Semiconductor processing methods, semiconductor circuitry,...

Details Semiconductor processing methods, semiconductor circuitry,... Semiconductor processing methods, semiconductor circuitry,...

2001-05-30

2002-10-08

Elms, Richard (Department: 2824)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

Insulated gate formation

C438S682000, C438S660000

Reexamination Certificate

active

06461950

ABSTRACT:

TECHNICAL FIELD
The invention pertains to methods of forming and utilizing antireflective materials. The invention also pertains to semiconductor processing methods of forming stacks of materials, such as, for example, gate stacks.
BACKGROUND OF THE INVENTION
Semiconductor processing methods frequently involve patterning layers of materials to form a transistor gate structure.
FIG. 1
illustrates a semiconductive wafer fragment
10
at a preliminary step of a prior art gate structure patterning process. Semiconductive wafer fragment
10
comprises a substrate
12
having a stack
14
of materials formed thereover. Substrate
12
can comprise, for example, monocrystalline silicon lightly doped with a p-type background dopant. 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.
Stack
14
comprises a gate oxide layer
16
, a polysilicon layer
18
, a metal silicide layer
20
, an oxide layer
22
, a nitride layer
24
, an antireflective material layer
26
, and a photoresist layer
28
. Gate oxide layer
16
can comprise, for example, silicon dioxide, and forms an insulating layer between polysilicon layer
18
and substrate
12
. Polysilicon layer
18
can comprise, for example, conductively doped polysilicon, and will ultimately be patterned into a first conductive portion of a transistor gate.
Silicide layer
20
comprises a metal silicide, such as, for example, tungsten silicide or titanium silicide, and will ultimately comprise a second conductive portion of a transistor gate. Prior to utilization of silicide layer
20
as a conductive portion of a transistor gate, the silicide is typically subjected to an anneal to improve crystallinity and conductivity of the silicide material of layer
20
. Such anneal can comprise, for example, a temperature of from about 800° C. to about 900° C. for a time of about thirty minutes with a nitrogen (N
2
) purge.
If silicide layer
20
is exposed to gaseous forms of oxygen during the anneal, the silicide layer can become oxidized, which can adversely effect conductivity of the layer. Accordingly, oxide layer
22
is preferably provided over silicide layer
20
prior to the anneal. Oxide layer
22
can comprise, for example, silicon dioxide. Another purpose of having oxide layer
22
over silicide layer
20
is as an insulative layer to prevent electrical contact of silicide layer
20
with other conductive layers ultimately formed proximate silicide layer
20
.
Nitride layer
24
can comprise, for example, silicon nitride, and is provided to further electrically insulate conductive layers
18
and
20
from other conductive layers which may ultimately be formed proximate layers
18
and
20
. Nitride layer
24
is a thick layer (a typical thickness can be on the order of several hundred, or a few thousand Angstroms) and can create stress on underlying layers. Accordingly, another function of oxide layer
22
is to alleviate stress induced by nitride layer
24
on underlying layers
18
and
20
.
Antireflective material layer
26
can comprise, for example, an organic layer that is spun over nitride layer
24
. Alternatively, layer
26
can be a deposited inorganic antireflective material, such as, for example, Si
x
O
y
N
z
:H, wherein x is from 0.39 to 0.65, y is from 0.02 to 0.56, and z is from 0.05 to 0.33. In practice the layer can be substantially inorganic, with the term “substantially inorganic” indicating that the layer can contain a small amount of carbon (less than 1% by weight). Alternatively, if, for example, organic precursors are utilized, the layer can have greater than or equal to 1% carbon, by weight.
Photoresist layer
28
can comprise either a positive or a negative photoresist. Photoresist layer
28
is patterned by exposing the layer to light through a masked light source. The mask contains clear and opaque features defining a pattern to be created in photoresist layer
28
. Regions of photoresist layer
28
which are exposed to light are made either soluble or insoluble in a solvent. If the exposed regions are soluble, a positive image of the mask is produced in photoresist layer
28
and the resist is termed a positive photoresist. On the other hand, if the non-radiated regions are dissolved by the solvent, a negative image results, and the photoresist is referred to as a negative photoresist.
A difficulty that can occur when exposing photoresist layer
28
to radiation is that waves of the radiation can propagate through photoresist
28
to a layer beneath the photoresist and then be reflected back up through the photoresist to interact with other waves of the radiation which are propagating through the photoresist. The reflected waves can constructively and/or destructively interfere with the other waves to create periodic variations of light intensity within the photoresist. Such variations of light intensity can cause the photoresist to receive non-uniform doses of energy throughout its thickness. The non-uniform doses can decrease the accuracy and precision with which a masked pattern is transferred to the photoresist. Antireflective material
26
is provided to suppress waves from reflecting back into photoresist layer
28
. Antireflective layer
26
comprises materials which absorb and/or attenuate radiation and which therefore reduce or eliminate reflection of the radiation.
FIG. 2
shows semiconductive wafer fragment
10
after photoresist layer
28
is patterned by exposure to light and solvent to remove portions of layer
28
.
Referring to
FIG. 3
, a pattern from layer
28
is transferred to underlying layers
16
,
18
,
20
,
22
,
24
, and
26
to form a patterned stack
30
. Such transfer of a pattern from masking layer
28
can occur by a suitable etch, such as, for example, a plasma etch utilizing one or more of Cl, HBr, CF
4
, CH
2
F
2
, He, and NF
3
.
After the patterning of layers
16
,
18
,
20
,
22
,
24
and
26
, layers
28
and
26
can be removed to leave a patterned gate stack comprising layers
16
,
18
,
20
,
22
, and
24
.
A continuing goal in semiconductor wafer fabrication technologies is to reduce process complexity. Such reduction can comprise, for example, reducing a number of process steps, or reducing a number of layers utilized in forming a particular semiconductor structure. Accordingly, it would be desirable to develop alternative methods of forming patterned gate stacks wherein fewer steps and/or layers are utilized than those utilized in the prior art embodiment described with reference to
FIGS. 1-3
.
SUMMARY OF THE INVENTION
In one aspect, the invention encompasses a semiconductor processing method. A metal silicide layer is formed over a substrate. An antireflective material layer is chemical vapor deposited in physical contact with the metal silicide layer. A layer of photoresist is applied over the antireflective material layer and patterned photolithographically.
In another aspect, the invention encompasses a gate stack forming method. A polysilicon layer is formed over a substrate. A metal silicide layer is formed over the polysilicon layer. An antireflective material layer is deposited over the metal silicide layer. A silicon nitride layer is formed over the antireflective material layer and a layer of photoresist is formed over the silicon nitride layer. The layer of photoresist is photolithographically patterned to form a masking layer from the layer of photoresist. A pattern is transferred from the masking layer to the silicon nitride layer, antireflective material layer, metal silicide layer and polysilicon layer to pattern the silicon nitride layer, antireflective mate

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