Semiconductor device manufacturing: process – Bonding of plural semiconductor substrates
Patent
1995-12-27
2000-01-11
Bowers, Charles
Semiconductor device manufacturing: process
Bonding of plural semiconductor substrates
438660, 257777, H01L 21603, H01L 2158
Patent
active
06013562&
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a process for simultaneously connecting two or more substrates having one or multiple electrical contacts using anodic bonding.
2. State of the Art
Simultaneously producing multiple electric contact points is a task that has to be mastered, particularly, in microelectronics. Several methods are used for this purpose, the best known ones are ultrasonic bonding and bump bonding. Although ultrasonic bonding is a finely perfected process, it has the disadvantage that, due to the thickness of the wire, the contact area has to be approximately 50 .mu.m.times.100 .mu.m. Another disadvantage is that a certain portion of the ultrasonic connections may be defective. In the course of time, the bond wires separate. The bondings are usually carried out automatically However, there are special components, such as, e.g., the so-called strip detectors for detecting ionizing radiation, in which up to several thousand contacts have to be manually bonded. This is an extremely complicated and expensive procedure, in which faulty connections may occur.
3. Description of the Invention
Bump bonding is a technologically sophisticated process, in which the contact points are coated with ball-shaped metals with a low melting point. During the connecting procedure, both components, the electronic chip and the substrate are placed on top of each other and heated. The contact balls alloy with the metal contacts on the substrate. This technology is not compatible with all components and is not available in many fabrications or laboratories.
The described disadvantages of both processes can be avoided by means of the invented process of simultaneously connecting multiple contact points. In this method, the known anodic bonding process used in sensor technology for connecting silicon chips to glass substrates is utilized. In this case, the clean, plane silicon surface is placed together with a clean, plane pyrex glass surface, heated to temperatures of approximately 400.degree. C., an electric field is applied and the two parts are pressed together locally. Under these conditions, close, permanent junction between the pyrex glass and the silicon chip is yielded.
This process has hitherto been employed in bonding techniques in order to, e.g., connect silicon sensor chips to a glass substrate, but not to produce electric contacts. An element of the present invention is that the process may be used to simultaneously connect a large number of electric lines. In this case, the enormous connecting power between pyrex glass and silicon, which presses the contacts together, into each other and onto each other, is utilized. The electric connection can be further improved by means of ultrasonic action or alloying prior to, during or following the bonding process. According to present knowledge, the anodic bonding works especially well between silicon and pyrex glass. For this reason, the two substrates to be connected in the bonding region preferably have to have a pyrex glass area respectively a silicon surface or a silicon oxide surface. In the most simple case, e.g., silicon chips can be directly bonded with metallized pyrex substrates. However, it is sometimes more advantageous to employ substrates of other material, which only have to be coated with pyrex glass respectively silicon only in the bonding region.
The simplest way to produce an electric connection between two substrates is if they each have a thin metal coat in the contact region. This metal coat may, e.g., as customary in fabricating semiconductors, be applied by means of a sputtering process and be photolithographically structured. If the contact areas of the substrates prepared in this manner are brought into contact, the bonding regions usually, as they lie lower, only touch if at least one of the both substrates is malleable. An air gap is created between the contact point and the bonding region, the width of this air gap being dependent on the space between the two substrates, their elasticity and under circums
REFERENCES:
patent: 5388460 (1995-02-01), Sakurai et al.
T. Anthony, "Dielectric isolation of silicon by anodic bonding", Journal of Applied Physics 58, pp. 1240-1247, Aug. 1985.
S. Ghandhi, "The theory and practice of microelectronics," John Wiley and Sons, pp. 175-178 (no month available), 1968.
Bowers Charles
Christianson Keith
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