Patent Application
20050237530
Not Applicable
Not Applicable
Not Applicable
This invention relates generally to the field of microscopy and more specifically to small spot optical characterization.
Optical characterization of materials has long been a valuable tool across many fields. Non-contact thermometry, electroluminescense, fluorescence, reflectance, and transmittance are some common forms of optical characterization. These techniques are greatly diverse in geometry, optical materials and wavelength, but they share a common trend. As technologies shrink in their physical dimensions, there exists a need to make the same measurement in a smaller area. As the measurement area reduces, the challenge of optical characterization becomes more difficult. This trend is very noticeable in the semiconductor industries where the scales are microscopic. Simple, non-contact, non-destructive optical techniques are heavily relied upon in the testing and failure analysis of semiconductors. When implemented in a manufacturing process, the optical tools must be simple, robust, easy to use and small enough to retrofit into existing equipment. When optical techniques are used in failure analysis, they must be flexible enough to handle different wavelengths and configurable for multiple detectors.
Small area optical characterization is generally done using either an imaging or non-imaging system.
Imaging systems are typically a microscope, which send a portion or all of the gathered light to a detector or a 2D focal plane array. The primary function of these tools is correlated to the spectral band pass characteristics of their optics and detector. FTIR, thermal imaging, and laser scanning are examples of specialized imaging systems for optical characterization.
Non-imaging systems typically use a collimated fiber or a small detector with a lens mounted orthogonal and close to the surface of the sample. The detector is generally mounted with some type of motorized automation, and the position is mapped using the known distance from an index point which is often the flat of a wafer. Non-imaging systems rely on the fixture to know their position and focus.
Imaging microscopes for optical characterization are highly specialized optical tools, which require more space and support than a standard microscope. The complexity of their design increases cost beyond what is justified for simple optical characterization in semiconductor processes. Furthermore, their physical size is generally too large to mount into existing equipment where space is of concern. Infrared versions of these microscopes that use thermal or near infrared 2D imagers also suffer from reduced resolution due to the low pixel density of current technologies. The combination of size and cost yield complex microscope designs impractical to implement on a large scale.
Non-imaging optical assemblies designed for optical characterization are small, simple and low cost but make it difficult to target the optical system onto a small well defined position. Supplementing the system with a microscope mounted at an angle relative to the assembly can reduce this issue, but suffers from parallax in systems that do not project a beam of light onto the surface of the sample. Furthermore, non-imaging systems have no feedback to the user of their focus. Because of the focus and alignment uncertainty, the chances of obtaining poor data are increased. Many of the non-imaging configurations also have very short working distances, which prohibit their use in applications that have obstructions. The increased challenge of robustly aligning non-imaging optical systems make them a poor choice for both production and failure analysis applications in the semiconductor industry.
The primary object of the invention is to provide a simple low cost means of optical characterization on the micrometer scale.
Another object of the invention is to integrate a real time optical imager to ease the alignment of micrometer scale optical characterization.
A further object of the invention is to be able to perform such optical characterization over a large spectral range.
Yet another object of the invention is to use a compact form small enough to me mounted into other equipment.
Other objects and advantages of the present invention will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.
In accordance with a preferred embodiment of the invention, there is disclosed an imaging apparatus for small spot optical characterization comprising: an optical housing, a beam splitter, and a turn mirror assembly. Said optical housing provides a focal plane and an image plane confocal to each other. Said turn mirror assembly integrates a reflective surface, aperture, airspace waveguide, and an optical port. The aperture integrated into the turn mirror assembly greatly simplifies the design while illumination incident on the aperture provides a projection of the optical port onto the surface of the object. The projected image of the optical port onto the object creates a dark target, which is viewable at the image plane using a low cost CCD camera. The field of view of the CCD camera is large compared to that of the optical port, but is spectrally narrow. The large field of view allows for real time alignment of the projected optical port onto the sample. The aperture is located at the focal plane. The aperture and optical port are joined with the airspace waveguide. Because of the aperture, the optical port has a narrow field of view compared to that of the CCD image. Because the optical path from the objective lens to the optical port is entirely reflective, the optical port has functionality over a wide spectral range.
The drawings constitute a part of this specification and include exemplary embodiments to the invention, which may be embodied in various forms. It is to be understood that in some instances various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention.
Detailed descriptions of the preferred embodiment are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure or manner.
The schematic representation of
In another embodiment, the aperture 305 is not located at the center of the turn mirror assembly's 300 radial diameter, but instead at any point on the coincidence line 311. The coincidence line 311 is the intersection of the focal plane 103 shown in
While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
