Photomask having an intermediate inspection film layer

#The present invention relates generally to an improved photomask used in photolithography for the manufacture of integrated circuits and other semiconductor devices, and more specifically, to the detection of defects in such photomasks after processing. In particular, the present invention is directed to a photomask, either blank or processed, having one or more intermediate layers deposited therein to improve inspection results of the photomask without sacrificing transmission properties at the exposure tool wavelength. Additionally, the present invention is directed to semiconductors or other integrated circuits manufactured using the improved photomask of the present invention.

#Photomasks are high precision plates containing microscopic images of electronic circuits. Photomasks are typically made from flat pieces of quartz or glass with a layer of chrome on one side. Etched in the chrome is a portion of an electronic circuit design, often referred to as “geometry”. Photomasks are used in wafer fabrication, mainly to make integrated circuits (“ICs”) and other semiconductor devices. In turn, ICs are used in a variety of different products, including computers, calculators, cars, cameras, stereos, etc. Photomasks are also used to make flat panel displays, thin film heads, PC boards, and other electronic products.

#One type of photomask known in the art is an embedded attenuated phase shift mask (“EAPSM”). EAPSMs are used in the production of semiconductor devices, and more particularly, EAPSMs are typically used to print contact layer holes in a semiconductor wafer. As shown in FIG. 1, a typical blank EAPSM 10 is comprised of four layers. The first layer is a layer of quartz or other substantially transparent material 11, commonly referred to as a substrate. The next layer is typically an embedded phase shifting material (“PSM layer”) 12, such as molybdenum silicide (MoSi), tantalum silicon nitride (TaSiN), titanium silicon nitride (TiSiN) or zirconium silicon oxide (ZrSiO) and other known phase materials. The next layer is typically an opaque material 13, such as chromium, which may optionally include an anti-reflective coating such as chromium oxynitride (CrON). The top layer is a photosensitive resist material 14.

#The above and related objects, features and advantages of the present invention will be more fully understood by reference to the following, detailed description of the preferred, albeit illustrative, embodiment of the present invention when taken in conjunction with the accompanying figures, wherein:

#FIG. 1 represents a blank or undeveloped EAPSM of the prior art;

#FIG. 2 represents the EAPSM of FIG. 1 after it has been partially processed;

#The present invention relates to a method and apparatus for improving the inspection of EAPSMs by interposing one or more intermediate layers in a conventional EAPSM, wherein the intermediate layer(s) is (are) made from materials which have properties that provide for additional attenuation (e.g., decrease transmission) of the mask at the inspection tool wavelength (e.g., 365 nm) while at the same time maintain a low transmission of light at the exposure tool wavelength (e.g., 248 nm, 193 nm or 157 nm). Thus, by using EAPSMs (whether blank or processed) having the intermediate layer(s) of the present invention, accurate results can be obtained in both the process for writing an image onto a semiconductor wafer and the process for inspecting the EAPSM.

#More particularly, in the preferred embodiment of the method and apparatus of the present invention, one or more intermediate layers are interposed in a blank EAPSM during the manufacture of such mask blanks. As explained below, the intermediate layer(s) should have a higher extinction coefficient (e.g., absorptivity of light) at the 365 nm inspection tool wavelength than at the various exposure tool wavelengths (i.e., 157 nm, 193 nm and 248 nm). More particularly, such materials should have an extinction coefficient which will absorb a sufficient amount of light to reduce the transmission of light through the PSM layer to 40-50% or less relative to quartz at the 365 nm inspection tool wavelength. Further, the extinction coefficient for these materials at the lower exposure tool wavelengths (e.g., 193 nm, 157 nm and 247 nm) should be sufficiently low so as permit a sufficient amount of light to be transmitted (e.g., 6-20%) through the mask.

#Additionally, the intermediate layer(s) should be relatively thin when compared to the thickness of the PSM layer. This is to ensure that the intermediate layer(s) does not absorb too much light so as to alter the optical properties of the mask in such a manner that the mask will be unable to meet the optical requirements of both inspection and exposure tools. More particularly, the PSM layer of an EAPSM typically has a thickness ranging from approximately 500 Å-1000 Å. For the purposes of the present invention, the intermediate layer(s) should have a thickness ranging from approximately 50 Å-150 Å. By choosing materials with these properties (e.g., a suitable absorptivity and thickness), accurate and reliable results can be obtained during both the inspection and exposure processes.