Paul Rissman

Proximity effect correction for electron beam lithography by equalization of background dose

Compensation for the proximity effect in electron lithography can be achieved by equalization of the backscattered dose received by all pattern points. This is accomplished by exposing the reverse tone of the required pattern with a beam diameter dc=2σb ×(1+ηe)−1/4 and dose Qc=Qe ×[ηe/(1+ηe)], where σb is the radius of the Gaussian spatial distribution function of backscattered electrons at normally exposed pixels, ηe is the ratio of backscattered to forwardscattered energy, and Qe is the dose delivered to normally exposed pixels. This correction method has been confirmed to work for 500‐nm features by computer simulation of electron beam exposure and development and by experiment on a raster scan electron beam lithography system.

Application of the GHOST proximity effect correction scheme to round beam and shaped beam electron lithography systems

The GHOST proximity effect correction scheme has been applied to a round beam lithography system and also to a shaped beam system. It is shown that the image contrast of the GHOST scheme is constant at all spatial frequencies at which forward scattering is insignificant: the flatness of the modulation transfer function corresponds to the removal of the proximity effect. The effects of errors in the correction dose, the correction beam diameter, and the registration between the pattern and correction exposures have been calculated analytically, and it is shown that the allowable tolerances for these parameters are wide.

Performance results of an electron beam lithography machine and process by means of dc electrical test structures

Direct current electrical tests have been used to measure the performance of electron beam resists and an exposure system. Resist characterization is done by using electrical tests to measure the linewidth defined as a function of an incremental dose. The quality of different resists can be compared by means of δ, the slope of the normalized linewidth versus the logarithm of the incident dose curve. Data have been measured for three negative resists (PCMS 30, PCMS 200, and OEBR 100) and PMMA for two development conditions. Resistors fabricated from 60 nm chromium films, 300 nm polysilicon films, or 60 nm titanium films gave results within ±40 nm of one another for 500 nm lines. Without proximity effect correction, linewidth difference from design value is more than ±300 nm and the 0.5P μm lines were undefined for PMMA and the given development conditions, and 0.5P and 1.0P μm lines were undefined for PCMS 30 and the given exposure conditions. With proximity effect correction, all line sizes are within 100...

GHOST solubility rate ratio: A new parameter for characterization of positive electron resists

Positive electron beam resists can be characterized by the GHOST solubility ratio parameter Srg defined as the ratio of the solubility at the nominal exposure dose Qe to the solubility at the GHOST correction dose, [ηe/(1+ηe)]xQe. This parameter removes the development time ambiguity inherent in resist characterization by means of a thickness remaining vs dose curve, and eliminates the experimental difficulty in characterization of resist based on measurements of unexposed solubility rate. Modeling data indicate that the Srg parameter is a good measure of resist performance. GHOST proximity effect correction results on PMMA exposed at doses from 10 to 200  μC/cm2 illustrate experimentally the dependency of feature quality on the value of Srg. The Srg method is a general technique for resist characterization, and is valid whether or not proximity effect correction is used. This parameter has been used to compare the performance of PMMA, EBR‐9, CP‐3 and Microposit 2400. Electrical test measurements show tha...

Hard stamp processes for the EVG 620 full field nanoimprint system

The EVG 620 nanoimprint system is a 4 in. full wafer system suitable for university and research environments (EV Group, A-4782 Sankt Florian am Inn, Austria). By limiting the area printed and by the use of hard masks, nanoimprint lithography resolution can be extended to well below the design resolution of the system. The EVG 620 has found application primarily with soft stamps, such as those made of polydimethylsiloxane [Plachetka et al., Microelectron. Eng. 73-74, 167 (2004)]. However, soft stamps can have limited resolution and are difficult to clean, meaning they should be disposed of after a single stamp. Hard stamps made from quartz wafers have ultimate resolution limited only by the e-beam exposure system used for definition and are easy to clean in sulfuric peroxide or oxygen plasma strippers. Hard stamps have been demonstrated on the EVG 620 instrument at Stanford Nanofabrication Facility with resolution down to 20 nm. Both positive tone (PMMA, ZEP-520) and negative tone templates [hydrogen sils...

0.5 μ SWAMI/NMOS process technology with electron beam lithography

This paper describes the process design and device characteristics of NMOS transistors with 0.5  μ mask layout in both channel width and channel length. Direct write electron beam lithography was used to fabricate submicron features. SWAMI (side wall masked isolation) and oxide spacer techniques were used to reduce both 2 Δ W and 2 Δ L to less than 0.3  μ with 6500 A field oxide and 200 A gate oxide. The device characteristics show that the threshold voltage of a 0.5  μ transistor is about 0.8 V, while the punch through and breakdown voltages are greater than 6.5 V. Short channel and narrow channel effects will also be presented.

High Speed Direct Write Electron Beam System

The total sales dollars of semiconductors over the past six years have grown roughly at the rate of 25% per year in spite of the fact that the price of some of the individual components has decreased dramatically. This has resulted in a significant reduction in the cost per function. As this occurs, new markets open up creating additional demands.