In the rapidly advancing semiconductor fabrication industry, there is a constant challenge to form devices with smaller feature sizes and which operate at faster speeds. Semiconductor devices operate using thousands or even millions of transistors such as MOSFET (Metal Oxide Semiconductor Field Effect Transistor) devices. The MOSFETs include NMOS transistors and PMOS transistors. These transistor devices utilize channels through which current flows when activated by the associated transistor gate. The current flows from the source to the drain of the transistor and the speed by which the current flows from the source to the drain is of paramount importance and is largely determined by the channel material. Replacement channels are often used when the transistor devices are formed on substrates formed of silicon or similar materials. With replacement channels, the silicon or other substrate material, is replaced with a different channel material that is a high mobility material which enables faster device speed than the silicon or other original channel material, prevents strain and is resistant to degradation. Epitaxial deposition methods are favored for producing replacement channels.
High dopant concentrations are advantageously utilized in many replacement channel materials to provide faster channel speeds. This is true for both P-type channels and N-type channels used in PMOS and NMOS transistors, respectively.
When replacement channel materials are formed using epitaxial deposition methods, however, it is difficult to achieve the high dopant concentration levels necessary to provide the increased device speed in a stable, reliable and defect-free material. This shortcoming can be attributed to the defects that are created when epitaxial deposition processes are used to produce replacement channel materials with high dopant concentrations. The defect density of the replacement channel material increases as does the dopant concentration level produced by the epitaxial deposition process used to form the replacement channel material.
USPTO Backgrounds
USPTO Backgrounds