US 7,072,502 B2 · Alternating phase-shift mask inspection method and apparatus

Abstract

A reticle inspection system and method for complete and fast inspection of phase shift mask reticles, both for incoming inspection and for periodic and pre-exposure inspection tool, is employable by facilities such as mask shops as an inspection tool compatible to the mask shop's customers. The inventive system and method detect phase errors in an aerial image by acquiring the image of the phase shift mask under the same optical conditions as the exposure conditions (i.e. wavelength, numerical aperture, sigma, and illumination aperture type). Images are acquired at a positive out-of-focus and a negative out-of-focus, and are compared in order to enhance possible phase error. The term “phase error” refers to the acceptable range of the phase deviation from the programmed 180° on the phase shift mask, by using the exposure system to achieve the image on the photoresist, satisfying the requirements of the wafer specification.

Claims33

Dependent claims

A method for inspecting a phase shift mask that is used with a photolithographic optical exposure system under a set of exposure conditions, said method comprising:

acquiring a plurality of aerial images produced by said phase shift mask using a transmitted light, said plurality of aerial images being acquired in an aerial imaging inspection system and within a process window of said exposure system by emulating said set of exposure conditions;
said plurality of aerial images including a first and a second aerial image produced by said phase shift mask;
wherein said first aerial image produced by said phase shift mask is in a first out of focus condition, and said second aerial image produced by said phase shift mask is in a second out of focus condition;
and
comparing said first and said second aerial images to each other to detect phase defects and errors in said phase shift mask, wherein
said first and said second aerial images are concurrently produced from the same light transmitted by the mask;
and,
wherein prior to said comparison step, said first and second aerial images are transformed to simulate a behavior of an exposure system and photoresist.

5 more elements

Dependencies are inferred from the claim text.

Alternating phase-shift mask inspection method and apparatus

Life of this patent

Alternating phase-shift mask inspection method and apparatus

Life of this patent

Abstract

Claims33