JP2002050593A - Plane-polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the high luminance polishing method of high productivity, which reduces a process for removing printing burrs and reduces an operation, such as inversion in a high luminance plane polishing process being one of the processes in the manufacturing of an inspection wafer for evaluating the quality characteristic of semiconductor crystal. SOLUTION: In the plane-polishing method of the wafer where an identification code is printed, polishing cost is set beforehand and quantitative polishing to a preset value is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for grinding a surface of a semiconductor crystal. In particular, the present invention relates to a method of grinding a wafer on which an identification code is printed, for example, a wafer for inspection for evaluating quality characteristics, with a surface grinder with high brightness.

[0002]

2. Description of the Related Art An ingot (single crystal rod) is pulled up by a Czochralski method (CZ method) or the like in a first step of a semiconductor wafer manufacturing process. In this single crystal manufacturing process, quality characteristics due to crystals are determined, and the main characteristics of the final wafer quality are controlled and managed in this process. For example, C
Taking a silicon crystal made by the Z method as an example, the crystal takes in oxygen in the silicon oxide melted out of the quartz crucible during the pulling. Oxygen in the crystal affects the electrical characteristics of the semiconductor, the strength of the wafer, and the ability to getter impurities.

The resistivity, which is a basic characteristic of a crystal, is also adjusted in a crystal manufacturing process by adding a necessary kind and amount of a doping agent in accordance with specifications required on the device manufacturing side.

[0004] The ingot obtained in the single crystal production process is not completely cylindrical when pulled up, and has a non-uniform diameter. Therefore, cylindrical grinding for trimming the outer diameter is performed. Also, the ingot is cut into blocks of a certain length to obtain a true cylindrical block.

[0005] After forming an orientation flat or a notch for indicating the orientation of the crystal, the process proceeds to a slicing step. Although this step is performed using an inner peripheral blade saw, a wire saw, or the like, it affects the subsequent mechanical quality (flatness, parallelism, warpage) of the wafer.

In addition, the sliced wafer is chamfered so as to prevent quality deterioration due to chipping (chipping) during wafer handling by taking a circumferential surface.

Next, after chamfering, the wafer is transferred to a lapping (surface grinding) process to correct the flatness, parallelism, warpage, etc. of the main surface. However, since a damaged layer exists near the surface in the wafer processing steps so far, the damaged layer is removed by chemical etching in the next step.

[0008] The final processing is a mirror polishing process, in which mechanochemical polishing is performed flat at least to the extent that a circuit can be formed on the surface of the wafer. Heat treatment for donor elimination (extinction) is performed. In recent years, a chamfered portion is also polished to a mirror surface.

[0009] Finally, the surface contamination is cleaned, rinsed and dried, and the production of the wafer is completed. After the inspection, the wafer is transferred to the device production side, where it becomes a memory, an LSI or the like.

The basic characteristics that are important as the quality of a semiconductor wafer forming a device include resistivity, oxygen concentration, carbon concentration and OSF (Oxidation-induced S).
tacking Fault), BMD (Bulk M
(Micro Defect). A quality standard is determined for these wafer characteristics according to the device design, and it is necessary for the wafer manufacturing side to manufacture based on the standard and to guarantee the quality.

The most straightforward method for inspecting quality characteristics and assuring the standards is to inspect a product that has undergone all wafer manufacturing processes and evaluate the quality. Then, the entire process time until the single crystal ingot is turned into a mirror wafer product is extremely long.
Therefore, in such a method, the evaluation judgment based on the test results
It greatly hinders management of manufacturing conditions, destination plans, and production plans. For example, if it is found that the specification of the destination is out of the plan after the completion of all the processes, a large time loss is caused and the production cost is increased.

The basic characteristics such as resistivity, oxygen concentration, carbon concentration, OSF, and BMD are bulk characteristics of a silicon single crystal, which are determined by a crystal pulling process, and are essentially changed in a wafer processing process. Never. Therefore, for the purpose of preventing the above-mentioned loss, a sample is secured by cutting out an inspection wafer immediately after manufacturing a single crystal ingot or extracting it at an early stage of a processing process, and evaluating the sample.

Furthermore, the surface condition of the inspection wafer should be a surface condition that can be finished through a process equivalent to that finished in the wafer processing process. Further, there are more preferable surface conditions depending on the inspection items. For example, in the case of an inspection using an infrared absorption method such as an oxygen concentration, the surface state is preferably substantially the same as the mirror-polished surface, and the surface state having a glossiness of 90 or more (the glossiness of the mirror-polished wafer). Is assumed to be 100). For measuring the resistivity, a lapping surface having an alumina particle size of 600 or more is recommended. However, the production of inspection wafers
Since it is necessary to simplify the process and finish it in a state that can be measured in a short time, it is necessary to finish it in a separate process to a surface condition necessary and sufficient for inspection. Further, it is preferable that the resistivity and the oxygen concentration can be measured with the same inspection wafer.

For this reason, in order to finish the inspection wafer to a surface state necessary and sufficient for the inspection and to make the surface state such that the resistivity and the oxygen concentration can be measured with the same sample, for example, an infeed type surface grinding machine is used. In the grinding step used, a wafer with a high-intensity surface ground surface processed using a grindstone having a grain size of # 1500 to # 2000 is produced. Here, high brightness refers to a surface state in which the glossiness of the ground surface is 90% or more.

The inspection wafer must have an identification code for identifying the origin (history) of the cut ingot, as a matter of course. This code is most preferably printed on the wafer itself so that it does not disappear even if the wafer is physically or chemically treated.
In recent years, laser engraving and printing have been performed at appropriate positions on the wafer. At this time, it is necessary to print the necessary and sufficient depth so that the print remains sharp even after surface grinding or the like.

The surface grinding is usually performed as a part of the wafer processing step. However, the so-called fixed size grinding for manufacturing a wafer having a constant thickness by setting the thickness of the wafer after grinding is performed. Have been. This is because, in the wafer processing step, it is preferable to make the thickness uniform in order to perform batch-type processing in a polishing step or the like after surface grinding.

On the other hand, in the manufacture of an inspection wafer, not only the thickness is kept within a certain control value, but also the identification code is printed, so it is important to process the print so that the print is not erased. is there. Since the thickness of the inspection wafer cut from the ingot varies, the variation in grinding allowance is large to keep the final thickness constant, and a considerable amount of grinding must be performed when the wafer is thick etc. . In this case, a situation occurs in which the identification code printed by the laser mark disappears. Therefore, first, rough grinding is performed from the back surface without printing by a fixed-size grinding method to adjust the thickness of most of the wafers, and then the inside-out operation is performed to perform high-intensity grinding of the wafer surface. Finally, the inside out operation is performed again, and the back surface is also ground by a procedure such as high brightness grinding. Also in this case, in the conventional method, the thickness is controlled by the fixed size grinding method, which is easy to control, and the process is such that the target thickness is finally obtained.

However, the conventional method has a further problem that burrs are raised on the edge of the printing groove printed on the wafer surface, and the printing surface is turned down at the time of the first grinding as described above. If you lie down on the surface, the whole surface will not touch and will rise on the burr. And when grinding the back side,
If the cutting pressure of the whetstone is applied to the surface, stress may be unevenly applied, and an accident that the wafer is cracked may occur.
In view of this, it has been customary to remove burrs using a deburring machine as disclosed in Japanese Patent Application Laid-Open No. 9-266185 and then proceed to high-intensity surface grinding.

[0019]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the prior art, and is directed to a wafer having an identification code printed thereon, for example, an inspection wafer for evaluating the quality characteristics of a semiconductor crystal. This is a surface grinding method related to the manufacturing method, which aims to provide a highly productive, high-intensity grinding method that eliminates the process of removing printing burrs and reduces operations such as reversal, without the identification code disappearing. And

[0020]

SUMMARY OF THE INVENTION The present invention is characterized in that in a surface grinding method for a wafer on which an identification code is printed, a grinding allowance is set in advance, and quantitative grinding is performed up to the set value.

The printing of the wafer identification code can be performed by printing to a certain desired depth. That is, the printing depth can be controlled to a desired depth, that is, a constant value by, for example, the output of a laser marker or the traveling speed of a beam, a pulse frequency, and the like, and the depth is known. If you set it below the printing depth,
The print will not disappear. Furthermore, if the necessary printing depth after surface grinding, which is necessary for visual clarity and reader sensitivity, is known, the difference between the printing depth before grinding and the printing depth after grinding is set as the grinding allowance. The purpose can be achieved by performing quantitative grinding.

Therefore, according to the method of the present invention, even when grinding is started from a surface having a print, there is no variation in the allowance for grinding due to variation in the thickness of the wafer. Since it is unlikely that the print is erased due to excessive shaving, the grinding can be started from the surface on which the identification code is printed. Therefore, the deburring step for removing the print groove burrs becomes unnecessary.

Further, the present invention is characterized in that the thickness after grinding is set in advance together with the grinding allowance, and the quantitative and fixed-size grinding is performed up to the set value.

[0024] Even for an inspection wafer, its thickness must be controlled within a control value according to the purpose. The final thickness control cannot be performed only by the quantitative grinding control due to the variation in the thickness of the cut wafer. Therefore, it is necessary to set the thickness after grinding in advance and also perform the step of performing fixed size grinding. This fixed-size grinding does not need to be conscious of the grinding allowance, that is, it is preferable to perform the grinding on a surface without printing.

Further, the present invention provides a method of surface grinding a wafer on which an identification code is printed, wherein the surface on which the identification code is printed is preset to a grinding allowance, and is quantitatively ground to the set value to obtain a high-brightness surface. Finishing, then set the thickness of the back surface of the wafer after grinding in advance, coarsely grind to the set value, further set the thickness after grinding the back surface, and perform constant size grinding to the set value, It is also characterized by finishing on the back surface with high brightness.

The main purpose of the surface on which the identification code is printed is to grind the surface with high brightness rather than to adjust the thickness.
Fine count (# 1500- #
Take a little time with a grindstone (approximately 2000) to set a grinding allowance until high brightness and perform high brightness grinding.

Next, the wafer is turned upside down, and the back surface is roughly ground so that the thickness of the wafer is now constant. Here, coarse grinding is a coarse grinding wheel (# 300- #
(Approximately 500) to shorten the time for grinding to the target dimension. Here, since there is no printing, there is no need to consider the grinding allowance.

Finally, with the wafer posture as it is,
In other words, high-intensity grinding is performed without changing the direction of the grindstone without changing the grinding wheel. At this time, it is preferable to carry out fixed-size grinding in which the thickness can be finely adjusted finally.

When this method is used, all the operations are completed by one reversal of the wafer, and the deburring can be eliminated, thereby greatly improving the productivity. Also, there is no influence of the variation in the thickness of the wafer at the beginning, and the high-luminance surface can be obtained without the identification code disappearing.

In the conventional method, when the number of times of changing the wafer is counted, the deburring set, the back surface rough grinding set, the front surface high-intensity grinding set, and the back surface high-intensity grinding set are totaled four times. In this case, as described above, the reduction was halved to only two times of the surface high-intensity grinding set and the (back-surface rough grinding + high-intensity grinding) set.

Further, the present invention is characterized in that the identification code is printed by a laser marker. As in the present invention, in order to obtain a print quality that can withstand sufficiently even through surface processing such as surface grinding, the wafer surface in the print pattern portion is melted and evaporated by the energy of the laser beam to engrave the print groove. It is preferable to use a means capable of obtaining a reliable, precise and sufficient machining depth.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings as specific examples. An example of a method of manufacturing an inspection wafer for evaluating quality characteristics as a wafer on which an identification code is printed will be described. As the inspection wafer, a 2.3 mm-thick wafer cut out from an ingot was used. A plurality of identification codes (an identification code for identifying ingot information and an identification code to be inspected) were printed on the laser marker using a YAG laser at a position where the inspection would not be hindered. About 10 for laser marker
The identification code was printed at a depth of 0 μm. This wafer is ground, processed into a high-intensity surface ground surface, and used for inspection.

(Comparative Example) FIG. 2 shows an example of a surface grinder usually used for high-intensity surface grinding. In FIG. 2, a workpiece 3 (an inspection wafer before grinding) is placed on a chuck table 4 driven to rotate by a table drive motor 5, and the workpiece 3 rotates together with the chuck table 4. ing. On the other hand, the grinding wheel 2 is driven to rotate by a grinding wheel shaft drive motor 1 via a grinding wheel shaft 7 and is moved up and down by a grinding wheel shaft lifting motor 6. With such a configuration, the grindstone 2 is lowered onto the rotating workpiece 3 on the rotating chuck table 1 while rotating at a high speed, and the grinding stone 2 is cut into the workpiece 3 and grinded while supplying a grinding fluid. This surface grinding machine is of a grinding system called in-feed grinding.

FIG. 3 is a sectional view of the wafer showing the steps of grinding the inspection wafer printed by the laser marker by the conventional method using the above-mentioned grinding machine or the like. In FIG. 3, reference numeral 11 denotes the inspection wafer, which is a workpiece;
Is a printing groove engraved with a laser, 13 is a burr generated by engraving, 14 is a portion removed by surface-side high-intensity grinding, 15
Is the portion removed by the backside high-brightness grinding, 16 is the portion removed by the backside rough grinding, Dc is the thickness after grinding set by the backside rough grinding, Dfb is the thickness after grinding set by the backside high-intensity grinding , Dfs indicate the thickness after grinding set by surface high-intensity grinding.

First, in FIG. 3A, the burrs 13 generated by printing the inspection wafer (sample) were removed by, for example, a deburring machine disclosed in Japanese Patent Application Laid-Open No. 9-266185.

Then, in FIG. 3 (2), the inspection sample (inspection wafer 11) is set on the grinder shown in FIG. ) Is set to # 320, the thickness Dc after the coarse grinding is set to 2080 μm with the four surfaces of the chuck table as the reference surfaces, and 16 portions are roughly ground while controlling the thickness with the in-process gauge 8. With this, fixed size processing (grinding) according to approximately the set thickness
Was done. The in-process gauge detects the difference between the surface of the chuck table 4 and the ground surface of the test sample and manages the thickness.

Next, the sample was set again toward the surface as shown in FIG. 3 (3), and the number (roughness) of the grindstone 2 was changed to # 20.
The thickness Dfs after surface high-intensity grinding was set to 2040 μm with reference to the four chuck table surfaces, and 14 portions were ground. As a result, sizing (grinding) was performed to substantially the set thickness.

Finally, the sample was set again toward the back surface as shown in FIG. 3 (4), the count (roughness) of the grindstone 2 was set to # 2000, and the thickness Dfb after the back surface high-intensity grinding was applied to the chuck table. Based on 4 surfaces, set to 2000 μm,
15 parts were ground. As a result, a wafer having a 2000-μm-thick double-sided high-intensity surface ground surface was produced.

In the above comparative example, about 2
Grinding of 00 μm is performed. The thickness variation of the wafer when cut out from the ingot is about ± 50 μm, and the grinding allowance greatly changes due to the variation. Therefore, if the surface on which the identification code is printed is ground from the beginning, the printing is likely to disappear. In the above comparative example, although the identification code can be prevented from disappearing, much time is required from the loading of the printed wafer to the finish, including the deburring, the actual process time of the grinding process, and the intermediate setup time. I was

(Embodiment) FIG. 1 shows an example of a surface grinder which can be used in an embodiment of the present invention. The basic configuration of the conventional surface grinder shown in FIG. 2 is almost the same as that of the conventional surface grinder. That is, FIG.
, The workpiece 3 is placed on a chuck table 4 driven to rotate by a table drive motor 5, and the workpiece 3 rotates together with the chuck table 4. On the other hand, the grindstone 2 is rotatably driven by a grindstone shaft drive motor 1 via a grindstone shaft 7 and is moved up and down by a grindstone shaft elevating motor 6. This apparatus is provided with a mechanism for performing quantitative grinding, and it is important to detect the surface position of the inspection wafer in order to perform quantitative processing.

In the apparatus of this embodiment, the wafer surface position is detected based on the load current generated when the inspection wafer comes into contact with the grindstone, and the timing of the load current and the feed amount of the grindstone shaft elevating motor 6 are determined. Is a mechanism that can be processed by a quantitative method. That is, the surface grinding machine is provided with a load current detecting means 9 for detecting a load current, and a control means 10 for controlling the feed amount by synchronizing the load current detecting means 9 with the grinding wheel shaft elevating motor 6. As another embodiment, a sensor for detecting the surface position of the inspection wafer may be provided, and by controlling the feed amount of the sensor and the grinding wheel shaft elevating motor 6, processing may be performed by a quantitative method. In the quantitative grinding process of the present invention, unlike the conventional method, it is not necessary to use a chuck table as a reference. However, in this embodiment, it is necessary that the measurement can be performed by both the quantitative method and the fixed size method. Processing is also possible with the grinding machine of FIG. That is, if the amount of change in the position of the terminal for detecting the wafer surface (ground surface) of the in-process gauge 8 is controlled and the thickness is controlled, it is possible to perform quantitative grinding.

FIG. 4 is a sectional view of the wafer showing the steps of grinding the inspection wafer printed by the laser marker by the method of the present invention using the above-mentioned grinding machine or the like. In FIG. 4, reference numeral 11 denotes the inspection wafer, which is a workpiece;
Is a printing groove engraved with a laser, 13 is a burr generated by engraving, 14 is a portion removed by surface-side high-intensity grinding, 15
Is a portion removed by the backside high-intensity grinding, 16 is a portion removed by the backside coarse grinding, Tfs is a grinding allowance set by the surface high-intensity grinding, Dc is a thickness after grinding set by the backside rough grinding,
Dfb indicates the thickness after grinding set by the backside high brightness grinding.

An inspection wafer was ground using the grinding machine shown in FIG. 1 or FIG. 2 modified so as to be capable of quantitative grinding. On the surface of the inspection wafer, identification marks were printed with a laser marker using a YAG laser at a plurality of positions that would not hinder the inspection at a depth of about 100 μm as in the comparative example.

In the present invention, the wafer without deburring is set with its surface facing upward as shown in FIG. 4A, the grinding allowance Tfs is set to 40 μm, and the count (roughness) #
Using 2,000 whetstones 2, 14 parts were ground quantitatively with a margin of Tfs only to finish the surface with high brightness. In this step, since the grindstone is sequentially cut from a portion having a burr, the burr is removed at the same time.

Next, as shown in FIG. 4 (2), the test sample was set upside down, the count (roughness) of the grindstone 2 was set to # 320, and the thickness Dc after the coarse grinding was set to the same value as in the prior art. The chuck table 4 is set as a reference plane and set to 2040 μm.
While controlling the thickness with the in-process gauge 8, 16 parts were roughly ground. As a result, dimensional processing (grinding) was performed according to the set thickness.

Finally, as shown in FIG. 4 (3), the sample is kept as it is, the count (roughness) of the grindstone 2 is set to # 2000, and the thickness Dfb after the back surface high-intensity grinding is determined with reference to the four surfaces of the chuck table. The surface was set to 2000 μm, and 15 portions were ground. As a result, a wafer having a 2000-μm-thick double-sided high-intensity surface ground surface was produced.

In the above embodiment, the identification code can be prevented from disappearing, and the substantial process time of the deburring and grinding processes, that is, the time from the loading of the printed wafer to the finish can be shortened. .

The surface state of the wafer manufactured as described above is a high-brightness flat surface with a gloss of 100%, and the thickness of the inspection wafer is controlled within the standard range, which is sufficient for the subsequent inspection. Inspection wafers that could be produced were made. Also, the identification code of the sample is clearly printed, and can be easily processed visually or by an automatic reader.

The present invention is not limited to the above embodiment. The above embodiment is merely illustrative, and has substantially the same configuration as the technical idea described in the claims of the present invention, and has the same function and effect.
Anything is included in the technical scope of the present invention.

For example, in this embodiment, a method of manufacturing a 2 mm-thick inspection wafer is described as an example of a wafer on which an identification code is printed, but a 1 mm-thick or other thickness wafer is required for the inspection wafer. There are cases. The present invention can be applied to wafers having different thicknesses. Particularly, in the case of a thin inspection wafer, it is effective because it is easily broken due to the burr of the laser mark.

In the apparatus for rough grinding and high-intensity surface grinding, the stage for holding the wafer may be shared, and the grindstone may be exchanged for grinding. A surface grinding machine for rough grinding and a surface grinding for high brightness It may be processed in parallel with the machine. In addition, as long as the apparatus is capable of quantitative grinding, the apparatus is not limited to the apparatus of the above embodiment, and can be used.

In the embodiment, the surface side is 40 μm from the beginning.
m high-intensity surface grinding, but in order to shorten the grinding time, the surface side is subjected to 30 μm rough grinding (grinding using a # 320 grindstone) by quantitative grinding, and then high-intensity surface grinding is performed for 1 hour.
It may be carried out by quantitative grinding of about 0 μm. What is necessary is just to grind the side on which the identification code is printed, and to process so that the print is not erased.

[0053]

As described above, according to the present invention, a high-brightness surface grinding step, which is one of the processes for producing a wafer on which an identification code is printed, for example, an inspection wafer for evaluating the quality characteristics of a semiconductor crystal. In this method, it is possible to provide a highly productive high-intensity grinding method that eliminates the step of removing printing burrs as in the related art without erasing the identification code and reduces operations such as inversion.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a surface grinding machine used in the present invention.

FIG. 2 is a schematic diagram of a normal surface grinding machine.

FIG. 3 is a cross-sectional view of a wafer showing a step of grinding an inspection wafer printed by a laser marker by a conventional method.

FIG. 4 is a cross-sectional view of a wafer showing a step of grinding an inspection wafer printed by a laser marker by the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF REFERENCE NUMERALS 1 wheel drive motor 2 wheel 3 work piece 4 chuck table 5 table drive motor 6 wheel shaft elevating motor 7 wheel shaft 8 in-process gauge 9 load current detecting means 10 control means 11 inspection wafer 12 print groove 13 print burr 14 surface Part removed by high-brightness grinding on the side 15 Part removed by high-brightness grinding on the back side 16 Part removed by rough grinding on the back side Dc Thickness after grinding set by rough grinding on the back side Dfb After grinding set by high brightness grinding on the back side Thickness Dfs Thickness after grinding set by surface high-intensity grinding Tfs Grinding allowance set by surface high-intensity grinding

Claims (4)

[Claims] 1. A surface grinding method for a wafer on which an identification code is printed, wherein a grinding allowance is set in advance and quantitative grinding is performed up to the set value. 2. The surface grinding method according to claim 1, wherein a post-grinding thickness is set in advance together with a grinding allowance, and the fixed and fixed-size grinding is performed up to the set value. 3. A surface grinding method for a wafer on which an identification code is printed, wherein the surface on which the identification code is printed is preset with a grinding allowance, is quantitatively ground to the set value, and is finished to a high brightness surface. Next, the thickness of the back surface of the wafer is set in advance after grinding, and the surface is roughly ground to the set value. The surface grinding method according to claim 1 or 2, wherein the back surface is finished. 4. The surface grinding method according to claim 1, wherein the identification code is printed by a laser marker.