U.S. patent number RE30,505 [Application Number 05/914,540] was granted by the patent office on 1981-02-03 for process and material for manufacturing semiconductor devices.
This patent grant is currently assigned to LFE Corporation. Invention is credited to Adir Jacob.
United States Patent |
RE30,505 |
Jacob |
February 3, 1981 |
Process and material for manufacturing semiconductor devices
Abstract
A process step and material for use in the manufacture of
semiconductor devices. To facilitate the etching of unmasked
silicon dioxide, silicon nitride, silicon monoxide, bare silicon
layers, or various refractory metals on preselected portions of a
semiconductor slice, the material is exposed to a low pressure RF
generated "cold" plasma (under 325.degree. C.) produced from a
homogeneous gaseous binary mixture of oxygen and a halocarbon. The
halocarbon is preferably a gas having one carbon atom per molecule
and is preferably fully fluorine-substituted.
Inventors: |
Jacob; Adir (Framingham,
MA) |
Assignee: |
LFE Corporation (Waltham,
MA)
|
Family
ID: |
33161828 |
Appl.
No.: |
05/914,540 |
Filed: |
June 12, 1978 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
252863 |
May 12, 1972 |
03795557 |
Mar 5, 1974 |
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Current U.S.
Class: |
438/710;
204/192.25; 204/192.32; 252/79.1; 438/719; 438/720; 438/723;
438/724; 438/729 |
Current CPC
Class: |
C23F
4/00 (20130101); H01L 21/3065 (20130101); H01L
21/32137 (20130101); H01L 21/32136 (20130101); H01L
21/31116 (20130101) |
Current International
Class: |
C23F
4/00 (20060101); H01L 21/02 (20060101); H01L
21/311 (20060101); H01L 21/3065 (20060101); H01L
21/3213 (20060101); B44C 001/22 (); C23F 001/02 ();
C03C 015/00 (); C03C 025/06 () |
Field of
Search: |
;156/643,646,657,659,662,659.1 ;252/79.1
;204/192E,192EC,298,164,165,168,169,170 ;250/531 ;219/121P |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
The Merck Index of Chemicals and Drugs, Seventh Edition, published
by Merck & Co., Inc. in 1960, p. 212..
|
Primary Examiner: Powell; William A.
Attorney, Agent or Firm: Kenway & Jenney
Claims
What is claimed is: .[.1. A process for chemically converting
material in a plasma environment, comprising the step of:
exposing the material to a gaseous plasma formed from a binary
mixture consisting essentially of oxygen and a halocarbon having no
more than two carbon atoms per molecule, wherein at least one
carbon atom in said molecule is linked to a predominance of
fluorine atoms to produce as an
intermediate low order oxides..]. 2. A process for .Iadd.chemically
.Iaddend.etching .Iadd.solid .Iaddend.material in a plasma
environment comprising the step of:
exposing the material to a gaseous plasma formed from a binary
mixture consisting essentially of oxygen and a halocarbon having
only one carbon atom per molecule, said carbon atom being linked to
a predominance of
fluorine atoms to produce as an intermediate a low order oxide. 3.
A process as in claim 2 wherein the reaction temperature is within
the range
of 25 to 300 degrees centigrade. 4. A process as in claim 2 wherein
said
halocarbon gas includes at least one hydrogen atom. 5. A process as
in claim 2 wherein said halocarbon and said oxygen are supplied to
a reactor
from separate sources. 6. A process as in claim 2 wherein said
halocarbon and said oxygen are supplied to a reactor from a common
premixed source.
A process as in claim 6 wherein said gaseous binary mixture
contains 8.5 percent oxygen and 91.5 percent tetrafluoromethane by
volume,
said mixture being supplied to said reactor at a total flow rate
within the range of 9 to 55 micromoles per second corresponding
total pressures of 220 to 850 microns mercury, and having RF energy
coupled to said mixture within the range of 20 to 400 watts. .[.8.
A composition of matter, useful for chemically converting material
in a plasma environment, consisting essentially of a binary gaseous
mixture of oxygen and a halocarbon having no more than two carbon
atoms per molecule, wherein at least one carbon atom in said
molecule is linked to a predominance of fluorine atoms..].
A composition of matter, useful in a process for .Iadd.chemically
.Iaddend.etching .Iadd.a silicon containing .Iaddend.material in
the presence of an organic etch mask by forming fluorine-based and
oxyfluoride-based compounds volatile in a low pressure-low
temperature plasma, consisting essentially of a binary gaseous
mixture of oxygen and tetrafluoromethane wherein said mixture
contains 1 to 25 percent oxygen by volume. .[.10. A composition of
matter, useful in a process for etching material in the absence of
an organic etch mask by forming fluorine-based and
oxyfluoride-based compounds volatile in a low pressure-low
temperature plasma, consisting essentially of a binary gaseous
mixture of oxygen and tetrafluoromethane wherein said mixture
contains 1 to 75 percent oxygen by volume..]. .[.11. A composition
of matter, useful in a process for etching material in the presence
of a metal etch mask by forming fluorine-based and
oxyfluoride-based compounds volatile in a low pressure-low
temperature plasma, consisting essentially of a binary gaseous
mixture of oxygen and tetrafluoromethane wherein said mixture
contains 1 to 75 percent oxygen by
volume..]. 12. A composition of matter, useful in a process for
.Iadd.etching silicon oxide in the presence of photoresist in
.Iaddend.manufacturing semiconductors, comprising a binary gaseous
mixture of oxygen and tetrafluoromethane, said oxygen containing
8.5 percent of the mixture by volume. .Iadd. 13. A process for
chemically etching solid material in a plasma environment,
comprising the step of:
exposing the material to a gaseous plasma at a pressure of at least
220 microns formed from a binary mixture consisting essentially of
oxygen and a halocarbon having no more than two carbon atoms per
molecule, wherein at least one carbon atom in said molecule is
linked to a predominance of fluorine atoms to produce as an
intermediate low order oxides. .Iaddend. .Iadd. 14. A process for
chemically etching solid material in a plasma environment,
comprising the step of:
exposing the material to a gaseous plasma formed in an RF field
from a binary mixture consisting essentially of oxygen and a
halocarbon having no more than two carbon atoms per molecule,
wherein at least one carbon atom in said molecule is linked to a
predominance of fluorine atoms to produce as an intermediate low
order oxides. .Iaddend..Iadd. 15. A process for chemically etching
solid material in a plasma environment, comprising the step of:
exposing the material to a gaseous plasma formed from a binary
mixture consisting essentially of oxygen and a halocarbon having no
more than two carbon atoms per molecule, wherein at least one
carbon atom in said molecule is linked to a predominance of
fluorine atoms to produce as an intermediate low order oxides and
wherein said mixture contains 1 to 25% oxygen by volume. .Iaddend.
Description
FIELD OF THE INVENTION
This invention relates in general to a process and material useful
in analytical procedures, and more particularly to a process and
material useful in the manufacture of semiconductor devices,
enabling the etching of various metals (molybdenum, tungsten,
tantalum, etc.) and common passivation or diffusion barrier
materials (e.g., SiO, SiO.sub.2, Si.sub.3 N.sub.4) during the
processing of such devices.
BACKGROUND OF THE INVENTION
In the conventional technique for the manufacture of semiconductor
devices, a slice of semiconductor material (p- or n-type) accepts a
relatively thin layer, typically 5,000 to 10,000 A., of an
insulating film grown or deposited on one or both of its surfaces.
A layer of photoresist material is then spun onto the insulating
layer of one side, and is subsequently exposed to UV light through
a mask having openings corresponding to those areas on the
semiconductor slice where it is desired to generate semiconductor
junctions. After exposure of the photoresist material through the
mask, the mask is removed and the layer of photoresist is developed
and processed by means of a suitable solvent, exposing select areas
of the underlying insulating layer. A wet acid-based dip is then
used to etch the insulating layer from the surface of the
semiconductor slice in the exposed areas, the remaining photoresist
material serving as an etch-mask for the surface covered by it.
Following the wet etching process, a water rinse and a drying step
are implemented. The remainder of the photoresist material is
subsequently removed, followed by an acid dip required for the
removal of inorganic residues. The photoresist material can also be
removed by a plasma process utilizing the halocarbon-oxygen gaseous
mixtures disclosed by the present inventor in his U.S. Pat.
application, Ser. No. 173,537, filed Aug. 20, 1971. Following a
further drying step, diffusion of dopant material into the exposed
areas of the semiconductor slice (where there is no insulating
layer) is commenced to produce a predetermined junction.
Among the problems and drawbacks associated with the etching step
used in this particular technique are:
(1) Physical degradation of a photoresist etch mask.
(2) Finite chemical degradation of a metallic etch mask.
(3) Impairment of line-line resolution due to (1) and/or (2).
(4) Enhanced undercutting effects creating undesirable slopes of
the etched channel.
(5) Severe chemical degradation (corrosion) of underlying
metalization layers; e.g., aluminum in multileveled structures.
(6) Slow and technically elaborate etching of silicon monoxide and
silicon nitride.
(7) Required post-etch water rinse and drying steps invariably
reducing production yields.
(8) Short shelf-life of etching solution due to inevitable
contamination.
(9) Generally very hazardous to personnel and undesirably
polluting.
Accordingly, the general object of the present invention is to
provide an improved process and new material that overcome the
aforementioned problems and provide uniform etching reactions at a
rapid rate.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a gas
discharge flow apparatus adapted to form a gaseous plasma within a
reaction chamber. It has been discovered that if the generated
plasma comprises reactive species resulting from the decomposition
and excitation of a gaseous binary mixture of oxygen and a
halocarbon that includes flourine as a major substituent,
passivation layers or diffusion barriers (e.g., SiO, SiO.sub.2,
Si.sub.3 N.sub.4) can be etched in excess of 3000 A./min. without
degradation of an organic photoresist etch mask. Polycrystalline
and single crystals of silicon, and a variety of metals (e.g.,
molybdenum, tantalum, tungsten, etc.) can be etched in excess of
2000 A./min. under similar conditions. While the above etch rates
are commensurate with the preservation of an organic photoresist
etch mask in this chemically hostile environment, appreciably
higher etch rates can be achieved with the utilization of metallic
etch masks (e.g., aluminum, gold, etc.). Metallic etch masks are
normally attacked by aqueous acidic etch solutions currently in
use; however, they are chemically inert to the etching plasma
disclosed herein.
DESCRIPTION OF THE DRAWING
In the drawing:
FIG. 1 is an illustration in diagrammatic form of a gas discharge
flow system useful in the process of this invention; and
FIG. 2 is an illustration in cross-sectional view of a typical
semiconductor slice at an intermediate stage of the manufacturing
process.
DESCRIPTION OF PREFERRED EMBODIMENT
FIG. 1 depicts diagrammatically an apparatus performing the process
described in the invention. The apparatus includes a reactor
chamber 2, typically made of quartz, having a cover 4 and a gas
inlet manifold 6. The side of the reactor 2 has been partially
broken away in the drawing so as to better illustrate the gas
diffusion tubes 7 which are disposed therein and are externally
connected to manifold 6. Such a reactor is disclosed in U.S. Pat.
No. 3,619,403, issued on Nov. 9, 1971, and assigned to LFE
Corporation.
A pressurized supply 8 of a binary gaseous mixture comprised of
oxygen and a halocarbon gas described below is connected through a
pressure regulating valve 10, a three-way solenoid valve 12, and a
flowmeter 14 to manifold 6. A vacuum gauge 16 provides an
indication of total reaction pressure in reactor 2. At any time,
and prior to introduction of the gas mixture to manifold 6, the
corresponding flow lines are constantly evacuated through the
three-way solenoid valve 12 leading to the mechanical vacuum pump
18, this being the case also under conditions where air at
atmospheric pressure prevails in reactor 2 through the utilization
of the three-way isolation valve 20. A source of radio frequency
power 22 provides exciting energy through a matching network 24 to
coil 26 which surrounds reaction chamber 2. Preferably, inductor 26
consists of a multiturn coil having two coil sections whose
respective coil turns are wound in opposite directions, as
disclosed in U.S. Pat. application Ser. No. 186,739, filed on Oct.
5, 1971, now U.S. Pat. No. 3,705,091, and assigned to LFE
Corporation. Although the binary gaseous mixture is preferably
premixed and supplied to the reactor from a single container 8, it
will be apparent that the oxygen and halocarbon gases may, if
desired, be supplied from separate sources via separate flow lines
and mixed within either manifold 6 or reactor 2. In operation, the
gaseous mixture is admitted to reaction chamber 2 where the
inductively coupled radio frequency energy creates a "cold" plasma.
Such a reaction system is commercially available from the Process
Control Division of LFE Corporation, under the trade designation
PDE-301 or PDE-504. Typically, the RF power employed is between 175
and 225 watts continuous radiation at 13.5 mHz.
The general process is one in which as many as 25 semi-conductor
wafers at an appropriate stage of the manufacturing process are
placed in reactor 2 and exposed to the plasma generated by the
admission of an appropriate gaseous mixture of oxygen and a
halocarbon gas. For the appropriate reactions to take place, the
reaction chamber is evacuated to a residual pressure of 20 to 50
microns mercury prior to the admission of the gaseous etchant. The
process provides rapid and uniform etching of dielectrics (up to
5000 A./min.) across a typical production batch of semiconductor
slices with negligible loss of an organic etch mask.
In FIG. 2 there is shown in cross-sectional view a portion of a
typical semiconductor device at a suitable processing stage for the
utilization of this invention. The semiconductor device consists of
a semiconductor material 30, such as silicon (or GaAs, GaAsP, InSb)
having a relatively thin (200 to 10,000 A.) layer of a dielectric
material 32 (e.g. SiO, SiO.sub.2, Si.sub.3 N.sub.4) either
deposited or thermally grown onto it. This dielectric layer 32
(sometimes p or n-type doped) is to be etched at the openings 34
and 36 in the overlying photoresist mask 38. These openings or
windows in the etch mask 38 represent fractional areas of less than
1 percent to 80 percent of the total area of the semiconductor
slice, and correspond to positions on the semiconductor slice where
it is desired to form a semiconductor junction by a subsequent
diffusion of suitable dopants.
If the semiconductor device, as depicted in FIG. 2, is exposed to
the prescribed plasma formed from a gaseous mixture of oxygen and a
halocarbon gas or vapor, the photoresist material will stay intact
while the exposed dielectric film 32 will be etched down to the
semiconductor layer 30 in openings 34 and 36. It has been found
that an effective halocarbon should be selected from the group of
organohalides no more than two carbon atoms per molecule and in
which the carbon atoms are attached to a predominance of fluorine
atoms. If a liquid halocarbon is considered, it should have a
boiling point between 20.degree. and 120.degree. C. associated with
a vapor pressure of at least 50 torr at 25.degree. C. The preferred
gaseous mixture is produced from a mixture containing 8.5 percent
by volume of oxygen and 91.5 percent tetrafluoromethane gas. This
optimum combination can be supplied from a prepared pressurized
mixture maintained in a commercially available metal cylinder.
Careful and close control of this dry etching process will permit
the manufacture of semiconductor devices with high line-line
resolution (0.15 mil.). It also provides a significant reduction in
the undercutting of the etch mask, coupled with the option to
control the slope of the etched channel. It further provides an
efficient and simultaneous means for etching various dielectrics
with an insignificant chemical or physical deterioration of
over-exposed underlying substrates such as aluminum, gallium
arsenide, indium antimonide, garnets, etc. Satisfactory results
were achieved with mixtures of up to 25 percent by volume of
oxygen. In general, for the mixture combinations in the
aforementioned group, an increase in the number of carbon atoms per
molecule tends to slow down the etching process, while an increase
in the mole fraction of oxygen (up to 0.5) tends to result in an
excessive etch rate of the dielectric layer 32 with associated
degradation of the photoresist mask and the line-line resolution.
Increasing the mole fraction of the halocarbon beyond 0.5 tends to
appreciably reduce the average etch rate.
The successful operation of this process is believed to include
competitive homogeneous and heterogenous reactions in the plasma
such that atomic oxygen, generated by the decomposition of
molecular oxygen, reacts with solid silicon dioxide layers to form
a reduced silicon oxide entity, e.g., silicon monoxide. This lower
oxide of silicon is further converted by the fluorocarbon-based
plasma to either volatile silicon tetrafluoride, SiF.sub.4, or to
volatile silicon oxyfluoride, Si.sub.2 OF.sub.6, that is removed
with the main gas stream to the vacuum pump. This reaction path,
via the lower oxide of silicon, gives rise to thermochemically
preferable reaction products as opposed to products that will ensue
from the direct attack of either fluorine atoms or fluorinated
hydrocarbon radicals on a silicon dioxide solid film. As a result,
the presence of molecular oxygen in the etchant mixture enhances
the etching (volatilization) of commonly encountered silicon
dioxide films, since this reaction is coupled with a
correspondingly higher probability of occurrence. By the same
token, it is also believed that etching of silicon nitride layers
proceeds via a similar lower oxide of silicon. In this case, the
overall reaction is more exothermic, leading to a correspondingly
enhanced etching of silicon nitride over silicon dioxide--a much
desired result currently unobtainable within the semiconductor
industry. It is this very feature of the plasma etch process that
enables the direct photoresist masking of silicon nitride layers
prior to etching, as opposed to indirect masking of such films by
silicon dioxide and photoresist films in a multistep procedure
currently employed with wet chemical etchants.
It has been found that the mixtures and operating parameters set
forth below produce acceptable results in the described process.
These parameters are intended to optimize the etch rate of
dielectric films at negligible loss or degradation of any
commercially available organic photoresist etch masks. Higher
gaseous flow rates, RF power levels, etc., will enable
correspondingly higher etch rates which may be used in conjunction
with inorganic (e.g., metal) etch masks whose degradation is
substantially avoided with this etching process.
__________________________________________________________________________
Etchant Total flow rate pressure RF Percent Etch (micromoles
(microns power area No. rate (A Etchant sec..sup.-1) Hg) (watts)
Material etched etched wafers min..sup.-1)
__________________________________________________________________________
CF.sub.4, 1% O.sub.2 42.6 695 200 Th..sup.1 SiO.sub.2 40 1 300
CF.sub.4, 8.5% O.sub.2 9 220 150 Th..sup.1 SiO.sub.2 5 1 620
CF.sub.4, 8.5% O.sub.2 52 780 200 Th..sup.1 SiO.sub.2 40 25 300
CF.sub.4, 8.5% O.sub.2 55 850 250 Th..sup.1 SiO.sub.2 20 1 1,000
CF.sub.4, 8.5% O.sub.2 22 450 150 Dep..sup.2 SiO.sub.2 on Al 5 1
2,600 CF.sub.4,8.5% O.sub.2 45 600 200 Molybdenum 70 1 1,500
CF.sub.4, 8.5% O.sub.2 15 340 250 Dep. Si.sub.3 N.sub.4 5 20 670
CF.sub.4, 8.5% O.sub.2 55 850 200 Tungsten 70 1 1,000
CF.sub.4,8.5%O.sub.2 55 850 200 Selenium 70 1 1,500 CF.sub.4, 8.5%
O.sub.2 15 340 200 Dep. Si.sub.3 N.sub.4 5 1 1,300 CF.sub.4, 15.5%
O.sub. 2 55 770 200 Th. SiO.sub.2 40 1 840 CF.sub.4, 23.5% O.sub.2
28 465 125 Th. SiO.sub.2 40 1 800 CF.sub.4, 29% O.sub.2 100 1,343
300 Th. SiO.sub.2 100 1 5,100 CF.sub.4, 50% O.sub.2 110 1,415 150
Th. SiO.sub.2 100 1 1,890 CF.sub.4, 69% O.sub.2 17 275 300 Th.
SiO.sub.2 100 1 1,000 CHF.sub.3, 41% O.sub.2 50 1,365 300 Th.
SiO.sub.2 100 1 2,000 CHF.sub.3,55% O.sub.2 38 1,005 125 Th.
SiO.sub.2 100 1 1,200 CHF.sub.3, 80.5% O.sub.2 133 3,496 400 Th.
SiO.sub.2 100 1 2,800 CHF.sub.3, 93.7% O.sub.2 115 2,996 300 Th.
SiO.sub.2 100 1 500 C.sub.2 F.sub.6, 50% O.sub.2 108 1,435 300 Th.
SiO.sub.2 40 1 500 CF.sub.2 ClCCl.sub.2 F, 75% O.sub.2 53 710 300
Th. SiO.sub.2 40 1 1,000
__________________________________________________________________________
.sup.1 Th = Thermally oxidized. .sup.2 Dep. = Vapor deposited.
* * * * *