Timothy W. Weidman

Polyalkylsilyne photodefined thin-film optical waveguides

Polysilynes, a new class of amorphous alkyl silicon network polymers, undergo a novel photo-oxidative crosslinking reaction associated with up to a 15% decrease in refractive index related to the loss of SiSi bonding. We describe the fabrication and initial measurements of waveguides formed with this index imaging technique in poly(cyclohexylsilyne) films on both SiO2 and poly(methyl methacrylate)-coated silicon wafers. Measurements of multimode guides show typical propagation losses of 0.68 dB/cm at 633 nm. Results indicate the polyalkylsilynes show promise as self-developing, planar optical waveguide media.

New photodefinable glass etch masks for entirely dry photolithography: Plasma deposited organosilicon hydride polymers

The low energy plasma induced dehydrogenative polymerization of various monosubstituted silanes (RSiH3) is shown to provide photosensitive films characterized as organosilicon hydride network materials with extensive Si—Si bonding. Plasma deposited films may be photo‐oxidatively patterned with mid‐deep ultraviolet light producing glasslike Si–O–Si crosslinked materials in exposed areas. Patterns can be developed by chlorine reactive ion etching with up to 5:1 selectivity, and transferred into underlying organic layers with ≳50:1 selectivity and sub‐half‐micron resolution. This provides a versatile, completely dry photolithographic process useful with current exposure and etching tools and is well‐suited for integration into cluster tool technologies.

Application of plasma polymerized methylsilane in an all dry resist process for 193 and 248 nm lithography

The performance of Plasma Polymerized Methylsilane (PPMS) as a single layer and bilayer resist system at 248 nm advanced lithography are exposed. PPMS based photolithographic processes are shown to be extendible for use in 193 nm lithography.

Propagation loss of index imaged poly(cyclohexylsilyne) thin film optical waveguides

The propagation loss of optical waveguides index imaged in a 0.5 μm poly(cyclohexylsilyne) (PCHS) film through photo‐oxidative cross linking with ultraviolet exposure at 310 nm is measured and compared to an experimental estimate of PCHS bulk propagation loss. Measured waveguide losses at 632.8 nm range from 0.6 dB/cm for TE operation of 2‐μm‐wide PCHS waveguides to 2.1 dB/cm for TM operated 4‐μm‐wide guides. Comparison to the bulk PCHS propagation loss estimate of 0.04 dB/cm at 632.8 nm indicates a significant increase in loss upon thin film waveguide fabrication.

Plasma polymerized organosilane network polymers: high-performance resists for positive- and negative-tone deep-UV lithography

We recently introduced a new class of high performance deep-UV photoresists which are deposited via the gas phase plasma polymerization of methylsilane. These materials, particularly plasma polymerized methylsilane (PPMS), undergo efficient oxidation on exposure to deep-UV light in air to form a glasslike siloxane network polymer, providing patterns which may be developed and transferred into underlying substrates using all dry plasma etch processes. Here we describe a simple new procedure which affords the opposite (positive) tone image in the same resist using a wet buffered oxide etch to remove exposed regions. Lithographic performance studies (dose latitude as well as linearity data) are presented for both the negative tone and the new positive tone versions of the process.

Wafer-level optical interconnection network layout

Two important issues will greatly influence the success of mapping optical interconnections into future waferlevel distributed computing systems: (1), the scalability of active optical devices with cointegration along side ULSI components, and (2), the scalability of optical networks and components to the wafer level. If these criteria can be met, planar integrated and free-space optics can potentially provide a very high performance communication network within the multi-wafer environment. With the predominantly planar geometry and processing of waferlevel circuits, process compatible integrated planar optical interconnections are especially attractive for providing network passive connectivity. As with their electrical counterparts, spatial, as well as time division multiplexing of optical interconnections is desirable, given that layout and area constraints are not too severe. Therefore here, emphasis is shifted away from the individual behavior of traditional long distance lightwave single mode waveguides towards the collective system behaviour (i.e. density, coupling, layout, etc.) of large dense arrays of multimode optical waveguides. In this paper, initial experimental optical coupling results are presented for arrays of multimode polysilyne polymer waveguides, both for straight configurations and for arrays with radial right angle bend layouts.

Toward cointegration of optical interconnection networks within silicon multichip systems

Si systems are rapidly evolving towards more efficient, compact parallel architectures characterized by a mix of both monolithic and hybrid technologies as silicon technology moves into the ultra large scale integration (ULSI) era. Previous distinctions between active chips and passive packaging will disappear within multi-chip modules (MCM) in which the Si interconnection substrate has evolved active devices supporting an interconnection network linking components within the module. As architectures emerge based upon multiple MCMs, the role optics plays as a performance enabling technology will be determined by how well it can provide a high performance interconnection network function which can efficiently bridge the physical substrate and package boundaries of the system. This paper motivates work experimentally exploring the compatibility of GaAs heteroepitaxy with submicron Si CMOS and the scaling of polymer high density optical waveguide arrays in order to achieve high density MCM-to-MCM optical interconnections compatible with emerging MCM environments.

Plasma deposition, characterization, and photochemistry of organosilicon hydride network polymers: versatile resists for all-dry mid-deep UV photolithography

Plasma polymerization of various mono- and di-substituted organosilanes (R1R2SiH2; R1 equals alkyl, aryl and R2 equals H or alkyl) provides an effective approach to a new class of organosilicon resists useful in all dry photolithographic processing. For example, parallel plate rf plasma deposition systems may be used to deposit photosensitive films from low power discharges in methylsilane (MeSiH3) gas between 200 and 500 mTorr. Characterization by FTIR, UV-Visible, and NMR spectroscopy suggests that methylsilane undergoes predominantly dehydrogenative coupling reactions, giving Si-Si bonded network materials of general composition [(MexSiHy)n], with x and y between 0.5 and 1.0. Such films exhibit intense, near-UV absorption band edges characteristic of materials with Si-Si backbones, and undergo photo-oxidative crosslinking with bleaching when irradiated with mid-deep UV light ((lambda) < 365 nm) in the presence of oxygen.