Type Photoresist Research Articles

New high temperature stable positive photoresists based on hydroxy polyimides and polyamides containing the hexafluoroisopropylidene (6‐f) linking group

AbstractIn this paper we describe the synthesis, characterization, and lithographic evaluations of novel positive photoresists based on hydroxy polyimides and polyamides containing 6‐F linking groups. The polymers were synthesized using solution condensation techniques and characterized using solution viscosity, GPC, FTIR, NMR, UV, TGA, and DSC. Tg's of these polymers range from 250 to 300°C. Both polyimides and polyamides are soluble in a variety of solvents commonly utilized for photoresist applications. When formulated with diazonaphthoquinone sensitizers, these polymers provide an improved high‐temperature resistant, aqueous base developable positive photoresist system with good photospeed, contrast, and resolution characteristics. High resolution relief images were obtained which are comparable to 1300 Series AZ type photoresists. No thermal deformation, loss in resolution or defects were noticed when relief patterns were annealed to 250°C. Additionally, the hydroxy polyamide based resists, when thermally annealed to 300°C, provide a photoresist system with even higher thermal stability (400 to 450°C) and excellent resistance to solvents. Also, the photoresist formulations have excellent storage stability at room temperature and can be processed like conventional positive photoresists using broad band UV radiation sources.

Laser enhanced polymer etching in different ambients

Excimer laser photoetching of various types of polymers is becoming a topic of great interest in several industries. For microelectronics applications, quantitative and qualitative models have been developed, e.g. for modelling of the removal depth [1,2] and the wall slope [3]. We have investigated the photodecomposition of a polyimide (Hitachi PIQ-13) and of a novolak type photoresist (JSR PFR-3003A), at 248 nm (KrF). Removal of these polymers was studied in four different ambients : air, vacuum, low pressure oxygen atmosphere and afterglow plasma. The transfer of a pattern in polyimide through laser enhanced etching has also been looked at.

Functional Monomers and Polymers CLXVIII. Syntheses and Photoreactions of Poly(methacrylate)s Containing Thymine Bases

Poly(methacrylate)s having thymine derivatives were studied for photodimerizations of thymine units in solution and in the film state, and photolithographic sensitivity tests for their applicability to negative type photoresists. In these homopolymers and copolymers, thymine bases were attached to the polymer chain at positions N1 or N3. Among these polymers, the alternate copolymer indicated the highest photosensitivity. The results are discussed from the viewpoint of intra- and/or intermolecular photodimerization and the quantum yields in solution and in the film state.

Functionalization of polysiloxanes by esterification of pendant epoxy groups: Cross‐linkable liquid polymers containing photo‐dimerizable ester units

AbstractPhoto‐dimerizable carboxylic acids were grafted onto linear silicone copolymers by amine catalyzed esterification of pendant epoxypropyl groups. The epoxy‐carboxy reaction was found to surpass in experimental simplicity, chemical selectivity and reproducibility, the modification methods involving the hydrosilylation of functionalized olefins. Liquid, photo‐crosslinkable polymers (8a and 8b) were finally obtained after acetylation of the hydroxy‐ester groups resulting from the addition of functional carboxylic acids, and no unwanted side‐reaction was detected. The practical sensitivity of photo‐reactive polysiloxanes of various average molecular weights containing 5–17 mol‐% of sensitive units, was measured by photoresist type insolubilization tests. The ultimate acetylation reaction was shown to have little or no influence on the dimerization process of 2‐cyano‐5‐phenyl‐2,4‐pentadienoic derivatives (8a), but to increase the rate of disappearance of trans‐cinnamic groups (in 8b) submitted to UV light irradiation.

Contrast Enhancement and Resist Wall Profile Control by Surface Crosslinkage

Contrast enhancement, wall profile control and sensitivity increase all are important factors for resists used in microlithography. The use of contrast enhancement layers is accompanied by a sacrifice of resist sensitivity and has been limited to application to positive type photoresists. SPACE process has been reported for a negative working electron beam resist. With a controlled UV-flood exposure, enhancements in both contrast and sensitivity of RD2000N resist have been obtained. However, its application is limited to a negative working resist.The concept of SPACE may be expanded to other types of resists and lithographies such as positive working photoresists. I wish to present here contrast enhancement and resist wall profile control by photochemical surface crosslinkage. With addition of a crosslinking agent like an aromatic bisazide which has its UV absorption band far away from an imaging wavelength, one can obtain contrast enhancement, control of resist wall profiles and reduction of resist thickness loss during image development after photochemical surface crosslinkage.There are several processes reported for maintaining resist wall profiles at high temperature. However, resist images thicker than 3μm tend to have surface reticulation after high temperature heating. Pulsed electron beam resist hardening solves this problem. Certain chemical treatments of resist images provide not only thermal flow resistance but also specific RIE resistance. These processes for maintaining resist wall profiles at high temperatures will also be presented.

Pyrimidine Polymers as High Resolution, High Sensitivity Deep-UV Photoresists

Polymethacrylates containing pyrimidine base derivatives, and copolymers of butadiene with methacrylate monomer containing pyrimidine bases were prepared and studied for photodimerization of pyrimidine base units, grafted to the polymer chain. These polymers were found to be applicable as negative type photoresists. Photolysis of the polymers caused dimerization of pyrimidine bases and leaded to the photocrosslinking of the polymer chains. The photolithographic evaluation of these polymers showed high sensitivity, high resolution values of ever 1μm.On the other hand, the application of polyamides synthesized by polycondensation of the thymine photodimer and various diamines into positive resists were studied. The photolysis of these polymers caused dissociation of the thymine photodimers, leading to the breakage of the polymer chains. These polymer indicated very high resolution values of even 0.3μm.

A-and B-parameter dependent submicron stepper performance of positive type photoresist

A systematical investigation of the g-line stepper performance of positive type photoresists with varying absorption properties has been carried out on highly reflective substrates. Numerous parameters such as photospeed, pattern profile, focus and exposure energy latitude are evaluated by SEM inspection of submicron resist lines after exposure with a stepper of NA=0.42. It is shown that the amount of non-bleachable absorption (B-value [1]) alters only slowly the imaging properties of the resists on aluminum surfaces, whereas changes in the bleachable absorption (expressed by the A-value) lead to large differences in the resist profiles and the tolerance of the lithographic process. Profile simulations with PROSIM [2] and PROLITH [3] indicate that the development characteristics rather than the optical properties determine the performance of the resists.

Diazopolysiloxanes: Unique imageable barrier layers

This paper describes new types of organosilicon photoresists, sensitive throughout the ultraviolet region from 2000 to 45Å. The synthesis is based upon a simple condensation reaction of 3-aminopropyl-substituted polysiloxanes with photosensitive naphthoquinone diazosulfonyl chlorides. These polymers when used in bilayer systems are very sensitive, high contrast negative photoresists with sensitivities of about 10 mJ/cm 2 at 4047Å and (γ) of 1.4. Because of the inorganic polysiloxane backbone, they are resistant to oxygen plasmas, with an etch rate ratio of 50:1 (photoresist/diazosiloxane), and they are thermally stable up to 400°C. The synthetic procedure, mechanisms of crosslinking and processing characteristics of these materials are discussed along with data concerning their resolution capabilities and lithographic applications.

Dry Etching of Tapered Contact Holes Using Multilayer Resist

Optimum coverage of contact holes by sputtered metals typically requires sloping of the sidewalls. A number of different types of photoresists and dry etch techniques have been examined for this purpose. Two processes which will be discussed include (i) replication of a presloped single‐layer AZ‐type photoresist profile by anisotropically etching the resist and the silicon dioxide at comparable rates, and (ii) controlled lateral etching of a vertical‐walled poly (methyl methacrylate) (PMMA) layer of a two‐layer resist, while etching silicon dioxide in the vertical direction. The latter process preserves the inherent accurate resolution of the vertical PMMA profile, while providing an opportunity for tailored and reproducible sidewall angles. The results of mass and emission spectroscopy suggest that atomic oxygen plays an important role in the lateral etching of the PMMA resist.

On selective electroplating of gold in fabrication of MIC's

The analysis of the reasons causing degradation observed in resist layer during selective gold plating on patterns for MIC's has resulted in an excellent combination of electrolytic bath and photoresist type. Thick layers of gold (i.e. more than 10 μm) have been deposited by the method presented here over a period of about 1 h without any deterioration in the photoresist property. This combination can be used in the fabrication of beam lead devices with better results.

Edge acuity and resolution in positive type photoresist systems : Phillip D. Blais. Solid. St. Technol. (August 1977)

Edge acuity and resolution in positive type photoresist systems : Phillip D. Blais. Solid. St. Technol. (August 1977)

Surface desorption of gases from photoresist

This work describes the analysis of gases desorbed in vacuum from photoresists manufactured by Shipley and Kodak, as a function of temperature. Test samples were prepared by spin coating of a special heating element prepared by photolithographic techniques on a nichrome, gold-coated alumina substrate, the degassing of this type of heating element is relatively low by comparison to that of the photoresist. The analysis of gases desorbed was performed at a pressure of 10 −6 torr utilizing a monopole mass spectrometer. The type of photoresist and temperature were the determining factors in the quantity and species of gases desorbed. In this manner the breakdown temperature of each type of photoresist was determined. The results of this work aid in choosing a photoresist compatible with microelectronic vacuum technology.

Microlenses for Coupling Junction Lasers to Optical Fibers

Microscopic lenses, fabricated on optical fiber surfaces, have quadrupled the efficiency for coupling astigmatic beams from GaAs junction lasers into 4-microm cores of single-mode fibers. A novel photolithographic technique was used to make hemispherical and hemicylindrical microlenses, with diameters between 4 microm and 10 microm, from commercially available negative type photoresist that is transparent at ir laser wavelengths. Geometrical profiles of photoresist lenses, documented with scanning electron photomicrographs, were remarkably smooth even though their dimensions were more than an order of magnitude smaller than other known lenses.

Photoresist Materials and Applications

Photoresists can be classified as either positive resists or negative resists depending on their mode of interaction with light. With the exception of photomasking, the process handling considerations for these two classes are similar. Photoresist performance is highly dependent on processing techniques. Typical processing procedures are discussed along with process problems and performance limitations of currently available materials. General materials chemistry of typical photoresists is discussed, and possible photomechanisms, development mechanisms, and adhesion mechanisms are considered. Substrates to which a resist is applied introduce another variable for consideration when evaluating resist performance.