Electric heating – Metal heating – By arc
Reexamination Certificate
2000-05-23
2004-08-10
Edmondson, L. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121690, C219S121730, C219S121850, C347S110000, C347S224000, C430S322000
Reexamination Certificate
active
06774340
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the shape of a dot mark and a method of forming the dot mark which is formed for product management or security in a specified position on the surface and the like of an item to be marked such as a semiconductor wafer, in a minute area on a scribe line, a rear surface of a wafer, a peripheral surface of a wafer, or an inner surface of a V-notch, a glass substrate such as a liquid crystal substrate, an electrode (pad) such as a bare chip, the surface of an IC, the rear surface of an IC, various ceramic products, and a lead portion of an IC. More specifically, the present invention relates to the shape of a dot mark of a small size having particular shape which secures optical visibility, and a method of forming the dot mark.
2. Description of the Related Art
For example, in semiconductor manufacturing processes, it is necessary to set various and strict manufacturing parameters for each process. In order to control the parameters, a mark such as numeral, character, or bar code is displayed by dots on the surface of a part of a semiconductor wafer. The number of manufacturing processes of a semiconductor is 100 or more and, moreover, a number of device forming processes and planarization processes are performed in each process. The processes include, for example, resist application, projection of a pattern onto a resist in a reducing manner, resist development, and planarization of various films such as an insulating film and a metal film for filling a gap which occurs by copper wiring or the like.
On the other hand, the mark made by dots is generally formed by irradiating the surface of a part of a semiconductor wafer with a continuous pulse laser beam through an optical system. The marking is not limited to once. In order to show historical characteristics of manufacturing processes, minimum historical data required in the manufacturing processes is usually marked. Since the marking area on the semiconductor wafer is, however, limited to an extremely narrow region, the size of the dot and the number of dots to be marked are accordingly limited. The marking area, the size of a dot, and the number of dots are specified by the SEMI standard and the like.
As disclosed in, for example, Japanese Laid-Open Patent Publication No. 2-299216, information of a semiconductor wafer on which the dot marking is performed is read as a change in reflectance of an emitted laser beam of an He-Ne laser or a change in vibration of a heat wave of an ordinary laser beam. On the basis of the read information, various manufacturing parameters in subsequent manufacturing processes are set. When the information is not accurately read and is read erroneously, therefore, all of semiconductor wafers become defective except for a coincidence. Most of the causes of the defective reading relates to an unclear mark formed by the dot marking. One of factors of the unclearness is the shape of a dot as an element of the mark.
It is generally considered that the influence by the depth of a dot is large. As disclosed in, for example, Japanese Laid-Open Patent Publication No. 60-37716, a dot is usually formed by melting and removing a part of the semiconductor wafer in a spot state with irradiation of a laser beam of a large energy so as to obtain a required dot depth. In, this case, the melted and removed portion is piled around the dot or scattered and adhered to the peripheral portion of the dot, and it may prevent device formation and exerts a large influence on the quality. Further, in case of dot marking performed by a YAG laser, due to the particularity of the YAG laser or the Q switch operation, a fluctuation is apt to occur in a laser output and a variation occurs in the depth or the size of a dot.
In order to solve the problems, for example, as disclosed in Japanese Laid-Open Patent Publication No. 59-84515 and 2-205281, the same point is repeatedly irradiated with a pulse laser beam of a relatively small energy. In the former Publication, in order to form a dot mark, while sequentially reducing the dot diameter pulse by pulse in order, the same point is repeatedly irradiated with a laser beam, thereby forming a deep dot. In the latter Publication, the frequency of a laser pulse of the first time is set to 1 kHz or lower and the frequency of a laser pulse subsequently emitted is set to a high repetitive frequency of 2 to 5 kHz to thereby form a dot having a depth of 0.5 to 1.0 &mgr;m or 1.0 to 1.5 &mgr;m.
On the other hand, since generation of dusts can not be avoided by the marking method as described above, a laser marking method which provides excellent visibility and suppresses the generation of dusts has been proposed in, for example, Japanese Laid-Open Patent Publication No. 10-4040. The disclosure of the publication relates to a laser marking method of forming a dot mark by projecting a liquid crystal mask pattern onto the surface of a semiconductor material by emitting a pulse laser beam, in which the energy density is set to 18 to 40 J/cm
2
, the pulse width is selected within a range from0.05 to 0.40 ms, the surface of the semiconductor material is irradiated with a pulse laser beam, and a number of small protrusions are created in the laser irradiation region in a process of melting and recrystallizing the surface of the semiconductor material.
According to the marking method, by the irradiation of the laser beam which is emitted on a pixel unit basis, a number of small protrusions each having the height of about 1 &mgr;m or less and the diameter of 0.5 to 1. 0 &mgr;m are formed on the surface of an article to be marked. The interval between neighboring protrusions is about 1.5 to 2.5 &mgr;m and the density of the protrusions is 1.6 to 4.5×10
7
pieces/cm
2
. The aggregation of a number of small protrusions are handled as a single dot mark which is read by utilizing an irregular reflection of light, and in case of such small protrusions, the generation of dusts in the event of the formation can be suppressed.
It is certain that one of the causes of unclearness of the dot mark having a hole shape (hereinbelow, the clearness of the dot is called “visibility”) relates to the depth of the dot. Even when the dot is formed deep enough, however, in the case where the diameter of the opening is large, for example, when a laser beam strong enough to obtain a required depth is emitted, the energy density has generally a Gaussian distribution. The dot has therefore a smooth curved surface which is a gentle slope as a whole, so that a case where the difference between the dot and the peripheral area is not easily discriminated by the reading means as described above occurs. In the above publication of Japanese Laid-Open Patent Publication No. 2-205281, although the dot depth is specifically described as 0.5 to 1.0 &mgr;m or 1.0 to 1.5 &mgr;m, the diameter of the dot is not described at all, and the shape of the dot is merely described as a Gaussian shape.
In the disclosure of Japanese Laid-Open Patent Publication No. 59-84515, since it is described that the diameter of the dot opening of the first time is 100 to 200 &mgr;m and the depth is 1 &mgr;m or less and, specifically, the laser beam is emitted four times, the depth of the dot in this case is at most 3 to 4 &mgr;m. In the drawings of the publication, the shape of the dot formed at a time is similar to the Gaussian shape.
It can be therefore considered that dots each having a required depth, whose sizes are uniform to a certain degree are formed by any of the marking methods disclosed in the above publications. The shape of the formed dot is, however, like a conventional shape and the diameter with respect to the depth is extremely large. Thus the visibility still lacks certainty. Since the reduction in size (diameter) of the dot to be formed is not disclosed, the disclosure does not intended to reduce the conventional dimension of 50 to 150 &mgr;m. The numerical values at the present time point which are specified by, for instance, the SEMI standard are simply
Chiba Teiichirou
Komura Ryuusuke
Bell Boyd & Lloyd LLC
Edmondson L.
Komatsu Limited
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