International Business Machines Corporation

Other

Joseph P Kirk

Timothy A Brunner

Christopher P Ausschnitt

Christopher J Progler

Gerhard Kunkel

Shahid Ahmad Butt

Nakgeuon Seong

Chester A Wasik

Charles A Gaston

Ronald Michael Martino

Josef Predatsch

Lo-Soun Su

A method is described for determining lens aberrations using a test reticle and a standard metrology tool. The method provides test patterns, preferably in the form of standard overlay metrology test patterns, that include blazed gratings having orientation and pitch selected to sample desired portions of the lens pupil. The method measures relative shifts in the imaged test patterns using standard metrology tools to provide both magnitude and sign of the aberrations. The metrology tools need not be modified if standard test patterns are used, but can be adapted to obtain additional information. The test reticles may be formed with multiple test patterns having a range of orientations and pitch in order to compute any desired order of lens aberration. Alternatively, single test patterns may be used to determine both the magnitude and sign of lower order lens aberrations, such as defocus or coma.

Phase shifted test pattern for monitoring focus and aberrations in optical projection systems

Methods and reticles for evaluating lenses are disclosed. In one instance, a reticle which permits light to pass therethrough is provided which includes a first surface with a grating profile formed thereon. The grating profile includes a plurality of grouped stepped portions. Each group of the stepped portions includes a first step which prevents light from propagating therethrough, a second step which propagates light therethrough and a third step which propagates light therethrough at an angle 60 degrees out of phase with the light propagated through the second step.

Grating patterns and method for determination of azimuthal and radial aberration

Exposures of a photosensitive material through an array of blazed gratings illuminate a lens asymmetrically to detect effects of a plurality of azimuthal aberrations including coma, astigmatism, and three-leaf and four-leaf clover aberrations. A plurality of such exposures of the array of blazed gratings at slightly differing focus allows detection of focus shift due to any aberrations present in the lens. Upon development of the plurality of exposures, contrast of each area is measured, for example, by reflection or scattering from the relief in the developed photosensitive material and the aberrations thus detected can be simulated by effective summation of individual aberration effects.

Blazed grating measurements of lithographic lens aberrations

A test photomask comprising a fresnel zone target (FZT) pattern may be used to verify the adjustment of a precision projector illumination system of an image projection system. The method comprises the steps of creating the FZT pattern on a photomask, projecting a pupil diagram onto an image plane using the FZT pattern, and evaluating the pupil diagram to determine the illumination system adjustment.

Fresnel zone mask for pupilgram

A device to measure a phase shift of a step in a reticle is disclosed. The phase shift measuring device has a common path interferometer for receiving light from a light source and providing two point images separated from each other by an adjustable distance. A microscope having an objective focuses two point images to form two focused points along a reticle surface of the reticle. The reticle is moved between first and second positions, wherein at the first position, light beams from the two focused points enter the reticle surface, and wherein at the second position, the light beams from the two focused points enter a step surface of the step A detector receives light from the reticle for detection of the step phase shift.

Point interferometer to measure phase shift in reticles

The preferred embodiments of the present invention provide a method and apparatus for visually inspecting features on a wafer that are smaller than can be optically resolved using normally using visible light. By providing a method for visually inspecting the features, the overall performance of the fabrication system can be determined. The preferred method patterns resist with two patterns having different spatial frequencies. The patterns combine to form a pattern in the resist that exhibits Moire beats. The Moire beat spatial frequency of the resulting pattern is significantly lower than the two spatial frequencies used, and thus can be visually inspected using light in the visible regions.

System and method for visually determining the performance of a

Uniform illumination of a photomask in optical lithography is achieved with annular illumination of the conjugate pupil plane in a lithography tool. A spinning diffraction filter is placed in a stepper so as to provide annular illumination on a time averaged basis. This approach provides annular illumination for resolution enhancement in an easily manufacturable and flexible way and without significant loss of light intensity. No illuminator redesign in the photolithographic exposure tool is required.

Diffraction pupil filler modified illuminator for annular pupil fills

Scanning optical system adapted for linewidth measurement in

An optical system and technique for monitoring a monotonic change in the thickness of a transparent film by means of optical interference, and for eliminating ambiguity in the identification of absolute film thickness. The system is particularly adapted for monitoring the etching of a dielectric film of uncertain initial thickness in microelectronic fabrication. The technique utilizes a white light source directed upon the film. Reflected light, modified by optical interference in the dielectric film, is monitored by photodetectors at two distinct wavelengths. The cyclic patterns of intensity change at the two wavelengths are compared to identify unambiguously the absolute thickness of the film, although the initial uncertainty in film thickness may have corresponded to several cycles of either wavelength pattern alone. To simplify phase comparison of the two cyclic patterns, wavelengths can be selected so that some particular coincidence of extrema in the two signals occurs at a film thickness less than the expected minimum initial thickness, and does not occur at any greater thickness up to and including the expected maximum. Determination of the absolute film thickness in this way permits further tracking of the etching process to the desired end point without overshoot.

Optical system and technique for unambiguous film thickness monitoring

An improved interferometer system for detecting the etch rate of an opaque material, such as silicon or metal. The system includes means for producing two parallel beams of light, with one beam being directed to the surface of the opaque material, and the other beam being directed to the surface of an adjacent masking material of transparent nature. The rate of etch of the opaque material is detected from the interference pattern changes between the first beam and the second beam. The system utilizes a novel arrangement of beam splitters which results in equal path lengths for the respective beams and further includes a viewing light which is passed by a system of dichroic filters to enable observation of the focus spot.

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Chelsea, NY, United States of America

Joseph P Kirk