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Ion Beam Scanning in a Circular Pattern

IP.com Disclosure Number: IPCOM000086016D
Original Publication Date: 1976-Jul-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Vadehra, SK: AUTHOR

Abstract

Traditionally, ion beams are scanned across regions such as semiconductor substrates into which ions are to be introduced in square patterns. It has been found that a circular scan pattern of the type to be described offers distinct advantages over the square scan pattern.

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Ion Beam Scanning in a Circular Pattern

Traditionally, ion beams are scanned across regions such as semiconductor substrates into which ions are to be introduced in square patterns. It has been found that a circular scan pattern of the type to be described offers distinct advantages over the square scan pattern.

The programming input voltages for the horizontal and vertical scan amplifiers of a typical electrostatically scanned ion implantation system are shown in Figs. 1 and 2. These are triangular waveforms and they produce a square scanned area when implanting a circular wafer. One of these inputs can be modified by a circuit shown in Fig. 3, so that the resultant scanning is restricted to a circular area, shown in Fig. 4. OPERATION

The circuit in Fig. 3 is comprised of two analog squaring modules 10 and 11, a summing amplifier 12, an analog comparator 13 and a function generator 14 whose output is a ramp which can be programmed with either a positive or negative slope. As shown in Fig. 3, the slope of V(x) is reversed by the comparator output whenever V(x)2 + V(y)2 is greater than A/2/. A/2/ is the absolute value of the peak-to-peak amplitude of V(y), squared. Components for this circuit are readily available and the resultant modification of V(x) and the scanned area are shown in Fig. 4.

The circular scan has advantages over the square scan because: Ion Beam Utilization(x) = Area of the wafer over Area of the scanning.

Let A be the scanning amplitude require...