MEMS英文课件4-MEMS

Resist Sensitive to the light source, typically 1 μm thick, and applied on a solid substrate for the pattern transfer Positive and negative resist
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Exposed regions remain after development
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Typical photolithography process sequence:
Wafer cleaning/drying Wafer cleaning is important!
Overview of thin-film deposition
Physical vapor deposition (PVD)
Chemical vapor deposition (CVD) Electrodeposition Physical deposition spin-on sol-gel
Overview of pattern transfer
Outline
Overview pf microfabrication processes
Photolithography
Surface micromachining Bulk micromachining SOI & LIGA processes Wafer bonding Summary
MEMS Fabrication-In General
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Surface micromachining-1
• Layers of films, totaling less than 10 microns, typically. • Layers deposited, patterned, etched. • Sacrificial material removed after completion. • Similar to standard semiconductor processes, like CMOS.
MEMS Fabrication-In General
• Typical MEMS fabrication involves the following conventional microelectronic fabrication processes: – Cleaning Processes – Deposition Processes – Patterning Processes – Etching Processes
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������ Spin resist To achieve a uniform thin coating of photoresist on a wafer surface, the photoresist is spun onto the wafer surface in a spinner spinning at several thousands revolution per minute (rpm). ������ Soft bake After spin coating the photoresist, the photoresist is then baked at a temperature from 75 to 100 0C for about 10 minutes to remove solvents and stress and to promote adhesion of the photoreisist layer to the wafer. This baking process is commonly referred to as soft baking.
Etching processes Deposition Processes Deposition Processes
MEMS Fabrication-In General
• Patterning From scraping to lithography Using light as a tool, parallel process, very high resolution (~30 nm using 193 nm DUV), … • Patterning From acid etch to a variety of etch methods Wet etching, dry etching, RIE, DRIE, ion beam milling, … • Multiple layers
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������ Exposure After soft baking, the photoresist-coated wafer is transferred to an exposure system where it is placed between a photomask and exposed with an ultra violet radiation with wavelengths from 150 to 500 nm. ������ Development After exposure, the photoresist-coated wafer undergoes a development stage where selective dissolving of photoresist takes place. ������ Post bake / hard bake After developing, the remaining photoresist must be baked at temperature for about 120 0C for 20 minutes to remove residual developing solvents and to promote interfacial adhesion of the photoresist weakened by developer penetration along the photoresistsubstrate interface or by swelling of the negative photoresist.
Overview of etching processes
Dry ectching (Gas phase)
Wet etching (Liquid phase)
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In microfabrication, pattern tansfer is normally achieved by a process known as photolithography. As the name implies, this process involves an optical as well as photogeaphic process. The optical process is achieved by using an ultra violet light source while the photograplic process is by an ultra-violet sensitive polymeric materil called photoresist. Three types of photolighography process:
Positive resist:
Resist becomes soluble through chain scission under deep UV illumination Unexposed regions remain after development
Negative resist: Under UV illumination, crosslinking of main chains or pendant side chains rendering the exposed parts of the resist insoluble
It is this batch processing (i.e., fabricate and processing many of these MEMS devices and/or substrates at the same time) that makes MEMS devices economically viable and readily acceptable in many system applications. Modifications of the conventional semiconductor or microelectronic processes are necessary, in most cases, for MEMS fabrication. There are specialized fabrication processes for MEMS such as surface micromachining, bulk micromachining, and many customized / specialized processes.
Microfabrication
Dabin Liu Department of Mechanical Engineering Chongqing University Weixin_ldb@sina.com
How do we do MEMS
Armor Decoration
Beginning heavily in the 15th century, armorersБайду номын сангаасbegan to decorate their suits using a variety of technologies.
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Elements of Lithography:
Light source Ultraviolet (UV) light, X-ray, electron or ion beams UV light with a wavelength of 250-450 nm is commonly used for silicon process Mask A chromium pattern on a light-transparent substrate (glass)
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Alignment marks: • Multiple-layer processes require patterns in successive layers to be properly aligned to one another.
• Typical alignment marks:
• Apply an acid-resistant coating (such as wax) • Scraped away the coating in the desired pattern • Etch with a weak acid (such as vinegar) • Accentuated by applying a colorant such as lamp-black to the cut-away portions
Mask: A optically flat glass (transparent to near UV) or quartz plate (transparent to deep UV) with a metal (e.g. chromium layer) absorber pattern
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