Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2000-06-16
2001-07-10
Potter, Roy (Department: 2822)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S612000, C438S617000
Reexamination Certificate
active
06258704
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to microelectronic fabrication, and more particularly, to electrical contacts between a metal surface and a semiconductor surface.
BACKGROUND OF THE INVENTION
In microelectronic fabrication, it is often desirable to form an electrical contact between a metal surface and a semiconductor surface. For example, microelectromechanical systems (MEMS) such as pressure sensors, accelerometers, yaw rate sensors, and micromotors may comprise a silicon mesa that is anodically bonded to an insulating substrate, such as glass, over a conductive trace. In such a design, the silicon mesa often operates as an anchor or support for a suspended structure such as a diaphragm, or microbeam, as is well known to those skilled in the art. The silicon mesa and conductive trace form an electrical contact which is preferably of low resistance, and ohmic in nature. Further, such an electrical contact should have minimum contact potential because of the sensitivity of many MEMS devices to electric charges or fields.
However, conventional techniques for forming low resistance, ohmic contacts between semiconductor surfaces and metal surfaces are often not satisfactory because they require several additional processing steps to prepare the semiconductor surface, or they produce inconsistent yields in terms of the electrical characteristics of the resulting contacts. For instance, one technique involves heavily doping the semiconductor substrate and then depositing a metal layer directly over the doped semiconductor surface. A sintering or annealing step is then performed to cause the diffusion of the metal layer into the semiconductor. The metal deposited on the semiconductor is essentially allowed to alloy slightly in order to form a better contact between the semiconductor surface and a metal surface. This technique is disfavored because, among other things, it requires several additional processing steps in order to prepare the semiconductor surface, which not only complicates the fabrication of the MEMS device, but also may increase the cost of the MEMS device.
An alternative technique is to directly bond the semiconductor substrate or surface to another substrate or surface over a metal trace so that the metal trace is pressed against the semiconductor substrate or surface. For example, if a semiconductor substrate (typically silicon) is anodically bonded to a glass substrate over a metal trace fabricated on the glass substrate, then the pressure of the contacting surface of the semiconductor substrate against the metal trace is relied upon to form the electrical contact. While it is generally recognized that heavily doped silicon pressed against a conductive trace may make an ohmic contact, it is also recognized that surface states and thin layers of oxide or other contaminants on the silicon surface may separate the silicon surface from the metal trace. The pressure of the anodic bond is generally not well controlled, and may not break through the layers of oxide or contaminants. Consequently, the resulting electrical contacts between the silicon and the metal trace generally have resistances that vary widely, and are typically high (e.g., from 100&OHgr; to greater than 10 M&OHgr;). Further, the resulting contacts are often non-ohmic, that is, the voltage drop across the contact is not proportional to the current, but rather, has a rectifying characteristic and/or a voltage offset or potential built into the contact. As a result, the operation, reliability, and stability of the resulting MEMS devices may be adversely affected.
Therefore, an unresolved need exists in the industry for a low resistance, ohmic contact between a metal surface and a semiconductor surface without depositing a metal layer directly on the semiconductor surface and without requiring other extensive preparation of the semiconductor surface.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved metal to semiconductor contact.
It is another object of the present invention to provide an improved method for fabricating electrical contacts between a metal trace and a semiconductor surface.
It is another object of the present invention to provide a low resistance, ohmic contact between a metal trace formed on an insulating substrate and a semiconductor surface bonded to the insulating substrate over the metal trace.
These and other objects are provided according to the present invention by a conductive dimple deposited on a metal surface that is in contact with a semiconductor surface, whereby the conductive dimple is interposed between the metal surface and the semiconductor surface. Upon bonding the semiconductor surface to an insulating surface such that the metal surface is positioned therebetween, the conductive dimple is essentially crushed by the forces bonding the semiconductor surface to the insulating surface. Thus, an intimate contact between the metal surface and the semiconductor surface is created. The electrical contact formed between the metal surface and the semiconductor surface is ohmic, and of consistently low resistance. Thus, the present invention provides an advantageous technique for obtaining a low resistance, ohmic contact without having to deposit a metal layer directly on the semiconductor surface. Further, the present invention consistently produces low resistance contact, which may significantly increase product yield, reliability, and stability (i.e., reduced long-term drift) of MEMS devices incorporating such a contact.
In accordance with an aspect of the present invention, a semiconductor device comprises an insulating substrate, a conductive trace formed on the insulating substrate, and a semiconductor element which is bonded to the insulating substrate, wherein a portion of the semiconductor element is bonded to the insulating substrate opposite the conductive trace so as to overlie and be in contact with the conductive trace. In addition, the present invention provides for a dimple comprising a layer of conductive material that is interposed between the conductive trace and the portion of the semiconductor element in contact with the conductive trace. The dimple is preferably fabricated on the conductive trace prior to the bonding of the semiconductor element to the insulating substrate. The dimple is formed so as to extend a sufficient height above the surface of the insulating substrate so that the dimple deforms during the bonding process. Thus, the dimple is able to create an intimate contact between the conductive trace and the semiconductor element. Further, the dimple is preferably of a compact, regular shape such as square or circle, though it will be recognized by those skilled in the art that the dimple may take elongated or other non-regular shapes as well.
The conductive trace may comprise a layer of almost any conductor, such as gold. The dimple may comprise a layer of the same material, such as gold or other soft metal such as silver, copper, potassium, sodium, lithium, cadmium, zinc, indium, gallium, aluminum, lead, tin, bismuth, antimony, arsenic, or their alloys. The insulating layer may comprise glass. If the insulating layer comprises glass, then the semiconductor element is preferably bonded to the glass substrate by anodic bonding.
In accordance with another aspect of the present invention, a microelectronic fabrication method for forming a pressure contact between a conductive trace and a semiconductor element comprises the steps of forming the conductive trace on an insulating substrate, forming at least one conductive dimple on the conductive trace, and attaching the semiconductor element to the insulating substrate opposite the conductive trace so as to overlie and contact the conductive dimple.
In the method, the step of attaching the semiconductor element to the insulating substrate may include the step of forming a eutectic bond comprising material from the conductive dimple and from the semiconductor element. In addition, the conductive trace may be formed by forming a rec
Fredrick Kris T.
Honeywell Inc.
Potter Roy
LandOfFree
Methods for fabricating dimpled contacts for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Methods for fabricating dimpled contacts for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Methods for fabricating dimpled contacts for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2523900