Abstract:
The present invention relates to a silicon material having a mark on the surface thereof and the method for making the same. The method comprises the following steps: (a) providing a silicon material; (b) providing a glass substrate; (c) putting the silicon material on the glass substrate; and (d) focusing a CO 2  laser beam on the silicon material as to form a mark on the bottom surface of the silicon material, wherein the material of the mark is silicon oxide. Whereby the cheap CO 2  laser is utilized to form the mark on the silicon material, and the mark can be erased easily by a proper chemical for recycling the silicon material.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a processing method of a silicon material, and more particularly, to a method for forming a mark on the surface of a silicon material. 
         [0003]    2. Description of the Related Art 
         [0004]    At present, laser is a marking technique widely used in the industry, and is applied to materials such as plastic, rubber, ceramics, metal, and silicon wafer. Compared with conventional manners, for example, mechanical engraving, chemical etching, screen printing, and ink printing, laser marking has the advantages of rapid production, high flexibility, and being controllable via a computer system. In addition, a prominent characteristic of laser marking is the permanence of the mark generated by a laser on the surface of a workpiece. 
         [0005]    There are many kinds of lasers and the femtosecond laser, excimer laser, or Nd:YAG laser are mostly used in silicon wafer marking. However, these lasers are generally very expensive, and the processing mechanism thereof is ablating the surface of the silicon wafer with a laser beam of high energy, which may damage the surface structure of the silicon wafer and result in many flying minute particles, i.e., the so-called “splashing fragments”. The fragments are prone to be attached to the silicon wafer, thus becoming difficult to erase. When proceeding to the subsequent device circuit process, a grip head is used to fix the edge of the silicon wafer. However, the clamping force is easy to make the residual fragments fall off and cause another splashing, which not only contaminates the process, but also severely affects the yield and quality of the product. Moreover, these lasers remove the surface of the product to form a mark, so the mark cannot be re-made, and once marked incorrectly, the product will be abandoned for uselessness, and the material cannot be recycled. 
         [0006]    Moreover, in the conventional fabrication process of semiconductor devices, the marking process is generally performed after the silicon wafer is diced into chips. As the technique is being constantly updated and the integrated circuits are becoming lighter, thinner, and smaller, the processing technique has also evolved into dicing the wafer after marking, so as to improve the efficiency of production and operation. However, as the size of the silicon wafer is getting larger, the thickness thereof stays unchanged or becomes smaller. Therefore, when the surface of the silicon wafer is ablated with a laser beam of high energy, a large amount of stress is easily accumulated on the surface of the silicon wafer, resulting in deformation and warping thereof. Though the stress can be eliminated by high temperature annealing, the basic property of the silicon wafer is greatly affected, which is disadvantageous for the subsequent production. 
         [0007]    In view of the disadvantages of using the above lasers, ROC (TW) Patent Publication No. 350797 provides a processing method for removing particles in the semiconductor industry, and particularly for removing silicon particles generated after making a mark with a laser on the chip. In the method, the wetting and catalytic effects are achieved with the hydroxyl in the aqueous ammonia, so as to oxidize the particles. ROC (TW) Patent Publication No. 434749 provides a marking method, in which the wafer mark can be recovered after a chemical-mechanical polishing process is performed on the wafer, and no silicon particles are generated during the marking. According to the method, the photoresist is exposed with a fiber optic cable, so as to form a mark on the photoresist, and a wafer mark is formed subsequently by etching with the photoresist having a mark formed thereon as a mask. ROC (TW) Patent Publication No. 359885 provides a method, in which a mark pattern on a tape is defined with a laser beam, then the tape is adhered onto a silicon wafer, then the pattern is transferred to the wafer by a wet or dry process, and the tape is finally stripped to finish making a mark on the silicon wafer. The above method can avoid causing splashing fragments. 
         [0008]    In Japanese Patent Publication No. 11-260675, a spot-shaped mark is fabricated on a silicon wafer with a laser, and a layer of transparent thin film is formed thereon. When a laser beam passes through the transparent thin film to make the spot-shaped mark regionally melt and deformed, a plurality of spot-shaped marks can be formed. This method can prevent the splashing fragments generated during the laser processing from being attached to the silicon wafer, and the definition and visibility are ensured by the shape of these spot-shaped marks. 
         [0009]    ROC (TW) Patent Publication No. I233197 provides a chip scale mark and a marking method of the same. According to the method, when a laser beam ablates the surface of a silicon wafer, the chip size mark is used to stably keep the laser system and the marking distance between the wafers by removing the wafer warp on the wafer support. ROC (TW) Patent Publication No. 200538304 provides a method for making a mark by forming an interference fringe on a body to be marked with a laser beam. 
         [0010]    Therefore, it is necessary to provide a method for forming a mark on the surface of a silicon material to solve the above problems. 
       SUMMARY OF THE INVENTION 
       [0011]    An objective of the present invention is to provide a method for forming a mark on the surface of a silicon material. The method includes the following steps: (a) providing a silicon material, which has a top surface and a bottom surface; (b) providing a glass substrate, which has a top surface; (c) disposing the bottom surface of the silicon material on the top surface of the glass substrate; and (d) focusing a CO 2  laser on the silicon material, so as to form a mark on the bottom surface of the silicon material. The material of the mark is silicon oxide. 
         [0012]    Another objective of the present invention is to provide a method for forming a mark on the surface of a silicon material. The method includes the following steps: (a) providing a silicon material, which has a top surface and a bottom surface; (b) providing a substrate, which has a top surface; (c) forming a metal film on the top surface of the substrate; (d) disposing the bottom surface of the silicon material on the top surface of the substrate; and (e) focusing a CO 2  laser on the silicon material, so as to form a mark on the bottom surface of the silicon material. The material of the mark is metal and oxide. 
         [0013]    In the present invention, the property that the silicon material fails to absorb the CO 2  laser with a light wavelength of 10.6 μm can be successfully changed by attaching a glass substrate or a substrate having a metal film coated glass substrate to the silicon material, thereby achieving the purpose of making a mark. The CO 2  laser is the cheapest laser among various lasers, so the present invention provides a method for marking the front and back sides of the wafer in a rapid and simple way, which costs less, consumes less energy, and has high reliability and quality. Moreover, stress can be avoided by utilizing low energy means of marking, such that the silicon material will not be deformed or warped. Further, the present invention does not utilize the laser beam in such a way of ablation, therefore the wafer will not be damaged after the processing, and no splashing fragments and dusts will be generated, thereby abating pollution and improving yield. Besides, it is not necessary to use a mask, and the photolithography process may not be affected, such that the capacity is improved. Additionally, when marked incorrectly with other lasers, the surface of the wafer product is usually damaged. However, in the present invention, a CO 2  laser is employed, and a common chemical can be used to erase the incorrect mark so that the silicon material may be recycled. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic diagram of a first embodiment of a method for forming a mark on the surface of a silicon material according to the present invention; 
           [0015]      FIG. 2  is a photograph of the silicon material having a mark on the surface thereof formed according to the first embodiment of the present invention, in which the mark is constituted by letters; 
           [0016]      FIG. 3  is a photograph of the silicon material having a mark on the surface thereof formed according to the first embodiment of the present invention, in which the mark is constituted by totems and random codes; 
           [0017]      FIG. 4  is a schematic diagram of a second embodiment of a method for forming a mark on the surface of a silicon material according to the present invention; and 
           [0018]      FIG. 5  is a schematic diagram of a third embodiment of a method for forming a mark on the surface of a silicon material according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]      FIG. 1  is a schematic diagram of a method for forming a mark on the surface of a silicon material according to a first embodiment of the present invention. In this embodiment, firstly, a silicon material  11  is provided, which has a top surface  111  and a bottom surface  112 . In this embodiment, the silicon material  11  is a silicon wafer, which can be pure silicon or have a multi-layered thin film. Additionally, the silicon material  11  can also be a silicon chip. In this embodiment, the silicon wafer is disposed with a polished surface facing upward (i.e., the top surface  111  of the silicon wafer is a polished surface) or with a rough surface facing upward (i.e., the bottom surface  112  of the silicon wafer is a polished surface). Alternatively, the silicon wafer can be a double-side polished silicon wafer (i.e., the top surface  111  and the bottom surface  112  of the silicon wafer both are polished surfaces). Preferably, the bottom surface  112  of the silicon wafer is a polished surface. 
         [0020]    Next, a glass substrate  12  is provided, which has a top surface  121 . Afterward, the bottom surface  112  of the silicon material  11  is disposed on the top surface  121  of the glass substrate  12 , and the top surface  121  of the glass substrate  12  is closely attached to the bottom surface  112  of the silicon material  11 . In this embodiment, a clamp (not shown) is used to clamp the glass substrate  12  and the silicon material  11 , such that the top surface  121  of the glass substrate  12  is closely attached to the bottom surface  112  of the silicon material  11 . 
         [0021]    Next, the glass substrate  12  and the silicon material  11  are disposed on a support platform  18 . 
         [0022]    After that, a CO 2  laser  14  is provided by a CO 2  laser generator  13 . Finally, the CO 2  laser  14  is focused on the silicon material  11  through a focusing mechanism having a reflecting mirror  15  and a focusing lens  16 , so as to form a mark on the bottom surface  112  of the silicon material  11 , in which the CO 2  laser  14  can be focused on the interior, the top surface  111 , or the bottom surface  112  of the silicon material  11 . The focusing position of the CO 2  laser  14  can be adjusted with the reflecting mirror  15  and the focusing lens  16 , or controlled by adjusting the direction of Z-axis of the support platform  18 , and the two methods for adjusting focusing position can be integrated. In this embodiment, the CO 2  laser  14  is focused on the top surface  111  of the silicon material  11 . By adjusting appropriate laser processing parameters, such as, the energy of the CO 2  laser source, scan times (about less than five times), and together by scanning the laser spot or moving the support platform  18 , a desired mark shape can be achieved. 
         [0023]    In this embodiment, the mark is not a curved groove, but a silicon oxide formed by growing or depositing, which is formed by the re-solidification of the oxidized or melt glass silicon oxide generated by the silicon material  11  under the temperature of the CO 2  laser  14 . Moreover, the mark can be of any shape, such as a numeral, a letter, or a totem. Therefore, if a part or the whole of the mark is undesired or incorrect, a cleaning chemical can be used to directly erase the mark. The chemical cleaning agent can be hydrofluoric acid (HF), buffered oxide etching (BOE), or a general chemical capable of erasing oxide. 
         [0024]    In the present invention, the silicon material  11  is processed by the CO 2  laser  14 . Under a normal condition, the CO 2  laser  14  that has a light wavelength of 10.6 μm cannot process the silicon material  11  that does not fall in the absorption band thereof. Therefore, in this embodiment, the property that the silicon material  11  does not absorb the CO 2  laser with a light wavelength of 10.6 μm can be successfully changed by attaching the glass substrate  12  to the silicon material  11 , thereby achieving the purpose of marking. The present invention has the following advantages: 1. the CO 2  laser is the cheapest laser among various lasers; 2. the present invention provides a method for marking the front and back sides of the water in a rapid and simple way, which costs less, consumes less energy, and has high reliability and quality; 3. stress can be avoided by utilizing low energy, such that the silicon material  11  will not be deformed or warped; 4. the present invention does not adopt the laser beam in the manner of ablation, such that the wafer will not be damaged after the processing, and no splashing fragments and dusts will be generated, thereby abating pollution and improving the yield; 5. it is not necessary to use a mask, and the photolithography process may not be affected, such that the capacity is improved; 6. the silicon material  11  can be a silicon wafer of pure silicon, and can also be a silicon wafer with a multi-layered thin film; 7. when marked incorrectly, as other lasers are used in the conventional art, the incorrect mark cannot be erased from the surface of the damaged product (for example, a groove is resulted). However, in the present invention, a CO 2  laser is used to generate a mark of silicon oxide, and a common chemical can be used to erase the incorrect mark for recycling the silicon material  11 . 
         [0025]    The processing condition of this embodiment is: the thicknesses of the silicon material  11  and the glass substrate  12  are both 500 μm; the power of the CO 2  laser  14  is 21 W and the focus point thereof is set on the top surface  111  of the silicon material  11 ; a mark is formed by directly photo-deposition once at a processing speed of 5 mm/sec, and the processing result is shown in  FIG. 2 . 
         [0026]      FIG. 2  is a photograph of the silicon material having a mark on the surface thereof formed according to the first embodiment of the present invention. The silicon material having a mark according to the present invention includes a silicon material  11  and a mark  17 . The silicon material  11  has a surface  112  (i.e., the bottom surface  112  in  FIG. 1 ). In this embodiment, the surface  112  is a polished surface, and it is to be understood that the surface  112  can also be a rough surface. The mark  17  is located on the surface  112  of the silicon material  11 , and the mark  17  is silicon oxide, which can be constituted by numerals, letters, or totems. In this embodiment, the silicon material  11  is a silicon wafer or a silicon chip, which can be pure silicon or have a multi-layered thin film. In this embodiment, the mark  17  is constituted by letters of “NCKU.” In other applications, the mark is other totems, or random codes, as shown in  FIG. 3 . 
         [0027]      FIG. 4  is a schematic diagram of a method for forming a mark on the surface of a silicon material according to a second embodiment of the present invention. In this embodiment, firstly, a silicon material  21  is provided, which has a top surface  211  and a bottom surface  212 . In this embodiment, the silicon material  21  is a silicon wafer, which can be pure silicon or have a multi-layered thin film. Additionally, the silicon material  21 , can also be a silicon chip. In this embodiment, the silicon wafer is disposed with a polished surface facing upward (i.e., the top surface  211  of the silicon wafer is a polished surface) or a rough surface facing upward (i.e., the bottom surface  212  of the silicon wafer is a polished surface). Alternatively, the silicon wafer can be a double-side polished silicon wafer (i.e., the top surface  211  and the bottom surface  212  of the silicon wafer both are polished surfaces). Preferably, the bottom surface  212  of the silicon wafer is a polished surface. 
         [0028]    Next, a glass substrate  22  is provided, which has a top surface  221 . Afterward, a metal film  27  is formed on the top surface  221  of the glass substrate  22 . Preferably, the metal film  27  is formed on the top surface  221  of the glass substrate  22  by coating, and the material of the metal film  27  can be selected from a group consisting of aluminum, titanium, chromium, tantalum, nickel, iron, cobalt, vanadium, tungsten, zirconium, zinc, copper, silver, and gold. The thickness of the metal film  27  is between 10-1000 nm. Preferably, the material of the metal film  27  is aluminum, titanium, chromium, tantalum, nickel, iron, cobalt, vanadium, tungsten, zirconium or zinc, and the thickness thereof is between 30-80 nm. 
         [0029]    Afterward, the bottom surface  212  of the silicon material  21  is disposed on the metal film  27  coated glass substrate  22 . And the top surface  221  of the glass substrate  22 , the metal film  27 , and the bottom surface  212  of the silicon material  22  are closely attached. In this embodiment, a clamp (not shown) is used to clamp the glass substrate  22  and the silicon material  21 . 
         [0030]    Next, the glass substrate  22  and the silicon material  21  are disposed on a support platform  28 . 
         [0031]    Afterward, a CO 2  laser  24  is provided by a CO 2  laser generator  23 . Finally, the CO 2  laser  24  is focused on the silicon material  21  through a focusing mechanism having a reflecting mirror  25  and a focusing lens  26 , so as to form a mark on the bottom surface  211  of the silicon material  21 , in which the CO 2  laser  24  can be focused on the interior, the top surface  211 , or the bottom surface  212  of the silicon material  21 . In this embodiment, the CO 2  laser  24  is focused on the top surface  211  of the silicon material  21 . In this embodiment, the mark is not a curved groove, but a metal and oxide formed by growing or depositing, which are formed by utilizing the temperature of the CO 2  laser to melt the metal film  27  and the top surface  221  of the glass substrate  22 , and re-solidifying the same, or to oxidize the metal film  27  with the silicon material  21 . Moreover, the mark can be of any shape, such as a numeral, a letter, or a totem. Therefore, if a part or the whole of the mark is undesired or incorrect, an appropriate cleaning chemical can be used to directly erase the mark. The chemical can be HF, BOE, or a general chemical capable of erasing metal and oxide. 
         [0032]      FIG. 5 , is a schematic diagram of a method for forming a mark on the surface of a silicon material according to a third embodiment of the present invention. In this embodiment, firstly, a silicon material  31  is provided, which has a top surface  311  and a bottom surface  312 . In this embodiment, the silicon material  31  is a silicon wafer, which can be pure silicon or have a multi-layered thin film. Additionally, the silicon material  31  can also be a silicon chip. In this embodiment, the silicon wafer is disposed with a polished surface facing upward (i.e., the top surface  311  of the silicon wafer is a polished surface) or with a rough surface facing upward (i.e., the bottom surface  312  of the silicon wafer is a polished surface). Alternatively, the silicon wafer can be a double-side polished silicon wafer (i.e., the top surface  311  and the bottom surface  312  of the silicon wafer both are polished surfaces). Preferably, the bottom surface  312  of the silicon wafer is a polished surface. 
         [0033]    Next, a substrate  32  is provided, which has a top surface  321 , and the material thereof is a material having low thermal conductivity except glass; for example, metal oxide, ceramics, or polymethyl methacrylate (PMMA). And then, a metal film  37  is formed on the top surface  321  of the substrate  32 . Preferably, the metal film  37  is formed on the top surface  321  of the substrate  32  by coating. The material of the metal film  37  can be selected from a group consisting of aluminum, titanium, chromium, tantalum, nickel, iron, cobalt, vanadium, tungsten, zirconium, zinc, copper, silver, and gold, and the thickness of the metal film  37  is between 10-1000 nm. Preferably, the material of the metal film  37  is aluminum, titanium, chromium, tantalum, nickel, iron, cobalt, vanadium, tungsten, zirconium or zinc, and the thickness thereof is between 30-80 nm. 
         [0034]    Next, the bottom surface  312  of the silicon material  31  is disposed on the metal film  37  of the top surface  321  of the substrate  32 . And the top surface  321  of the substrate  32 , the metal film  37 , and the bottom surface  312  of the silicon material  31  are closely attached. In this embodiment, a clamp (not shown) is used to clamp the glass substrate  32  and the silicon material  31 . 
         [0035]    Afterward, the glass substrate  32  and the silicon material  31  are disposed on a support platform  38 . 
         [0036]    Afterward, a CO 2  laser  34  is provided by a CO 2  laser generator  33 . Finally, the CO 2  laser  34  is focused on the silicon material  31  through a focusing mechanism having a reflecting mirror  35  and a focusing lens  36 , so as to form a mark on the bottom surface  312  of the silicon material  31 , in which the CO 2  laser  34  can be focused on the interior, the top surface  311 , or the bottom surface  312  of the silicon material  31 . In this embodiment, the CO 2  laser  34  is focused on the top surface  311  of the silicon material  31 . In this embodiment, the mark is not a curved groove, but a metal and oxide are formed by growing or depositing, which are formed by utilizing the temperature of the CO 2  laser  34  to melt the metal film  37  and the top surface  321  of the glass substrate  32 , and re-solidifying the same, or to oxidize the metal film  37  with the silicon material  31 . Moreover, the mark can be of any shape, such as a numeral, a letter, or a totem. Therefore, if a part or the whole of the mark is undesired or incorrect, an appropriate cleaning chemical can be used to directly erase the mark. The chemical can be HF, BOE, or a general chemical capable of erasing metal and oxide. 
         [0037]    While several embodiments of the present invention have been illustrated and described, various modifications and improvements can be made by those skilled in the art. The embodiments of the present invention are therefore described in an illustrative but not restrictive sense. It is intended that the present invention should not be limited to the particular forms as illustrated, and that all modifications which maintain the spirit and scope of the present invention are within the scope as defined in the appended claims.