Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2001-08-06
2003-04-22
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S306000, C356S237400, C382S144000
Reexamination Certificate
active
06552331
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the field of semiconductors. The invention relates to an apparatus and a method for imaging and scanning masks for semiconductor production.
Such photomasks are needed for the exposure steps in semiconductor production. In order, for example, to be able to implement structure sizes of 180 nm in a CMOS process, photomasks with structure sizes of about 700 nm (that is to say about four times the structure size to be produced) are needed. The exposure of the semiconductor substrate coated with photosensitive lacquer is then carried out through such photomasks. Typically, etching and evaporation steps then follow the exposure step.
For the purpose of quality control in the production of such photomasks, because of the typical structure size of 700 nm, optical microscopy is the clear choice. A photomask includes a glass substrate, onto which the desired structure is applied by evaporating molybdenum silicide (MoSi) or chromium. The transparent and opaque areas of the photomask can be represented with good contrast by using optical microscopy methods.
In addition to optical microscopy, scanning methods such as scanning probe microscopy are gaining significance in the analysis of photomasks. In the case of such methods, a probe scans the height profile of the mask surface. Piezoceramic actuators permit the highly accurate positioning of the probe relative to the mask surface so that the height relief on the layer side of the mask can be registered with high resolution. In the use of scanning probe microscopy, a problem arises relating to placing the scanning probe at the correct point on the mask surface at the start of the scanning operation. In the case of manually position of the probe on the mask, it is often not clear which area of the surface is currently being scanned. Therefore, it would be helpful to be able to position the probe with a view of the mask.
Prior art includes equipping a scanning probe microscope or a surface profilometer with imaging optics and a miniature camera for enabling a track of the position of the probe on the mask surface. The drawback with such a solution is, first, the small field of view of the camera. Second, in such an embodiment of the scanning probe microscope or the surface profilometer, a significant number of functions have to be integrated in an extremely small space, which makes the handling of the scanning instrument more difficult. It is difficult to carry out adjustment work and to replace damaged scanning probes.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a device and method for combining scanning and imaging methods in checking photomasks that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that makes the scanning and imaging of defined areas of the mask surface easier.
With the foregoing and other objects in view, there is provided, in accordance with the invention, an apparatus for imaging and scanning masks for semiconductor production, the masks having a layer side and an opposing side, the apparatus including a scanning instrument having a probe, the probe disposed to scan a layer side of a mask, an optical microscope for imaging a detail of the mask from a side of the mask opposing the layer side, the optical microscope disposed opposite the scanning instrument with respect to the mask, a positioning device positioning the scanning instrument and the optical microscope relative to one another such that the optical microscope images the probe and the mask simultaneously, and a displacing device connected to the mask and laterally displacing the mask between and relative to the scanning instrument and the optical microscope to permit selection,of an imaged detail of the mask while a relative position between the scanning instrument and the optical microscope is maintained.
In the case of the apparatus according to the invention, the scanning of the mask is carried out from the layer side, while the optical microscope images the mask structures from the side of the mask facing away from the layer side. By using such an inverted microscope, the upper side of the mask can be scanned while the optical imaging is being carried out from the underside of the mask at the same time. As such, the scanning instrument and the optical microscope are prevented from hampering each other. The two instruments can be positioned freely relative to the mask and relative to the respective other instrument.
In addition, the apparatus according to the invention has a positioning device or means for positioning the scanning instrument and the opposing optical microscope, with which the two instruments can be positioned relative to each other such that the probe of the scanning instrument can be imaged by the optical microscope at the same time. As soon as the probe of the scanning instrument can be detected in the microscope image, the two instruments are in mutually opposite positions, which are connected by an axis running at right angles to the mask surface (so-called “on-axis” position). In such a position, the scanning instrument is fixed relative to the optical microscope.
In the solution according to the invention, the probe is positioned on the mask by lateral displacement of the mask relative to the two instruments fixed in the relation to each other. For such a purpose, the apparatus according to the invention includes a displacing device or means for the lateral displacement of the mask. With the displacing device, the imaged detail of the mask can be selected while maintaining the relative position between the scanning instrument and the opposing optical microscope. Because the relative position between the scanning instrument and the opposing microscope has been fixed once for all in the “on-axis” position, the position of the probe in the field of the view of the optical microscope remains unchanged. The probe is, therefore, continuously visible in the image supplied by the optical microscope, even when the position of the mask surface is changed relative to the probe.
As soon as the two instruments have been fixed once in the “on-axis” position in relation to each other, various areas of the photomask can be moved to and examined. Thus, the time-consuming and tiresome search for the probe in the field of view of the optical microscope is eliminated. Such elimination makes possible rapid and precise positioning of the probe on the mask surface. Various critical production structures on the photomask can be moved to one after another and then respectively be imaged and scanned.
With the objects of the invention in view, there is also provided a method of imaging and scanning masks for semiconductor production including the steps of placing a scanning instrument having a probe at a position to scan a layer side of a mask with the probe, placing an optical microscope on a side of the mask opposite the layer side at a position to image a detail of the mask from the side of the mask opposite the layer side, positioning the scanning instrument and the optical microscope relative to each other such that the optical microscope images the probe and the mask at the same time, laterally displacing the mask while maintaining a relative position between the scanning instrument and the optical microscope, and at least one of imaging and scanning a selected detail of the mask.
The method according to the invention for imaging and scanning masks for semiconductor production includes three steps. In a first step, the scanning instrument and the optical microscope are positioned relative to each other. The positioning is carried out such that the probe of the scanning instrument can be imaged by the optical microscope at the same time. The position of the probe of the scanning instrument can, therefore, be detected from the image of the mask supplied by the optical microscope. Such. image shows that the scanning instrument and the opposing optical microscope are located in the
Greenberg Laurence A.
Infineon - Technologies AG
Locher Ralph E.
Sohn Seung C.
Stemer Werner H.
LandOfFree
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