The present application relates to integrated circuit devices and methods which employ amorphous silicon carbide resistor materials, including field emission devices, as well as methods for fabricating and using the foregoing.
The development of high density integrated circuit technology has been limited by the inability to provide suitable materials for integrated circuit resistor elements. Such materials typically must possess the ability to withstand intense electric fields without suffering breakdown, since their dimensions are so small. Moreover, the small size of these components requires high, tunable resistivity in order to achieve useful component resistances in many applications.
One promising application for integrated circuit technology is in the fabrication of flat panel displays that employ cold cathode field emission. Efforts to develop such devices have sought to utilize a large number of microtip emitters in each display pixel to achieve useful field emission current levels. But shorts, which can occur between some of the emitters and the gate can make the device inoperable. Variations in emitter geometries and in surface chemical properties can result in non-uniform field emission and varying brightness across the display. It has been proposed to insert a resistor layer between the microtip emitters and their current source (normally a cathode electrode) to overcome these problems.
A key to the successful development of such flat panel field emission displays, therefore, is the development of a resistor material having sufficiently high resistivity and capable of withstanding the intense electric fields which arise when breakdown occurs at the microtip emitters.
High speed, high density static RAM applications require the fabrication of integrated circuit resistor elements of very small dimensions, and consequently, require materials having high resistivity and the capability to withstand intense electrical fields. Similar requirements exist in other integrated circuit applications in which resistor elements are useful.
For a material to be suitable for this application, it should be possible to form electrical contacts with the material readily and the resistor material must be compatible with other materials used in fabricating the device. For example, the material should not react with other materials in the device.
The cost of device fabrication is another very important consideration. Materials which require high fabrication temperatures typically are undesirable since this limits the choice of compatible materials which can withstand such high temperatures without an undesirable change in their properties. In the case of flat panel field emission displays, low temperature processing is desirable to permit the use of less expensive substrates. At the same time, the resistor material should form a highly uniform film when it is deposited at such low temperatures. Another important consideration is the ability to selectively etch the materials to achieve the desired structure.
Yet another important consideration is that a suitable resistor material should have characteristics which either do not change after deposition as a result of further cathode processing, or else change in a limited and predictable way. Likewise, over time as the device is used repeatedly, the characteristics of the resistor material should either remain the same or change in a limited and predictable fashion.
While silicon has been proposed for use as such a resistor material, it is impractical to fabricate silicon resistor layers possessing sufficiently high resistivity for many applications. To achieve high resistivity in silicon, it is necessary to deposit this material in a very pure form which substantially increases fabrication cost.
It has been proposed to use cermet materials for use as resistor layers in flat panel field emission devices. However, it has proven very difficult to provide cermet resistor layers having sufficiently high resistance, as well as to select a desired resistance of such materials through doping. The resistivity of cermet also changes with thermal cycling and it is difficult to deposit and etch this material uniformly. Moreover, cermet has a grain structure that leads to uneven contact with the microtip emitters of the device and consequently, affects the resistances between the emitters and cathode electrode uncontrollably. This leads to uneven resistance values which result in non-uniform emission among the emitters.
Amorphous materials lacking such a grain structure do not share this drawback, and they are readily fabricated and processed. However, amorphous materials are thought to be unstable, tending to change their properties substantially over time or as a result of further processing after layer formation. Amorphous silicon with hydrogen added can have a suitably high resistivity, but hydrogen gas evolution can cause problems in amorphous materials processed at higher temperatures since it results in changes in material properties, and in some cases can form gas bubbles which disrupt the material.