Brian Maxwell

Lithographic properties of novel acetal-derivatized hydroxy styrene polymers

Lithographic properties of a variety of acetal-derivatized styrene based polymers are reported. The structural modifications in the polymers involve varying the size of the pendent acetal moiety. the lithographic performances of the resists containing structurally modified acetals were found to be superior to the conventional acetals. In the cases where the acidolysis products of the modified acetals are non-volatile alcohols, the post-exposure volatilization, film shrinkage and plasma etch resistance were found to be significantly improved.

Manipulation of chemically amplified resist dissolution rate behavior for improved performance

The properties of the PAG and the type of the blocking group combined with the process temperature affect the slope of the dissolution rate curves within the critical lithographic area of the curve significantly. The location of the steepest dissolution rate switching and the photospeed of the resist are primarily a function of the PAG type and base ratio. The resist inhibition is largely influenced by the blocking level of the polymer. The total phenolic (OH) content of de-blocked polyhydroxystyrene (PHS) based resist systems is the only parameter that affects their maximum dissolution rate (Rmax).

Optimizing a DUV positive resist for metal layers

Structurally modified acetal resist is designed for lithography on metal layers. The acetal-based polymer used in the resist has intrinsically low post-exposure volatilization and superior metal etch resistance. This resist is designed to have excellent substrate compatibility as indicated by a foot size of less than 10 nm for 250 nm feature size. Lithographic evaluations reveal that this resists is capable of resolving sub-200 nm features on TiN substrates with high photosensitivity, dose latitude and excellent process windows for line and post features. The reduced foot size and enhanced resolution could be achieved by optimizing the resist chemistry and the processing conditions.

Effect of developer normality on the resist dissolution rate and performance

Process simulation is necessary to investigate possible enhancements of some selective resist performance properties as a result of changes in the developer concentration. Accurate dissolution parameters are needed for different developer normalities to simulate their effect on the resist dissolution rates. Only qualitative similarities are observed in the dissolution behavior of similar chemistry based resist as a function of developer normalities. Quantitative differences in the dissolution rates and curve shapes are detected between resist based on different chemistries. No single universal dissolution model capable of describing the behavior of all different resists was found. However, individual resist dissolution/developer concentration models can be constructed.

Design and process of a new DUV ARCH3 resist

A new concept for polymer design is described which can extend the utility of acetal chemistry in the development of advanced chemically amplified deep-UV resists for KrF excimer lasers. Many acetal blocked polymers only impart marginal thermal flow properties to the photoresist matrix. This polymer design concept can overcome this thermal flow deficiency and also improve photoresist contrast and resolution. This concept involves the formation of crosslinked acetal polymers from linear acetal blocked polymers via acid labile crosslinks. The resulting branched polymers have increased Tg and therefore impart improved thermal flow properties to the resist. Furthermore, the acid lability of the crosslinks results in a large molecular weight differential between exposed and unexposed areas of the resist leading to larger dissolution rate discrimination between exposed and unexposed regions. The ultimate result is improved resolution capability of the resist system. This design concept has been incorporated into the ARCH3 resist series.

Formulation optimizations for variable DUV resist thickness applications based on the same polymer matrix

We are investigating strategies of resist optimization for various target thicknesses based on the same polymer. The photo acid generator (PAG) and base levels are optimized for each application thickness. The polymer of choice, used in this work, contained sufficient tertiary-butyl ester groups to provide high dissolution rate after exposure (high Rmas) while its initial dissolution rate in the developer is very low (low Rmin). The polymer structure was also designed to provide a high ratio of carbon to hydrogen atoms to be adequately resistant to plasma etching. Other polymer properties, such as solubility in resist solvents, long shelf life stability, good coating properties, good adhesion to different substrates, low solution viscosity, low coating defects and good wettability are only a few examples of many required characteristics for good resist performance.