William R. Livesay

61.5: LED-Based Light-Recycling Light Sources for Projection Displays

LED-based light sources utilizing novel light-recycling cavities have been developed that have small output etendue. A portion of the light emitted by the LED source is recycled back to the LEDs to enhance both the average brightness of the source and the brightness of the cavity output. Experimentally, we have achieved brightness enhancement factors of approximately 1.3x–2.0x.

Mechanism studies of scanning electron microscope measurement effects on 193-nm photoresists and the development of improved line-width measurement methods

The effect of scanning electron microscope (SEM) measurements on the dimensions of resist features was studied for 193nm resist materials. Initial measurements showed that resist lines became smaller as they were repeatedly measured, with size changes of up to 40 to 50 nm after 50 to a 100 measurements. There was a significant size change for the two 193nm resist systems tested, an acrylate based single layer system and a hybrid single layer system, although the magnitude of the effect was different for each system. The total dose per SEM measurement seen locally by the resist was calculated to be on the order of 100 (mu) C/cm

E-beam curing effects on the etch and CD-SEM stability of 193-nm resists

_2), a significant amount by the standards of e-beam induced chemistry. Entire wafers of the hybrid system were cured in an e-beam curing system to enable chemical characterization of irradiated resist. It was found that there was loss of the anhydride functionality when blanket-coated wafers of the hybrid system were cured and a corresponding reduction in film thickness. The remaining material was cross-linked. However, to our surprise, we found that e-beam curing of exposed line and space patterns id not result in any critical dimension (CD) change, any height change, or any profile change. What is more, the cured line and spaces patterns did not show significant line width change when repeatedly measured in a SEM. It is speculated that the resists gets hot while being measured and how hot affects how much shrinkage is seen. Depending on the temperature reached, either cross-linking or annealing will be the fastest process; and the balance between the two will determine how much shrinkage is seen during measurement.

Modification of 193-nm (ArF) photoresists by electron beam stabilization

Electron beam (e-beam) curing techniques are known to improve etch and CD-SEM stability of 248 and 193nm resists. The effects of three different e-beam curing processes (standard, LT and ESC) on the methacrylate and hybrid type 193nm resists were studied with respect to resin chemistry changes, resist film shrinkage, pattern profiles, etch rates, and CD SEM stability. Both methacrylate and hybrid type 193nm resists lose carbonyl groups from the resins, with possibly a reduction in the free volume leading to improved etch resistance/selectivity. Methacrylate resist films shrink ca. 22-24% and hybrid resist films shrink ca. 23-27%. The LT process shrinks the least compared to the ESC and standard process. The ESC and LT processes were found to stabilize the patterns uniformly compared to the standard process. Etch rate, selectivity and resist surface roughness after etch of both methacrylate and hybrid resists were improved using the e-beam curing process. E-beam curing drastically reduces the CD SEM shrinkage (from ca. 15% to 2- 5%); however, considerable shrinkage occurs during the curing process itself.

Investigation of electron beam stabilization of 193-nm photoresists

For the sub 130nm technology nodes, 193nm(ArF) lithography has become the technology path of choice. Similar to the 248nm technology set, the resist systems being used for 193nm lithography are based on chemical amplification to achieve high throughput at the low exposure energy at 193nm. The current ArF resist systems have experienced problems with etch selectivity and line slimming during CD-SEM measurement. Both of these issues are related to the resist platform and constituents used to achieve the desired lithographic performance. This investigation evaluates electron beam stabilization as a way of addressing both the etch selectivity and line slimming issues associated with some of the current 193nm resist systems. Varying levels of electron beam dose were evaluated in an attempt to understand the effects of energetic electrons on ArF resist materials. Chemical changes in the resist were monitored for blanket resist films by FTIR, film shrinkage, and changes in index of refraction, all as a function of dose level. An increase in modification of the resist is seen with increasing dose. Blanket resist etch rate studies were performed as a function of stabilization condition. The etch rate of the resist was found to decrease with increasing dose as compared to untreated resist. Correlation of the chemical changes and etch rate reductions are proposed for the resists considered. The CD changes induced by the electron beam stabilization were monitored as a function of dose applied. Minimal CD change was seen as a result of the stabilization process. The impact of the electron beam process on line slimming was evaluated by performing repeated measurements on resist features with different levels of electron beam dose. The line slimming was found to be significantly reduced for the higher dose levels considered. Etch selectivity was evaluated by cross-section SEM measurements after etch of features with different levels of stabilization. An increase in the etch selectivity and pattern stability were observed with increasing stabilization dose.

Advanced metal lift-off process using electron beam flood exposure of single layer photoresist

193nm lithography is a promising candidate for the fabrication of microelectronic devices at the 130nm design rule and below. With smaller feature sizes, below 130nm, reduced resist thickness is essential because of the pattern collapse issues at high aspect ratios and the limited depth of focus with 193nm lithography tools. However, ArF resists have shown problems with etch selectivity, especially with the thin resist layers necessary. Additionally, pattern slimming during CD-SEM measurement, due to the nature of the resist chemistry, is an issue with feature stability after patterning. At present, many studies have been performed for improving the etch selectivity of resists and addressing line slimming issues. In this study, the electron beam stabilization process has been applied for improving the etch selectivity of resist patterns having an aspect ratio less than 3.0. The electron beam stabilization has been applied to two different ArF resist types; acrylate and cyclic-olefin- maleic-anhydride (COMA), which have been evaluated with respect to materials properties, etch selectivity, and line slimming performance as a function of electron beam dose and etch condition. Film shrinkage and the change in index of refraction were monitored as a function of stabilization condition. The chemical properties were characterized before and after electron beam stabilization using FTIR analysis. Blanket resist etch rate studies were performed as a function of stabilization condition for each resist type. Cross- sectional views of resist patterns after etch processing were also investigated to evaluate the improvement in etch resistance provided by the electron beam process. CD SEM measurements were performed to evaluate the impact of the stabilization process on the patterned features. The issue of line slimming has also been evaluated, with and without electron beam stabilization, for the different ArF resist materials considered. The results were compared with a KrF resist currently used in production. Based on the experimental results, the electron beam process provides a method for improving etch selectivity and reducing line slimming issues of ArF resists.

Low-temperature technique for thick film resist stabilization and curing

In the manufacture of many types of integrated circuit and thin film devices, it is desirable to use a lift-of process for the metallization step to avoid manufacturing problems encountered when creating metal interconnect structures using plasma etch. These problems include both metal adhesion and plasma etch difficulties. Key to the success of the lift-off process is the creation of a retrograde or undercut profile in the photoresists before the metal deposition step. Until now, lift-off processing has relied on costly multi-layer photoresists schemes, image reversal, and non-repeatable photoresist processes to obtain the desired lift-off profiles in patterned photoresist. This paper present a simple, repeatable process for creating robust, user-defined lift-off profiles in single layer photoresist using a non-thermal electron beam flood exposure. For this investigation, lift-off profiles created using electron beam flood exposure of many popular photoresists were evaluated. Results of lift-off profiles created in positive tone AZ7209 and ip3250 are presented here.

Electron beam processing of Deep-UV resist

For a range of thick film photoresist applications, including MeV ion implant processing, thin film head manufacturing, and microelectromechanical systems processing, there is a need for a low-temperature method for resist stabilization and curing. Traditional methods of stabilizing or curing resist films have relied on thermal cycling, which may not be desirable due to device temperature limitations or thermally-induced distortion of the resist features.

Photoresist stabilization for ion implant processing

To advance production processing well beyond 0.30 micrometer design rules, it is considered necessary to introduce deep-UV photolithography. Currently, most deep-UV photoresist systems are based on poly(4-hydroxystyrene) (PHS) resins, which have good thermal properties. When combined with photo-acid generators (PAG) and dissolution inhibitors, the thermal properties of the resulting resists are severely reduced. Since the Tg of these types of advanced resists are in the 100 to 120 degree Celsius region, it is necessary to apply a stabilization process to the resists prior to processing at high temperatures. This study investigates the application of electron beam stabilization processing to deep-UV resist materials. A PHS based deep-UV resist, and a solution of the PHS resin material, have been evaluated to determine the nature of the reactions induced by electron beam exposure. Chemical changes induced in the resist, or resin, are evaluated via FTIR analysis. Changes in optical properties are evaluated using UV/visible reflectance as well as changes in index of refraction. Film shrinkage is determined for all processing conditions. Thermal properties are evaluated by DSC and TGA techniques. The Tg of the processed resist is presented as a function of electron beam exposure. Thermal flow properties are evaluated via SEM cross sections of resist features exposed to high temperatures after electron beam stabilization. Electron beam stabilized films are demonstrated to withstand temperatures in excess of 200 degrees Celsius. The resist or resin materials properties are evaluated as a function of electron beam dose level and stabilization process temperature. Trends in materials properties are evaluated and optimized process conditions are presented for a range of production processing applications.

Electron beam hardening of photo resist

In this study, a non-thermal photoresist stabilization process is considered for ion implant processing. The stabilization process utilizes a flood electron beam system that uniformly exposes the entire thickness of the photoresist film. A photoresist stabilization process is critical for some ion implant processes to reduce out-gassing, provide thermal stability, and facilitate its subsequent removal. Stabilization becomes more critical for advanced photoresists where, due to the high photoactive compound content, the thermal stability of the photoresist is low and the post ion implant removal process becomes more complicated. In this evaluation three i-line photoresists are considered, OiR-32, OiR-32 medium dye, and OiR-897 10i. The non-thermal aspect of the electron beam stabilization process eliminates the shrinkage and flow associated with thermal stabilization processes. Parameters evaluated include critical dimension variation, thermal stability, and post ion implant photoresist removal. The electron beam stabilized photoresist shows significantly reduced post implant shrinkage and critical dimension variation compared to UV/thermal processing. The thermal stability of the photoresist is dramatically improved by the electron beam stabilization process. Finally, the post ion implant removal processing is improved, as indicated by the elimination of popping and contamination during a standard removal process. Thus, the electron beam process is demonstrated to provide improved thermal stability, reduced critical dimension variation, and improved microwave downstream plasma photoresist removal characteristics after ion implant processing.