Electron-beam-projection-exposure apparatus use an electron beam to transfer a mask image onto a sensitized wafer or other substrate. Such apparatus are important in the manufacture of electronic devices, particularly integrated circuits and displays.
Electron-beam-projection-exposure apparatus are extremely sensitive to contaminants, such as particles, metallic ions, chemicals, and bacteria. Many of these contaminants can be deposited on the wafer or mask during fabrication and can ultimately cause the failure of integrated circuits that are subsequently produced. Fabrication plants take extensive precautions to ensure that levels of contaminants in the fabrication area are reduced. For example, adhesive floor mats are used to strip particles from workers' shoes, the workers wear special contamination-preventing clothing, and air showers are used to blow contaminants off of the clothing before the workers enter the fabrication area. Nevertheless, certain levels of contaminants remain in the fabrication area.
Inspection devices have been developed for detecting such contaminants adhered to a mask. If the inspection device detects contamination, the mask is transferred to a contaminant-cleaning device. After the mask is cleaned, it can be returned to the electron-beam-projection-exposure apparatus for exposing sensitized wafers. Conventionally, the inspection device, cleaning device, and the electron-beam-projection-exposure apparatus are all independent from each other so that the mask must be exposed to an external environment as the mask is moved from one device to the next. Consequently, even though the inspection device detects contamination, new contamination can become attached to the mask after the mask is moved to the cleaning device. After the mask is cleaned, still more contamination can become attached to the mask en route to the projection-exposure apparatus. Transferring the mask between independent inspection, cleaning, and projection-exposure apparatus also causes long delays, thereby further increasing the possibility of contaminants adhering to the mask.
Recently developed inspection devices may cause even further delays. For example, mask patterns used to generate submicron line widths require an inspection device with high resolution, such as a scanning electron microscope. Such high-resolution devices require inspection in a vacuum, which further slows the process and increases the likelihood of contamination.