Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
1999-10-20
2001-06-12
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S591000, C438S287000, C257S324000, C257S406000
Reexamination Certificate
active
06245606
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains generally to forming aluminum oxide dielectrics at low temperatures, and more particularly to forming aluminum gate oxide layers with high thickness uniformity.
BACKGROUND OF THE INVENTION
Semiconductors are widely used in integrated circuits for electronic devices such as computers and televisions. These integrated circuits typically combine many transistors on a single crystal silicon chip to perform complex functions and store data. Semiconductor and electronics manufacturers, as well as end users, desire integrated circuits that can accomplish more functions in less time in a smaller package while consuming less power. Miniaturization is a common approach to help meet these goals.
With increasing miniaturization, one concern is the thickness of the gate dielectric used in conventional CMOS circuits. The current drive in a CMOS transistor is directly proportional to the gate capacitance. Since capacitance scales inversely with gate dielectric thickness, higher current drive requires continual reductions in thickness for conventional dielectrics. Present technology uses silicon dioxide (SiO
2
) based films with thicknesses near 5 nm. However, projections suggest the need for 2 nm (20 Å) films for future small geometry devices.
SUMMARY OF THE INVENTION
Pure SiO
2
gate dielectrics will not be scaleable below 2 nm because of reliability problems (premature breakdown) and high leakage. This lack of scaleability motivates the search for higher dielectric constant materials. Generally, the search has centered on materials with &egr;>20-50, thus providing significant margin. However, we believe that even moderate dielectric constant materials (&egr;=10) can provide useful gate dielectrics, if a suitable manufacturing method is developed. Al
2
O
3
's thermodynamic stability on Si and moderate dielectric constant (&egr;=10) makes it a potential choice for a gate dielectric. We believe this usefulness may exist even though many artisans have avoided aluminum contact with Si, due to the potential of spiking.
The current method typically used for forming Al
2
O
3
is sputtering pure Al in an AR/O
2
ambient. This sputter deposition method of Al in an O
2
ambient tends to oxidize the Si substrate at onset of deposition, forming an undesirable SiO
2
layer. It is also difficult to reproducibly deposit ~30-60 angstroms this way.
Sputter deposition, rapid thermal oxidation and furnace annealing are three current methods for forming aluminum oxide gate dielectrics. However, current methods do not reliably produce gate oxides with the thickness uniformity and interface smoothness that will be needed to make devices with approximately 2-4 nm gate oxides practical. Additionally, these methods add significantly to the wafer's thermal budget.
We disclose a low temperature method for forming a thin aluminum oxide gate dielectric on a silicon surface, the method includes providing a partially completed integrated circuit on a semiconductor substrate with a clean silicon surface; determining a first planned temperature—no greater than about 300 degrees C.—for an aluminum oxide film formation; thereby substantially determining a potential thickness of oxidizable aluminum. The method further includes forming a uniformly thick layer of aluminum on the silicon surface to form a temporary aluminum layer, the temporary aluminum layer having a thickness no greater than the potential thickness of oxidizable aluminum; stabilizing the substrate at the first planned temperature; and exposing the temporary aluminum layer to an atmosphere including ozone, while maintaining the substrate at the first planned temperature. In this method, the exposing step creates a first, uniformly thick, aluminum gate oxide film. The method also typically includes forming a gate electrode on the aluminum gate oxide film.
In some embodiments, exposing the aluminum layer to an atmosphere including ozone uses a commercial ozone generator, while others include exposing the aluminum layer to an atmosphere including molecular oxygen, while irradiating at least a portion of the atmosphere with an ultraviolet light, where the light transforms some of the oxygen to ozone. In some embodiments, the atmosphere further includes an inert gas, such as argon. Preferably, the ozone at the aluminum layer is not in an excited energy state, such as a plasma. However, a plasma kept away from the wafer may be acceptable.
In some embodiments, the clean silicon surface is atomically flat. Typically, the semiconductor substrate contains some areas that already have some structure, such as a field oxide. In some embodiments, the substrate has a plurality of clean, atomically flat, silicon surfaces. This might occur when the gate oxide is applied to surfaces exposed by etching “windows” in a layer overlying a silicon surface; or when overlying layers are added to the silicon surface, except where “islands” have been masked off.
In some embodiments, the first planned temperature is about 25 degrees C. and the aluminum gate oxide film has a thickness of about 10 angstroms. In other embodiments, the first temperature may be up to about 300 degrees C., or even up to 530 degrees C. These temperatures will grow thicker oxides (up to about 50 angstroms) as shown in FIG.
3
.
In another aspect of this method, the method further includes depositing a uniformly thick layer of aluminum on the first aluminum oxide film to form a temporary aluminum layer, the temporary aluminum layer having a thickness no greater than the potential thickness of oxidizable aluminum. This potential thickness is found by determining a second planned substrate temperature for a second oxide film formation, the planned temperature no greater than about 300 degrees C.—often the same as the first planned temperature. This planned temperature substantially determines the potential thickness of oxidizable aluminum. After depositing the aluminum, the method further includes exposing the temporary aluminum layer to a second atmosphere containing ozone, while the substrate is at the planned substrate temperature. This exposing step oxidizes the temporary aluminum layer to form a second, uniformly thick, aluminum oxide film extending to the first oxide film; thereby creating a single (combined), uniformly thick, aluminum oxide film.
In some embodiments, the method further includes stabilizing the substrate at the second planned substrate temperature before the exposing step.
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Wallace Robert M.
Wilk Glen D.
Blum David S
Bowers Charles
Brady III Wade James
Denker David
Telecky , Jr. Frederick J.
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