Killer Defects Generated in Aluminum Metal Etch Processes

Killer Defects Generated in Aluminum Metal Etch Processes

Material Name: Aluminium
Record No.: 10
Primary Chemical Element in Material: Al
Sample Type: Layer
Uses: Etching
Etchant Name: None
Etching Method: Dry etching
Etchant (Electrolyte) Composition: No data
Procedure (Condition): No data
Note:
During metal etch processes (etching aluminum line), Cl2 and BCl3 are the main reactive gases to etch aluminum. Ar, N2, CF4, CHF3, C2H4, or O2 are also used during etching and WAC processes. Therefore, the selected chamber materials have to demonstrate high corrosion (and erosion) resistance to these gases under the high density plasma. For silicon etch processes, SF6, NF3, HBr and HCl are the main reactive gases used to etch silicon. Other gases may also be used in the etching and WAC processes. The selected chamber materials should have a high corrosion resistance to both F-based gases and HBr corrosion. In particular, the corrosion of HBr mixed with a very tiny amount of water on the heat effected zone of stainless steel has been an issue for a long time. For dielectric etching processes, CxFx based reactive gases are usually used with a high applied power in order to etch oxide. Chamber materials selected have to show high corrosion and erosion resistance at a relatively high temperature and high power. For special etch processes such as metal hard mask etch, MRAM etch, high K etch and Bevel etch, special process gases and chamber conditions are applied. Therefore, the requirements to corrosion resistance chamber materials may be different. Since some plasma etching processes even etch noble metals such as Pt, Ru and Ir, one has to find chamber materials which can survive in these aggressive plasma etching conditions. Therefore, chamber materials which are submitted to sputtering, chemical etching, ion-enhanced etching, as well as ion-enhanced inhibitor etching have to be studied and characterized thoroughly for each special etching applications. There is no any material which can meet all plasma etching applications. In summary, some of the key requiements of chamber materials is listed below:
- Low erosion rate under vigorous plasma bombardment.
- Low chemical reaction rate under many chemistries such as
- Cl2/BCl3-containing plasma,
- Fluorine-containing plasma,
- HBr/HCl/Cl2-containing plasma,
- Oxygen-containing plasma.
- Low transition metal transport to the workpiece.
- Low or zero particle contamination from surfaces.
- Strong interface bonding of surface coatings for long part lifetime.
- Excellent and repeatable dielectric properties for RF energy coupling.
- Pore-free ceramic materials and low porosity surface coating to avoid undercut corrosion and to eliminate substrate attack.
- Excellent adhesion of etch by-products and polymers.
- Excellent corrosion resistance in wet chemistry cleaning.
- Cost effective in manufacturing.
- Excellent repeatability from part to part and wafer to wafer.
The killer defects which are generated during metal etching processes fall on metal lines and cause the loss of production yield in wafer fabrication. The killer defects may either come from chamber materials or etch by-products. For etching process requirement, a metal etch film stack and common issues are shown in Fig. 1.
The corrosion/erosion patterns of chamber materials showed three different patterns under plasma. Fig. 3 shows the three different patterns.
Reference: Hong Shih (2012). A Systematic Study and Characterization of Advanced Corrosion Resistance Materials and Their Applications for Plasma Etching Processes in Semiconductor Silicon Wafer Fabrication, Corrosion Resistance, Dr Shih (Ed.), ISBN: 978-953-51-0467-4, InTech, Available from: http://www.intechopen.com/books/corrosion-resistance/a-systematic-study-and-characterization-of-advancedcorrosion- resistance-materials-and-their-applica.

Figure 1: Aluminum metal film stack and common issues in etching processes.

Figure 2: Killer defects generated in aluminum metal etch processes.

Figure 3: Corrosion/erosion patterns of chamber materials under plasma etching (pictures are at 10,000x magnification). Model A indicates a uniform corrosion/erosion which can either be higher or low; Model B shows the attack at grains of materials; and Model C shows the attack at grain boundaries of materials.