Patent Application
20060060930
This invention relates to the fabrication of MOS field effect transistors.
As transistors are continuing to scale or become smaller in size, gate leakage is becoming unacceptably high. Using smaller transistors means more complex operations can be done by lower cost devices.
One way to continue gate scaling while maintaining acceptable leakage is to use gate dielectrics with higher dielectric constants. These higher dielectric constant materials currently have limited use because of severe electron mobility degradation and unfavorable reactions with polysilicon (which may be utilized as the gate electrode in some cases). Thus, both with polysilicon and metal gate electrodes, high dielectric constant gate dielectrics may experience problems.
Thus, there is a need for better ways to form transistors.
Referring to
Referring to
A metal precursor B may be stored in a closed, pressurized, heated reservoir 12a. The metal precursor may, for example, be hafnium chloride (HfCl4) in connection with forming a hafnium containing dielectric film. In another embodiment, the reservoir 12a may hold zirconium chloride. The reservoir 12a communicates with the chamber 20 via line 16a, whose flow is controlled by a high speed valve 14a. The precursor B may be a liquid that is converted to a vapor by the heater 11.
A silicon precursor C is contained within a reservoir 12c. The silicon precursor may be silicon chloride (SiCl4). Again, the precursor C is also in liquid form but is released as a gas through the valve 14c upon heating by a heater 11 which surrounds the reservoir C. Thus, each of the reservoirs 12 may be heated by a heater 11. Each heater 11 may be controlled to produce the desired amount of vapor for injection into the chamber 20. Thus, the more heat that is applied, the more vapor that may result from any given reservoir 12.
Referring to
After the prestabilization stage 22, the metal precursor B, such as hafnium chloride, is vaporized and injected as a pulse into the chamber 20. The pulse length is set by the valve 14a. The metal precursor pulse may be followed by a purge cycle. In the purge cycle, the metal precursor gas that was previously applied is exhausted using a neutral gas such as nitrogen and a vacuum pump. The duration of the pulse and purge may be controlled as desired to achieve particular film thicknesses in particular situations.
After the purging of the precursor B, a pulse of oxidant, such as water, may be applied from reservoir 12b, followed by a purging of the oxidant. Next, a pulse of the precursor C, such as silicon chloride, may be applied, again followed by a purge pulse. Then, another oxidant pulse and another purge pulse are applied. This sequence of eight pulses in the specified order may be repeated to achieve a desired film thickness formed of monolayers built up by each pulse. A monolayer is a layer of material having the thickness of one molecule. In one embodiment, the sequence may be repeated three or four times. However, in other cases, the pulses are simply repeated until the desired thickness is achieved.
In one embodiment of the present invention, the chamber 20 reaches a temperature of approximately 200 to 400° C. during the prestabilization period. The temperature of the precursor B may be from about 150 to about 250° C. The temperature of the precursor C may be from about 10 to about 40° C. The temperature of the precursor A may be from approximately 10 to approximately 40° C. The temperature in the chamber 20 may be from about 200 to about 400° C. in one embodiment of the present invention.
Referring finally to
Examples of n-type metals for an n-type metal gate transistor include zirconium, hafnium, titanium, tantalum, aluminum, and their alloys including metal carbides that includes these elements, such as hafnium carbide, zirconium carbide, titanium carbide, tantalum carbide, and aluminum carbide.
Examples of p-type metal for forming p-type metal layers over a silicate of zirconium or hafnium dioxide include ruthenium, palladium, platinum, cobalt, nickel, and conductive metal oxides, including ruthenium oxide.
While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.
