IR aligner

Last update: 2003/03/24

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A low-cost infrared alignment system 
for MEMS research 

Z. Yang ^1,2 and R. Maeda ¹

1 Mechanical Engineering Systems, AIST, Tsukuba, Japan 305-8564 
2 NEDO, Tokyo, Japan  

ABSTRACT

The design and performance of a low-cost infrared rays alignment system was presented. A commercial domestic video camera equipped with a macro lens was used for alignment. IR LEDs were used as illumination source. The system can be applied for the alignments of glass to silicon, silicon to silicon, or mask to wafer. A 100 mm silicon wafer was aligned with a 100 mm glass wafer to demonstrate the precision of the system and a mismatch of 5 μm was observed. The total cost of the system is less than 1/20 of commercial aligner. It shows the possibility for normally funded laboratories to do MEMS researches.

Keywords: Infrared aligner; Photolithography; Wafer bonding; Direct pattern generation

1. Introduction 

The MEMS research and development communities grow up continuously. The participants of MEMS2002 were increased to 26 countries. Various applications such as biological, chemical, communication, medical and military requirements are looking for the possibilities of MEMS solutions. The rapidly spread of MEMS technologies is also due to their properties of controllable processes and compatibility with mass production. MEMS technologies extend mechanical manufacture to more precision field. MEMS technologies originate from semiconductor industry. Photolithography guarantees the precision of fabrication processes. Plasma dry etching or chemical wet etching method avoids the fabrication errors introduced from vibration or fabrication tools consumption, which is difficult to be overcome in traditional mechanical fabrications. On the other part, MEMS technologies need special fabrication and evaluation equipments. Even in developed countries, only a few well-funded laboratories are afforded of such a large equipment investment. To spread MEMS technologies to normal laboratories, one successful approach is MEMS foundary services but is not available inside China. Other possibility is to equip with some less expensive essential fabrication equipments in these laboratories. For special treatments and evaluations, wafer relay services are worth to try. 
Aligner is one of the essential equipments for photolithography and for wafer bonding. Only countable makers can supply aligner’s lens. For IR, applications, professional IR camera is also expensive. Until recently, aligner systems are limited in semiconductor industry. These factors make the commercial aligner system becomes high-end equipment for normally funded laboratories. We used a different approach. A home video camera equipped with a macro lens was used for optical monitoring. This method greatly decreased the cost of IR aligner.

2. Materials and methods

3. Results and discussion 

4. Conclusions

ACKNOWLEDGEMENTS

REFERENCES

1. E. D. Palik, Handbook of Optical Constants of Solids. Academic Press, New York, 1985, pp. 564-566.

2. D. E. Aspnes, Optical functions of intrinsic Si: region of near transparency, in IEE (ed.) Properties of Silicon, IEE/Inspec, 1988, pp. 64.

Fig. 1. Photo of the IR aligner with working samples. 

Fig. 3. Photos of left and right alignment marks through glass wafer obtained using a measuring microscope. The mismatch of lower silicon wafer (with + mark) to upper glass wafer (with mark) was 5 mm.

Fig. 4. The transmitting spectrum of silicon in the thickness of 400 mm (Redraw after the data in [1]). Silicon is transparent from its indirect absorption edge, 1.107 mm (1.12 eV) at room temperature [2].

For a carbon copy of the paper, email your airmail address to : Zhen.YANG@aist.go.jp