Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
2000-08-25
2002-06-11
Clark, Jhihan B (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S750000, C257S757000, C257S763000
Reexamination Certificate
active
06404057
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to materials used in semiconductor device fabrication for interconnects, contacts, electrodes and other conductive applications. More particularly, this invention relates to materials having desirable interdiffusion barrier properties, desirable adhesion properties, and/or low contact resistances.
Semiconductor devices, also called integrated circuits, are mass produced by fabricating hundreds of identical circuit patterns on a single semiconductor wafer. During the process, the wafer is sawed into identical dies or “chips”. Although commonly referred to as semiconductor devices, the devices are fabricated from various materials, including conductors (e.g., aluminum, tungsten), non-conductors e.g., silicon dioxide) and semiconductors (e.g., silicon). Silicon is the most commonly used semiconductor, and is used in either its single crystal or polycrystalline form. Polycrystalline silicon is often referred to as polysilicon, or simply “poly”. The conductivity of the silicon is adjusted by adding impurities—a process commonly referred to as “doping”.
Within an integrated circuit, thousands of devices (e.g., transistors, diodes, capacitors) are formed. These devices are formed by various fabrication processes, including doping processes, deposition processes, etching processes and other processes. Interconnects are formed to serve as wiring lines connecting the many devices. Contacts are formed where a device interfaces with other devices. Electrodes are formed for capacitors and other devices. Gate structures are formed for transistor devices. These interconnects, contacts, electrodes and gates are formed using conductive materials or alloys.
In forming interconnect stacks, for example, it is desirable to perform an annealing step to densify material formation and improve material properties. Often, such processes include exposing the wafer to elevated temperatures, such as 500° C. or higher. Exposure to these elevated temperatures may result in undesirable effects, such as interdiffusion of metals, morphology changes, melting or other undesirable reactions with adjacent materials. Incorporating alloys with aluminum, for example, is used to raise the melting point and reduce electromigration effects. However, even at a low temperature, such as 100° C., aluminum and silicon may react, interdiffusing with each other. Such interdiffusion alters the desired device properties, resulting in product defects. Accordingly, it is known to provide a barrier layer at a silicon/metal interface. Known barrier materials for such interfaces include titanium nitride (TiN), titanium-aluminum-nitride (Ti—Al—N), titanium-tungsten (TiW), tantalum-nitride (TaN), and other materials. Such barrier layers often are 100 to 1000 Å thick.
Conventional diffusion barriers such as TiN and TiW, while generally effective at lower temperatures such as room temperature, tend to fail at elevated temperatures. As many preferred semiconductor fabrication processes require elevated temperatures, these materials often prove unsatisfactory. As a result the implemented diffusion barrier often limits the types of fabrication processes that can be performed. The Ti—Al—N material as disclosed in U.S. Pat. No. 5,231,306 is an improvement over the TiN and TiW materials being more effective and being more thermally stable at elevated temperatures. Other barrier materials for preventing interdiffusion also are desirable.
Further, as more complex wiring line structures are implemented for decreasingly smaller line pitches, additional layers are being included. One difficulty in dealing with the smaller dimensions and the increasingly complex structures is promoting adhesion among the layers. Accordingly, there is a need for materials useful at decreasing line pitches having improved adhesion qualities.
SUMMARY OF THE INVENTION
According to the invention, tantalum-aluminum-nitrogen (“Ta—Al—N”) is deposited on a semiconductor wafer to define a portion of a contact, interconnect, gate or electrode. In various embodiments the Ta—Al—N material serves as a diffusion barrier, promotes adhesion, or serves as a cap layer of an interconnect stack. In these and other embodiments, the alloy material is used for its desirable material properties at small dimensions and over varying and/or prolonged temperature ranges.
According to one aspect of the invention, the tantalum-aluminum-nitrogen serves as a diffusion barrier. In various embodiments, the Ta—Al—N material serves as a diffusion barrier between (i) two conductor layers, (ii) a semiconductor layer and a conductor layer, (iii) and insulator layer and a conductor layer, (iv) an insulator layer and a semiconductor layer, and (v) two semiconductor layers.
According to another aspect of the invention, the tantalum-aluminum-nitrogen promotes adhesion between adjacent layers. In various embodiments the Ta—Al—N material promotes adhesion between (i) two conductor layers, (ii) a conductor layer and an insulator layer, (iii) a semiconductor layer and a conductor layer, and (iv) two semiconductor layers.
According to another aspect of the invention, the Ta—Al—N material includes respective atomic concentrations of aluminum, tantalum and nitrogen as follows: between 0.5% and 99.0% aluminum; between 0.5% and 99.0% tantalum; and between 0.5% and 99.0% nitrogen. According to preferred embodiments, the material includes an atomic concentration of aluminum between 1.0% and 35%, an atomic concentration of tantalum between 20% and 50%, and an atomic concentration of nitrogen between 20% and 60%. Exemplary thicknesses are between 50 and 6000 Å. In embodiments in which the material is used to define a contact or electrode structure the thickness range extends up to approximately 2 microns.
According to another aspect of the invention, the tantalum and aluminum deposited to form part of a Ta—Al—N layer come from organometallic sources.
According to another aspect of the invention, the tantalum and aluminum deposited using sputtering techniques.
According to various embodiments of the invention, the Ta—Al—N material serves as a diffusion barrier layer in a wiring line stack; a cap layer in a wiring line stack; a contact structure between a substrate or layer and a wiring line; an interface layer between a contact and a metallization layer; an electrode for a capacitor; and a layer in a device gate stack.
According to one advantage of the invention, the Ta—Al—N layer serves as an effective diffusion barrier at elevated temperatures for typical process times, and at room temperatures for extended times. According to another advantage of the invention, the Ta—Al—N layer promotes adhesion with surrounding layers of the semiconductor device. According to another advantage of the invention, there are Ta—Al—N compounds which have better thermal stability than Ti—Al—N compounds. In addition, tantalum is less attractive to oxygen than titanium and, thus, forms less oxide molecules during compound (Ta—Al—N) formation and deposition as compared to Ti—Al—N. These and other aspects and advantages of the invention make Ta—Al—N an effective material for use in interconnects, contacts, gates and electrode structures formed on a substrate.
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Stanley Wolf, “Silicon Processing for the VLSI Era”, Volume II: Process Integration, pp. 121
Akram Salman
Meikle Scott G.
Clark Jhihan B
Micro)n Technology, Inc.
Traskbritt
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