Etching methods, methods of removing portions of material,...

Details Etching methods, methods of removing portions of material,... Etching methods, methods of removing portions of material,...

1998-05-18

2001-05-22

Liott, Caroline D. (Department: 1751)

Etching a substrate: processes

Gas phase etching of substrate

Application of energy to the gaseous etchant or to the...

C216S079000, C134S001100, C438S714000, C438S719000, C438S723000, C438S724000, C438S905000

Reexamination Certificate

active

06235213

ABSTRACT:

TECHNICAL FIELD
The invention pertains to etching methods, such as, for example, methods of forming silicon nitride spacers.
BACKGROUND OF THE INVENTION
A commonly utilized method for removing at least some of a material is plasma etching. Such method can be used, for example, in semiconductor processing. An enormous diversity of materials can be removed by appropriately adjusting etchant components and etching parameters. Among the materials that can be removed are polycrystalline silicon, silicon nitride and silicon oxides. Etchants that can be utilized for removing polycrystalline silicon include HCl, HBr, HI, and Cl
2
, alone or in combination with each other and/or one or more of He, Ar, Xe, N
2
, and O
2
. A suitable etchant that can be utilized for removing a silicon oxide, such as silicon dioxide, is a plasma comprising CF
4
/CHF
3
, or CF
4
/CH
2
F
2
. Additionally, a suitable etchant for removing silicon oxide is a plasma comprising a large amount of CF
3
, and a minor amount of CH
2
F
3
. A suitable etchant for removing silicon nitride is a plasma comprising CF
4
/HBr.
An example prior art reaction vessel
10
is illustrated in FIG.
1
. Reaction vessel
10
comprises a plurality of sidewalls
12
surrounding an internal reaction chamber
14
. Also, reaction vessel
10
comprises a radio frequency (RF) generating coil
16
surrounding a portion of reaction chamber
14
and connected to a first RF source
18
. RF coil
16
is configured to generate a plasma within reaction chamber
14
.
A substrate
20
is received within internal chamber
14
and connected to a second RF source
22
. Second RF source
22
is configured to generate an RF bias at substrate
20
. Additionally, reaction vessel
10
can comprise coolant coils (not shown) configured to cool a backside of substrate
20
and thereby maintain substrate
20
at a desired temperature during an etching process. It is to be understood that vessel
10
is an exemplary etching vessel. Other constructions are possible. For instance, reaction vessel
10
utilizes a cylindrical inductively driven source geometry, but planar or other inductively driven source geometries can be used. Also, reaction vessel
10
is shown utilizing two separate RF sources,
18
and
20
, but other constructions can be used wherein a single RF source can be utilized and the RF power from such source split to form a first RF power at coil
16
and an RF bias at substrate
20
.
Substrate
20
can comprise, for example, a monocrystalline silicon wafer. To aid in interpretation of the claims that follow, the term “semiconductive substrate” is defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
In operation, plasma gases (not shown) are flowed into internal chamber
14
and converted into a plasma by energy input from reaction coil
16
. An RF bias is generated at substrate
20
, and such RF bias draws plasma components to a surface of substrate
20
to etch a material at such surface.
During etching of a component from substrate
20
, the materials produced by chemical reaction to the substrate with etch gases are released into the internal chamber. Such materials are referred to herein as etch reaction products, or as etchant debris. A method of determining when an etch has penetrated a material is to monitor the concentration of the evolved reaction products and/or etchant gases as the etch proceeds. Monitoring of the etchant debris can be accomplished by, for example, spectroscopic methods, including, for example, ultraviolet-visible spectroscopy and mass spectrometry. Preferably, the monitoring will be performed by an automated system, with software configured to detect when a concentration of a monitored material decreases within the etchant debris.
In the shown embodiment, a monitoring device
28
is provided to observe etchant debris within reaction chamber
14
through a window
26
. Monitoring device
28
can comprise, for example, a spectrometer. The spectrometer can be configured to, for example, display a signal corresponding to a concentration of a particular component in the etchant debris, and/or to send such signal to an automated mechanism which performs a function in response to particular signal characteristics. An example automated system is a system comprising an algorithm to analyze the signal and determine from the analysis when an etch penetrates a particular material. The automated system can be configured to terminate the etching process in response to a determination that the etch has penetrated the particular material.
An etch will frequently be conducted in two distinct etching steps, particularly if the etching is to remove a thickness of material that is greater than or equal to 200 Angstroms. First, a highly physical (non-selective) etch is utilized to etch through the majority of a material. Second, a chemical-type etch (highly selective) is utilized to etch through a remainder of the material. A less selective (physical-type) etch generally has better center-to-edge uniformity than a more selective (chemical-type) etch. Center-to-edge uniformity can be understood by reference to
FIG. 2
wherein a semiconductive wafer
40
is illustrated. Wafer
40
comprises an edge region
42
and a center region
44
. Generally, an etch process will etch material from both edge region
42
and center region
44
, as well as from regions intermediate edge region
42
and center region
44
. Etching frequently progresses at a different rate at edge region
42
than at center region
44
. Thus, as an etch progresses further into a material of semiconductive wafer
40
, a disparity between etchant depth at center region
44
and edge region
42
becomes more pronounced. Center-to-edge uniformity is a measure of a degree of disparity between an etch rate at edge region
42
versus an etch rate at center region
44
.
Physical-type etch processes generally have a high degree of center-to-edge uniformity, and therefore etch edge region
42
at about the same rate as center region
44
. In contrast, chemical-type edges typically have a lower degree of center-to-edge uniformity, and accordingly etch edge region
42
at a significantly different rate than center region
44
.
A reason for utilizing a physical-type etch initially in an etching process is to maintain a high degree of center-to-edge uniformity as the bulk of a material is etched. The etching process is then changed to a more chemical-type etch as a final portion of the material is removed to obtain a high degree of selectivity for the material relative to other materials that can be exposed during latter stages of an etch.
A chemical-type etch and a physical-type etch can utilize the same etchants but vary in power settings and pressures, or can utilize different etchants at either the same or different power settings and pressures. If the physical-type etch and chemical-type etch comprise the same etchants, the physical-type etch generally comprises a higher bias power at a substrate, and a lower pressure within a reactor than the chemical-type etch. For example, both chemical-type etching and physical-type etching of a silicon nitride material can utilize an etchant comprising CF
4
/HBr. However, the physical-type etching will utilize an RF power to primary RF coil
16
of from about 250 to about 800 watts, a bias power to substrate
20
of from about 75 to about 400 watts, and a pressure within internal chamber
14
of from about 5 to about 15 mTorr. In contrast, a chemical-type etch will utilize a power to primary RF coil
16
(
FIG. 1
) of from about 300 to about 900 watts, a bias power to substrate
20
of less than about 20 watts, and a pressure within internal cha

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