Vladimir G. Kutchoukov

Through-wafer copper electroplating for three-dimensional interconnects

Through-wafer electrical connections are becoming increasingly important for three-dimensional integrated circuits, microelectromechanical systems packaging and radio-frequency components. In this paper, we report our current results on the formation of through-wafer metal plugs using the copper electroplating technique. Several approaches for via filling are investigated, such as filling before or after wafer thinning. Among the methods experimented, the one-side Cu plating and bottom-up filling appears to be the most suitable technique for copper filling into high aspect ratio vias. Using this method, we demonstrate the successful filling of vias with an aspect ratio of up to 7. Copper plugs as small as 20 × 20 μm2 are obtained uniformly over 4 inch Si wafers.

Through-wafer interconnect technology for silicon

This paper presents a novel method for creating through-wafer interconnects via an anisotropically etched groove in a (100)-silicon wafer. The idea is based on the realization of interconnection lines on the inclined sidewalls of the anisotropically etched grooves, which transfer the metalization to the back side of the wafer without open through-holes. The process itself is compatible with standard semiconductor technology and can be applied at the wafer level resulting in low packaging costs. All post interconnect processes are developed independently and can be added to any IC fabrication process. They are performed at the back side of the wafer at the packaging step, so during this processing the front side of the wafer can be protected from scratches and pollution. The key feature of the method presented is the coating of the anisotropically etched grooves with a polyimide and an electrodeposited photoresist. Further, methods to improve the photoresist uniformity over three-dimensional structures are discussed. Copper interconnects have been realized to show the feasibility of this through-wafer technique for front-to-back electrical interconnections. The thickness of the copper interconnects has been increased by copper electroplating to reduce their electrical resistance further and to increase their mechanical strength.

Patterning of polyimide and metal in deep trenches

Abstract This paper presents a method to spin coat and pattern photo-sensitive polyimide in deep grooves and cavities. The polyimide can be used as dielectric layer to isolate metal interconnects from each other and from the substrate. The advantage of using a polyimide base layer for the metallization is that it smoothens the corners of the grooves and cavities to facilitate a good patterning of subsequent metal layers with standard resist process. Another advantage of polyimide over oxide or nitride for passivation is that relatively thick polyimide layers can be applied to minimize the capacitive coupling of the metallization to the substrate. The coating is performed in two steps. In the first step the wafer is spin coated in a conventional way in saturated solvent atmosphere and after that the wafer is rotated again, upside down to improve the uniformity of the layer. The preliminary coating with polyimide facilitates a uniform coating with standard photoresist for patterning metal layers. Additional improvement in the corner coverage is achieved by smoothening all obtuse corners by a short etch dip of the wafer in TMAH prior to polyimide coating.

Structured illumination microscopy using extraordinary transmission through sub-wavelength hole-arrays

A new microscopy method for multi diffraction-limited spot illumination is based on extraordinary light transmission through a periodic metal grid (typical period of 600 nm) of sub-wavelength holes (150 nm). Multiple spots illuminate a fluorescently labeled sample and the emission is collected by far-field optics. Theoretical comparison with a confocal microscope reveals equivalent spot sizes and a scanning method with the advantage of multiple illumination spots. The system is used to measure the actual transmitted field with a fluorescent sample in far-field. The obtained results are consistent with the theoretical prediction and provide a proof of concept of the midfield microscope.

Toward the development of a Three-Dimensional Mid–Field Microscope

Recently, an extraordinary transmission of light through small holes (<200 nm) in a thin metallic film has been described. This phenomenon has been shown to be the result of the photon-plasmon interaction in thin films where a periodic structure (such as a set of holes) is embedded in the film. One of the extraordinary results is that the beam that passes through a hole has a very small diffraction in extreme contrast to the wide angle predicted by diffraction theory. Based on this effect, we propose here a new type of microscopy that we term mid-field microscopy. It combines an illumination of the sample through a metallic hole-array with far-field collection optics, a scanning mechanism and a CCD. When compared to other high resolution methods, what we suggest here is relatively simple because it is based on a thin metallic film with an array of nano-sized holes. Such a method can be widely used in high-resolution microscopy and provide a novel simple-to-use tool in many life-sciences laboratories. When compared to near-field scanning optical microscopy (NSOM), the suggested mid-field method provides a significant improvement. This is chiefly for three reasons: 1. The penetration depth of the microscope increases from a few nanometers to a few micrometers, hence the name mid-field microscope. 2. It allows one to measure an image faster because the image is measured through many holes in parallel rather then through a single fiber tip used in conventional near-field microscopy, and 3. It enables one to perform three-dimensional reconstruction of images due to a semi-confocal effect. We describe the physical basics of the photon-plasmon interaction that allows the coupling of light to the surface plasmons and determines the main spectral characteristics of the device. This mechanism can be ascribed due to the super-periodicity of the electron oscillations on the metallic surface engendered by the grating-like structure of the hole-array.

Nanofabrication of a gold fiducial array on specimen support for electron tomography.

Abstract Here we describe the production, using lithography and micro-engineering technologies, of patterned arrays of nanofabricated gold dots on a thin Si3N4 electron transparent layer, supported by silicon. We illustrate that the support with a patterned structure of nanosized gold can be exploited for (cryo) electron tomography application as a specimen support with predefined alignment markers. This nanogold patterned support has several advantages. The Si3N4 window provides a 50nm thin, strong and flat support with a ∼0.7mm2 large electron-beam transparent window. The nanogold pattern has a user-defined size and density, is highly regular and stable. This facilitates accurate tracking during tilt series acquisition, provides sufficient contrast for accurate alignment during the image reconstruction step and avoids an uneven lateral distribution and movement of individual fiducials. We showed that the support is suitable for electron tomography on plastic sections.

A novel concept for a mid-field microscope

When light passes through a hole smaller than the wavelength of the light, the transmission is very low and the light is diffracted. This however changes if holes are arranged in a periodic array on metal. In that case the light couples to surface plasmons; this results in enhanced transmission, spectral selection and a small angular diffraction. We develop a novel microscopic method based on a periodic hole-array, which will be used as a multiple-apertures near-field source for illuminating a biological sample while the light is collected in far-field. The measurement speed is high, due to the use of an array instead of a single source. The main advantage of this microscope originates from the low diffraction of light through a relatively thick sample with enhanced transmission. It results in the ability to measure the samples interior and 3D reconstruction can be made by semi-confocal techniques. This overcomes the major limitation of near-field methods for which only a shallow layer of the surface (~20 nm) is detectable. For our measurements we use glass coated devices. The holes are processed with a focused ion beam. The photon-plasmon coupling process is characterized as a function of the wavelength. Our experiments aim on gaining a better understanding of the transmission process. We tested the dependence of the transmitted spectrum on angle of incidence was tested as well as far-field spectral imaging measurements of the transmission in both Koehler and collimated light illumination. The results as well as the description of the microscope that we are constructing are presented.

Fabrication of nanochannels using glass to glass anodic bonding

In this work, we present a technology for fabrication of nanochannels created in glass with which bio-analysis can be performed in combination with fluorescence microscopy. The technology is based on a glass-to-glass anodic bonding process. In the bonding process, an intermediate layer (thin insulating film) is deposited on one of the two glass wafers. The channel is then defined, with one photo-patterning step, in the intermediate layer. In our approach, a 33 nm thick amorphous silicon layer (deposited by LPCVD) was used as an intermediate layer. The depth of the channel is defined during the etching of this layer.

Optical detection of electrokinetically manipulated single molecules in a nanofluidic chip

We report on the progress of a novel nanofluidic device for detecting and manipulating single molecules in solution. This paper discusses the development of an earlier proposed molecule separation method, where electrokinetic forces separate different molecules based on their masses and charges. Optical imaging using confocal microscopy is applied to perform the detection of the single molecules. Potential applications of this device will be assessed. This research aims for the high spatial and spectral resolutions, both in manipulation and detection, which can lead to molecular identification.

Novel approaches for near and far field super-resolved imaging

In this paper we start by presenting one recent development in the field of near field imaging where a lensless microscope is introduced. Its operation principle is based upon wavelength encoding of the spatial information through non periodic holes array and right after decoding the spatial information using a spectrometer. In the second part of the paper we demonstrate a remote super sensing technique allowing monitoring, from a distance, the glucose level in the blood stream of a patient by tracking the trajectory of secondary speckle patterns reflected from the skin of the wrist.