A method and apparatus for inspecting a photolithography mask for defects is provided. The inspection method comprises providing a defect area image to an image simulator wherein the defect area image is an image of a portion of a photolithography mask, and providing a set of lithography parameters as a second input to the image simulator. The defect area image may be provided by an inspection tool which scans the photolithography mask for defects using a high resolution microscope and captures images of areas of the mask around identified potential defects. The image simulator generates a first simulated image in response to the defect area image and the set of lithography parameters. The first simulated image is a simulation of an image which would be printed on a wafer if the wafer were to be exposed to an illumination source directed through the portion of the mask. The method may also include providing a second simulated image which is a simulation of the wafer print of the portion of the design mask which corresponds to the portion represented by the defect area image. The method also provides for the comparison of the first and second simulated images in order to determine the printability of any identified potential defects on the photolithography mask. A method of determining the process window effect of any identified potential defects is also provided for.

Visual inspection and verification system

A simulated wafer image of a physical mask and a defect-free reference image are used to generate a severity score for each defect, thereby giving a customer meaningful information to accurately assess the consequences of using a mask or repairing that mask. The defect severity score is calculated based on a number of factors relating to the changes in critical dimensions of the neighbor features to the defect. A common process window can also be used to provide objective information regarding defect printability. Certain other aspects of the mask relating to mask quality, such as line edge roughness and contact corner rounding, can also be quantified by using the simulated wafer image of the physical mask.

System and method of providing mask defect printability analysis

A system and method of analyzing defects on a mask used in lithography are provided. A defect area image is provided as a first input, a set of lithography parameters is provided as a second input, and a set of metrology data is provided as a third input. The defect area image comprises an image of a portion of the mask. A simulated image can be generated in response to the first input. The simulated image comprises a simulation of an image that would be printed on a wafer if the wafer were exposed to a radiation source directed at the portion of the mask. The characteristics of the radiation source comprise the set of lithography parameters and the characteristics of the mask comprise the set of metrology data.

Visual analysis and verification system using advanced tools

Mask simulation tools are typically extremely complicated to learn and to use effectively. Therefore, providing access to a mask simulation tool over a wide area network (WAN) to multiple on-line users can be very cost effective. Specifically, in a network-based simulation server, multiple users can view the same mask image, simulations, and analysis results and provide real-time comments to each other as simulation and analysis are performed, thereby encouraging invaluable problem-solving dialogue among users. The user interface for this mask simulation tool can advantageously facilitate this dialogue. For example, the user interface can include an enter box for a user to enter a message and a talk box for capturing any message sent by any user of the simulation tool using the enter box.

User interface for a networked-based mask defect printability analysis system

Masks that include optical proximity correction or phase shifting regions are increasingly being used in the manufacturing process. These masks, either initially or after repair, can have “soft” defects, e.g. phase and/or transmission defects. In accordance with one feature of the invention, soft defect information can be computed from standard test images of a mask. This soft defect information can be used to generate an accurate simulated wafer image, thereby providing valuable defect impact information to a user. Knowing the impact of the soft defect can enable a user to make better decisions regarding the mask. Specifically, a user can now with confidence accept the mask for the desired lithographic process, repair the mask at certain critical locations, or reject the mask, all without exposing a wafer.

Soft defect printability simulation and analysis for masks

This paper describes a direct phase-shift measurement system with transmitted deep-UV illumination for phase shifting mask (PSM) using a lateral shearing interferometer system. This interferometer has new structure developed for this purpose. The mirror mount of the interferometer is made of SiC ceramics that promote stability against vibration and ambient temperature drift. The illumination employs a xenon mercury arc lamp that has a spectrum close to the wavelength of KrF excimer laser. The repeatability of measurements is 0.5 degree in 3 sigma. The system can measure a small pattern down to 1 μm with an alternating type PSM with the objective of N.A.=0.4. Influence of incident angle of illumination on phase-shift measurement is investigated by experiment. The results show similar effects with simulation for circular illumination. The phase-shift measurement results on quartz step meet well with a calculation from step height and known refractive index including the effect of incident angle of illumination. The deep-UV measurement results also have good correlation with calculations from the results with another direct phase-shift measurement system that wavelength is 365nm. The simulation for focus latitude of alternating type PSMs agree with the experimental results of wafer exposure and the phase measurement. The accuracy of this system is sufficient for application to development of phase shift mask process.

Direct phase-shift measurement with transmitted deep-UV illumination

The performance of an i-/g-line direct-phase measurement system Lasertec MPM- 100 has been evaluated. The minimum measurable pattern sizes is 2.5 .μm for holes on an 8%-i-line transmittance halftone phase shift masks (HPSMs). The effect of the focus position is not significant for hole pattern of above 3.5 μm. Both short-term repeatability and long-term stability are excellent, being less than 0.5 deg. The effect of the illumination NA has been investigated theoretically and experimentally, and the use of correction factors based on experiment is proposed for estimating effective phase shifts from phase shifts obtained by MPM- 100.

Performance of i- and g-line phase-shift measurement system MPM-100

Lasertec has developed a novel phase-shift measurement system 1PM11, which uses a differential heterodyne interferometer. In 1PM11, phase information is converted into a low- frequency heterodyne beat that is easily measurable by an electric current. Two-frequency laser beams which are oscillated from a He-Ne laser (632.8 nm) tube are used. When a 40X objective lens being used, the beam is 2.3 micrometers in diameter and the distance of the two beams is adjustable from 3.0 to 6.0 micrometers . The performance of 1PM11 for three types of phase-shift masks: (1) the shifter of etched quartz, (2) spin-on-glass shifter on etch- stop/quartz, and (3) the attenuating shifter, is reported.

Direct phase measurement in phase-shift masks with a differential heterodyne interferometer

A phase shift amount measurement apparatus able to further correctly measure a phase shift amount of a phase shifter, wherein a laterally offset interference image of a phase shift mask is formed by a shearing interferometer, the interference image is captured by a two-dimensional imaging device, an output signal output from each light receiving element of the two-dimensional imaging device is supplied to a signal processing device, the phase shift amount is calculated for each light receiving element, the light receiving area of the light receiving element is very small, therefore the phase shift amount of any light receiving element outputting a peculiar phase amount due to incidence of diffraction light or multi-reflection light is excluded and the phase shift amount is determined based on the phase shift amount found from output signals of the remaining light receiving elements.

Phase shift amount measurement apparatus and transmittance measurement apparatus

Transmittance measurement of small object such as Ga-stain of repair or particle on photomask is getting to be important. This paper. describes the characteristic of transmittance measurement with a shearing interferometer microscope comparing with a conventional method. Measurement wavelength are 436, 365 and 248nm. In this system the transmittance is calculated from interference signal amplitude that is free from a flare light caused by reflection of optical parts.

Hideo Takizawa

Papers

Direct phase-shift measurement with transmitted deep-UV illumination

Performance of i- and g-line phase-shift measurement system MPM-100

Direct phase measurement in phase-shift masks with a differential heterodyne interferometer

Phase shift amount measurement apparatus and transmittance measurement apparatus

Transmittance measurement with interferometer system