Active solid-state devices (e.g. – transistors – solid-state diode – Miscellaneous
Reexamination Certificate
2000-10-13
2002-08-20
Sherry, Michael (Department: 2829)
Active solid-state devices (e.g., transistors, solid-state diode
Miscellaneous
Reexamination Certificate
active
06437454
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor base material having a dot mark employed for processing history, product management and the like in a manufacturing process of a semiconductor wafer or a semiconductor device. More particularly, the present invention relates to a semiconductor base material having a dot mark formed in such a region that least influence on subsequent reading precision in a process for manufacturing a semiconductor wafer and a semiconductor device and is free from influence on electric characteristics of the wafer itself, the dot mark having a desired amount of information allocated therein and a fine, specific and readable shape by means of laser irradiation.
2. Description of the Related Art
In a semiconductor manufacturing process, for example, it is required to set various and strict manufacturing conditions in each step. In order to manage these conditions, a mark consisting of numeric, characters, bar codes or the like is dot displayed on a partial surface of a semiconductor wafer. Meanwhile, there are a hundred or more steps of manufacturing a semiconductor, and moreover, a number of element-forming processes or flattening processes are performed in each step. These processes include, for example, resist application, reductive projection of a pattern onto a resist, resist developing, and flattening by forming various films such as insulation film or metal film for embedding a gap generated by copper wires or the like.
On the other hand, the foregoing dot shaped mark is generally formed by irradiating a partial surface of a semiconductor wafer with continuous pulse laser beam via an optical system. Moreover, marking for that purpose is not limited to once, but the required minimum of history data is often marked in each manufacturing process in order to recognize the history characteristics of each manufacturing process. However, the marking region in the semiconductor wafer is limited to a very small area. Thus, the dot size and number of dots to be marked are limited, and the marking region, dot size, the number of dots are specified in accordance with the SEMI specification and the like.
In a dot marked semiconductor wafer, as disclosed in Japanese Patent Laid-open Publication No. 2-299216, for example, a change in reflection factor cause by He-Ne laser beam irradiation or a change in thermal wave vibration of general laser beam is read. Based on the thus read information, various manufacturing conditions in the subsequent manufacturing steps are set. Therefore, in a case where the aforementioned reading is not made accurately, and incorrect information is read, all items are found to be faulty except that they are correctly read incidentally. A majority of causes of such reading fault is caused by unclearness of the mark formed by dot marking. One of the factors of this blurring is attributed to the shape of a dot forming a mark.
In general, mark reading is greatly influenced by dot depth. In order to obtain a required dot depth, as disclosed in Japanese Patent Laid-open Publication No. 60-37716, for example, part of a semiconductor wafer is generally fused and removed in a spot shape by laser beam irradiation with one large energy, thereby forming a dot. In this case, the thus fused and removed object is deposited high in the peripheral portion of the dot. Or, the fused and removed object is scattered to adhere to the peripheral portion of the dot, so that it makes it impossible to form an element and degrade a quality of the product. Further, in a case of YAG laser dot marking, variation is prone to occur in laser output due to specificity of the YAG laser or its Q switch operation, so that deviation in the dot depth or size occurs.
In order to eliminate such fault, according to Japanese Patent Laid-open Publication No. 59-84515 and Japanese Patent Laid-open Publication No. 2-205281, pulse laser beam with comparatively small energy is irradiated at the same point so as to be overlapped. In the former publication, the dot diameter is reduced sequentially in each pulse in forming one dot mark, and the laser beam is irradiated at the same point several times so as to be overlapped. Then, while the dot hole diameter is reduced sequentially, a deep dot is formed. In the latter publication, the first laser pulse irradiation is set at a frequency of 1 KHz or less, and a frequency of the subsequently irradiated laser pulse is set at a high repetition of 2 to 5 KHz, whereby a dot of 0.5 to 1.0 &mgr;m or 1.0 to 1.5 &mgr;m in depth is formed.
On the other hand, according to the aforementioned marking methods, an occurrence of dust cannot be eliminated. Therefore, a laser marking method having a superior visibility and less occurrence of dust is proposed in Japanese Patent Laid-open Publication No 10-4040, for example. This publication discloses a laser marking method irradiating pulse laser beam, thereby projecting a liquid crystal mask pattern onto a semiconductor material surface to making a dot mark, wherein the energy density is set to be 18 to 40 J/cm
2
; the pulse width is set to be in a range of 0.05 to 0.40 ms; pulse laser beam is irradiated to a semiconductor material surface; and a number of fine projections are generated in a laser irradiation region in a process in which the semiconductor material surface is fused and re-crystallized.
According to this marking method, a number of fine projections of substantially 1 &mgr;m or less in height, 0.5 to 1.0 &mgr;m in diameter, substantially 1.5 to 2.5 &mgr;m in mutual interval, and 1.6 to 4.5×10
7
pieces/cm
2
in density are formed on a surface of a object to be marked by laser beam irradiation passing through a unit of one pixel. Due to random light reflection caused by such a large number of fine projections, a dot mark formed has superior visibility, and moreover, an occurrence of dust can be prevented during the marking.
It is evident that one of the causes for the unclearness (herein, referred to as visibility) in reading a dot lies in its depth as mentioned above. Even if a dot depth is made to be deep, in a case where a diameter of an opening of the dot is large, when sufficient laser beam is irradiated in order to obtain a required depth, the dot has a smoothly curved face consisting of a gentle inclined face as a whole because the energy density is generally defined in a Gaussian distribution. Therefore, a difference from the periphery of the dot cannot be discriminated by the aforementioned reading means. The foregoing Japanese Patent Laid-open Publication No. 2-205281 specifically describes that the dot depth is 0.5 to 1.0 &mgr;m or 1.0 to 1.5 &mgr;m as described above. This publication fails to describe a diameter of the dot, and merely describes that the dot shape is a Gaussian shape.
In addition, the above Japanese Patent Laid-open Publication No. 59-84515 discloses that the opening diameter of a first dot is 100 to 200 &mgr;m while its depth is I am or less. Specifically, this publication describes that laser beam irradiation are made four times. In this case, the dot depth is at most 3 to 4 &mgr;m. In addition, from the accompanying drawings of the publication, the dot shape formed at the first time is similar to a Gaussian shape.
Therefore, it can be considered that a dot with a required depth and a uniform size to a certain degree can be formed according to these marking methods as disclosed in these publications. However, the formed dot shape is close to a conventional shape, and its diameter is large with respect to its depth. Thus, it is still lack of visibility. Further, remarkable disclosure is not made in that the size (diameter) of the formed dot is made to be fine. Therefore, 50 to 150 &mgr;m that is a conventional size has not yet been changed by these prior inventions. Thus, it is merely defined based on a value as specified in accordance with the SEMI specification or the like at the present time, so that a significant increase cannot be substantially expected with respect to the number of dots and th
Chiba Teiichirou
Komura Ryusuke
Mori Akira
Bell Boyd & Lloyd LLC
Komatsu Limited
Pert Evan
Sherry Michael
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