also experimentally verified. It has been proven by modeling, simulations, and experiments that the time constant of the photodiode does not change significantly with the illumination spot area. This effect is due to temporary variations, going in opposite directions, of the equivalent series resistance, and the junction capacitance values found at the first instant a photogenerated charge are locally stored in the photodiode p-n junction. Also, the dependence of the degradation of the sensitivity on the incident wavelength and the diode vertical stack is examined through analysis and experimentation.

\hbox{p}^{+}\hbox{-}\hbox{n}

Silicon p+n photodiodes fabricated by a pure boron deposition technology are evaluated for detection in the Vacuum Ultra-Violet (VUV) spectral range from 115 nm to 215 nm wavelengths, where the attenuation length in silicon is only a few nanometers. It is demonstrated that the junctions formed by the B-layer process are so ultrashallow that the photodiodes are able to provide a very good sensitivity, in the order of 0.1 A/W, in the whole VUV range. Moreover, the demonstrated stability also appears to be very good if isolating layers on the diode surface are avoided.

VUV/EUV Photodiodes

Recently, silicon ultrashallow p+ n photodiodes, fabricated by a pure boron deposition technology (B-layer diodes), were evaluated for detection in the Vacuum Ultra-Violet (VUV) spectral range from 115 nm to 215 nm wavelengths, where the attenuation length in silicon is only a few nanometers. Superior sensitivity in the order of 0.1 A/W in the whole VUV spectral range was reported [1]. Next to the sensitivity, another important parameter of any photodetector is the response time, which is directly related to its series resistance. In this work a study of the relation between the sensitivity and the series resistance of the B-diodes is presented, supported by simulation results and optical/electrical experimental results. Moreover, practical methods for designing a high sensitivity VUV photodiodes while keeping a relatively low series resistance, are proposed. The experimental results demonstrate that by modifying the diode structure, the series resistance can be effectively reduced. At the same time, the B-layer diodes still maintain a high VUV sensitivity.

Optical stability investigation of high-performance silicon-based VUV photodiodes

A novel multi-period interface system for impedance measurement, based on a first-order oscillator, is presented. The system is designed for sterility testing of aseptically packed food products by noninvasive measurement of the conductivity of the packaged food. In this application the measured impedance can be modeled as a resistor, representing the conductivity of the food in series with a capacitor, representing the electrical behavior of the walls of the food container. The measurement range is: 50 pF to 220 pF for the capacitive component and 10 /spl Omega/ to 150 /spl Omega/ for the resistive component. By applying auto-calibration, a relative error of 0.3% for the resistive component R/sub x/ and 0.1% error for the capacitive component C/sub x/ is achieved. The output signal is a period-modulated square wave signal, which can be processed directly by a microcontroller, without any additional interface circuit. To calculate the values for R/sub x/ and C/sub x/, a data processing algorithm has been developed. The details of a prototype design have been discussed together with the experimental results.

Series resistance optimization of high-sensitivity si-based VUV photodiodes

This paper presents a review of the latest advances in the field of capacitive, inductive (eddy current), and magnetic sensors, for measurement of absolute displacement. The need for accurate displacement and position measurement in the micrometer, nanometer, and subnanometer scales has increased significantly over the last few years. Application examples can be found in high-tech industries, metrology, and space equipment. Besides measuring displacement as a primary quantity, absolute displacement sensors are also used when physical quantities such as pressure, acceleration, vibration, inertia, etc., have to be measured. A better understanding of the commonalities between capacitive, inductive, and magnetic displacement sensors, as well as the main performance differences and limitations, will help one make the best choice for a specific application. This review is based on both theoretical analysis and experimental results. The main performance criteria used are: sensitivity, resolution, compactness, long-term stability, thermal drift, and power efficiency.