No abstract

Large-area wafer bonding of different III-V compound semiconductors in an ultrahigh vacuum background is demonstrated. The bonding procedure, the microstructure, and the mechanical strength of the bonded GaAs/InP and GaAs/GaP interfaces were studied. The cleaning procedure and the bonding were separated in order to avoid undesired artifacts and thermal stress at the interface. First, thermally generated atomic hydrogen was employed to clean the surfaces. Then, the wafers were brought into contact below 150°C. At contact, the interface formed spontaneously over the whole wafer area without application of a mechanical load. Transmission electron microscopy showed the formation of atomically direct interfaces and misfit dislocation networks. The fracture surface energy was measured as being comparable to that of respective bulk materials. Heat treatments of the bonded GaAs/InP samples led to relaxation of the interfaces but also to the formation of nanoscopic voids in the interface plane and volume dislocations.

During the last years GaN‐technology has proven to fulfill the requirements of solid state lighting. Lighting requirements are mainly driven by brightness, operation voltage and lifetime. Brigthness is determined by internal efficiency as well as extraction efficiency whereas the ohmic losses determining the operating voltage are dominated by series resistance and contact resistance. Both, brightness and voltage, strongly depend on the device structure as well as the chip design. SiC based [1, 2] as well as Sapphire based LEDs [3] have proven their capability for high brightness devices, still suffering from various compromises such as cost, ESD‐stability, high series resistance etc. Recently OSRAM‐OS has demonstrated its newly developed product line based on the so called ThinGaN™ technology, a true thinfilm approach that overcomes most of the compromises mentioned. The technology allows highest brightness levels at lowest operating voltage, is scalable and supports all wavelengths. The devices act as true surface emitters with a lambertian emission pattern. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In microsystems technologies, frequently complex structures consisting of structured or plain silicon or other wafers have to be joined to one mechanically stable configuration. In many cases, wafer bonding, also termed fusion bonding, allows to achieve this objective. The present overview will introduce the different requirements surfaces have to fulfill for successful bonding especially in the case of silicon wafers. Special emphasis is put on understanding the atomistic reactions at the bonding interface. This understanding has allowed the development of a simple low temperature bonding approach which allows to reach high bonding energies at temperatures as low as 1508C. Implications for pressure sensors will be discussed as well as various thinning approaches and bonding of dissimilar materials. q 1999 Elsevier Science S.A. All rights reserved.

A method of large-area wafer bonding of GaAs is proposed. The bonding procedure was carried out in an ultrahigh vacuum. The wafer surfaces were cleaned at 400 and 500°C by application of atomic hydrogen produced by thermal cracking. The wafers were brought into contact either immediately after the cleaning, or at temperatures as low as 150°C, without application of a load, and successfully bonded over the whole area. High-resolution transmission electron microscopy revealed that the wafers could be directly bonded without any crystalline damage or intermediate layer. From a mechanical test, the fracture surface energy was estimated to be 0.7-1.0 J/m 2 , which is comparable to that of the bulk fracture. Furthermore, this bonding method needs no wet chemical treatment and has no limits to wafer diameter. Moreover, it is suitable for low temperature bonding.