Semiconductor device manufacturing: process – Formation of electrically isolated lateral semiconductive... – Having substrate registration feature
Reexamination Certificate
2001-08-08
2003-04-29
Zarabian, Amir (Department: 2822)
Semiconductor device manufacturing: process
Formation of electrically isolated lateral semiconductive...
Having substrate registration feature
C438S462000, C438S975000, C257S797000
Reexamination Certificate
active
06555441
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of microstructure fabrication, and in particular to a method of aligning microstructures on opposite sides of a wafer.
2. Description of Related Art
The manufacturing of Micro-Electro-Mechanical Systems (MEMS) often requires the alignment of structures located on the front side of a silicon wafer to structures located on the back side of the same silicon wafer as to ensure proper machining.
Special alignment systems capable of back side alignment are used to perform the alignment of structures located on the front side of a silicon wafer to structures located on the back side of the same silicon wafer as to ensure proper machining of MEMS. These special systems use split field optics and/or through-the-silicon-wafer infrared imaging to perform 1× direct contact alignment or 1× proximity contact alignment of the structures on both sides of the silicon wafer.
One example of a prior art alignment system is the MA1006 contact aligner manufactured by K&W Gmbh. This system is capable of handling 1× masks of sizes of up to 7″×7″ and silicon wafers of up to 6″diameter. The transfer of a 1× mask located on the back side of the silicon wafer into the photoresist also located on the back side of this silicon wafer while aligning this transferred 1× photoresist pattern to the structures already located on the front side of the same silicon wafer is carried out by first illuminating the 1× mask located on the back side of the silicon wafer with an intense infrared light not absorbed by the photoresist also located on the back side of the silicon wafer. Next, through infrared transmission, the dynamic alignment of the 1× mask closely positioned against the photoresist coated back side of the silicon wafer and the structures located on the front side of the same silicon wafer is observed using the image transmitted through a 5×-35× zooming microscope objective and captured from the Charge-Coupled-Device (CCD) infrared sensor of a Hamamatsu alignment camera a resulting infrared imaged magnified by 150×-1000× zoom on a Sony 14″ Monitor. The 1× mask and the photoresist coated back side of the silicon wafer are contacted with more or less pressure (0.03 N/cm
2
-0.16 N/cm
2
) when proper alignment is achieved. Finally, the photoresist coated on the back side of the silicon wafer is exposed with ultra-violet light of 240 nm-450 nm wavelength to transfer the pattern of the 1× mask into the photoresist.
The resulting alignment of the already existing pattern located on the front side and of the newly transferred 1× pattern into the photoresist of the back side of the wafer is claimed to be of the order of 1 &mgr;m.
Another known system is the MA6 contact aligner manufactured by the company Karl Suss, also of Germany. This system is also capable of handling 1× masks of sizes of up to 7″×7″ and silicon wafers of up to 6″ diameter. In this system, the 1× mask on the back side of the silicon wafer is first illuminated with infrared light. Using a splitfield CCD video camera and through infrared transmission, the alignment of the 1× mask near the back side and the structures of the front side of the silicon wafer are observed using the image transmitted through a 10× microscope objective. The 1× mask and the photoresist coated back side of the silicon wafer are contacted with more or less pressure when proper alignment is achieved. Finally, the photoresist coated on the back side of the silicon wafer is exposed with ultra-violet light as to transfer the pattern of the 1× mask into the photoresist.
The optical resolution of the transferred pattern into the photoresist is claimed to be of the order of 1 &mgr;m when using vacuum contact between the 1× mask and the photoresist.
Another system is the contact aligner also manufactured by Karl Suss. Unlike the MA6 aligner, which is capable of aligning wafers of up to 6″ in diameter, the MJB 3 UV400 IR 6 contact aligner is only capable of handling 1× masks of sizes of up to 4″×4″ and silicon wafers of up to 3″.
In this system, the 1× mask on the back side of the silicon wafer is first illuminated with infrared light. Using a splitfield Vidicon video camera and through infrared transmission, the alignment of the 1× mask near the back side and the structures of the front side of the silicon wafer is observed using the image transmitted through a 10× microscope objective. The 1× mask and the photoresist coated back side of the silicon wafer are contacted with more or less pressure when proper alignment is achieved. Finally, the photoresist coated on the back side of the silicon wafer is exposed with ultra-violet light as to transfer the pattern of the 1× mask into the photoresist.
The optical resolution of the transferred pattern into the photoresist is also claimed to be of the order of 1 &mgr;m when using vacuum contact between the 1× mask and the photoresist.
The EV620 contact aligner manufactured by the company Electronic Visions is also capable of handling 1× masks of sizes of up to 7″×7″ and silicon wafers of up to 6″ diameter. In this system the 1× mask on the back side of the silicon wafer is first illuminated. Using a splitfield video camera, the alignment of the 1× mask near the back side and the structures of the front side of the silicon wafer is observed using the image transmitted through a 3.6×, 4×, 5×, 10× or 20× objective equipped with digital Zoom. The 1× mask and the photoresist coated back side of the silicon wafer are contacted with more or less pressure (0.5 N to 40N) when proper alignment is achieved. Finally, the photoresist coated on the back side of the silicon wafer is exposed with ultra-violet light to transfer the pattern of the 1× mask into the photoresist.
The alignment accuracy between the transferred patterns into the photoresist of the back side and the patterns of the front side is claimed to be better then about 1 &mgr;m.
The OAI 5000 contact aligner manufactured by the company Optics Automation Instrumentation is capable of handling 1× masks of sizes of up to 9″×9″ and silicon wafers of up to 8″ diameter. In this system the 1× mask on the back side of the silicon wafer is illuminated with infrared light. Using a splitfield video camera and through infrared transmission, the alignment of the 1× mask near the back side and the structures of the front side of the silicon wafer is observed using the image transmitted through a 6× or 32× objective. The 1× mask and the photoresist coated back side of the silicon wafer are contacted with more or less vacuum (2 to 15 inch of mercury) when proper alignment is achieved. Finally, the photoresist coated on the back side of the silicon wafer is exposed with ultra-violet light to transfer the pattern of the 1× mask into the photoresist.
The optical resolution of the transferred pattern into the photoresist is claimed to be 0.73 &mgr;m when using 365 nm i-line exposure of the 1× mask into suitable photoresist.
All of these special alignment systems use split field optics and/or through-the-silicon-wafer infrared imaging to perform 1× direct contact alignment or 1× proximity contact alignment of the structures located on the front side of the silicon wafer and structures located on the back side of the same silicon wafer as to ensure proper machining of MEMS. They also all require physical contact between the photoresist and the 1× mask using more or less pressure in order to align the patterns of the front side and the transferred 1× pattern of the back side with alignment accuracy of the order of 1 &mgr;m and optical resolution also of the order of 1 &mgr;m.
SUMMARY OF THE INVENT
(Marks & Clerk)
Dalsa Semiconductor Inc.
Vockrodt Jeff
Zarabian Amir
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