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Browse Prior Art Database

LOCAL RESIST COAT PLANARIZATION OF ALIGNMENT TARGETS

IP.com Disclosure Number: IPCOM000005772D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2001-Nov-05
Document File: 2 page(s) / 119K

Publishing Venue

Motorola

Related People

Whitson G. Waldo: AUTHOR [+2]

Abstract

Planarization structures in proximity to alignment targets act to minimize alignment variation caused by asymmetrical photoresist coating of alignment target features. Asymmetric resist pileups on target features are prevented by dummy border pattern placement, helping to stabilize alignment shifts caused by asymetric alignment light absorption, asymmetric signal reflection, and local variations in the resist's index of refraction.

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m MOlVROlA Technical Developments August 1989

LOCAL RESIST COAT PLANARIZATION OF ALIGNMENT TARGETS

by Whitson G. Waldo and John Helbert

   Planarization structures in proximity to alignment targets act to minimize alignment variation caused by asymmetrical photoresist coating of alignment target features. Asymmetric resist pileups on target features are prevented by dummy border pattern placement, helping to stabilize alignment shifts caused by asymetric alignment light absorption, asymmetric signal reflection, and local variations in the resist's index of refraction.

   Registration of semiconductor features is critical for integrated circuit function and performance. One of the components of registration is alignment. Typically, two global targets are aligned on a wafer. This alignment serves as a prealignment so the local alignment targets (1) come within the capture range. After alignment, the die are exposed with the desired pattern. Minimizing alignment variation becomes increasingly important as integrated circuit features shrink. Also, improving alignment reduces the need to shrink feature sizes, which translates into more resolution latitude. Resist coating asymmetry induced misalignment will result in varia- tions in the alignment mean values. This will lower throughput and slow cycle times, since, it may be necessary to run test wafers to center the alignment means.

   It is desirable that all the nested families of variation of alignment be minimized. These include site-to-site, wafer-to-wafer, and lot-to-lot variations. One of the sources of alignment variation is asymmetry of the alignment signal used to determine the position of the alignment target. This asymetric target may be caused by asym- metric resist pileup around resist features due to local nonplanar conditions, especially at pattern edges as demonstrated in Figure. Using interference microscopy, Wilson and Piacente have shown coating asymmetry occurs at the leading and trailing edges of target-like pitch features. By transfering these edge nonuniformities
to dummy patterns outside of the detection area, alignment target asymmetry problems should be avoidable. Photoresist is sensitive to a large range of different wavelengths and absorption of light within its range of photosensitivity changes the index of refraction. This results in a change in the transparency of the resist to the light. Typically, the effect is largest at the actinic, or exposure, wavelengths since resists are specifically chosen based upon favorable sensitivity at these wavelengths. If the photoresist coating is nonplanar over the alignment target, l...