hydrogen plasma

Hydrogen plasma also has certain special properties due to its special reducing properties. H2 is a diatomic molecule. The reaction of high-frequency discharge to form hydrogen plasma is not as simple as that of typical Ar discharge. It involves more types of particles. In addition to electrons (e), hydrogen plasma also contains various hydrogen ions (H+, H+2, H+3, H-), ground state and electronic excited state hydrogen atoms and hydrogen molecules, which can etch and reduce the surface of materials and easily react with surface molecules to form new substances such as water and hydrocarbons.

Reduction effect of hydrogen plasma

Hydrogen is a reducing gas that can reduce metal oxides or metal salts into metal elements at a certain temperature. In a hydrogen plasma environment, some reduction reactions that require high-temperature heating can be achieved at low temperatures.

Argon-hydrogen plasma cleaning of copper lead frames

Lead frame packaging is still the mainstream packaging, and copper alloy is used as the main lead frame material due to its good thermal conductivity, electrical properties, processing performance and low price. However, copper oxides and other contaminants can cause delamination between molding compound and copper lead, reduce device reliability and thus affect the quality of chip bonding and wire bonding.

The use of hydrogen and argon mixed gas can effectively remove pollutants on the metal layer of the lead frame. During the cleaning process, hydrogen plasma can remove oxides and argon can promote the increase of hydrogen plasma through ionization.

Hydrogen plasma passivation

Polycrystalline silicon thin films have broad applications in large-area microelectronics and liquid crystal displays, but polycrystalline silicon thin films contain a large number of grain boundaries, and grain boundary defects will produce certain grain boundary barriers that seriously affect their electrical properties. Hydrogen will saturate the dangling bonds of semiconductor material silicon, and the application of hydrogen plasma can effectively passivate these defect states. In addition, it can neutralize electrically activated shallow impurities or deep impurities, such as vacancy-impurity complexes, or substitutional noble metals, transition impurities, etc. The introduction of hydrogen is very beneficial to light-emitting devices, power devices, etc.

In the hydrogen plasma state, hydrogen diffuses into the sample and combines with the defect states therein to form saturated bonds, thereby achieving the purpose of passivating the internal defect states of the material.

In the presence of charged ions, an appropriate high-frequency electromagnetic field can ionize low-pressure hydrogen to produce a mixed plasma of hydrogen ions, activated hydrogen atoms, hydrogen molecules and electrons. During the glow discharge process, the electron temperature is as high as 104-105K, and the energy is about 16×10-19J. These electrons couple almost all of their energy to hydrogen through inelastic collisions. Therefore, H and H+ have energies far higher than the average kinetic energy of thermal motion of hydrogen molecules (~0.064×10-19J). On the other hand, H is the smallest and lightest atom, so it can squeeze into the silicon surface at room temperature and interact with defects. H in silicon is an interstitial impurity and the fastest diffusing impurity. H or H+ entering the sample can diffuse rapidly to fill various types of vacancy defects.

There have been many studies on the use of hydrogen plasma to passivate various defects in semiconductor materials. H or H+ not only easily combines with dangling bonds (vacancies, etc.), but also can passivate many deep impurities and thermal defects in silicon.