Yutaka Misawa

Encapsulated copper interconnection devices using sidewall barriers

The concept of treating interconnections as a device and designing them while keeping both materials and structures in mind is presented. An example using molybdenum and copper is demonstrated. Copper introduces new problems such as diffusion in addition to the traditional problems for interconnections such as adhesion. A new structure called a sidewall barrier is used as part of a copper interconnection. This structure can be combined with a multilayer thin film resulting in a completely encapsulated interconnection. The technique is versatile enough that almost any material including dielectrics can be used as the encapsulation material and the sidewall barrier can be either on the outside of a feature or the inside of a space. Several potential metals (Mo, TiN, W) for encapsulating copper are examined and molybdenum is chosen and used. Both sputtering and switched-bias sputtering are used to deposit molybdenum sidewall barriers followed by anisotropic etching for patterning. Electromigration measurements of bilayered copper films reveal that there are problems with TiN and tungsten barriers. Copper oxidation, stress, electromigration, hillock growth, resistivity, diffusion and adhesion are all studied.

A new multilevel interconnection system for submicrometer VLSI's using multilayered dielectrics of plasma Silicon Oxide and low-thermal-expansion polyimide

A new multilevel interconnection system for submicrometer VLSIs has been developed that utilizes multilayered dielectrics of inorganic and organic materials. This system was achieved by using the low-thermal-expansion polyimide PIQ-L100 underlying plasma CVD silicon oxide and doing an etch-back of overthick PIQ-L100. As the most important parameters of this system, the multilayered dielectric thickness and etch-back process of overthick PIQ-L100 were investigated.

Development of highly reliable Al-Si-Pd alloy interconnections for VLSI

An Al-Si-Pd alloy developed to improve the reliability of VLSI interconnections is discussed. Dry etching characteristics of the Al-Si-Pd alloy in submicrometer patterning proved to be much better than those of the Al-Si-Cu alloy used previously. Both electro- and stress-induced migration resistances of the Al-Si-Pd alloy were at least at the same level as those of the Al-Si-Cu alloy. Long-term reliability tests of resin-molded 1.3- mu m-process MOS devices using an Al-Si-Pd alloy interconnection gave satisfactory results. >

Low Thermal Expansion Polyimides and their Applications

Thermal expansion coefficients (TECs) for polyimides differ very much depending on their chemical structures. Polyimdes with a rod-like structure as their backbone chains have lower TEC values. This is attributed to restraining of thermal expansion by rod-like molecules within intermolecular spaces, analogous to glass fibers in FRPs. The development of new polyimides which can closely match TECs of inorganic materials, such as metal or Si, can eliminate problems produced by thermal stress including warping, cracking or delamination. A new multilevel interconnection system using multilayered dielectrics consisting of low thermal expansion polyimide and inorganic materials has been proposed as one future technology for submicron VLSIs. Consequently, adhesiveless, high quality flexible printed circuit boards have been developed using a polyimide with the same TEC as copper foil. Their most significant property is a high dimensional stability after heat treatments, such as in a soldering process. Furthermore, they have very high adhesion strength at elevated temperatures.

A self-aligning polysilicon electrode technology (SPEL) for future LSIs

A Self-aligning Polysilicon ELectrode technology (SPEL) is proposed to realize future high performance LSIs. This technology, based on a preferential dry etching of a highly doped polysilicon, makes it possible to halve the contact region areas of MOS and bipolar transistors as compared to conventional ones. Additionally, reduction of parasitic capacitance and resistance are demonstrated for the former transistors.

Polarization-Modulation Emission FT-IR Measurement of Thin Organic Films on Metal Surfaces

A polarization-modulation technique has been combined with Fourier transform infrared (FT-IR) spectrometry to eliminate the large background radiation which interferes with the infrared emission from thin organic films on metal surfaces. A step scan and a continuous scan interferometer which were combined with a photoelastic modulator were also studied, and the step scan system was found to be stabler and have a better S/N. The spectrum of a 12-nm perfluoropolyether film was obtained at 120°C by this system.

Diffusion of hydrogen in post‐plasma‐hydrogenated amorphous silicon film

In order to elucidate the diffusion mechanism of hydrogen in post‐plasma‐hydrogenation of amorphous silicon (a‐Si) film prepared by chemical vapor deposition (CVD), the change in the hydrogen depth profiles with plasma exposure time and with successive hydrogenation of hydrogen isotopes were measured by secondary ion mass spectrometry and infrared absorption. The post‐hydrogenation process of the CVD a‐Si film is explained by a model composed of fast diffusion (small activation energy) of atomic hydrogen through weakly bound sites such as interstitials, its capture by reactive sites such as weak SiSi bonds and dangling bonds, and an exchange between weakly bound and bonded hydrogens.

Electrical and magnetic properties of the high-Tc superconductors (Y1−xMx)Ba2Cu3Oy and Y(Ba1−xMx)2Cu3Oy (M=Mg, Ca, Sr, Ba)

The superconducting state of YBa2Cu3Oy substituted at the II a group was investigated by X-ray powder diffraction, iodometric titration, electrical resistivity and magnetization measurements. The Tc is shifted to low temperature by the substitution of Y or Ba from a heavy atom to light atom at x=0.1, and depends on the ionic radius. In the results obtained from the magnetic hysteresis loop, it is interesting that in the case of the substitution of Ca for x=0.1, the magnetization for Y is larger than that for Ba with decreasing temperature, and the magnetization in the case of Ba for Y is rapidly lowered at x=0.1.

Electrical Conduction of Silicon Nitride Films Deposited by SiH4-NH3 Reaction

The electrical conduction of silicon nitride films deposited pyrolytically on silicon substrates by the reaction of silane (SiH4) and ammonia (NH3) is caused by the Pool-Frenkel mechansim at room temperature and by the tunnel mechanism at a temperature of 208 K. When the deposition temperature is 850°C, the electrical conductivity of the films at room temperature and 208 K decreases with increasing NH3/SiH4 ratio. When the NH3/SiH4 ratio is 30, the electrical conductivity of the films at room temperature and 208K is the lowest value at a deposition temperature 90O°C and 850°C, respectively.

Dislocations and Tungsten Concentration Profiles in Tungsten-Silicon Contact Areas

Dislocation formation and impurity distributions in metal-silicon contact areas were investigated by means of cross-sectional transmission electron microscopy (TEM) images and energy-dispersive X-ray measurement. Dislocations were formed in the (111) plane in the [110] direction by annealing at 700°C when W was used as barrier metal. As the diameter of contact holes decreased, dislocations became more significant. Both W and As concentration profiles in the horizontal direction showed maxima at the edges of contact holes. The diffusion length of W in the edge areas was about twice that in the center according to depth profile. This implied that stress in edge areas increased the W diffusion coefficient by a factor of about four.