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Enhancement of Metal-Halogen Reaction for Etching and Patterning

IP.com Disclosure Number: IPCOM000106129D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 109K

Publishing Venue

IBM

Related People

Haring, RA: AUTHOR [+6]

Abstract

This is a method for laser stimulated halogen gas etching of a metal in the presence of an active gas, starting with a non-corrosive gas such as CCl2F2 (FREON 12*).

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This is the abbreviated version, containing approximately 52% of the total text.

Enhancement of Metal-Halogen Reaction for Etching and Patterning

      This is a method for laser stimulated halogen gas etching of a
metal in the presence of an active gas, starting with a non-corrosive
gas such as CCl2F2 (FREON 12*).

      A plasma is generated in a non-corrosive gas of which the
molecules contain halogen atoms.  In the plasma some of the gas
molecules will dissociate.  The active species produced by the
dissociation of the gas, such as the halogen atoms of Cl or Br,
attack the metal to be patterned.

      Narrow (>8 micron) copper lines can be directly patterned on a
substrate using laser etching.  The mechanism involves a Cu/Cr
reaction with Cl2  or Br2  gas molecules to form CuCl or
CuBr.  The laser beam then removes the reaction compound.  The
patterning is achieved by imaging the laser beam through a mask.
That method offers a simple process without lithographic steps and
achieves a finer line-width than obtained by wet etching, but the
laser etching process is relatively slow.  for example, when etching
in Cl2  gas at about 350 mJ/cm sup(2)  fluence, the average etch rate
is about 160 nm/sec at a laser pulse rate of 40 pps.  Below 40 pps,
the etch rate increases with the pulse rate, indicating that the
reaction product formed is thicker than the material removed by each
pulse.  Above 40 pps, the etch rate saturates with pulse rate,
indicating that the etch rate is limited by the Cu-Cl2  reaction
rate between pulses.  With a faster reaction, the etch rate is
enhanced at high pulse rates.  This has been demonstrated by a
reaction in Br2  gas.  This article describes an alternative
method to achieve a high reaction rate for metal-halogen compounds
using less corrosive and toxic gases.  Cu-Cl is used as an example.

      There is evidence that metals react faster with ionic or atomic
halogen species compared to reaction with molecular species.  When Cu
or CuCl is in contact with Cl2  molecules, there is a precursor
state for the Cl2  molecules at the surface.  These Cl2
gas molecules can also be desorbed from the surface before a reaction
with the Cu to form CuCl can happen, thus reducing the chance for a
reaction.  With Cu exposed to ionic or atomic Cl, the surface
sticking coefficient or reaction possibility is greatly enhanced
compared to molecular Cl2  gas.  Therefore, if Cu to ionic or
atomic Cl is exposed, the faster reaction rate gives rise to faster
etch rates.

      This can be done by a laser-plasma hybrid process.  A plasma
generator can be placed near the metal surface to be etched.  This
can be done by a number of methods: (1) a dc discharge -- a high
voltage probe near the sample or using the sample itself as the high
voltage electrode.  (2) an rf discharge -- an rf plasma is generated
by an exte...