Integrated Circuit Photomasks Research Articles

Partially coherent periodic stop filtering for inspection of periodic objects

A partially coherent system is introduced for defect inspection of periodic objects such as integrated circuit photomasks. An experimental investigation demonstrates that the new system is more robust in the presence of optical setup noise than the corresponding coherent spatial filtering system. The system illumination is provided by an array of mutually incoherent point sources that image onto a grid of opaque spots at the pupil plane. Nonperiodic defects are displayed at the image plane as bright structures against a dark background.

Development and analysis of an automated dimension measuring microscope

SUMMARYA theoretical model is developed to describe the operation of a bright field, optical microscope intended to be used for making automated measurements of features as small as 0·3 μm. The measurement of gap lengths in magnetic recording heads and linewidths on integrated circuit photomasks is discussed in detail. Different measurement techniques are investigated theoretically and their perfomances in the presence of aberrations, focus errors and non‐ideal transducer responses are assessed.An automated measurement technique based on image shearing is presented and compared with other measurement techniques based on bright field image scanning. It is demonstrated that the automated image shearing method is much less prone to measurement errors due to system parameters.The model was used to develop an optimized design for the measurement system and a complete instrument was built. The performance of the practical measurement system agreed well with theoretical predictions. A calibration standard and a simple but accurate calibration algorithm were also developed.

Inspection of Integrated Circuit Photomasks using Optical Data Processing Techniques

AbstractThe application of optical signal processing techniques for the inspection of integrated circuit photomasks, could prove to be a fast and cheap means of photomask inspection. In this paper we discuss two possible optical inspection techniques and their suitability for use as a practical inspection tool.

Holographic Optical Processing For Submicrometer Defect Detection

A holographic optical processor has been built for efficient, fast, wide-field detection of submicrometer defects in repetitive subject formats such as integrated circuit photomasks. This paper describes the advantages gained by combining holography with standard optical processing techniques and presents results obtained on a 2 in. field-of-view prototype and 7 in. field-of-view fully automated mask inspection system.

Optical measurement of the IC photomask pattern area

Optical measurement of the integrated-circuit (IC) photomask pattern area is performed. The relationship between aperture dimension and diverging angle of diffracted light is numerically estimated after scalar electromagnetic theory, and the expected measurement error is derived. The experimental measurement of the pattern area is made using typical IC photomasks. In the experiment, converging optics and an integrating sphere are suitably arranged so as to minimize the error introduced by omitting the higher-order diffraction. Some of the measured data are compared with values which are calculated from the IC layout design data, and they are found to be in good agreement.

Inspection of Integrated Circuit Photomasks by Means of Spatial Filtering

Inspection of Integrated Circuit Photomasks by Means of Spatial Filtering

Intensity spatial filtering applied to defect detection in integrated circuit photomasks

An intensity spatial filter has been devised and used for the semiautomatic photoelectric detection of 2.5-µ defects in 5-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> photolithography masks for silicon integrated circuits. The filter is based on a simple geometric approximation to the form factor or envelope function for the intensity in the Fourier-transform plane, and permits small-area diffraction-limited illumination. This approach complements the Watkins' method.

Integrated circuit photomask inspection by spatial filtering : L. S. Watkins, Solid St. Technol., September (1969), p. 29

Integrated circuit photomask inspection by spatial filtering : L. S. Watkins, Solid St. Technol., September (1969), p. 29

Inspection of integrated circuit photomasks with intensity spatial filters : L. S. Watkins, Proc. IEEE, 57, No. 9, September (1969), p. 1634

Inspection of integrated circuit photomasks with intensity spatial filters : L. S. Watkins, Proc. IEEE, 57, No. 9, September (1969), p. 1634

Inspection of periodic patterns with intensity spatial filters

This reports the application of spatial filtering to integrated circuit photomask inspection. Experiments were performed that used intensity filters and took advantage of the grating effect of the periodic array. A stop filter corresponding to the periodic distance was placed at the diffraction plane. The transmitted image showed tip the nonperiodic errors, i.e., contamination pinholes, scratches, missing or extra features and incorrectly registered patterns.

Inspection of integrated circuit photomasks with intensity spatial filters

Spatial filtering is shown to be an effective method for integrated circuit photomask inspection. Results show that errors of 0.2 mils can be detected using f/9.5 lenses and that the use of f/2.0 lenses detects errors of below 0.1 mil. Contamination, missing and added features, and step and repeat errors are all displayed. The method allows the observation of nonperiodic errors and can be used immediately for contamination inspection with very little increase in sensitivity. The procedure only needs alignment of the mask in rotation, and means that the mask can be totally inspected by scanning it through a laser beam.