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Uniformity Improvement in the RF Plasma Process

IP.com Disclosure Number: IPCOM000051199D
Original Publication Date: 1982-Aug-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Bright, AA: AUTHOR [+4]

Abstract

Where uniform treatment across a wafer dimension is essential for the LSI fabrication process, RF-plasma processes have been widely used for thin-film growth sputter etching and reactive ion etching. In Josephson technology, an 0(2) plasma is utilized to grow a very thin tunnel barrier oxide and one of the most important aspects to be iMproved is a uniform distribution of the tunnel current over the wafer which requires precise control of the barrier thickness within an accuracy of less than one atomic layer.

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Uniformity Improvement in the RF Plasma Process

Where uniform treatment across a wafer dimension is essential for the LSI fabrication process, RF-plasma processes have been widely used for thin-film growth sputter etching and reactive ion etching. In Josephson technology, an 0(2) plasma is utilized to grow a very thin tunnel barrier oxide and one of the most important aspects to be iMproved is a uniform distribution of the tunnel current over the wafer which requires precise control of the barrier thickness within an accuracy of less than one atomic layer.

In the tunnel barrier process currently being practiced, the tunnel current is controlled by adjusting plasma parameters, such as O(2) pressure and RF voltage, and systematically varies along the cathode radius due to a non-uniform distribution of O/+/(2) in the radial direction. Detailed studies on the O/+/(2) profile have shown that the O/+/(2) radial distribution is also sensitive to the pressure and RF voltage, so that one cannot control both tunnel current and its spread independently by simply adjusting the plasma parameters.

In the pressure range of <50 mTorr, the O/+/(2) population is higher at the canter of the cathode and gradually decreases towards the edge of the cathode as shown in the figure, where the open circles represent the O( ) concentration as a function of the cathode radius at 10 mTorr 0(2) and the open triangles represent that at 20 mTorr 0/+/(2) with an RF voltage of 325 V(pp) and a diode spacing of 2.25 in. This O/+/(2) profile reflects the non-uniform distribution of the excitation electrons which tend to escape from the discharge region near the c...