Jan Haisma

Mold‐assisted nanolithography: A process for reliable pattern replication

A process for reproducibly and reliably realizing thin‐layer patterning having details with dimensions of 100 nm or even less is described. This process has been called mold lithography. It is a two‐step process: First, a photopolymerization‐replication step is carried out, after which pattern transfer is realized through, e.g., wet or dry etching into the substrate material. We performed a number of elementary experiments to evaluate this process. Processing conditions are given and the obtained results are discussed. The strengths of this process are its simplicity and low cost while maintaining compatibility with (standard) semiconductor‐technology processing.

Diversity and feasibility of direct bonding: a survey of a dedicated optical technology

The aim of this paper is to review almost a decade of direct-bonding activities at Philips Research including the diversity and feasibility of direct bonding. The bondability of a material is determined by its geometrical shape and mechanical, physical, and chemical surface states. Physically direct bonding provides a vacuumtight bond, which is jointless and glueless, and it permits engineering of the interfaces to be bonded. Layers can be buried, and reflective-lossless bonds between optical elements can be created. A variety of materials are investigated: (refractory) metals, a semimetal, boron, diamond, a carbide, fluorides, nitrides, oxides, and a chalcogenide. The applications that we describe relate to interface engineering, waveguiding, and the direct bonding of a fiber plate.

Contact bonding, including direct-bonding in a historical and recent context of materials science and technology, physics and chemistry historical review in a broader scope and comparative outlook

Abstract Bonding is a subject matter, which on the one hand is at least as old as written history, and on the other hand is as modern as ultrahigh-vacuum (UHV) technology. In this paper, we present the main threads of its historical evolution and modern evaluation. Bonding has always been a high-tech technology, which used to be governed by an ‘ object in view ,’ and nowadays is governed by the ‘ state-of-the-art .’ Direct-bonding, i.e. the glueless joining of two solid bodies, is more or less embodied in what we have called ‘ contact bonding ,’ i.e. a large variety of bonding and annealing techniques. Reasonably weak van der Waals attractions are transferred into strong chemical bonds by annealing. Sir Isaac Newton was the first to see direct-bonding, as testified by his famous central black spot surrounded by ‘ Newton rings ,’ established between an optical contact of a flat and a convex optical surface. Before World War II, direct-bonding was mainly applied in classical optical instruments (such as interferometers); after World War II it was primarily applied in semiconductor technology, optoelectronics, micromechanics and microelectromechanics. This leads to the need for the thinning of one of the wafers for appropriate applications, such as silicon-on-insulator (SOI). More recently, direct-bonding has been investigated for a large variety of materials, thus leading to significant upgrades in terms of flatness, smoothness and cleanliness. A polishing strategy is one consequence of this, which we will deal with in some detail. During the last decade of the 20th century, great progress was made in UHV-bonding, a technology comparable to lateral solid-phase epitaxial growth (SPEG). Bonding and crystal growing have, therefore, become united disciplines. Wafer thinning now has a new impact, for example, by dedicated ion implantation and low-temperature annealing, called ‘ smart-cut .’ A great deal of effort has been exerted to master lattice mismatch in the form of dislocations, i.e. compliant layers. The outlook of these technologies is promising, to say the least, and might one day surpass the physical limits of those of bulk monocrystalline materials such as silicon. All these subject matters are treated step-by-step in this paper. We take a phenomenological approach, sometimes alone or in combination with other disciplines, but not specifically application-directed. The paper covers pragmatic issues and also treats know-how.

SURFACE PREPARATION AND PHENOMENOLOGICAL ASPECTS OF DIRECT BONDING

Abstract Various intrinsic and extrinsic parameters that play a role in the preparation of materials for direct bonding are discussed in this paper. The constitution of a material or a wafer can be described on the basis of its shape and its mechanical, chemical and physical surface finish. Subsurface damage is also of importance with respect to direct bonding applications. Different polishing strategies have been evaluated for polishing the surfaces of different materials to a finish suitable for direct bonding. Optical elements can be polished by means of mechanical polishing; refractory metals by means of dedicated mechanical polishing; III–V compounds by means of chemical polishing; semiconductors by means of tribochemical, i.e. chemomechanical polishing; hard materials by means of enhanced tribochemical polishing; noble metals by means of organo-liquid-supported tribochemical polishing; non-noble metals by means of oxidation-stimulated polishing. After such preparative treatments the material or wafer has to be cleaned, using a suitable method. Certain aspects of the bonding phenomenon itself will also be discussed in this paper.

Transparent single-point turning of optical glass:: A phenomenological presentation

Abstract Single-point turning of optical glasses by continuous chip generation at elevated temperature is described in this paper: appropriate temperatures are ranged around the American softening point. Optimisation of tool-setting, depth of cut, local heat supply and other parameters resulted in transparent turning of a number of optical glasses by a process combining abrasive turning by single-point machining and viscous relaxation of the glass surface immediately after removal of the continuous chip

Lattice-constant-adaptable crystallographics: II. Czochralski growth from multicomponent melts of homogeneous mixed-garnet crystals

Abstract Homogeneous mixed crystals of rare-earth garnets containing Ca 2+ , Mg 2+ , Zr 4+ , Hf 4+ and Ge 4+ as guest ions have been grown from multicomponent melts. Garnet compositions that grow with distribution coefficients k eff (cat) of unity or nearly unity have been found. These crystals could be classified into mixed-crystal systems and groups. Crystal-structural parameters are used for the graphic representation of these mixed-garnet compositional series. The distribution coefficients of the cations are adjusted to unity by appropriate choice of the melt compositions. The lattice constants of the mixed garnets can be varied in the range from 1.240 up to 1.286 nm. Single crystals have been grown with dimensions between 18 and 100 mm in diameter and 50 and 120 mm in length. The crystal quality is comparable with that found in unsubstituted garnets.

Damage-free tribochemical polishing of diamond at room temperature: a finishing technology

Abstract Polished surfaces are characterized by a geometric shape and a surface finish, the latter being defined by surface roughness (smoothness) and subsurface damage. In general, mechanically polished surfaces have a high geometric precision and are optically smooth, but they are subjected to surface and subsurface damage. Tribochemical polishing gives smooth surfaces and damage-free subsurfaces, but the surface geometric precision is often poor at the submicron level. Diamond is the hardest material known, and the standard polishing technique for such hard materials is mechanical polishing, causing surface and subsurface damage. In this paper a novel method of tribochemical polishing of natural and synthetic monocrystalline diamond at room temperature is described, which gives very smooth surfaces of, at least, (100) planes, free from surface and subsurface damage within the instrumental detection limits. Such diamond surfaces are van der Waals bondable to other materials. With this novel technology only low material removal rates can be achieved. Therefore, it is mostly adapted as a finishing technique. The described polishing technology can be applied to other (hard) materials as well.

Direct bonding in patent literature

Abstract Patent literature tells its own story of technological innovations. This story is evaluated here in the case of direct bonding. It is concluded that, on a worldwide basis, direct bonding has been approached via three avenues: optical, silicon technology and silicon wafer preparation.

Surface-related phenomena in the direct bonding of silicon and fused-silica wafer pairs

Abstract Direct bonding is the result of a complex interaction between chemical, physical and mechanical properties of the surfaces to be bonded and is therefore strongly correlated with the surface state of the materials. Phenomena characteristic of the actual bonding process are (a) the formation of an initial bond area, (b) bond energy, and (c) bond-front velocity. The effects of variations in surface state on these process characteristics have been investigated for silicon, oxidized silicon and fused-silica wafer pairs. The surface bond energy of hydrophilic wafers is in the range of 0.05–0.2 J/m 2 and is largely determined by the hydrogen bonds formed. The bond energy of hydrophobic wafers is a factor of 10 smaller and is determined by Van der Waals attractive forces. The bond-front velocity is determined by the surface state and the stiffness of the wafer. Both bond energy and bond-front velocity show ageing effects.

Direct bonding of organic polymeric materials

Abstract Direct bonding of organic polymeric materials can be realized when their surfaces are prepared in such a way that they are clean, smooth and susceptible to direct-bonding. In the surface-preparation process, tribo-chemical polishing is an essential step. Polymeric materials such as polymethylmethacrylate (PMMA), polyarylate, polyimide and polycarbonate were bonded either to themselves, to another polymer or to an inorganic material such as silicon or fused silica. The surfacial bond energy of the room temperature bond is surprisingly high: 0.1–0.2 J/m 2 . Heating strengthens the direct bond; for example, for a bonded PMMA/PMMA wafer pair annealed at the glass-transition temperature of PMMA (105°C), the surfacial bond strength increases to 7.8 J/m 2 . This indicates that the bonded surfaces are fused and are interlinked by chemical bonds. When polymers are bonded to low-thermal-expansion materials such as Si and fused silica, during annealing treatments, thermal stresses can induce fracturing of the inorganic part of the bonded wafer pair. By limiting the maximum annealing temperature or the size of the bonded area, fracturing can be avoided.