UV pretreatment process for ultra-thin oxynitride formation

Details UV pretreatment process for ultra-thin oxynitride formation UV pretreatment process for ultra-thin oxynitride formation

2001-04-17

2002-09-17

Everhart, Caridad (Department: 2825)

Semiconductor device manufacturing: process

Coating of substrate containing semiconductor region or of...

Insulative material deposited upon semiconductive substrate

C438S792000, C438S786000, C438S778000, C438S770000, C438S787000

Reexamination Certificate

active

06451713

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to processes for minimizing the surface roughness of ultra-thin dielectric films for ULSI applications. The processes have particular advantage when used for forming silicon nitride films on silicon semiconductor substrates with chemical vapor deposition (CVD) techniques.
BACKGROUND OF THE INVENTION
As the channel length of the metal-oxide-semiconductor field-effect transistors (MOSFET) is reduced, the gate dielectric thickness must be reduced in order to maintain acceptable short-channel effects and to maximize drain current. The fundamental limit to the scaling of thin silicon dioxide (SiO
2
) is the large leakage current due to direct tunneling. The gate oxide layer is typically formed by thermal oxidation of a silicon semiconductor substrate in a substantially pure oxygen atmosphere. In ultra large scale integrated (ULSI) circuits, however, such gate oxide layers in the MOSFET can exhibit undesirable characteristics, such as relatively high defect densities and charge trapping, and relatively low reliability and low resistance to hot carrier effects.
Various in-situ multi-layer gate stack processes have been used to improve gate dielectric characteristics. One example includes an in-situ dry cleaning of the silicon semiconductor substrate, followed by a sequence of rapid thermal processing (RTP). The in-situ dry cleaning process typically comprises three steps: (1) applying UV-ozone (100 Torr pressure); (2) applying HF-methanol vapor (100 Torr pressure); and (3) applying UV-chlorine (10 Torr pressure). The UV-ozone and UV-Cl
2
dry cleaning removes organic residues and metallic contaminants, respectively, from the substrate surface to prepare the surface for subsequent deposits of desired gate dielectric layers. The HF-methanol vapor removes any surface oxides formed during the UV-ozone treatment. Once the substrate surface has been cleaned, it is subjected to a series of RTP processes that may consist of: (1) growing an oxynitride layer with nitric oxide (NO); (2) depositing a silicon nitride (SiN
x
) layer with a rapid thermal chemical vapor deposition (RTCVD) process; (3) rapid thermal annealing the substrate with the SiN layer in an ammonia (NH
3
) environment; and (4) rapid thermal annealing the substrate in an N
2
O environment.
The surface roughness of a CVD silicon nitride film deposited on a silicon dioxide layer has been found undesirably high (i.e., root mean square (RMS) roughness of about 10 Å and even up to 20 Å when the physical thickness of the nitride layer is about 25 Å and below. Published research papers have indicated that the coalescence of nitride nucleation islands does not take place until the silicon nitride film physical thickness exceeds about 20 Å. See H. Resinger and A. Spitzer, “Electrical Breakdown Induced by Silicon Nitride Roughness in Thin Oxide-Nitride-Oxide Films,”
J. Appl. Phys
., V. 79, p. 3028 (1996); M. Copel, et. al., “Nucleation of Chemical Vapor Deposited Silicon Nitride on Silicon Dioxide,”
Appl. Phys. Lett
., V. 74, p. 1830 (1999); and Y. Hu, et al., “An In-Situ Real Time Measurement of the Incubation Time for Si Nucleation on SiO
2
in a Rapid Thermal Process,”
Appl. Phys. Lett
., V. 66, p. 700 (1995). Thus, because the growth of silicon nitride films on oxide layers appears to be dependent upon having sufficient nucleation sites, thinner nitride films have had unacceptable surface roughness leading to unacceptable gate dielectric characteristics.
One proposed solution to resolve this problem uses low energy ion beams (N
−
, H
+
or He
+
) to pre-treat the oxynitride surface and increase nucleation sites. Y. Hu, et al., “In-situ Surface Pretreatment Effect on Nucleation and Film Structure of Polysilicon in a RTCVD System,” 4
th
Int'l Conf. Advanced Thermal Processing of Semiconductors, RTP '96, p. 128 (1996). More recently, some studies showed that remote plasma oxidation may improve the ultra-thin oxide interface. See Lucovsky, et al.,
Appl. Phys. Lett
., V. 74, p. 2005 (1999). Unfortunately, remote plasma oxidation requires special processing equipment and is complicated to use. Alternative approaches to create more nucleation sites and reduce surface roughness of thin silicon nitride films are still being sought.
SUMMARY OF THE INVENTION
In this invention, we use UV-excited gas (preferably chlorine(Cl
2
), nitrogen (N
2
) and mixtures of Cl
2
and N
2
) to pre-treat the oxide or oxynitride film formed on a semiconductor substrate surface to create more nucleation sites for CVD nitride deposition. In our process, after an oxynitride layer is formed on a semiconductor substrate (preferably a silicon semiconductor substrate), the oxynitride layer is treated with UV-excited gas. Then, after such pre-treatment, a silicon nitride film is deposited over the treated oxynitride layer. Preferably, the oxynitride layer is formed using rapid thermal processing at a temperature of at least about 800° C. Preferably, the silicon nitride film is deposited onto the oxynitride layer using chemical vapor deposition (CVD) processing at a temperature in the range of about 700° C. to about 850° C., most preferably 700° C. to 800° C., and at a pressure in the range of about 1.5 Torr to about 3 Torr, and with a gas flow ratio of 1:40:50 of SiH
4
:NH
3
:Ar.
We have found that the surface roughness of the silicon nitride film is substantially reduced following such pre-treatment. In one example, when a 22.6 Å thick silicon nitride layer (physical thickness) was deposited on an untreated oxide, the surface roughness RMS was 9.2 Å. By contrast, when a 22.5 Å thick silicon nitride layer (physical thickness) was deposited on an oxide layer that had been pre-treated with UV-excited chlorine gas, the surface roughness was reduced to RMS 2.1 Å. The process thus improved the quality of the layer that was deposited.
The UV-excited gas pretreatment step may be used to prepare the semiconductor surface to receive the nitric oxide treatment to grow an oxynitride layer. The pretreatment step according to the invention is conducted prior to the silicon nitride deposition step to enhance nucleation site density and prepare the oxynitride surface layer for silicon nitride processing.


REFERENCES:
patent: 4581622 (1986-04-01), Takasaki et al.
patent: 5178682 (1993-01-01), Tsukamoto et al.
patent: 5534107 (1996-07-01), Gray et al.
patent: 5578848 (1996-11-01), Kwong et al.
patent: 6020024 (2000-02-01), Maiti et al.
patent: 6121130 (2000-09-01), Chua et al.
patent: 6153504 (2000-11-01), Shields et al.
patent: 6291866 (2001-09-01), Wallace et al.
patent: 6291867 (2001-09-01), Wallace et al.
patent: 6326231 (2001-12-01), Subramanian et al.
patent: 0 227 839 (1987-07-01), None
Lucovsky, et al., “Bonding Constraints and Defect Formation At Interfaces Between Crystalline Silicon and Advanced Single Layer and Composite Gate Dielectrics”Applied Phys. Lett.W. 74, No. 14 (Apr. 15, 1999).
Rosato, J.J. et al. “Ultra-high Capacitance Nitrie Films Utilizing Passivaton on Rugged Polysilicon”J. Electrochem Soc., Manchester, NH, vol. 139, No. 12 (Dec. 1, 1992).
Y. Hu, et al., “Real Time INvestigation o fNucleation an Growth of Silicon on Silicon Dioxide Using Silane and Disilane in a Rapid Thermal Processing System,”J. Vac Sci Technol. B 14(2) Mar./Apr. 1996 pp. 774-749.
M. Copel, et al.. “Nucleation of Chemical Vapor Deposited Silicon Nitride on Silicon Dioxide,”Applied Physics Lettersvol. 74, No. 13, Mar. 29, 1999. pp. 1830-1832.
H. Reisinger, et al., “Electrical Breakdown Induced By Silicon Nitride Roughness in Thin Oxide-Nitride-Oxide Films,”J. Applied Physics, vol. 79, NO. 6, pp. 3028-3035 (Mar. 15, 1996).
Hu, et al., “In Situ Surface Pretreatment Effect on Nucleation and Film Structure of Polysilicon in a RTCVD System.” 4thInt'l Conf. Advanced Themal Processing of Semiconductors, RTP '96 pp. 128-135 (1996).

Affiliated with

Also associated with

Rating

UV pretreatment process for ultra-thin oxynitride formation does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with UV pretreatment process for ultra-thin oxynitride formation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and UV pretreatment process for ultra-thin oxynitride formation will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2867925