In this topic, we mainly have three directions:
    1.Qualitative determination of exposure induced pH.
    2. Focus latitude determination of photoacid generation
    3. Single molecule spectroscopy and diffusion.

What we are doing right now is to work with Shipley in continued development of a fast, convenient, and robust technique to evaluate the efficiency of candidate PAGs for 193 nm resists based on spectroscopic imaging, and to work with Shipley to use single molecules as nano-probes for measurement of the diffusion of acids in chemically amplified photoresist on the 10 nm length scale.

The traditional technique for characterizing PAGs (PhotoAcid Generators) involves:

1. coating a series of wafers for each PAG,
2. flood exposing the wafers, each with a different dose,
3. stripping off the resists, and
4. performing spectrometric titration in vitro to determine the amount of acid generated in each resist.

as shown in the figure on the left.

Our project is to develop a fast, convenient, quantitative, and robust technique to evaluate PAGs for 193 nm resists.

The solution is:

1. dope test resists with a pH sensitive fluorescent dye (500 ppm)
2. coat one wafer per PAG
3. expose each wafer with a dose matrix
4. perform spectroscopic imaging of each wafer

Advantage: entire response curve of each PAG is encoded spatially and spectrally in fluorescence images of a single wafer (on-wafer titration).

As a result, we obtained a quantitative understanding of the Optical Titration Curves in 248 nm and 193 nm resist matrices, and did a comparative study of six candidate 193 nm photoacid generators. Our future work includes working to reduce the noise associated with stray light. The following are some fluorescence titration images at 193nm exposure. TOP

Focus latitude determination of photoacid generation.

The diagram on the left shows our instrumentation scheme.

Conclusions:

1. Optical contrast for 140 nm features using pH sensitive dyes (Depth Of Modulation)
2. At low concentrations dyes are compatible with existing resist formulations.
3. Fast (~ 1 min) and non-destructive technique for determining appropriate focus latitude. TOP

Single molecule spectroscopy and diffusion.

It has the following application:

1. Spatial Profile - Acid Profile and Diffusion along various features / SM position
2. Local Mesostructure - SM orientation / emission polarization
3. Local Composition - Local pH and E-Field sensitivity / spectral position
4. Local Dynamics ¨C Deprotection (chemistry) / time-resolved spectral behavior.

We have successfully demonstrated single molecule imaging and localization technique, proved the principle ¨C locally sensitive molecular probe ¨C often emit only a few photons before bleaching. For further research, a highly sensitive technique with spatial and spectroscopic resolution is required, like a way of determining energy of each photon (STJ). Some singel molecule images are shown below. TOP