R. McGouey

High-speed signal propagation on lossy transmission lines

This paper addresses some of the problems encountered in propagating high-speed signals on lossy transmission lines encountered in high-performance computers. A technique is described for including frequency-dependent losses, such as skin effect and dielectric dispersion, in transmission line analyses. The disjoint group of available tools is brought together, and their relevance to the propagation of high-speed pulses in digital circuit applications is explained. Guidelines are given for different interconnection technologies to indicate where the onset of severe dispersion takes place. Experimental structures have been built and tested, and this paper reports on their electrical performance and demonstrates the agreement between measured data and waveforms derived from analysis. The paper addresses the problems found on lossy lines, such as reflections, rise-time slowdown, increased delay, attenuation, and crosstalk, and suggests methods for controlling these effects in order to maintain distortion-free propagation of high-speed signals.

The use of organosilicon polymers in multilayer plasma resist processing

Abstract The unique resistance of organosilicon polymers to oxygen plasmas has led to their widespread use in multilayer resist processing. A study of their etching properties shows a correlation between their structure and etching characteristics. Often, these characteristics are obtained by means of laser interferometric techniques. Using a model of this laser signal we have identified various processes which combine to form an oxygen plasma resistant layer atop these organosilicon polymers. In particular, we have discovered that the etching characteristics of these polymers is relatively independent of the specific structure. Rather, the silicon content of these polymers plays the dominant role in providing resistance to these plasmas. For polymers having a high silicon content, the laser signal is regular and sinusoidal; for lower concentrations (

Fabrication and performance studies of multilayer polymer/metal interconnect structures for packaging applications

Multilayer copper/polyimide interconnect structures were fabricated using a reactive-ion-etching-based lift-off technique. Conductor cross-sectional area control, planarity, and a gap-free structure were made possible by the use of a novel siloxane-polyimide. The resultant structure consisted of two signal wiring layers between two ground planes with a nominal impedance of 40 Omega . Although redundant metallization processes were found to repair open lines, they resulted in an increase of the number of processing steps and could result in an increase of defects. Stud chain structures were found to survive cooling to 77 K with very little change in their characteristics, while heating of the copper interconnections to 350 degrees C in a reducing environment reduced their resistance by 3%.<<ETX>>

Factors affecting the interconnection resistance and yield in multilayer polyimide/copper structures

The use of a lift-off technique to fabricate a high-density structure consisting of multiple layers of metal/polyimide thin-film structures on a silicon substrate is described. To achieve better performance and high yield, the process design, the processing parameters, the thickness of the Cr/Cu/Cr metallurgy, and the use of suitable polyimide dielectrics, were evaluated. The plasma processing conditions, the types of passivation metals on Cu, and the use of a siloxane-polyimide as the gap-fill/etch-stop material were all shown to play a critical role in affecting the interconnection resistance and yield of the multilayer thin-film structures. By optimizing these parameters the feasibility of fabricating high-density thin-film wiring layers with good yield is demonstrated. >

ADHESION PROPERTIES OF A STRUCTURAL ETCH STOP MATERIAL FOR USE IN MULTILAYER ELECTRONIC WIRING STRUCTURES

A thermally stable copolymer of a polyimide and a dianiline terminated polydimethylsiloxane has been developed for use as a structural oxygen etch barrier material in high performance multilayer electronic wiring structures. We report on the preparation of the etch barrier material and on investigations of the etch stop and adhesion properties of this material. Studies on the effects of adhesion-promoting plasma treatments are supported by x-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS) data. Before plasma treatment, it is observed that the siloxane component segregates to the surface. After either an O 2 reactive ion etch treatment or H 2 O plasma exposure, the unusual XPS charging effects are interpreted as a surface layer containing two distinct phases: the etched polyimide fraction and a partial overlayer of a carbon containing SiO 2

Comparison of vapor and liquid phase silylation processes of photoresists

Abstract Organosilicon groups can be incorporated into photoresists, rendering them resistant to erosion by oxygen plasmas. This process, known as silylation, can be implemented using either liquid or vapor sources. A comparison of these two methods was performed using mono-,di- and trifunctional organosilicon compounds with reactive Si-N-bonds. Among the four monofunctional compounds studied, hexamethyldisilazane is about 10 times less reactive in silylation of AZ 4110 films at normal pressure (126°C) compared to tetramethyldisilazane or dimethylaminotrimethylsilane. Mixed vapors of difunctional compounds (10% of bis/dimethylamino/methylsilane) and toluene silylate resist films at 111°C at a high rate forming crosslinked materials with an increased stability in O 2 plasmas (etch rate of about 50 A/min after 2 min silylation). Trifunctional compounds (tris/dimethylamino/methylsilane) do not silylate resist films due to the formation of a crosslinked diffusion barrier on the surface. Difunctional silylating agents like bis(dimethylamino)dimethylsilane effectively silylate resist films at 80–85°C in toluene soluyion (which does not contain any diffusion promotors like NMP) without any distortions or thickness loss. The chemistry of silylation is discussed.

Factors affecting the interconnection resistance and yield in the fabrication of multilayer polyimide/metal thin film structures

The use of a lift-off technique to fabricate a high-density structure consisting of multiple layers of metal/polyimide thin film structure on a silicon substrate is described. To achieve better performance and high yield, the authors evaluated the process design, the processing parameters, and the thickness of the Cr/Cu/Cr metallurgy, along with the use of suitable polyimide dielectrics. The plasma processing conditions, the types of passivation metals on Cu, and the use of a siloxane-polyimide as the gap-fill etch-stop material were all shown to play a very critical role in affecting the interconnection resistance and yield of the multilayer thin film structures. By optimizing these parameters the feasibility of fabricating high-density thin film wiring layers with good yield is demonstrated.<<ETX>>

Silylation of resist materials using di- and polyfunctional organosilicon compounds

Abstract Different types of polyfunctional organosilicon compounds (chloro-, alkoxy-, acetoxysilanes, linear and cyclic silazanes and silylamines) were studied as silylating agents in the diffusion limited heterogeneous silylation process. It was shown that compounds with reactive silicon nitrogen bonds were most effective at silylating AZ4110 resist. Surprisingly, it was found that the higher the organosilicon compound reactivity, the lower the degree of silylation of the photoresist. One of the most effective silylating agents was found to be bis (dimethylamino)dimethylsilane (BDAMS). The chemistry of silylation of both novolak resins and 1,2,5-naphthoquinone diazo type photoactive compounds (PAC) leading to the formation of crosslinked materials is discussed. The formation of triazine derivatives was also detected. Photoresist images which were UV irradiated at 365 nm after exposure and development were found to be more amenable to silylation than those which had not.

Chemical And Physical Aspects Of Multilayer Resist Processing

A multilayer resist structure is typically composed of at least two materials, an oxygen plasma resistant layer and a planarising layer which is eroded in an oxygen based plasma. This structure is then subjected to a variety of excited and ground state species generated in the plasma. To understand the final etched profile produced by such a system, it is necessary to characterise both the chemical nature of the plasma, and its impact upon the structure subjected to the etching process. This paper will discuss the effect of the intrinsic plasma properties such as composition, density, potential and electron energy distribution upon the processes which produce etching of both the planarising and etch resistant layers. The effect of the chemical composition of organometallic etch barriers based on silicon, germanium and iron and the process by which they resist these plasmas will also be presented and compared with the properties of the planarising layers. The etching properties of the planarising layer will be shown to depend strongly upon the plasma excitation frequency.

RBS analysis of Si diffusion in photoresist during silylation

Abstract The diffusion of Si in thin films of photoresist during silylation was investigated using Rutherford backscattering spectroscopy (RBS) and the chemical reaction was studied by X-ray photoemission spectroscopy (XPS). Initially, Si diffuses very rapidly, then it slows down as the silylation time increases. Almost all the Si needed to form a stable cross-linked matrix is achieved within 5 min of silylation. With reactive ion etching (RIE) the etch rate of the silylated photoresist depends on the silylation time and whether the sample is blown dry, air-dried or rinsed immediately after the silylation process. A long silylation time results in the formation of a thin layer of SiO2 on the resist, which increases the RIE resistance.