1. Field of the Invention
This invention relates to a method for producing a laser-marked semiconductor wafer wherein laser marks are formed in the vicinity of a notch on the wafer.
2. Description of the Related Art
As an example of the method for producing a laser-marked semiconductor wafer by forming laser marks in the vicinity of a notch on the wafer, there is known a production method wherein a slicing step of cutting out a disc-shaped wafer from a single crystal ingot and a lapping step of making uniform a thickness of the thus obtained disc-shaped wafer are conducted, and thereafter laser marking is applied to the surface of the wafer in a state that a lapping powder layer remains on the surface of the wafer, and then the wafer is subjected to a cleaning with an alkaline aqueous solution for removing splattered particles generated by the laser marking together with the lapping powder layer (e.g., see JP-A-2006-186173).
In the above conventional method, the splattered particles and the like to be removed, which are generated by the laser marking, are removed together with the lapping powder layer by cleaning with the alkaline aqueous solution. After the cleaning with the alkaline aqueous solution, polishing is carried out with a polishing solution containing abrasive grains to prepare a final semiconductor wafer. In this case, a semiconductor wafer having a good flatness even at laser-marked places can be obtained since no influence of the splattered particles generated by the laser marking is confirmed at all.
However, in further inspections on the method for producing a semiconductor wafer, it has been found that when polishing with a polishing solution containing no abrasive grain is conducted instead of the polishing with the polishing solution containing abrasive grains after the laser marking and cleaning with the alkaline aqueous solution, there is caused a problem of retaining the splattered particles and the like generated by the laser marking, which is out of question in the polishing with the polishing solution containing abrasive grains. In particular, there are caused influences based on minute and uneven elevated portions formed in the periphery of the print site by the laser marking, welding of Si splattered particles generated during the printing and the like.
It is, therefore, an object of the invention to advantageously solve the above problems and to provide a method for producing a laser-marked semiconductor wafer in which the deterioration of flatness in the vicinity of print sites can be prevented by eradicating influences based on minute and uneven elevated portions formed in the periphery of the print site by the laser marking, welding of Si spattered particles generated during the printing and the like.
The inventors have made various studies about the method for producing a laser-marked semiconductor wafer in order to solve the above problems. As a result, it has been found that the influences based on the minute and uneven elevated portions formed in the periphery of the print site by the laser marking, welding of Si splattered particles generated during the printing and the like cannot be removed only by the conventional cleaning with the alkaline aqueous solution after the laser marking. Moreover, it has been discovered the above problems could be solved by mechanical polishing with abrasive grains as in the conventional polishing with the polishing solution containing abrasive grains, but when the polishing with a polishing solution containing no abrasive grain is used, the influences based on the minute and uneven elevated portions formed in the periphery of the print site by the laser marking, welding of Si splattered particles generated during the printing and the like, which can not be removed completely by the cleaning with the alkaline aqueous solution, remains as they are.
The invention is based on the above knowledge and the summary and construction thereof are as follows.
(1) A method for producing a laser-marked semiconductor wafer which comprises a slicing step of cutting out a disc-shaped wafer from a single crystal ingot; a planarization step of making a thickness of the cut disc-shaped wafer uniform; a laser mark printing step of printing laser marks for wafer identification on the surface of the planarized wafer through laser; a grinding step of grinding at least the laser-marked surface of the laser-marked wafer by a predetermined thickness considering (1) the removal of uneven elevated portions formed in the periphery of the laser mark-printed site and (2) the preservation of a depth of the laser mark-printed site; an etching step of etching at least the laser mark-printed site of the wafer after the grinding; and a polishing step of polishing the wafer surface after the etching with a polishing solution containing no abrasive grain.
(2) A method for producing a laser-marked semiconductor wafer according to the item (1), wherein the predetermined thickness to be ground in the grinding step is 5 to 50 μm.
(3) A method for producing a laser-marked semiconductor wafer according to the item (1), wherein the planarization step is conducted by lapping both surfaces of the cut wafer.
(4) A method for producing a laser-marked semiconductor wafer according to the item (1), wherein the laser marks printed in the laser mark printing step are formed on the surface of the wafer in the vicinity of a notch.
(5) A method for producing a laser-marked semiconductor wafer according to the item (1), wherein the etching step is conducted with an alkaline solution.
(6) A method for producing a laser-marked semiconductor wafer according to the item (1), wherein the polishing step comprises a double-sided first polishing step of simultaneously first-polishing both surfaces of the wafer with a polishing solution containing no abrasive grain and a one-side finish polishing step of finish-polishing at least one surface of both the first-polished surfaces of the wafer, one surface at a time, with a polishing solution containing no abrasive grain.
According to the method for producing a laser-marked semiconductor wafer according to the invention, the grinding step of grinding at least the laser-marked surface of the laser-marked wafer by a predetermined thickness considering (1) the removal of uneven elevated portions formed in the periphery of the laser mark-printed site and (2) the preservation of a depth of the laser mark-printed site is conducted after the laser mark printing step, whereby even if polishing with a polishing solution containing no abrasive grain is conducted in the subsequent polishing step, influences based on the minute and uneven elevated portions formed in the periphery of the print site by the laser marking, welding of Si splattered particles generated during the printing and the like can be eradicated to prevent the deterioration of flatness in the vicinity of the print sites.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawings will be provided by the Office upon request and payment of the necessary fee.
The invention will be described with reference to the accompanying drawings, wherein:
Next, the method for producing a laser-marked semiconductor wafer according to the invention will be described in detail with reference to the drawings.
Then, each step of the method for producing a laser-marked semiconductor wafer according to the invention in the flow chart of
<Slicing Step>
<Planarization Step>
<Laser Mark Printing Step>
<Grinding Step>
In the grinding step of the invention, a thickness of the wafer to be removed by grinding is important.
<Etching Step>
<Polishing Step with No Abrasive Grain>
The polishing step with no abrasive grain (step 6) of the invention is a step wherein the surface of the etched wafer is polished with a polishing solution containing no abrasive grain. The important point in the polishing step with no abrasive grain of the invention is that although the same polishing method as the conventional polishing method is used, the conventional polishing using a polishing apparatus with a polishing solution containing abrasive grains is changed into a polishing using a polishing apparatus with a polishing solution containing no abrasive grain in the invention.
In the polishing step with no abrasive grain of the invention is generally conducted a multistage polishing comprising the first polishing and the second polishing (finish polishing). Here, the first polishing is preferable to be a double-sided first polishing step of simultaneously first-polishing both surfaces of the wafer with a polishing solution containing no abrasive grain. In the first polishing, the wafer is held in the apparatus and upper and lower platens each lined with a polishing cloth are pushed onto both the front and back surfaces of the wafer to rotate the wafer on its axis and also around while supplying a polishing solution containing no abrasive grain. Thereby, the front and back surfaces of the wafer are polished simultaneously. The second polishing is preferable to be a one-side finish polishing step of finish-polishing at least one surface of both the first-polished surfaces of the wafer, one surface at a time. The second polishing includes polishing of only one surface and/or polishing of both surfaces. When both surfaces are polished, first one surface is polished and then the other surface is polished.
According to the above-mentioned method for producing a laser-marked semiconductor wafer according to the invention, the grinding step (step 4) of finish-grinding at least one surface or both surfaces including the laser mark-printed portions with a high accuracy and a low strain is conducted after the laser mark printing step (step 3) of printing marks by laser shooting in the vicinity of the notch for identifying the wafer and before the etching step (step 5), whereby it is made possible to grind minute and uneven elevated portions at the interface between the wafer surface and the laser mark-printed site, and welding of Si splattered particles. Therefore, even if the subsequent polishing step (step 6) containing no abrasive grain is conducted, it is possible to prevent the deterioration of the flatness due to the laser marking in a final semiconductor wafer.
Hereinafter, actual examples will be described. It should be noted that the invention is not limited to the following examples.
A semiconductor wafer of Invention Example is prepared according to the flow chart of
Then, a state of a laser mark at each step is observed by using an optical microscope after the ends of the laser making printing step (step 3), the grinding step (step 4) and the polishing step with no abrasive grain polishing step (step 6), respectively. Moreover, the flatness of the finally obtained semiconductor wafer is measured by using a capacitive sensor for thickness measurement.
A semiconductor wafer of Reference Example is prepared in accordance with a flow chart of removing the grinding step (step 4) from the flow chart of the invention by sequentially conducting a slicing step (step 1) of cutting out a disc-shaped wafer from a single crystal ingot; a planarization step (step 2) of making a thickness of the cut disc-shaped wafer uniform; a laser mark printing step (step 3) of printing laser marks for wafer identification on the surface of the planarized wafer through laser; an etching step (step 5) of etching at least the laser mark-printed sites of the wafer after the grinding; and a polishing step (step 6) of polishing the wafer surface after the etching with a polishing solution containing no abrasive grain.
Then, a state of a laser mark at each step is observed by using an optical microscope after the ends of the laser making printing step (step 3), the etching step (step 5) and the polishing step with no abrasive grain polishing step (step 6), respectively. Moreover, the flatness of the finally obtained semiconductor wafer is measured by using a capacitive sensor for thickness measurement.
According to the method for producing a laser-marked semiconductor wafer according to the invention, even if polishing with a polishing solution containing no abrasive grain is conducted in the polishing step, influences based on the minute and uneven elevated portions formed in the periphery of the print site by the laser marking, welding of Si splattered particles generated during the printing and the like can be eradicated to prevent the deterioration of flatness in the vicinity of the print sites.
Number | Date | Country | Kind |
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2009-172717 | Jul 2009 | JP | national |