Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2002-08-28
2004-08-31
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S253000, C438S396000
Reexamination Certificate
active
06784049
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to method of forming a refractory metal (preferably, tantalum) oxide layer, and particularly to a method of forming a tantalum pentoxide layer, on a substrate using a reactive deposition process with a refractory metal precursor compound with an ether.
BACKGROUND OF THE INVENTION
In integrated circuit manufacturing, microelectronic devices such as capacitors are the basic energy storage devices in random access memory devices, such as dynamic random access memory (DRAM) devices, static random access memory (SRAM) devices, and ferroelectric memory (FERAM) devices. Capacitors typically consist of two conductors, such as parallel metal or polysilicon plates, which act as the electrodes (i.e., the storage node electrode and the cell plate capacitor electrode), insulated from each other by a layer of dielectric material.
The continuous shrinkage of microelectronic devices over the years has led to a situation where the materials traditionally used in integrated circuit technology are approaching their performance limits. Silicon (i.e., doped polysilicon) has generally been the substrate of choice, and silicon dioxide (SiO
2
) has frequently been used as the dielectric material to construct microelectronic devices. However, when the SiO
2
layer is thinned to about 10 Å (i.e., a thickness of only 4 or 5 molecules), as is desired in the newest micro devices, the dielectric layer no longer effectively performs effectively as an insulator due to the tunneling current running through it. This SiO
2
thin layer deficiency has lead to a search for improved dielectric materials.
Refractory metal oxides such as tantalum pentoxide (Ta
2
O
5
), titanium dioxide (TiO
2
), zirconium dioxide (ZrO
2
), and hafnium dioxide (HfO
2
), are some of the most promising SiO
2
replacements for future DRAM devices since they meet the requirements for large scale processing and fabrication using conventional microelectronics processing equipment. Furthermore, these oxides have excellent step coverage, and they exhibit comparatively low leakage current. Ta
2
O
5
is of particular interest as layers of amorphous Ta
2
O
5
have a dielectric constant of about 25. Ta
2
O
5
layers can be formed using chemical vapor deposition (CVD) processes. For example, reacting vapors of Ta(OC
2
H
5
)
5
(pentaethoxy-tantalum) with oxygen or by reacting vapors of TaF
5
with an O
2
/H
2
plasma can form Ta
2
O
5
.
Annealing can improve the crystallinity and resulting dielectric constant of refractory metal oxide layers. For example, the dielectric constant of an amorphous Ta
2
O
5
layer can be increased to at least 40 by annealing the deposited layer at temperatures over 700° C., causing a change in crystallinity from an amorphous state to what is believed to be a preferred (001) orientation of a crystalline hexagonal phase of Ta
2
O
5
. Unfortunately, this increase in dielectric constant of annealed crystalline Ta
2
O
5
layers is counterbalanced by higher leakage currents through the crystal boundaries. High temperature annealing of a Ta
2
O
5
layer on polysilicon also inevitably produces a thin SiO
2
interfacial layer between the Ta
2
O
5
layer and the polysilicon due to ambient oxidation during the deposition process and during any post-processing such as annealing. This SiO
2
layer insures better interfacial properties but also causes a reduction of the global dielectric constant of the Ta
2
O
5
capacitor. A metal nitride barrier layer can be applied to the polysilicon substrate prior to formation of the Ta
2
O
5
layer to avoid formation of the SiO
2
interfacial layer but at the cost of adding another processing step. Metal nitride barrier layers are also likely to be oxidized by high temperature anneal processes.
Changing the nature of the substrate and curing conditions during CVD processing can improve the dielectric constant of resulting Ta
2
O
5
layers. For example, Kishiro et al., “Structure and Electrical Properties of Thin Deposited on Metal Electrodes,” Jpn. J. Appl. Phys., 37:1336-1338 (1998) report crystalline Ta
2
O
5
layers having dielectric constants over 50 made by depositing the layers on platinum and ruthenium substrates rather than on poly-Si electrodes and annealing at 750° C. For another example, Lin et al., “Ta
2
O
5
thin films with exceptionally high dielectric constant,” Applied Physics Newsletter, 74(16):2370-2372 (1999) report that if a Ta
2
O
5
layer is deposited on a Ru/TiN/Ti/SiO
2
layered substrate, its dielectric constant can be increased up to 90-110 after N
2
O plasma treatment and then rapid thermal nitridation (RTN) at 800° C.
To date, efforts to improve the dielectric constant of Ta
2
O
5
layers have either required high temperature processing that has led to various layer deficiencies or have required specialized processing or substrate considerations. Thus, there remains a need for a vapor deposition process to form Ta
2
O
5
layers that have high dielectric constants and low current leakage, and that preferably do not require high temperature annealing, do not utilize oxidizers that can cause the formation of SiO
2
interfacial layers on polysilicon substrates, and do not require specialized processing or substrate considerations.
SUMMARY OF THE INVENTION
The present invention is directed toward using a vapor deposition process using refractory metal precursor compounds and ethers to form refractory metal oxide layers, especially tantalum pentoxide (Ta
2
O
5
) layers, on substrates. The vapor deposition process is preferably a reactive vapor deposition process that involves co-reacting the precursor compounds and the ethers.
The methods of the present invention involve forming a refractory metal oxide layer on a substrate by using a vapor deposition process and one or more refractory metal precursor compounds of the formula MY
n
(Formula I), wherein M is a refractory metal, each Y is independently a halogen atom, and n is an integer selected to match the valence of the metal M, and one or more ethers of the formula R
1
—O—R
2
, wherein R
1
and R
2
are each independently organic groups.
In one embodiment, a method of forming a layer on a substrate is provided that includes: providing a substrate (preferably a semiconductor substrate or substrate assembly such as a silicon wafer); providing a vapor that includes one or more refractory metal precursor compounds of the formula MY
n
, wherein M is a refractory metal (e.g., tantalum), each Y is independently a halogen atom (preferably, F, CI, I, or combinations thereof, and more preferably, F), and n is an integer selected to match the valence of the metal M (e.g., n=5 when M=Ta); providing a vapor that includes one or more ethers of the formula R
1
—O—R
2
, wherein R
1
and R
2
are each independently organic groups (e.g., alkyl groups, alkenyl groups, aryl groups, silyl groups, and combinations thereof); and directing the vapors of the one or more refractory metal precursor compounds and the one or more ethers to the substrate to form a refractory metal oxide layer on one or more surfaces of the substrate.
The present invention also provides a method of manufacturing a memory device. The method includes: providing a substrate (preferably a semiconductor substrate or substrate assembly such as a silicon wafer) having a first electrode thereon; providing a vapor that includes one or more refractory metal precursor compounds of the formula MY
n
, wherein M is a refractory metal, each Y is independently a halogen atom, and n is an integer selected to match the valence of the metal M; providing a vapor that includes one or more ethers of the formula R
1
—O—R
2
, wherein R
1
and R
2
are each independently organic groups; directing the vapors that include the one or more refractory metal precursor compounds and the one or more ethers to the substrate to form a refractory metal oxide dielectric layer on the first electrode of the substrate; and forming a second electrode on the dielectric layer.
The present invention also provides a vapor deposition apparatus t
Kennedy Jennifer M.
Micro)n Technology, Inc.
Mueting Raasch & Gebhardt, P.A.
Niebling John F.
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