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METHOD OF PROTECTING GAAS SURFACES FOR PATTERNING IN MIXTURES OF CHLORINE AND FLUORINE PLASMAS

IP.com Disclosure Number: IPCOM000009846D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2002-Sep-23
Document File: 2 page(s) / 113K

Publishing Venue

Motorola

Related People

J. K. Abrokwah: AUTHOR [+3]

Abstract

Plasma etching of GaAs and other III - V compounds is oftentimes required for isolating device structures, forming portions of devices such as emitter and collector regions of heterojunction bipolar transistors, and forming facets for optical devices. A method of protecting GaAs surfaces with a hardmask when etching in combinations of fluorine and chlorine plasmas such as BCl31SF6 or SiCI41SF6 is described.

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MOTOROLA

Technical Developments

METHOD OF PROTECTING GAAS SURFACES FOR PATTERNING IN MIXTURES OF CHLORINE AND FLUORINE PLASMAS

by J. K. Abrokwah, M. Sadaka and F. Clayton

ABSTRACT

Plasma etching of GaAs and other III - V compounds is oftentimes required for isolating device structures, forming portions of devices such as emitter and collector regions of heterojunction bipolar transistors, and forming facets for optical devices. A method of protecting GaAs surfaces with a hardmask when etching in combinations of fluorine and chlorine plasmas such as BCl31SF6 or SiCI41SF6 is described.

STATEMENT OF THE PROBLEM

Plasma etchants BCI31SF 6 or SiO41SF 6 are often used for etching GaAs and other IlI-V compounds.

For some applications, photoresist serves as the etch mask, allowing various device patterns to be transferred onto the GaAs substrate. Mter dry etching, the photoresist is stripped by oxygen ashing and/or wet treatments. For devices that operate with high electric fields, the plasma processing and resist stripping are critical steps in determining the reliability and operating voltages of the devices.

Damage from the plasma etch and post dry etch photoresist stripping may have a strong degrading effect on parameters such as breakdown voltage and reliability of the devices. Devices of the type discussed include high voltage heterojunction bipolar devices, PIN diodes, IMPATT diodes, and the like. This publication describes a method of protecting GaAs surfaces with a hard-mask prior to etching in mixtures of chlorine and fluorine plasmas without masking with photoresist during the plasma etching, thus maintaining high device breakdown voltages.

SOLUTION

The hard-mask consists of AlNISiN, typically having a dimension of 300A to 4O0A. An additional sacrificial SiN layer of about 4OOA is deposited on

Motorola. Inc. 2000

the AIN to facilitate photoresist patterning of the AlN/SiN hardmask stack. Photoresist developers are basic and may attack AlN if the photoresist patterning is directly performed on the A1N. Thus, the hard-mask is first patterned with photoresist and the top SiN is etched with a suitable dry etch such as SF 6. The photoresist is stripped off by oxygen ashing, then the A1N windows are etched with dilute ammonium hydroxide solution. The top SiN and lower SiN in the open windows are subsequently etched by SF6 chemistry, exposing the GaAs surface for plasma etching.

Before etching the GaAs, the AlN hard mask is fluorinated by treating in SF 6 plasma to fofll1 a thin AlF layer (10A - 50A). With the hard AlF cap layer.

the GaAs may be etched in BC131SF6 or SiCI4ISF.o chemist...