Optical: systems and elements – Optical modulator – Light wave directional modulation
Reexamination Certificate
2002-05-03
2004-08-10
Thompson, Tim (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave directional modulation
C359S305000, C359S308000, C359S286000, C369S116000, C369S097000, C369S121000
Reexamination Certificate
active
06775051
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to systems and methods for scanning a beam of light across a specimen. Certain embodiments relate to systems and methods that may include acousto-optical deflectors configured to deflect a beam of light at various angles.
2. Description of the Related Art
Fabricating semiconductor devices such as logic and memory devices may typically include processing a specimen such as a semiconductor wafer using a number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that typically involves transferring a pattern to a resist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes may include, but are not limited to, chemical-mechanical polishing, etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a semiconductor wafer and then separated into individual semiconductor devices.
During each semiconductor device fabrication process, defects such as particulate contamination and pattern defects may be introduced into the semiconductor devices. Such defects may be isolated to a single semiconductor device on a semiconductor wafer containing several hundred semiconductor devices. For example, isolated defects may be caused by random events such as an unexpected increase in particulate contamination in a manufacturing environment or an unexpected increase in contamination in process chemicals which may be used in fabrication of the semiconductor devices. Alternatively, the defects may be repeated in each semiconductor device formed across an entire semiconductor wafer. In an example, repeated defects may be systematically caused by contamination or defects on a reticle. A reticle, or a mask, may be disposed above a semiconductor wafer and may have substantially transparent regions and substantially opaque regions that are arranged in a pattern that may be transferred to a resist. Therefore, contamination or defects on a reticle may also be reproduced in the pattern transferred to the resist and may undesirably affect the features of each semiconductor device formed across an entire semiconductor wafer in subsequent processing.
Defects on semiconductor wafers may typically be monitored manually by visual inspection, particularly in the lithography process because many defects generated during a lithography process may be visible to the naked eye. Such defects may include macro defects which may be caused by faulty processes during this step. Defects which may be visible to the human eye typically have a lateral dimension greater than or equal to approximately 100 &mgr;m. Defects having a lateral dimension as small as approximately 10 &mgr;m, however, may also be visible on unpatterned regions of a semiconductor wafer. Prior to the commercial availability of automated defect inspection systems such as the systems illustrated in U.S. Pat. Nos. 5,917,588 to Addiego and 6,020,957 to Rosengaus et al., which are incorporated by reference as if fully set forth herein, manual inspection was the most common, and may still be the most dominant, inspection method used by lithography engineers.
A method for manual inspection of a semiconductor wafer may involve placing the semiconductor wafer on a semiautomatic tilt table and rotating the wafer through various angles under a bright light. The semiautomatic tilt table may rotate the semiconductor wafer about a central axis while positioning the semiconductor wafer at different inclinations relative to a plane normal to the central axis. In this manner, an operator may visually inspect the semiconductor wafer for defects as it rotates. The operator may then determine if the defects present on the semiconductor wafer are within an acceptable limit of defects on the semiconductor wafer. An example of a visual inspection method is illustrated in U.S. Pat. No. 5,096,291 to Scott and is incorporated by reference as if fully set forth herein.
Automated inspection systems were developed to decrease the time required to inspect a wafer surface. Such inspection systems may typically include two major components such as an illumination system and a collection-detection system. An illumination system may include a light source such as a laser that may produce a beam of light and an apparatus for focusing and scanning the beam of light. Defects present on the surface may scatter the incident light. A detection system may detect the scattered light and may convert the detected light into electrical signals that may be measured, counted, and displayed on an oscilloscope or other monitor. The detected signals may be analyzed by a computer program to locate and identify defects on the wafer. Examples of such inspection systems are illustrated in U.S. Pat. Nos. 4,391,524 to Steigmeier et al., 4,441,124 to Heebner et al., 4,614,427 to Koizumi et al., 4,889,998 to Hayano et al., and 5,317,380 to Allemand, all of which are incorporated by reference as if fully set forth herein.
Acousto-optical deflection may generally be described as a technique for altering a path of a beam of light that typically involves propagating sound waves through a solid material. Sound waves propagating through the solid material may alter a property such as a refractive index of the solid material. As a result, a beam of light passing through the solid material may be deflected at various angles by the solid material due to the sound waves propagating through the material. In technical applications, acousto-optical deflectors (“AODs”), which may also be commonly referred to as acousto-optical scanners, in conjunction with focusing optics, may be used to scan a focused spot of light across a surface of a specimen. Such a technical application may include, for example, inspection of a specimen such as a semiconductor wafer.
An example of a system that includes an AOD is illustrated in U.S. Pat. No. 4,912,487 to Porter et al., which is incorporated by reference as if fully set forth herein. The system includes an argon ion laser beam that may illuminate a specimen surface. An acousto-optical deflector is driven with a chirp signal and placed in the path of the beam to cause it to sweep out raster scan lines. The target is placed on an XY translation stage capable of bi-directional movement. The beam has an angle of incidence normal to the target and the stage moves so that it is scanned along adjacent contiguous strips of equal width. Additional examples of systems that may include AODs are illustrated in U.S. Pat. Nos. 5,633,747 to Nikoonahad, 5,833,710 to Nikoonahad et al., 5,864,394 to Jordan, III et al., and 6,081,325 to Leslie et al., which are incorporated by reference as if fully set forth herein.
SUMMARY OF THE INVENTION
Increasing demands for higher throughput and lower cost requirements in semiconductor device manufacturing overall translates into a need for processing and inspection systems having higher accuracy and speed than currently available systems. Such inspection systems may include an AOD. Leading edge AOD scanning inspection systems may include an AOD having a high bandwidth and long acoustic propagation time to provide substantially higher throughput systems with substantially simpler XY translation stages. In addition, such a system may be required to produce substantially uniform spot sizes and substantially uniform brightness across a scan line for substantially constant sensitivity throughout the scan. If a sensitivity of such a system is not consistent across the scan line, system-to-system matching as in multiple machine system applications and environments may be problematic. In addition, producing substantially constant spot sizes across larger scan lengths may improve a data acquisition rate of a system because a larger portion of a specimen may be scanned in a single scan. In this manner, a throughput of such a system may also be increased.
In an embodiment, a syste
Gibson John
Johnson Ralph
Li Ming-guang
Sullivan Jamie
Vella Eric
Conley & Rose, P.C.
KLA-Tencor Technologies
Mewherter Ann Marie
Thompson Tim
LandOfFree
Systems and methods for scanning a beam of light across a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Systems and methods for scanning a beam of light across a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Systems and methods for scanning a beam of light across a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3296225