Patent Application
20090124067
Backside metallization (BSM) deposition is a process of applying a thin film of atoms, such as titanium (Ti), onto a back surface of a silicon (Si) wafer. After deposition, high tensile stresses may result in the thin film causing delamination.
The claimed subject matter will be understood more fully from the detailed description given below and from the accompanying drawings of disclosed embodiments which, however, should not be taken to limit the claimed subject matter to the specific embodiment(s) described, but are for explanation and understanding only.
Referring to
When the thin film is normally deposited and sets in flat wafer deposition, it causes a large tensile stress within the thin film. As a result, the wafer is more susceptible to die warpage and BSM delamination at the Die Prep Saw, Tape Reel Die Sort (TRDS), and Chip Attach Module (CAM) Deflux steps in the production process.
Referring to
By using a domed chuck to mount the wafer and create convex bend in the wafer, the backside of the wafer will undergo tension, and the front (active) side of the wafer will undergo compression. This will allow the Si atoms on the backside of the wafer to spread further apart during target material deposition and when the wafer is relaxed after deposition, the Si atoms will return to their normal spacing and the tensile stress in the thin film will be decreased.
As an example of a mechanism creating bend, the wafer may be held over a dome shaped table with up to a 15 μm center height. A vacuum from the chuck table makes the wafer conform to the dome shaped surface, thus forcing the wafer to hold a convex position as shown. It should be noted that any mechanism may be used to create tension in the back surface of the wafer. Non-limiting examples include dome shaped table, chuck, or other suitable tools. A chuck may be any shape and not necessarily domed, and any dimensions, as long as it increases the spacing between atoms on the surface of the wafer without damage to the wafer.
Further, wafer 48 may be fastened to the chuck 50 by a ring clip (not shown). This is simply a ring that touches the wafer perimeter and holds it down to the chuck. Other mechanisms devised to hold the wafer such as an “E chuck” or electrostatic chucks, etc. may be used.
Although reference has only been made to backside metallization, it is understood that the embodiment(s) disclosed may also apply to front side application of a second substance onto a wafer of a first substance.
Further, the scope of the embodiment(s) is not limited to Si and Ti applications, but may include other suitable materials/substances. For example, the wafer may be made of another semiconductor. Other thin films deposited on the backside of the wafer for BSM may include nickel-vanadium (NiV), gold (Au), and other suitable substances. In addition, one embodiment may include multiple layers of deposition of thin films corresponding to desired thicknesses.
Referring to
In the method, the predetermined shape may be determined by a chuck, which may be dome-shaped. The method may position the wafer on a chuck to create tension and compression. The tension on the back surface of the wafer provides additional space between adjacent atoms on the back surface of the wafer. The method may use a silicon wafer and a titanium target material for deposition, both silicon and titanium having different atomic spacing. Other substances may be used for the deposition process.
According to the method, after releasing the wafer after deposition of the thin film, the atoms of the first substance return to their original spacing before bending of the wafer. The atoms of the second substance have less spacing between them than if the thin film had been deposited without bending of the wafer.
It is appreciated that a method and apparatus to decrease thin film tensile stresses resulting from physical vapor deposition has been explained with reference to one general exemplary embodiment, and that the disclosed subject matter is not limited to the specific details given above. References in the specification made to other embodiments fall within the scope of the claimed subject matter.
Reference in the specification to “an embodiment,” “one embodiment,” “some embodiments,” or “other embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments, of the claimed subject matter. The various appearances of “an embodiment,” “one embodiment,” or “some embodiments” are not necessarily all referring to the same embodiments.
If the specification states a component, feature, structure, or characteristic “may”, “might”, or “could” be included, that particular component, feature, structure, or characteristic is not required to be included. If the specification or claim refers to “a” or “an” element, that does not mean there is only one of the element. If the specification or claims refer to “an additional” element, that does not preclude there being more than one of the additional element.
Those skilled in the art having the benefit of this disclosure will appreciate that many other variations from the foregoing description and drawings may be made within the scope of the claimed subject matter. Indeed, the invention is not limited to the details described above. Rather, it is the following claims including any amendments thereto that define such scope and variations.
