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Application of ultra-low temperature plasma etching technology for plasma surface treatment

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04 Jan,2021

Application of ultra-low temperature plasma etching technology for plasma surface treatment:

 

Baklanov's team has reported that porous organosilicate material has been etched into plasma-surface processors at extremely low temperatures. This material is often used as insulation and filler in the Damascus process for semiconductor backends. It is found that when the plasma etching temperature of plasma surface processor is lower than -100℃, the low-k Damage generated in the etching process of the material will be sharply reduced, and its dielectric constant does not increase significantly, so that the material characteristics do not change significantly. At the same time, the damage of the etching process to the dielectric material under different bias pressure is compared. The low bias or zero bias ultra-low temperature etching of plasma surface processor can significantly reduce the PID of the material with low dielectric constant, and at the same time, the dielectric property of the material has no obvious change compared with that before etching.

 

Hess's team at Georgia Tech reported in 2015 that copper, gold and silver materials were etched at low temperatures in plasma surface processors using gas plasma etches. Conventional metal Cu etching uses Cl2 gas plasma to react with it at high temperature to produce CuCl2, which is then removed in the subsequent process. Hess's team reported the successful implementation of Cu etching in ICP etching chamber of plasma surface processor by using H2 gas plasma etching at low temperature (10℃). As shown in the scanning electron micrograph, the etching process uses SiO2 as the hard mask material to form the figure, and the 100nm thick Cu film etched by H2 gas plasma obviously forms the step-like structure, and Si substrate under the Cu film is exposed. In contrast to the Ar plasma etching process, the loss of Cu film after etching is not obvious. This indicates that unlike Ar gas plasma etching, which relies on physical bombardment of Cu films, H2 gas plasma etching mainly relies on chemical etching. During the reaction process, copper hydrides are formed and Cu metal bonds are destroyed, thus reducing the reaction potential energy. The hydride of the formed copper can be easily removed from the surface of the material and the reaction chamber. Similarly, Au and Ag are etched by H2 gas plasma or other H-containing plasma, forming metal hydrides that can reduce the reaction potential energy.

 

Ultra-low temperature etching process need hardware setup with normal plasma surface treatment machine inductively coupled plasma (ICP) etching device are very similar, just need to add liquid helium or nitrogen cooling device, makes the silicon wafer substrate temperature down to - 100 ℃, the use of SF, and O2 as the premise of plasma gas source, deep grooves or silicon Gao Shenkuan than silicon structure can also by Electron Cyclotron Resonance (Electron Cyclotron Resonance, ECR) etching. When the plasma surface processor increases the relative flow rate of O2 in the low-temperature ECR etching process, the silicon etching rate will significantly increase, and the ratio of F content to O2 content plays an important role in the etching process. Today and in the production process of plasma surface treatment machine, low temperature plasma etching process can not be widely used among the main difficulty is that in the actual production process is very difficult to keep the wafer substrate at low reaction temperature, the etching reaction cavity will be very complex, and change the silicon wafer in process temperature takes quite a long time, so that the effective Gao Changkuan than etching process cannot enter into industrial applications.

plasma surface treatment

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