Patent Application
20070251980
The present invention relates to wire bonding of semiconductor devices, and more particularly, to providing a cover gas to the bond site area of a wire bonding machine.
In the manufacturer of various semiconductor devices, wire bonding techniques are often used to connect components in the devices. For example, wire bonds (or wire loops) are often used to provide interconnection between a die and contacts on a leadframe. An exemplary conventional wire bonding operation involves (1) bonding to a first bonding location on a die (e.g., using ball bonding), (2) extending a wire toward a second bonding location on a leadframe, (3) bonding the end of the extended wire to the second bonding location, and (4) cutting the wire. In such ball bonding, an electronic flame off (i.e., EFO) wand or the like is typically used to form a “ball” (aka a free air ball) at the end of the wire.
Often, gold wire (which is substantially non-reactive with oxygen) is used in wire bonding processes; however, in certain applications, more reactive metals (e.g., copper, silver, palladium, aluminum, etc.) are used. These more reactive metals may react, for example, in the presence of oxygen and form oxides/oxidation on the wires (and/or wire ends or tails) which are undesirable for wire bonding.
In view of such potential oxidation, certain wire bonding systems include subsystems for providing a cover gas to the end of a wire during formation of the ball by the EFO wand. For example, U.S. Pat. No. 6,234,376, which is incorporated by reference in its entirety, discloses such a system.
Unfortunately, such cover gas subsystems do not protect the entire wire (or the entire duration of the wire bonding process) from potential oxidation, and as such, oxidation problems in wire looping with reactive metals still exists.
Thus, it would be desirable to provide a method and apparatus for reducing oxidation in wire bonding.
According to an exemplary embodiment of the present invention, a wire bonding machine is provided. The wire bonding machine includes (1) a bond site area for holding a semiconductor device during a wire bonding operation, and (2) a gas supply line configured to provide a gas at the bond site area from above the bond site area.
In certain exemplary embodiments of the present invention, the wire bonding machine may also include (1) an electronic flame off wand and (2) an electronic flame off gas supply line. Such an electronic flame off gas supply line may be configured to provide a gas during formation of a ball on an end of a wire via the electronic flame off wand. The gas provided by the gas supply line and the electronic flame off gas supply line may be the same type of gas, and in fact, may be provided from the same gas source.
According to another exemplary embodiment of the present invention, a method of processing a semiconductor device is provided. The method includes providing a wire bonding machine including a bond site area for holding a semiconductor device during a wire bonding operation. The method also includes supplying a gas to the bond site area from above the bond site area during the wire bonding operation.
Portions of the method of the present invention may also be embodied as an apparatus (e.g., as part of the intelligence of a wire bonding machine), or as computer program instructions on a computer readable carrier (e.g., a computer readable carrier used in connection with a wire bonding machine).
The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures:
U.S. Pat. Nos. 5,205,463, 6,062,462, and 6,156,990, as well as United States Patent Publication No. 2004/0152292, relate to wire bonding technology, and are herein incorporated by reference in their entirety.
As used herein, the term “gas supply line” refers to any structure (e.g., a gas supply tube such as tube 20 disclosed herein) configured to direct a gas (e.g., a cover gas such as nitrogen, argon, etc.) to a bond site area of a wire bonder. The term “gas supply line” is not intended to be limited to any particular configuration or design.
According to certain exemplary embodiments of the present invention, a gas (e.g., a cover gas such as a gas including nitrogen, argon) (where the gas may or may not include a reducing gas such as hydrogen) is provided in the vicinity of the bond site area of a wire bonding machine. For example, during a wire bonding operation, a constant supply of the gas may be provided at the bond site area such that during the wire bonding operation there is a reduced potential for oxidation of the wires. Depending upon the gas (and temperature) used, there may also be a reduction of oxide/oxidation already present on the wires, similar to the effect of applying a reducing gas during formation of a free air ball.
For example, during a wire bonding operation, after completing a wire loop (and prior to forming the next free air ball) a wire tail (e.g., the end portion of wire suspended from a capillary tip) may be subjected to oxygen or the like resulting in oxides forming on the wire tail. Such oxides may be undesirable for bonding, even if the wire tail is later formed into a free air ball. The present invention addresses such a situation by providing (in certain exemplary embodiments) a constant supply of cover gas in the bond site area such that the wire tail is protected from oxidation prior to formation of the next free air ball. The present invention also helps to protect against oxidation of the wire (and/or wire ends) during various other phases of the wire bonding cycle such as, for example, (1) when forming the second bond in the bond site area, (2) when lowering a formed free air ball to the bond site area, amongst others.
As will be explained in greater detail below with respect to
Referring now to
The process illustrated in
The flow of cover gas (e.g., cover gas 26) from the gas supply tube (e.g., gas supply tube 20) may be a continuous flow of cover gas during the entire wire bonding operation. Alternatively, the flow may be a controlled flow (e.g., controlled using a controller integrated with the wire bonding machine) that is provided, for example, during periods of greatest concern regarding potential oxidation.
The drawings provided herein illustrate exemplary structures (e.g., gas supply tube 20) for directing a cover gas from above the bond site area to the bond site area; however, the invention is not limited thereto. The present invention contemplates any type of structure, system or process for providing cover gas to the bond site area from above (or substantially above) the bond site area.
When the present invention is used in connection with a wire formed of a reactive metal (e.g., copper, aluminum, etc.) the cover gas is desirably non-reactive with the metal and may be reducing. For example, the cover gas may be an effectively inert gas such as nitrogen or argon. A reducing gas (e.g., hydrogen) may be added to react with any oxygen that may be present; however, the cover gas system of the present invention may be utilized to exclude air from the bond site area without the need for hydrogen in the cover gas. This is a further advantage of the present invention because of the difficulties of using large quantities of highly flammable hydrogen.
The teachings of the present invention may also be utilized in connection with non-reactive bonding wire, such as gold wire. For example, the cover gas may be utilized to provide a shield of clean gas at the bond site area, thereby providing a desirable environment for formation of gold wire loops.
Although the present invention has been described primarily with respect to cover gases such as nitrogen and argon (with or without a forming gas such as hydrogen), it is not limited thereto. Any gas may be utilized so long as it does not react undesirably with the metal used as a bonding wire.
The processing techniques of the present invention may be implemented in a number of alternative mediums. For example, the techniques can be installed on an existing computer system/server as software (a computer system used in connection with, or integrated with, a wire bonding machine). Further, the techniques may operate from a computer readable carrier (e.g., solid state memory, optical disc, magnetic disc, radio frequency carrier medium, audio frequency carrier medium, etc.) that includes computer instructions (e.g., computer program instructions) related to the wire bonding techniques.
Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.
