Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With particular semiconductor material
Reexamination Certificate
1998-01-05
2001-07-03
Everhart, Caridad (Department: 2825)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With particular semiconductor material
C257S615000, C257S613000, C438S604000, C438S605000, C438S662000
Reexamination Certificate
active
06255671
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to microelectronic device fabrication methodologies and, in particular, to the formation of protective passivation layers that are applied to surfaces of microelectronic devices, such as integrated circuits and chip carriers, as well as to the formation of conductive interconnects and resistance elements.
BACKGROUND OF THE INVENTION
Passivation layers are used in a wide range of semiconductor CMOS and bipolar devices and packages. The primary function of a passivation layer is to hermetically seal and/or electrically isolate semiconductor devices/circuits in a multi-layer stack.
There are two general types of passivating layers that are currently used. The first type comprises inorganic nitrides and oxides which are generally hard, chemically inert, and impervious to moisture. These materials exhibit an adequate thermal conductivity as well as a high electrical resistivity and a high dielectric breakdown strength that provides excellent electrical isolation. However, the first type of passivating layers usually require high temperature processing for their deposition (>400 C.). Furthermore, in many cases the materials are non-transparent, thereby complicating certain processing steps involving lithography.
The second type of passivating layers comprise organic polymers, such as polyimide. In general these polymers are soft, partially transparent, are not totally impervious to moisture and certain solvents, acids, or bases, and are limited to use at low temperatures (<350 C.). However, their ease of deposition makes them an attractive choice in a number of applications.
Both of the above types of passivation layers require standard photolithography processing if they are to be patterned. Patterning is necessary in many applications in order to make metal contacts through the passivation layer to connect the upper metal layer on microelectronics devices to layers below. However, patterning introduces a number of additional steps such as photoresist deposition, photolithography, and reactive ion or wet chemical etching to produce contact holes in the insulator and metallization to facilitate electrical connection. Further, the contact hole topography and edge profile can affect the extent to which the metallization conformally covers same, and can also affect the contact resistance and reliability of the interconnection between levels. While shallower wall profiles in thin insulator layers are generally most conducive to achieving good step coverage, steep wall profiles are required in order to achieve a high area density of contacts. Furthermore, providing a good dielectric breakdown voltage necessitates the use of thicker insulators. These conflicting requirements detrimentally limit the choice of metallization processes as well as an upper bound on practical contact densities in devices. Consequently, there is a long-felt need for a robust, transparent and impervious passivation layer that can be easily deposited, patterned and interconnected in fewer process steps. It is further desirable to achieve a contact hole and metal fill structure in a coplanar morphology to avoid the above-mentioned step coverage related issues.
Aluminum nitride is hard, robust, chemically inert, optically transparent, impervious to moisture, and exhibits a high thermal conductivity and electrical resistivity. That is, the use of AlN provides a passivation layer having excellent mechanical, thermal and dielectric properties. The physical properties of AlN are shown in Table 1.
TABLE 1
Properties of AlN
Hardness
7 Mohs/1200 Knoop
Resistivity
10
13
Ohms/cm
Dielectric Constant
8.5
Thermal Conductivity
0.3 W/cm K
Solubility
Impervious to most acids and bases
In addition, AlN has the property that when exposed to ultraviolet radiation above a certain power density, for example greater than 100 mJ/cm
2
, the nitrogen in the AlN preferentially desorbs leaving behind a thin film of Al. This property was observed in bulk AlN by Li et al., Mat. Res. Soc. Symp. Proc. 390, 257 (1995).
In U.S. Pat. No.: 5,225,251, issued Jul. 6, 1993, entitled “Method for Forming Layers by UV Radiation of Aluminum Nitride”, H. Esrom describes a process for irradiating an aluminum nitride layer with ultraviolet radiation in the range from 240 nm to 270 nm, resulting in the elimination of the nitrogen component from the aluminum nitride for forming an aluminum layer. The aluminum layer is then reinforced with another metal using a metal deposition process.
OBJECTS AND ADVANTAGES OF THE INVENTION
It is a first object and advantage of this invention to provide an improved passivation layer that overcomes the foregoing and other problems.
It is a further object and advantage of this invention to provide a process that uses a metal nitride passivation material, in which process electrically conductive features, which may have a controlled value of resistance, are fabricated within the passivation material using a thermal process.
It is another object and advantage of this invention to provide a process that uses one or a stack of Group III metal nitride films, in which process electrically conductive metal circuit interconnects are fabricated within the film or films using electromagnetic radiation having wavelengths selected for causing illuminated portions of the film(s) to convert to the Group III metal or metals.
SUMMARY OF THE INVENTION
The foregoing and other problems are overcome and the objects of the invention are realized by methods and apparatus in accordance with embodiments of this invention, wherein a structure includes a metal nitride film of the form MN, where M is selected from the group consisting of Ga, In, AlGa, AlIn, and AlGaIn. The structure has at least one electrically conductive metal region that is formed within and from the metal nitride film by a thermal process driven by absorption of light having a predetermined wavelength. Single films comprised of AlN are also within the scope of this invention, wherein an Al trace or interconnect is formed by laser radiation of wavelength 248 nm so as to electrically contact circuitry that exists under the film. The use of multi-layered stacks of films are also within the scope of the teachings of this invention. In this case each film layer may be separately deposited and then illuminated to selectively form the desired electrical connection(s), which may also connect to conductive feature(s) in an underlying layer, or a plurality of metal nitride layers are stacked bottom to top in order of increasing electronic band gap energy value, and then conductive features are written into selective ones of the layers by controlling the wavelength of the light to be absorbed in a desired layer. The teachings of this invention can be employed to fabricate fuses and anti-fuses enabling selective circuit customization, test and repair.
Also disclosed is a technique for forming electrical resistors in a metal nitride layer by adjusting the electrical resistance of the metallization formed from the metal nitride film layer.
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patent: 4706377 (1987-11-01), Shuskus
patent: 5145741 (1992-09-01), Quick
patent: 5225251 (1993-07-01), Esrom
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L. Maya, et al. “Gold nanocomposites” J. Vac. Sci. & Tech. B; vol. 13, No. 2; pp. 361-365, Apr. 1995.
Bojarczuk, Jr. Nestor Alexander
Guha Supratik
Gupta Arunava
Purushothaman Sampath
August, Esq. Casey P.
Everhart Caridad
International Business Machines - Corporation
Perman & Green LLP
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