METHOD FOR INSPECTING A PHOTOMASK CONTAINED IN A TRANSPARENT POD

A method is provided for inspecting a photomask. The photomask is formed with upper and lower faces and four lateral faces. The method includes using a transparent pod to contain the photomask, inserting the transparent pod in an inspecting machine, using a light source to cast light over one of the upper and lower faces of the photomask, using an image sensor to receive at least some of the light from the upper or lower face of the photomask via the transparent pod, and determining whether there is contamination on the upper or lower face of the photomask based on the light received by the image sensor.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to inspection of a face of a photomask and, more particularly, to inspection of a face of a photomask contained in a transparent pod to minimize risks of contaminating the photomask during the inspection and maximize the yield of production of semiconductor products.

2. Related Prior Art

Photomasks are used in photolithography. During storage or transportation of a photomask, the photomask is very likely to suffer defects such as particles or smog caused by materials such as gas used in the photolithography, particles peeled from parts used in the photolithography, oil dropped from any of the parts, and/or other contaminants caused by deposition of and chemical reaction of gaseous molecules. Therefore, during the transportation or storage, the photomask is contained in a highly clean, air-tight and antistatic pod, Reticle SMIF Pod (“RSP”) to avoid contamination.

To avoid contamination of the surface of the photomask before or during the lithography, an inspecting machine is operated to inspect the surface of the photomask regularly or irregularly. Conventionally, a robot is operated to take the photomask from the pod before the inspection. The surface of the photomask can be contaminated. Abrasion or collision can happen to the photomask to produce particles or static charges that render the face of the photomask more vulnerable to contamination. In such cases, the photomask must be cleaned and/or repaired. Such cleaning or repairing inevitably reduces the life of the photomask and jeopardize the yield of production of semiconductor products. Hence, there is a need for more spare photomasks, and this inevitably increases the cost of the production of the semiconductor products.

SUMMARY OF INVENTION

It is an objective of the present invention to provide a method for inspecting a photomask contained in a transparent pod so that two opposite faces of the photomask can be inspected synchronously.

It is another objective of the present invention to provide a method for inspecting a photomask contained in a transparent pod without having to use a mechanism to take the photomask from the transparent pod.

To achieve the foregoing objectives, the method includes using a transparent pod to contain the photomask, inserting the transparent pod in an inspecting machine, using a light source to cast light over a face of the photomask, using an image sensor to receive at least some of the light from the face of the photomask via the transparent pod, and determining whether there is contamination on the face of the photomask based on the light received by the image sensor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring toFIGS.1and2, there is shown a method for inspecting a photomask100according to the preferred embodiment of the present invention. The photomask100includes lower and upper faces101and four lateral faces102. The lower and upper faces101are in parallel to each other. The lower and upper faces101are rectangular faces. Accordingly, the lateral faces102are classified into two pairs of two lateral faces102in parallel to each other. The lower or upper face101is formed with a pattern105(FIG.3) corresponding to a layout of a circuit.

The method includes providing a transparent pod for containing the photomask100at S11, inserting the transparent pod in an inspecting machine60at S12, providing a light source to cast light toward a lateral face of the photomask100at S13, providing an image sensor to inspect at least one of the lower and upper faces101of the photomask100at S14, and determining whether there is contamination on the lower or upper face101at S15.

At S11, the transparent pod is provided for containing the photomask100. The transparent pod includes a lower lens11corresponding to the lower face101and an upper lens12corresponding to the upper face101. The lower and upper lenses11and12are made of a transmittance equal to or larger than 90%. Each of the lower and upper lenses11and12includes a transparent portion equal to or larger than the pattern105of the photomask100.

Preferably, the transparent pod includes two lateral lenses13and14corresponding to the lateral faces102of the photomask100(FIG.2). The lateral lenses13and14are in parallel to each other. Each of the lenses13and14is made of a transmittance equal to or larger than 90%. Each of the lateral lenses13and14includes a transparent portion larger than each of the lateral faces102of the photomask100(FIG.6).

Preferably, the lower and upper lenses11and12and the lateral lenses13and14are made of 99.995% pure quartz so that they exhibit excellent transmittance regard ultraviolet light, visible light and infrared light.

Preferably, the transparent pod includes a base15and a cover16. The lower lens11is connected to the base15. The upper lens12is connected to the cover16. The lateral lenses13and14are connected two opposite portions of a periphery of the cover16. The base15and the cover16can be made of metal or plastic except for the lower, upper and lateral lenses11,12,13and14.

At S12, the transparent pod is inserted in the inspecting machine60. The transparent pod is inserted in the inspecting machine60after the photomask100is inserted in the transparent pod. The inspecting machine60includes an upper image sensor61and lower image sensor62. Each of the upper and lower image sensors61and62can be a CCD or CMOS sensor. The inspecting machine60further includes two light sources65and66corresponding to the lateral lenses13and14of the transparent pod. The light source65is operable to emit a ray650. The light source66is operable to emit a ray660.

Alternatively, the light sources65and66can be located corresponding to the lower and upper lenses11and12instead of the lateral lenses13and14.

At S13, at least one of the light sources65and66is operated to cast light toward at least one of the lateral faces102of the photomask100. At least one of the light sources65and66is operated to cast a ray650or660toward at least one of the lateral faces102of the photomask100via the lateral lens14or13after the transparent pod is inserted in the inspecting machine60. The ray650or660travels over the lower or upper face101of the photomask10.

Alternatively, at least one of the light sources65and66is operated to cast a ray650or660onto the lower or upper face101of the photomask100via at least one of the lower and upper lenses11and12. In such a case, it is preferred that an image sensor be located on a side of the photomask100opposite to the light source65or66.

At S14, at least one of the image sensors61and62is operated to inspect the upper or lower face101of the photomask100. As mentioned above, the ray650or660travels over the lower or upper face101of the photomask10. If there is contamination on the upper or lower face101, the ray650or660will be scattered by the contamination. The image sensor61or62will sense the scattered light.

At S15, it is determined whether there is contamination on the upper or lower face101. A human/machine interface unit70is electrically connected to the inspecting machine60. The human/machine interface unit70can be a touch panel. The human/machine interface unit70is operated to show an image detected by the image sensor61or62. A worker is allowed to observe the image and determine whether there is contamination on the upper or lower face101.

As discussed above, in the method for inspecting a photomask according to the present invention, the photomask100is inserted in the transparent pod. The ray650or660is cast to the photomask100from the light source65or66via the lateral lens13or14. Then, light travels to the image sensors61or62from the upper or lower face101of the photomask100via the lower lens11or the upper lens12.

As discussed above, the photomask100is contained in and hence protected by the transparent pod throughout the inspection. Hence, the risk of contamination of the photomask100is minimized. Moreover, the yield of production of semiconductor produces by use of the photomask100is maximized. Furthermore, the size and cost of the inspecting machine60are minimized because there is no need to include a mechanism for taking the photomask100from the transparent pod to allow inspection of the photomask100.