Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
2000-08-25
2003-02-25
Dang, Trung (Department: 2823)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C438S051000, C438S054000, C438S070000
Reexamination Certificate
active
06524881
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to marking techniques for semiconductor wafers and devices. More specifically, the present invention relates to methods and apparatus using laser and other optical-energy reactive materials for marking the surface of a bare semiconductor die.
BACKGROUND OF THE INVENTION
An individual integrated circuit semiconductor die or chip is usually formed from a larger structure known as a semiconductor wafer, which is typically comprised primarily of silicon, although other materials such as gallium arsenide and indium phosphide are also sometimes used. Each semiconductor wafer has a plurality of integrated circuits arranged in rows and columns with the periphery of each integrated circuit being substantially rectangular. In response to the ever-increasing demand for smaller, higher performance semiconductor dice, wafers are typically thinned (i.e., have their cross sections reduced) by a mechanical and/or chemical grinding process. After thinning, the wafer is sawn or “diced” into rectangularly shaped discrete integrated circuits along two mutually perpendicular sets of parallel lines (streets) lying between each of the rows and columns thereof on the wafer. Hence, the separated or singulated integrated circuits are commonly referred to as semiconductor die or semiconductor dice. While semiconductor dice may carry information of the active surface thereof regarding the manufacturer, specifications, etc., such information cannot be easily read without the use of optical devices. Subsequent to the wafer-dicing process, individual semiconductor dice are commonly subjected to a marking process wherein various easily read information is placed on the backside or inactive side of the semiconductor die for purposes of corporate identity, product differentiation and counterfeit protection.
Recently, lasers have supplanted the ink stamping process as the quickest and most efficient way to mark finished bare semiconductor dice or packaged semiconductor dice. Thus, lasers are currently used to mark semiconductor dice with a manufacturer's logo, as well as alphanumeric marks and bar codes specifying the company's name, a part or serial number, or other information such as lot or die location. In particular, lasers have become especially useful in marking high production items such as bare or packaged semiconductor dice. The high speed and precision of laser marking makes their use highly desirable for high throughput automated processes.
Conventional laser marking techniques utilize a very high intensity beam of light to alter the surface of a semiconductor die directly by melting, burning, or abating the device surface directly, or by discoloration or decoloration of a laser reactive coating applied to a surface of the bare semiconductor die or packaged semiconductor die. The beam of light may be scanned over the surface of the bare semiconductor die or packaged semiconductor die in the requisite pattern, or can be directed through a mask which projects the desired inscriptions onto the desired surface of the bare semiconductor die or packaged semiconductor die. The surface or coating of the bare or packaged semiconductor die thus modified, the laser marking creates a reflectivity different from the rest of the surface of the bare or packaged semiconductor die.
Numerous methods for laser marking are known in the art. One method of laser marking involves applications where a laser beam is directed to contact the surface of a semiconductor device directly, as is illustrated in U.S. Pat. No. 5,357,077 to Tsuruta, U.S. Pat. No. 5,329,090 to Woelki et al., U.S. Pat. No. 4,945,204 to Nakamura et al., U.S. Pat. No. 4,638,144 to Latta, Jr., U.S. Pat No. 4,585,931 to Duncan et al., and U.S. Pat. No. 4,375,025 to Carlson. In these direct marking applications, the roughness of the laser-marked surface is different from that of the unmarked surface. Thus, the contrast generated by this type of laser marking is the result of several factors, including surface depressions and asymmetry in surface lines. The inscriptions created by burning the surface of the semiconductor die can therefore be read by holding the device at an angle to a light source. An additional factor that may affect the contrast is the remnants of any burnt compounds generated by the laser marking which have a different reflectivity from the original material.
Another method of laser marking makes use of various surface coatings, e.g., carbon black and zinc borate, of a different color than the underlying device material. When the laser heats the coating to the point of vaporization, a readable mark is created by virtue of the contrast in the two layers. An example of this type of marking method was described in U.S. Pat. No. 4,707,722 to Folk et al. The methods disclosed by Folk involve the deposition of an ablative coating made of electroless nickel layer, in a form highly absorptive of radiant energy, on a surface of a metal package. The ablative coating is then vaporized by a laser, allowing the shiny metal of the package to show through in the form of a mark.
A further method used in the marking of a chip uses materials known in the art to be capable of changing color when contacted by a laser beam. For example, U. S. Pat. No. 5,985,377 to Corbett, assigned to the assignee of the present invention, describes a laser reactive material, such as a material containing a B-stage epoxy with an added pigment of a desired color, that reacts with heat to form a new compound on the surface of the chip and subsequently cures to a desired color. Corbett additionally discloses use of an ink-bearing material, such as a ribbon, which transfers ink to the surface of a chip when exposed to a laser. U.S. Pat. No. 4,861,620 to Azuma discloses a laser-reactive coating formed of various pigments, incorporating mercury and other heavy metals, which will thermally decompose, and hence change colors, when heated to a predetermined temperature by a laser beam. The result is a mark having a different color from the background color of the chip package.
U.S. Pat. No. 4,753,863 to Spanjer describes a laser-markable molding compound incorporating titanium oxide and/or chromium oxide as a coloring material, polyamide, epoxy, or silicone as a plastic resin, and a filler made of silicon oxide or aluminum oxide. When exposed to a laser, the originally grey molding composition turns a bright gold color. U.S. Pat. No. 5,928,842 to Shinmoto et al. discloses a silicon and polyolefin resin-based marking composition which a laser will turn from dark brown to black.
Each of these marking methods, however, is subject to a number of drawbacks and limitations. In methods involving the laser marking of a bare die, the ideal result is that the burned portion of the surface of the semiconductor die becomes sufficiently roughened to become visibly distinguishable from the semiconductor die's intact smooth surface. However, the laser mark is not always easily recognizable due to insufficient contrast between the roughened and smooth surfaces. This is particularly the case with semiconductor dice that have been subjected to backgrinding as part of a wafer thinning process.
As a result of wafer thinning, the grinding wheel used to abrade silicon from the backside of a wafer having a plurality of locations of semiconductor dice formed thereon tends to create swirling patterns on the backside surface of the wafer and portions of swirling patterns on the backside surface of the semiconductor dice. These swirling patterns or portions thereof may be sufficiently rough to interfere with an ablative laser process—making it much more difficult to burn a distinguishing mark on the surface of the semiconductor die. As a further result of the operation of the grinding wheel, the pattern left by the grinding process varies for semiconductor dice taken from one side of the wafer as opposed to the other, thus adding to the difficulty of reading the mark. An additional problem with bare die laser marking is that the high intensi
Street Bret K.
Tandy William D.
Brewster William M.
Dang Trung
Micro)n Technology, Inc.
TraskBritt
LandOfFree
Method and apparatus for marking a bare semiconductor die does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for marking a bare semiconductor die, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for marking a bare semiconductor die will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3174611