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Basic technical principles of plasma cleaning in semiconductor packaging

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Published on:

04 Sep,2020

Basic technical principles of plasma cleaning in semiconductor packaging:

In the production process of semiconductor devices, due to the influence of materials, technology and environment, various particles, organic matters, oxides and residual abrasive particles can not be seen on the surface of wafers. Plasma cleaning is a high-quality process method.

On the premise of not damaging the surface properties, thermal properties and electrical properties of the wafer and other materials used, cleaning and removing harmful contaminants from the wafer surface is particularly important for the functionality, reliability and integration of semiconductor devices. Otherwise, they will seriously affect the performance of semiconductor devices, greatly reduce product yield and restrict the further development of semiconductor devices.

The basic technical principle of plasma cleaning is as follows:

1, in a sealed vacuum cavity, through constant suction vacuum pump, makes the stress value decreased gradually and vacuum degree enhances unceasingly, the spacing between the molecules is widening, molecular inter-atomic forces, using plasma generator to produce high voltage alternating electric field will Ar, H2 O2, N2, and CF4 gas excitation, the shock formation with high reactivity and high energy of plasma, then react with organic pollutants and micro particle pollution or the formation of volatile substances, by the working gas flow and the vacuum pump will these out volatile substances, so as to achieve the surface cleaning, activation, etching, etc. As shown in the figure below:

2, plasma cleaning will not damage the intrinsic characteristics of materials or products are processed, change only the surface, the thickness of the nano-scale materials or products to be cleaned surface contaminant has been removed, molecular bonds on the extremely small structural changes, forming a certain roughness or is produced on the surface hydrophilicity of functionality, makes the reliability of the metal welding to enhance and improve the bonding force between different material, so as to improve product reliability, stability, prolong the service life of the product.

3. According to the reaction types of semiconductor packaging plasma cleaning, it can be divided into the following three types:

A. Physical reaction cleaning: Inert gases such as Ar can be used to easily avoid reaction with other substances, and ions are relatively heavy. Physical bombardment of the material surface can remove pollutants or break the bonds of polymers to form a rough surface of microstructure.

Example: Ar+e- →Ar++2e- Ar++ contamination → volatile contamination

Ar+ is accelerated to generate kinetic energy under the action of self-bias or external bias, and then bombarded on the surface of the cleaned workpiece placed on the negative electrode. It is generally used to remove oxides, epoxy resin spills or micro-particle pollutants, while carrying out surface activation.

B. Cleaning of chemical reaction: Make use of the properties of H2, O2 and other active gases to make them undergo reduction reaction or form active functional groups with multi-bond structure, carry out surface modification and improve hydrophilicity, etc.

Example 1: O2+ E - →2O*+ E-O *+ organic matter →CO2+H2O

It can be seen from the reaction formula that oxygen plasma can change non-volatile organic compounds into volatile H2O and CO2 through chemical reaction.

Example 2: H2+ E - →2H*+ E-h *+ non-volatile metal oxides → metal +H2O

It can be seen from the reaction formula that hydrogen plasma can remove the oxide layer on the metal surface through chemical reaction and clean the metal surface.

C. Cleaning of physical and chemical reactions: different process gases, such as Ar and H2 mixture, are injected according to needs, with good selectivity, cleanability and uniformity as well as good directivity.

Basic technical principles of plasma cleaning in semiconductor packaging

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