Patterned plasma nitridation for selective epi and silicide...

Details Patterned plasma nitridation for selective epi and silicide... Patterned plasma nitridation for selective epi and silicide...

2001-07-03

2002-07-30

Niebling, John F. (Department: 2812)

Semiconductor device manufacturing: process

Coating of substrate containing semiconductor region or of...

C438S775000, C438S788000

Reexamination Certificate

active

06426305

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to semiconductor device manufacturing, and more particularly to methods of incorporating nitrogen at or near a silicon surface so as to be capable of forming either an epi-silicon-containing layer or a silicide layer on selective portions of the silicon surface.
BACKGROUND OF THE INVENTION
In the manufacturing of semiconductor devices, it is well known that nitrogen present at or near the silicon surface of a semiconductor device changes many surface properties of the silicon. The ability to introduce nitrogen in different areas of a semiconductor chip or wafer allows for fabrication of different structures and devices in a cost effective manner, by reducing the number of steps required to make the structure.
As stated above, nitrogen affects many surface, or near surface properties of a semiconductor device. Some of the more significant ones include: (i) oxidation rate; (ii) silicide formation; (iii) selective epitaxial growth; and (iv) boron diffusion.
In regard to oxidation rate, it is well known that nitrogen reduces oxidation rate and that a higher concentration of nitrogen formed within or near a silicon surface results in slower oxidation rate. Insofar as silicide formation is concerned, nitrogen serves to block or reduce silicide formation by preventing the reaction between a refractory metal, e.g., Ti or Co, and the underlying silicon layer.
In epitaxial growth, which occurs on bare silicon surfaces without nitrogen at the surface, nitrogen can be used in such a process to prevent the single crystal deposition of epitaxial silicon. That is, nitrogen can be used as a surface masking layer so as to prevent epitaxial silicon growth from occurring in the regions containing nitrogen.
With respect to boron diffusion, nitrogen reduces boron diffusion; therefore nitrogen can be used to prevent channeling of boron into silicon surfaces, i.e., boron diffusion from a gate region into an underlying silicon surface.
Various prior art methods for patterned incorporation of nitrogen into a surface of a silicon-containing substrate are known and have been successfully employed in the semiconductor industry. For example, it is known in the prior art to implant nitrogen into selective regions by utilizing photoresist patterning. Such a prior art process is depicted in
FIG. 1
wherein reference numeral
10
denotes a Si-containing substrate, reference numeral
12
denotes a patterned photoresist and reference numeral
14
denotes N
+
or N
2
+
ions being incorporated into Si-containing substrate
10
via ion implantation. The region labeled as
16
in
FIG. 1
denotes the area in which nitrogen is implanted within substrate
10
. The prior art process depicted in
FIG. 1
is advantageous because the ion implantation process is typically carried out at room temperature which is directly compatible with the patterned photoresist.
Despite the above advantages, the prior art nitrogen ion implantation process, which is typically performed at high doses, causes resist hardening. Hardened resist are difficult to remove using conventional stripping processes well known in the art. Additionally, prior art nitrogen ion implantation processes may cause undesirable contamination problems. In particularly, prior art nitrogen ion implantation processes may result in implant damage in the substrate which may lead to increased oxidation rate and degraded mobility of implanted ions within the substrate. Moreover, in the prior art, nitrogen is typically implanted well below the surface of the silicon, not at the surface. Hence, a thermal cycle is needed to diffuse the implanted nitrogen ions to the silicon surface and residual nitrogen may be left in the substrate where it can have undesirable effects.
Another prior art method of introducing nitrogen into a surface is by utilizing a thermal nitridation process. Typically, prior art thermal nitridation processes are performed at temperatures greater than about 700° C. using NO, N
2
O or NH
3
as the nitrogen-containing ambient. A typical prior art nitridation process is shown, for example, in
FIGS. 2A-D
. Specifically,
FIG. 2A
comprises Si-containing substrate
10
, hard masking layer, e.g., an oxide or nitride,
18
, and patterned photoresist
12
. Such a structure is fabricated using conventional techniques well known in the art. Since the photoresist cannot withstand the high-temperature nitridation process, it is employed in the prior art as a means for
10
patterning the underlying hardmask, which can withstand the high-temperatures associated with prior art nitridation process.
FIG. 2B
shows the structure that is formed after a conventional dry etching process such as reactive ion etching is employed in transferring the pattern from the photoresist to the hardmask and after the resist has been removed.
FIG. 2C
shows the resultant structure formed during a typically prior art thermal nitridation process. Note that nitrogen-containing layer
20
is formed during the thermal nitridation process.
FIG. 2D
shows the structure that is formed after hardmask
18
has been removed from the structure.
One advantage of prior art thermal nitridation processes is that they are capable of implanting nitrogen at or near the surface of a silicon-containing substrate. Disadvantages of prior art nitridation process, however, include: (i) not directly compatible with resist processing because the resist cannot withstand high-temperatures associated with prior art nitridation processes; (ii) to achieve selective nitridation other sacrificial materials such as the hardmask illustrated in
FIGS. 2A-2D
must be employed (this causes the need for utilizing extra etching, deposition and stripping processes); and (iii) nitrogen may leak through the various layers, e.g., hardmask
18
, used to block the silicon surface contaminating areas which are meant to be nitrogen-free.
Another prior art method which can be used in forming a patterned nitrogen-containing region at or near a surface of silicon is described, for example, in U.S. Pat. No. 6,110,842 to Okuno, et al. Specifically, Okuno, et al. disclose a method for forming integrated circuits having multiple gate oxide thicknesses utilizing a high-density plasma nitridation process to reduce the effective gate dielectric thickness in selective areas only. In one embodiment disclosed in Okuno, et al., a patterned mask is formed over a substrate and a high-density plasma nitridation process (low-temperature process) is used in forming a thin layer of nitride or oxynitride on the surface of the substrate. The patterned nitride is thereafter removed and an oxidation is performed. The thin nitride or oxynitride layer retards oxidation, whereas in the areas in which the nitride and oxynitride layer is not present, oxidation is not retarded.
Okuno, et al. disclose a second embodiment in which a thermal oxide is first grown on a substrate. Next, a pattern is then formed that exposes areas where a thinner effective gate oxide is desired. A high-density plasma nitridation is performed converting a portion of the gate oxide to a nitride or oxynitride; the effective thickness of the combined dielectric is reduced.
Although the Okuno, et al. disclosure provides a low-temperature patterned nitridation process for forming a gate dielectric having dual thicknesses, Okuno, et al. do not teach or suggest that the disclosed methods can be used during selective epi or silicide formation. Hence, there is still a need for providing a method that is capable of forming a selective epi or silicide layer on predetermined portions of a silicon-containing substrate using a masked nitridation process that overcomes the drawbacks mentioned in regard to prior art nitrogen ion implantation and thermal nitridation.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a selective method of forming a nitrogen-containing layer at or very near the surface of a Si-containing substrate so as to provide a layer that prevents the subsequent formation of an epi-Si-contain

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