Latent image exposure monitor using scatterometry

Conference · Tue Sep 01 00:00:00 EDT 1992

OSTI ID:10174068

Milner, L M; Hickman, K C; Gaspar, S M; Bishop, K P; Naqvi, S S; McNeil, J R ^[1]; Blain, M; Draper, B L ^[2]

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1. New Mexico Univ., Albuquerque, NM (United States). Center for High Technology Materials
2. Sandia National Labs., Albuquerque, NM (United States)

We discuss the use of light scattered from a latent image to control photoresist exposure dose and focus conditions which results in improved control of the critical dimension (CD) of the developed photoresist. A laser at a non-exposing wavelength is used to illuminate a latent image grating. The light diffracted from the grating is directly related to the exposure dose and focus and thus to the resultant CD in the developed resist. Modeling has been done using rigorous coupled wave analysis to predict the diffraction from a latent image as a function of the substrate optical properties and the photoactive compound (PAC) concentration distribution inside the photoresist. It is possible to use the model to solve the inverse problem: given the diffraction, to predict the parameters of the latent image and hence the developed pattern. This latent image monitor can be implemented in a stepper to monitor exposure in situ, or prior to development to predict the developed CD of a wafer for early detection of bad devices. Experimentation has been conducted using various photoresists and substrates with excellent agreement between theoretical and experimental results. The technique has been used to characterize a test pattern with a focused spot as small as 36{mu}m in diameter. Using diffracted light from a simulated closed-loop control of exposure dose, CD control was improved by as much as 4 times for substrates with variations in underlying film thickness, compared to using fixed exposure time. The latent image monitor has also been applied to wafers with rough metal substrates and focus optimization.

• Research Organization: Sandia National Labs., Albuquerque, NM (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AC04-76DP00789
• OSTI ID: 10174068
• Report Number(s): SAND-92-0971C; CONF-9203177-2; ON: DE92019427
• Resource Relation: Conference: International Society for Optical Engineering (SPIE) symposium on microlithography,San Jose, CA (United States),8-13 Mar 1992; Other Information: PBD: [1992]
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
47 OTHER INSTRUMENTATION
36 MATERIALS SCIENCE
PHOTORESISTORS
LIGHT SCATTERING
MONITORING
LASER RADIATION
DIFFRACTION GRATINGS
IMAGES
QUALITY CONTROL
ALUMINIUM
DEFECTS
SURFACE PROPERTIES
426000
440600
360104
COMPONENTS
ELECTRON DEVICES AND CIRCUITS
OPTICAL INSTRUMENTATION
PHYSICAL PROPERTIES