In semiconductor manufacturing plasma ashing is the process of removing the photoresist from an etched wafer. A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that Photoresist is a Light -sensitive material used in several industrial processes such as Photolithography and Photoengraving to form a patterned coating Etching is used in Microfabrication to chemically remove layers from the surface of a wafer during manufacturing Using a plasma source, a monatomic reactive species is generated. In Physics and Chemistry, plasma is an Ionized Gas, in which a certain proportion of Electrons are free rather than being bound In Physics and Chemistry, monatomic is a combination of the words "mono" and "atomic" and means "single Atom. Oxygen or fluorine are the most common reactive species. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Fluorine, fluorum meaning "to flow" is the Chemical element with the symbol F and Atomic number 9 The reactive species combines with the photoresist to form ash which is removed with a vacuum pump. A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial Vacuum.
Typically, monatomic (single atom) oxygen plasma is created by exposing oxygen gas (O2) to non-ionizing radiation. Non-ionizing radiation (or esp in British English, non-ionising radiation) refers to any type of Electromagnetic radiation that does not carry enough This process is done under vacuum in order to create a plasma. At the plasma is formed, many free radicals are created which could damage the wafer. In Chemistry, radicals (often referred to as free radicals) are atoms molecules or ions with Unpaired electrons on an otherwise Open shell Newer, smaller circuitry is increasingly susceptible to these particles. Originally, plasma was generated in the process chamber, but as the need to get rid of free radicals has increased, many machines now use a downstream plasma configuration, where plasma is formed remotely and the desired particles are channeled to the wafer. This allows electrically charged particles time to recombine before they reach the wafer surface, and prevents damage to the wafer surface.
Two forms of plasma ashing are typically performed on wafers. High temp ashing, or stripping, is performed to remove as much photo resist as posible. While the "descum" process is used to remove residual photo resist in trenches. The main difference between the two processes are the temperature the wafer is exposed to while in an ashing chamber.
Monatomic oxygen is electrically neutral and although it does recombine during the channeling, it does so at a slower rate than the positively or negatively charged free radicals, which attract one another. Effectively, this means that when all of the free radicals have recombined, there is still a portion of the active species available for process. Because a large portion of the active specie is lost to recombination, process times may take longer. To some extent, these longer process times can be mitigated by increasing the temperature of the reaction area.
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