Jeffrey D. Gelorme

N-type organic thin-film transistor with high field-effect mobility based on a N,N′-dialkyl-3,4,9,10-perylene tetracarboxylic diimide derivative

N,N′-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8H) thin films have been implemented into organic thin-film field-effect transistors. Mobilities up to 0.6 cm2 V−1 s−1 and current on/off ratios >105 were obtained. Linear regime mobilities were typically half of those measured in the saturation regime. X-ray studies in reflection mode suggest a spacing of ∼20 A for thin evaporated films of PTCDI-C8H, which is consistent with the value of ∼21±2 A obtained from our simulations when an interdigitated packing structure is assumed.

Negative photoresists for optical lithography

Negative photoresists are materials that become insoluble in developing solutions when exposed to optical radiation. They were the first systems used to pattern semiconductor devices, and still comprise the largest segment of the photoresist industry because they are widely used to define the circuitry in printed wiring boards. However, the current use of negative resists in the semiconductor industry has been limited by past difficulties in achieving high-resolution patterns. Recent advances in the chemistry of negative-resist systems, however, have provided materials with wide processing latitude and high resolution that are used to manufacture IBMs advanced CMOS devices and to achieve high-aspect-ratio patterns for micromachining applications. This paper provides an overview of the history and chemistry of negative-resist systems and their development in IBM.

High-aspect-ratio resist for thick-film applications

In recent years, increased activity in micromachining has driven the need for high aspect ratio thick films resist systems. This paper discusses a new epoxy based resist that can be used to achieve high aspect ratios (> 10:1) using UV lithography. The resulting negative resist system provides sharp, clean images in thick films (> 200 micrometers ). Because of the high aspect ratio and short exposure times, this material may be a viable candidate for producing the images required for micromachined parts. The resist images exhibit straight sidewalls and developed patterns, have excellent thermal stability, good adhesion, and chemical resistance. The high aspect ratio and high thermal stability make these epoxy resists suitable for other packaging applications such as plating stencils and optical wave guides.

Introducing Biobased Materials into the Electronics Industry

Abstract: Lignin, a biopolymer formed in the cell walls of plants, is a by-product of paper manufacturing. In research at IBM, it was incorporated into a resin used in the fabrication of printed wiring boards (PWB) for the microelectronics industry. The resin had physical and electrical properties similar to those of current laminate resins. PWBs fabricated from the lignin-based resin passed most of the standard physical, electrical, and reliability tests for an “FR4”-grade laminate. A comparison of the lignin-based resin and current resins via life-cycle assessment indicated up to 40% lower energy consumption for the biobased resin. Large-scale manufacture of lignin-based resins would require an inexpensive source of lignin with low ionic contamination.

Polymeric Optical Waveguides

The present work describes the characterization of internally developed epoxy ridge optical waveguides which exhibit low propagation loss (0.3 dB/cm at 1.3 μm), high environmental stability (low sensitivity to moisture), have smooth walls (100 nm sidewall roughness), and high temperature stability (275°C). The techniques used to fabricate these waveguides are compatible with the planar processes used in the manufacture of high performance electronic packages.

Wafer IMS (Injection molded solder) — A new fine pitch solder bumping technology on wafers with solder alloy composition flexibility

In this paper, we will describe a new low cost solder bumping technology for use on wafers. The wafer IMS (injection molded solder) process can form fine pitch solder bumps on wafers, while offering greater solder alloy flexibility. This method is also applicable to form uniform solder bump heights when a wafer has different size and shape of I/O pads. The wafer IMS bumping process uses a solder injection head that melts the desired bulk solder alloy composition and then dispenses the molten solder into resist material cavities on wafers within a nitrogen environment. The injected molten solder contacts and wets to the metal pads without flux, thus forming intermetallic compounds at the solder/pad interface. After stripping the resist material, solder bumps exhibit straight side walls and round tops as the solders have solidified inside the cavities of this resist film. This particular geometry is unique and offers a ready-for-substrate bonding condition without an additional reflow step. In the case of using Cu pillars, one resist material is used for both Cu electroplating and molten solder injection. After patterning the resist material, the Cu pillars are electroplated to the desired height, and the remaining cavities of resist material are filled by the injection of molten solder. The final bump height is defined by the thickness of the resist material. Therefore, any non-uniformity of Cu pillar height across a wafer is masked by the final solder bump uniformity. A prototype tool for wafer IMS bumping technology has been developed and solder bumping has successfully been demonstrated with Sn-3.0Ag-0.5Cu solder on 200mm wafers. The test wafer employed interconnects pads of four different diameters and three different shapes. Other solder compositions have also been tried successfully.

Mixing, rheology, and stability of highly filled thermal pastes

Thermal pastes play an important role in transmitting heat generated by an integrated circuit chip from its back side to a cooling cap or heat sink which transfers the heat to the environment. Most thermal pastes are formulations of solid, thermally conducting particles in a liquid matrix loaded to very high solids content. The mixing process for such pastes is complex but important, since it determines several of the paste properties. In particular, paste rheology is related to the work imparted to the paste during the mixing process. It determines the minimum bondline between solid surfaces that can be attained with a particular paste during the assembly process, which is essentially a squeeze flow process. Paste stability depends on the amount of entrapped air incorporated during the mixing process; this is demonstrated by infrared (IR) visualization of the degradation of air-containing paste in a computer-chip-heat-sink gap and the absence of this degradation mechanism in vacuum-mixed paste. This paper describes two different mixing processes for highly filled thermal pastes, the associated changes in their rheological behavior, and paste degradation in chip-heat-sink gaps during thermal stressing.

High-speed aqueous-developing negative resist based on triflic-acid-catalyzed epoxy polymerization

The need for higher resolution is a continuing driving force in the development of new lithographic materials. In this paper we discuss a new high speed, high resolution negative photoresist based on acid catalyzed epoxy polymerization. These materials are copolymers of two monomers that each provide a separate function in the photoresist. This combination provides a unique new material with aqueous processability in metal ion-free developers and high sensitivity to photogenerated triflic acid. Imaging characteristics in electron beam and i- line exposure systems are discussed.

Negative DUV photoresist for 16Mb-DRAM production and future generations

This paper discusses a new negative tone aqueous base developable photoresist that has demonstrated excellent sub-half micron resolution with commercially available DUV (deep ultraviolet) exposure systems. This system which consists of a phenolic resin (pHOST), a glycoluril crosslinker (TMMGU), and a triflic acid generating material is currently in use for the manufacturing of 16 M b-DRAM and related CMOS logic technology. We provide supporting manufacturing data relating to our experiences with this program, along with the benefits realized by the implementation of a negative tone photoresist system.

Lithographically fabricated fiber guides for optical subassemblies

A new optoelectronic packaging technology is presented which permits highly accurate fiber-to-chip alignment at low cost. Instead of the more common methods employed in fabricating optical subassemblies, which use leadframe, precision plastic-molding, or silicon-optical-bench technology, here fiber guides are fabricated in a photoresist by use of standard photolithographic procedures. By this means the fiber guides are directly created on an entire wafer of either VCSELs or receivers, resulting in structures with very tight dimensional tolerances fabricated at very low cost. After dicing, a fiber is interfaced with a chip under computer control using a very simple semiautomatic tool to insert the fiber into the fiber guide. This new technology may be used in the fabrication of a wide variety of single or multi-channel optoelectronic transceivers.