Bawa Singh

Reactive ion etching end‐point determination by plasma impedance monitoring

Impedance monitoring of a rf glow discharge is successfully used to determine the end point of reactive ion etching. The feasibility of using this technique is demonstrated on diode, triode, and magnetic multipole enhanced triode reactors applied to etching polycrystalline silicon on SiO2 on Si and Si3N4 on Si in an SF6 plasma, and to stripping photoresist on Al on Si in an O2 plasma. The end point of etching is determined by monitoring changes in the induced dc bias, the rf voltage, the rf current, or the phase relationship between them on either of the powered electrodes (in the cases of the triode configurations). This method is easily applicable as in in‐process end‐point detector and eliminates the need of optical access to either the plasma or the substrate.

Magnetic multipole‐based reactive ion etching reactor

The addition of a simple inexpensive magnetic multipole to a parallel plate triode results in a magnetic enhanced etch reactor configuration that has impressive low pressure characteristics. The multipole electrode which is in the form of a cylindrical multipolar bucket, open at both ends, is added to the powered electrode of the triode being employed as a plasma etching system. The multipole becomes, in effect, an extension of the ground shield, surrounding either electrode. The resulting electrode configuration produces an extremely uniform, dense plasma at pressures as low as 2–3×10−4 Torr. The effect of the magnetic enhancement (electron containment, uniformity profile modification, and low substrate bias) is particularly pronounced at lower pressures. Significant improvement over existing triode schemes is obtained using the grounded cylindrical multipolar bucket as an extension of the ground shield of the driven electrode (not the substrate electrode). This system is considerably simpler than dual f...

Wafer temperature measurements and end‐point detection during plasma etching by thermal imaging

Thermal imaging by an infrared television camera has been successfully employed as an in situ method for end‐point detection during plasma etching of polycrystalline silicon layers on a SiO2/Si substrate. In addition, it is also shown that thermal imaging can be used for remote sensing of etch rate, heat of reaction, wafer temperature, and for measuring thermal time constants during plasma etching. From these measurements, the heat‐transfer coefficient of the thermal contact between the silicon wafer and the water‐cooled electrode can be determined.

Development of emissivity models and induced transmission filters for multiwavelength imaging pyrometry

The results of our work on the development of emissivity models and IR filters for applications in multi-wavelength imaging pyrometry are presented. Techniques such as Fourier transform IR spectroscopy have been deployed to determine the emissivity of Si and SiO2/Si in the temperature range of 331 to 1235 K. These measurements have been obtained for n-Si, p-Si and SiO2/Si in the oxide thickness range of 60 to 500 nm. These results coupled with calculations of emissivity from first principles lead us to model the wavelength dependence of emissivity. Preliminary measurements of emissivity of HgCdTe are reported.

Application of thermal imaging methodology for plasma etching diagnosis

This paper describes the application of thermal imaging by an infrared CCD TV camera with PtSi Schottky-barrier detectors for in-situ monitoring of plasma etching parameters. In-situ radiometric measurements were successfully employed for wafer temperature measurements and end-pint detection during plasma etching of polycrystalline silicon film on oxidized Si substrate for normal as well as oblique viewing. It was shown that thermal imaging can also be used for remote sensing of etch rate, heat of reaction and for measuring thermal time constants. The heat transfer coefficient of the thermal contact between the Si wafer and the water-cooled electrode can be determined from these measurements. The values of the heat transfer coefficients for the wafers just placed on the electrode without any provision of a good thermal contact were found to fall in the range of 8 to 12 J/m2-s-K and increased to about 200 J/m2-s-K when vacuum oil was used to improve the thermal contact.

Etch-induced damage in high-density inductively coupled plasma etching reactors

A fundamental understanding of damage to thin oxides in inductively coupled plasma (ICP) etching reactors is required to enable their widespread acceptance. XPS, C - V, DLTS and electrical breakdown techniques were used to study damage in a ICP reactor configuration capable of generating very uniform plasma. A Langmuir probe was employed to study the uniformity but any micro-nonuniformity close to the wafer surface could not be clearly identified. Etch induced electrical damage to thin oxide was found to be in good agreement with physical damage. It was observed that the degradation to thin oxide is associated with the high-energy electron bombardment when only the rf coil is powered with a floating rf electrode that holds the wafer. However, when both the coil and the electrode are powered the intensity of damage is a function of rf power.

Surface Modifications of Mechanical Heart Valves

For more than four decades, the advent of prosthetic heart valves has revolutionized the treatment of cardiac valvular dysfunctions. Compared to patients with dysfunctional cardiac valves who did not undergo valve replacement, patients who did have cardiac valve replacement operations for severe valve disease have increased survival, enhanced cardiovascular function, and improved quality of life (1,2). More than 80 models of prosthetic heart valves have been introduced and used globally, and more than 60,000 cardiac valve replacement surgeries are performed annually in the United States alone (3).