Intensity and phase fields behind Phase Shifting Masks studied with High Resolution Interference Microscopy

The proximity printing industry is in real need of high resolution results and it can be done using Phase Shift Mask (PSM) or by applying Optical Proximity Correction (OPC). In our research we are trying to find out details of how light fields behind the structures of photo masks develop in order to determine the best conditions and designs for proximity printing. We focus here on parameters that are used in real situation with gaps up to 50 μm and structure sizes down to 2 μm. The light field evolution behind the structures is studied and delivers insight in to precisions and tolerances that need to be respected. It is the first time that an experimental analysis of light propagation through mask is presented in detail, which includes information on intensity and phase. The instrument we use is known as High Resolution Interference Microscopy (HRIM). HRIM is a Mach-Zehnder interferometer which is capable of recording three dimensional distributions of intensity and phase with diffraction limited resolution. Our characterization technique allows plotting the evolution of the desired light field and therefore printable structure till the desired proximity gap. In this paper we discuss in detail the evolution of intensity and phase fields of elbow or corner structure at different position behind a phase mask and interpret the main parameters. Of particular interest are tolerances against proximity gap variation and the resolution in printed structures.

Intensity and phase fields behind phase-shifting masks studied with high-resolution interference microscopy

Hans Peter Herzig, Myun Sik Kim, Ali Naqavi, Krishnaparvathy Puthankovilakam, Toralf Scharf

We try to find out the details of how light fields behind the structures of photomasks develop in order to determine the best conditions and designs for proximity printing. The parameters that we use approach real situations like structure printing at proximity gaps of 20 to 50 μm 50 μm and structure sizes down to 2 μm 2 μm . This is the first time that an experimental analysis of light propagation through a mask is presented in detail, which includes information on intensity and phase. We use high-resolution interference microscopy (HRIM) for the measurement. HRIM is a Mach–Zehnder interferometer, which is capable of recording three-dimensional distributions of intensity and phase with diffraction-limited resolution. Our characterization technique allows plotting the evolution of the desired light field, usually called the aerial image, and therefore gives access to the printable structure until the desired proximity gap. Here, we discuss in detail the evolution of intensity and phase fields of elbow or corner structures at different positions behind a phase mask and interpret the main parameters. Of particular interest are tolerances against proximity gap variation and the theoretical explanation of the resolution in printed structures.

SPIE-Intl Soc Optical Eng2016

Lightfields behind amplitude masks Creating phase discontinuities

Hans Peter Herzig, Myun Sik Kim, Wilfried Noell, Krishnaparvathy Puthankovilakam, Toralf Scharf

Shaping of light fields behind amplitude and phase masks the basis the lithographic structure reproduction. The aerial image or better the intensity distribution defines the resolution of the structure to be printed. Contrast is the main parameter and to achieve high contrast feature phase plays an important role. In our contribution we discuss the phase and intensity evolution of light fields behind different structures serving the same aim: correcting extensive corner rounding for proximity lithography. To do so we analyze the intensity characteristics behind in a binary mask having high resolution Optical Proximity Correction (OPC) at different proximity gaps and include phase evolution. The corner correction represent a two dimensional problem which is difficult to handle with simple rule based approaches. Implementation of small amplitude structures leads to sharp phase changes. The analysis has been done with an instrument called High Resolution Interference Microscopy (HRIM), a Mach - Zehnder interferometer that gives access to three dimensional phase and amplitude images.

Ieee2016

Phase analysis of amplitude binary mask structures

Hans Peter Herzig, Krishnaparvathy Puthankovilakam, Toralf Scharf

Shaping of light behind masks using different techniques is the milestone of the printing industry. The aerial image distribution or the intensity distribution at the printing distances defines the resolution of the structure after printing. Contrast and phase are the two parameters that play a major role in shaping of light to get the desired intensity pattern. Here, in contrast to many other contributions that focus on intensity, we discuss the phase evolution for different structures. The amplitude or intensity characteristics of the structures in a binary mask at different proximity gaps have been analyzed extensively for many industrial applications. But the phase evolution from the binary mask having OPC structures is not considered so far. The mask we consider here is the normal amplitude binary mask but having high resolution Optical Proximity Correction (OPC) structures for corners. The corner structures represent a two dimensional problem which is difficult to handle with simple rules of phase masks design and therefore of particular interest. The evolution of light from small amplitude structures might lead to high contrast by creating sharp phase changes or phase singularities which are points of zero intensity. We show the phase modulation at different proximity gaps and can visualize the shaping of light according to the phase changes. The analysis is done with an instrument called High Resolution Interference Microscopy (HRIM), a Mach-Zehnder interferometer that gives access to three-dimensional phase and amplitude images. The current paper emphasizes on the phase measurement of different optical proximity correction structures, and especially on corners of a binary mask.

Spie-Int Soc Optical Engineering2016