Life time measurement method and sample transportation tray

Abstract

To provide a new method that contributes to a reduction in a lead time of a quality inspection of a singly crystal silicon sample.SOLUTION: A life time measurement method comprises: a sample mounting step of mounting a silicon sample cut out from a silicon ingot onto a sample mounting surface of a sample transportation tray in an outside of a life time measuring apparatus; a tray carry-in step of mounting the sample transportation tray to which the silicon sample is mounted onto a measurement stage in the life time measuring apparatus; a life time measurement step that measures a life time of the silicon sample by detecting a reflection light by irradiating a front surface of the silicon sample with light; and a tray carry-out step of carrying out the sample transportation tray to which the silicon sample is mounted after the measurement of the life time to the outside of the life time measuring apparatus.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a lifetime measurement method and a tray for sample transfer, and more particularly to a lifetime measurement method for a silicon sample and a tray for sample transfer.

Background Art

[0002] As methods for growing single crystal silicon ingots, the CZ (Czochralski) method, the FZ (Floating Zone) method, etc. are known. By performing various processes on wafers cut out from the grown single crystal silicon ingots, single crystal silicon wafers shipped as products are manufactured.

[0003] In the manufacturing process of single crystal silicon wafers, quality inspections may be performed, for example, as follows. After the single-crystal silicon ingot is peripherally ground to adjust its diameter, the top and tail parts are cut off, and then the cylindrical ingot is longitudinally divided and cut to process it into a silicon block of a predetermined length. Then, in order to examine whether the cut silicon block satisfies the desired crystal quality over its entire length, sample wafers (generally called "slag sample wafers") for quality inspection are cut out from both ends of the silicon block (see, for example, Patent Document 1 and Patent Document 2), and inspections of various quality items are performed. Then, based on the inspection results of various quality items, a pass / fail determination of the silicon block quality is made. Hereinafter, the sample wafers and sample pieces prepared for quality inspection as described above are also referred to as "inspection samples". For example, when the quality inspection result of the inspection sample satisfies the target quality level, predetermined product processing is advanced for the silicon block from which this inspection sample was cut out. For example, a plurality of silicon wafers are cut out by slicing the silicon block using a wire saw. Then, by performing various processing steps such as etching, grinding, polishing, and cleaning on the cut silicon wafers, the silicon wafers to be shipped as products are completed. On the other hand, when the quality inspection result of the inspection sample does not meet the target quality level, the silicon block from which this inspection sample was cut out is determined to be a defective product, and no subsequent product processing is performed on this defective silicon block. In this way, it is possible to prevent silicon blocks that do not meet the quality standards from being subjected to various processes for wafer productization.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the manufacturing process of a single crystal silicon wafer, shortening the lead time of quality inspection of a test sample cut from a silicon block obtained from an ingot as described above is desirable because it will ultimately improve the wafer production yield.

[0006] In view of the above, an aspect of the present invention aims to provide a new method that contributes to shortening the lead time of quality inspection of a single crystal silicon sample.

Means for Solving the Problems

[0007] As an example of the quality inspection items for single-crystalline silicon, the lifetime measured by the μ-PCD method (micro-wave photoconductive decay method) can be cited. In the μ-PCD method, a laser beam is irradiated in pulses simultaneously with the irradiation of microwaves onto the single-crystalline silicon. When the photon energy of the irradiated laser beam becomes a state above the bandgap in the single-crystalline silicon, electrons and holes (carriers) are generated in the single-crystalline silicon. As the generated carriers recombine through the positions of the energy levels formed in the bandgap such as defects and impurities in the single-crystalline silicon and the number gradually decreases, the intensity of the reflected wave or transmitted wave of the microwaves changes. The intensity of the reflected wave or transmitted wave of the microwaves is measured, and the time from the point when the intensity is maximum to the point when it reaches a certain intensity is determined as the "lifetime", which is the time that the carriers can exist in the single-crystalline silicon wafer. When performing lifetime measurement in a lifetime measurement device, in the case where the single-crystalline silicon to be measured is a wafer in a disc shape, for example, the extraction of the wafer from a wafer transfer cassette containing a plurality of wafers, the transfer of the wafer into the lifetime measurement device, the lifetime measurement of the wafer in the lifetime measurement device, the transfer of the wafer out of the lifetime measurement device, and the re-accommodation into the cassette can be continuously automated for a plurality of wafers, for example. On the other hand, in the quality inspection of the slag sample wafer, in order to reduce the number of slag sample wafers prepared for quality inspection, a plurality of sample pieces obtained by dividing the slag sample wafer into a plurality are prepared, and each sample piece is subjected to different quality inspections. Specific examples of the shape of such sample pieces include, for example, a quarter-circle shape, a semi-circle shape, etc. obtained by dividing a disc-shaped wafer. Also, there are cases where sample pieces of any shape and any size such as a rectangle are cut out from a block cut out from an ingot. Thus, since the shape and / or size of the inspection sample cut out from the ingot can be various, conventionally, the inspection sample cut out from the ingot has to be placed one by one on the measurement stage of the lifetime measurement device by the operator himself / herself, and after the lifetime measurement is completed, the operator has to take it out from the lifetime measurement device himself / herself.In contrast, as a result of intensive studies by the present inventors, conventionally, a single-crystal silicon sample to be measured was directly placed on the measurement stage of a lifetime measurement device, whereas a single-crystal silicon sample to be measured is placed on a sample transfer tray outside the lifetime measurement device, and the following new lifetime measurement method including loading and unloading the tray into and out of the lifetime measurement device has been found. In such a lifetime measurement method, for example, a series of steps from loading to unloading the sample to be measured into the lifetime measurement device can be automated regardless of the shape and size of the sample to be measured. Thereby, it becomes possible to shorten the lead time of quality inspection. Also, the monitoring work of the lifetime measurement device by the operator can be eliminated, and the work burden of the operator can be reduced.

[0008] That is, one aspect of the present invention is as follows. In the present invention and this specification, "silicon" shall mean single-crystal silicon unless otherwise specified.

[0009] [1] A sample placement step of placing a silicon sample cut from a silicon ingot on a sample placement surface of a sample transfer tray outside a lifetime measurement device; A tray loading step of placing the sample transfer tray on which the silicon sample is placed on a measurement stage inside the lifetime measurement device; A lifetime measurement step of measuring the lifetime of the silicon sample by irradiating light on the surface of the silicon sample and detecting the reflected light of the light; A tray unloading step of unloading the sample transfer tray on which the silicon sample is placed after the lifetime measurement outside the lifetime measurement device; A lifetime measurement method having the above steps. [2] The sample transfer tray has a recess on the sample placement surface, In the sample placement step, the silicon sample is placed in the recess, and the lifetime measurement method according to [1]. [3] After the tray loading step, there is further a measurement target area specifying step of specifying a measurement target area by detecting a placement area of the silicon sample on the sample transfer tray in the lifetime measurement device, In the lifetime measurement step, the lifetime of the silicon sample is measured by irradiating light onto the surface of the silicon sample located in the measurement target area and detecting reflected light of the light, according to the lifetime measurement method described in [1] or [2]. [4] In the measurement target area specifying step, the placement area of the silicon sample is detected by irradiating infrared rays toward a sample placement surface on which the silicon sample is placed and detecting reflected light of the infrared rays, according to the lifetime measurement method described in [3]. [5] The sample transfer tray has a notch groove at an outer edge, according to the lifetime measurement method described in any one of [1] to [4]. [6] The sample transfer tray is a resin tray, according to the lifetime measurement method described in any one of [1] to [5]. [7] There is further a cassette preparation step of preparing a cassette in which a plurality of sample transfer trays with silicon samples placed on a sample placement surface are accommodated at intervals in a height direction, In the tray loading step, one sample transfer tray with a silicon sample placed on a sample placement surface is taken out from the cassette and placed on a measurement stage in the lifetime measurement device, In the tray unloading step, after the lifetime measurement, the sample transfer tray with the silicon sample placed thereon is unloaded outside the lifetime measurement device and rearranged in the cassette, according to the lifetime measurement method described in any one of [1] to [6]. [8] The sample transfer tray has a recess in the sample placement surface, In the sample placement step, the silicon sample is placed in the recess, After the tray loading step, there is further a measurement target area specifying step of specifying a measurement target area by detecting a placement area of the silicon sample on the sample transfer tray in the lifetime measurement device. In the lifetime measurement step, the lifetime of the silicon sample is measured by irradiating light onto the surface of the silicon sample located in the measurement target area and detecting reflected light of the light. In the measurement target area specifying step, the placement area of the silicon sample is detected by irradiating infrared rays toward a sample placement surface on which the silicon sample is placed and detecting reflected light of the infrared rays. The sample transfer tray has a notch groove at its outer edge. The sample transfer tray is a resin tray. The lifetime measurement device includes an infrared sensor, and in the measurement target area specifying step, the placement area of the silicon sample is detected by the infrared sensor. The method further includes a cassette preparation step of preparing a cassette in which a plurality of sample transfer trays with silicon samples placed on a sample placement surface are accommodated at intervals in the height direction. In the tray loading step, one sample transfer tray with a silicon sample placed on a sample placement surface is taken out from the cassette and placed on a measurement stage in the lifetime measurement device. In the tray unloading step, after the lifetime measurement, the sample transfer tray with the silicon sample placed thereon is unloaded out of the lifetime measurement device and re-accommodated in the cassette. The lifetime measurement method according to any one of [1] to [7]. [9] A resin disk-shaped tray, having a notch groove at the outer edge of the disk shape, having a recess on the sample placement surface, and a silicon sample cut out from a silicon ingot is placed in this recess. A sample transfer tray.

[10] The outer shape of the recess is substantially the same as the outer shape of the silicon sample. The sample transfer tray according to [9].

[11] The resin is polyvinyl chloride, polytetrafluoroethylene, or polyether ether ketone, and is the sample carrier tray according to [9] or

[10] .

Advantages of the Invention

[0010] According to one aspect of the present invention, a new method that contributes to shortening the lead time for quality inspection of single crystal silicon samples can be provided.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0012] One aspect of the present invention relates to a method for measuring the lifetime of a silicon sample (also simply referred to as the "lifetime measurement method" or the "measurement method"). The above measurement method includes the following steps. A sample placement step of placing a silicon sample cut from a silicon ingot on the sample placement surface of a sample carrier tray outside the lifetime measurement device; A tray loading process of placing a sample carrier tray on which the silicon sample is placed on a measurement stage inside a lifetime measurement device; A lifetime measurement process of measuring the lifetime of the silicon sample by irradiating light on the surface of the silicon sample and detecting the reflected light of the light; A tray unloading process of unloading the sample carrier tray on which the silicon sample is placed after the lifetime measurement outside the lifetime measurement device.

[0013] Hereinafter, the details of the above various processes and various processes that can be optionally performed will be described. Hereinafter, the description may refer to the drawings. However, the embodiments shown in the drawings are examples, and the present invention is not limited to the embodiments illustrated in the drawings.

[0014] [Sample placement process] <Silicon sample to be measured> The measurement object of the above measurement method is a silicon sample cut from a silicon ingot. Such a silicon sample is a wafer piece obtained by dicing a silicon wafer in the thickness direction. The silicon sample cut from the silicon ingot may be an inspection sample cut directly from the silicon ingot, or may be an inspection sample cut from a silicon block obtained by, for example, longitudinally dividing and cutting the silicon ingot as described above. Further, the method for growing the silicon ingot from which the silicon sample is cut is not particularly limited, and is, for example, a silicon ingot grown by the CZ method or the FZ method. The shape of the measurement object silicon sample is arbitrary and is not limited. From the viewpoint of reducing the number of slag sample wafers prepared for various quality inspections such as lifetime measurement, it is preferably a shape other than a disc shape. For example, the measurement object silicon sample can be prepared by cutting disc-shaped sample wafers from both ends of a silicon block and cutting samples of a plurality of wafer pieces from this sample wafer. The shape of the sample of the silicon wafer piece thus prepared is more preferably a shape obtained by dividing a disc-shaped sample wafer into partial circles (for example, quarter circles, semi-circles, etc.). A "quarter circle" is a partial circle obtained by dividing a circle into 1 / 4, and a "semi-circle" is a partial circle obtained by dividing a circle into 1 / 2. Also, a silicon sample having an arbitrary shape such as a rectangle may be used. A rectangle is not limited to one in which all four sides are straight lines, and includes those in which one or more of the four sides include curves. Note that the shape of the sample is allowed to include shape errors that can occur in normal working processes.

[0015] <Sample transfer tray> The sample transfer tray on which the measurement object silicon sample is placed is preferably a disc-shaped tray from the viewpoint of ease of placement on a lifetime measurement device commonly used for inspection of semiconductor wafers.

[0016] In a tray for transporting a sample, the placement surface (also referred to as the "sample placement surface" or "placement surface") on which the silicon sample to be measured is placed is a flat surface in one form. Here, the "flat surface" is a surface that does not have a recess for placing the silicon sample to be measured as described later.

[0017] In another form, in a tray for transporting a sample, the placement surface on which the silicon sample to be measured is placed has a recess, and the silicon sample to be measured is placed within this recess. FIGS. 1 to 3 are schematic plan views of an example of a tray for transporting a sample having a recess for placing a silicon sample. The sample transport tray 1 shown in each figure has recesses 11A, 11B, or 11C in the placement surface 10 on which the silicon sample to be measured is placed. Hereinafter, the recesses 11A, 11B, and 11C are collectively referred to as the "recess 11". Regarding the outer shape of the recess 11, the outer shape of the recess 11A of the placement tray 1 shown in FIG. 1 is a quarter-circle shape, the outer shape of the recess 11B of the placement tray 1 shown in FIG. 2 is a semi-circle shape, and the outer shape of the recess 11C of the placement tray 1 shown in FIG. 3 is a rectangular shape.

[0018] The outer shape of the recess of the sample transfer tray is preferably substantially the same as the outer shape of the silicon sample to be measured placed in this recess. Here, "substantially the same shape" means that the shape types are the same, and the outer dimensions (vertical dimension and / or horizontal dimension of the outer shape) may be the same or different. For example, it is preferable to place a silicon sample to be measured with a quadrant shape in a recess with a quadrant shape. Similarly, it is preferable to place a silicon sample to be measured with a semi-circular shape in a recess with a semi-circular shape. Similarly, it is preferable to place a silicon sample to be measured with a rectangular shape in a recess with a rectangular shape. In order to accommodate the silicon sample to be measured in the recess of the sample transfer tray, it is preferable that the outer dimensions of the recess of the sample transfer tray are larger than the outer dimensions of the silicon sample to be measured. That is, when the silicon sample to be measured is accommodated in the recess of the sample transfer tray, it is preferable that there is a gap between the outer edge of the silicon sample to be measured and the outer edge of the recess. The gap can be, for example, more than 0 mm and 10 mm or less. The depth of the recess of the sample transfer tray may be larger than, the same as, or smaller than the value of the thickness of the silicon sample to be measured. That is, it is not essential that the entire thickness direction of the silicon sample to be measured fits within the recess of the sample transfer tray.

[0019] From the viewpoints of light weight and durability, the sample transfer tray is preferably made of resin, and preferably made of a thermoplastic resin, a thermosetting resin, etc. As described later, when identifying the placement area of the silicon sample on the tray using an infrared sensor in the measurement target area identification process before lifetime measurement, in order to facilitate or enable the detection of the sample placement area by the infrared sensor, it is desirable that the material of the sample transfer tray has a low light transmittance. From this point, as the material of the sample transfer tray, resins such as PVC (polyvinyl chloride), PTFE (polytetrafluoroethylene), and PEEK (polyetheretherketone) are particularly desirable. The formation of the above-mentioned recess can be performed by a known method.

[0020] From the viewpoint of continuously and automatically carrying out the transfer of wafers into the lifetime measurement device, the lifetime measurement within the lifetime measurement device, and the transfer out of the lifetime measurement device for a plurality of silicon samples, it is preferable to accommodate a plurality of sample transfer trays each having a silicon sample placed on a sample placement surface in a cassette with a space in the height direction. Examples of such a cassette include commercially available cassettes commonly used for transferring semiconductor wafers, such as commercially available FOUP (Front-Opening Unified Pod) or FOSB (Front Open Shipping BOX). From the viewpoint of using such a wafer transfer cassette, the sample transfer tray is preferably a disc-shaped tray. From the viewpoint of ease of alignment when accommodating the sample transfer tray with the silicon sample to be measured placed thereon in the cassette and / or when placing the sample transfer tray with the silicon sample to be measured placed thereon in the lifetime measurement device, the sample transfer tray preferably has a notch groove as an alignment mark on its outer edge. Such a notch groove can have the same shape as the notch (V-notch shape) usually provided on a semiconductor wafer. The sample transfer trays shown in each of FIGS. 1 to 3 are provided with such notch grooves.

[0021] [Tray Loading Step] The sample transfer tray on which the silicon sample to be measured is placed in the sample placement step is placed on the measurement stage within the lifetime measurement device in the tray loading step. When placing the sample transfer tray on the measurement stage or when taking out the sample transfer tray out of the device system, usually, the wafer transfer mechanism employed in the lifetime measurement device for semiconductor wafers as products can be used, and a disc-shaped wafer transfer arm can be adopted as the tray transfer arm.

[0022] [Measured Region Specifying Step] After the sample transfer tray on which the silicon sample to be measured is placed is transferred into the lifetime measurement device in the tray transfer process, the measurement target area in the subsequent lifetime measurement process can be specified by detecting the placement area of the silicon sample on the sample transfer tray within the measurement device. The detection of the above placement area can be performed using an infrared sensor usually provided in the lifetime measurement device. As a specific example of the infrared sensor, a reflection type sensor that includes a light emitting element and a light receiving element and can detect the position of the object to be detected by receiving the infrared light emitted from the light emitting element and reflected by the irradiated surface can be mentioned. For example, such an infrared sensor can detect the area (for example, a quarter circle shape area, a semi-circle shape area, a rectangular area, etc.) where the silicon sample to be measured is placed on the sample transfer tray. Specifically, the placement area of the silicon sample to be measured is detected by irradiating infrared light toward the sample placement surface on which the silicon sample to be measured is placed and detecting the reflected light of the infrared light. Such detection can be performed, for example, by specifying the coordinate position. The area thus detected can be specified as the measurement target area.

[0023] [Lifetime Measurement Process] In the lifetime measurement process, a pulsed laser beam and microwaves are irradiated onto the surface of the silicon sample located in the measurement target area. Then, the lifetime of the silicon sample is measured by detecting the microwaves reflected from the sample surface with a microwave detector. The details of the lifetime measurement principle are as described above. As the lifetime measurement device, a commercially available μ-PCD device can be used. Also, the measurement target area can be specified, for example, by performing the above measurement target area specification process.

[0024] [Tray Unloading Process] The sample transfer tray on which the silicon sample whose lifetime has been measured is placed is unloaded outside the lifetime measurement device by, for example, a tray transfer arm and accommodated in a cassette.

[0025] [Specific Example of Lifetime Measurement Automation System] Hereinafter, a specific example of a system for continuously and automatically measuring the lifetimes of a plurality of silicon samples will be described. Here, "automation" means that it is not necessary for an operator to manually place a plurality of silicon samples one by one on the measurement stage of a lifetime measurement device and then remove them from the lifetime measurement device after the lifetime measurement is completed by the operator himself / herself.

[0026] FIG. 4 is an explanatory diagram of a specific example of a lifetime measurement automation system. Hereinafter, the specific example shown in FIG. 4 will be described.

[0027] In FIG. 4(a), a plurality of sample transfer trays 1 on which silicon samples are placed are accommodated in a cassette 3 with a space in the height direction. Inside the lifetime measurement device 2, a sample arm 20, a measurement stage 22, and a measurement probe 23 are provided. The details of the sample transfer tray 1 and the silicon samples placed thereon are as described above. The arm portion of the tray transfer arm 20 is telescopic, and a vacuum suction mechanism (not shown) is provided at the tip of the arm portion, and the back surface of the sample transfer tray 1 can be adsorbed and held. The measurement stage 21 has a plurality of support pins 22. These support pins 22 can move up and down. The measurement probe 23 is provided with a pulse laser irradiation mechanism, a microwave irradiation mechanism, a microwave detector, an infrared irradiation mechanism, and an infrared light receiving sensor (not shown).

[0028] The tray transfer arm 20 places one of the plurality of sample transfer trays 1 stored in the cassette 3 on the arm portion with the arm portion extended (Fig. 4(b)), moves inside the lifetime measuring device 2, and places the sample transfer tray 1 above the measurement stage 22 (Fig. 4(c)). The plurality of support pins 22 move upward (in the direction of the arrow in Fig. 4(c)) and protrude from the surface of the measurement stage 21 to support the back surface of the sample transfer tray 1 opposite to the placement surface on which the silicon sample of the sample transfer tray 1 is placed (Fig. 4(c)). Fig. 5 is a schematic view showing the support state of the sample transfer tray 1 in Fig. 4(c) (a plan view of the back side of the sample transfer tray 1).

[0029] With the back surface of the sample transfer tray 1 supported by the support pins 22, after the arm portion of the tray transfer arm 20 is retracted, the support pins 22 are moved downward, and the support pins 22 are accommodated in the measurement stage 21. In this way, the sample transfer tray 1 is placed on the measurement stage 21 (Fig. 4(d)).

[0030] After the sample transfer tray 1 is placed on the measurement stage 21 as described above, the measurement probe 23 moves above the sample transfer tray 1 (Fig. 4(d)), irradiates the surface of the silicon sample with infrared light, and receives the reflected light from the silicon sample with an infrared sensor to detect the placement area of the silicon sample on the placement surface of the sample transfer tray 1. The placement area of the silicon sample thus detected is specified as the measurement target area. The shape of the measurement target area thus specified can be, for example, a partial circular shape (such as a quarter circular shape, a semi-circular shape, etc.), a rectangular shape, etc., as described above.

[0031] Next, the surface of the silicon sample located in the measurement target area specified as described above is irradiated with laser light and microwaves, and the microwave reflected from the sample surface is detected by a microwave detector to measure the lifetime of the silicon sample placed on the sample transfer tray 1. After the lifetime measurement is completed, the measurement probe 23 is moved from above the sample transfer tray 1 back to its original position.

[0032] Subsequently, the plurality of support pins 22 are moved upward again to provide a gap between the surface of the measurement stage 21 and the back surface of the sample transfer tray 1, the arm portion of the tray transfer arm 20 is extended again, and the sample transfer tray 1 is placed on the arm portion (FIG. 4(e)).

[0033] By moving the plurality of support pins 22 downward (in the direction of the arrow in FIG. 4(e)), the support of the sample transfer tray 1 by the support pins 22 is released (FIG. 4(e)). Subsequently, the tray transfer arm 20 with the sample transfer tray 1 placed on the arm portion moves inside the lifetime measurement device 2 and re-accommodates the sample transfer tray 1 in the cassette 3 (FIG. 4(e)).

[0034] Next, when the cassette is moved downward (in the direction of the thick arrow in FIG. 4(g)), the sample transfer tray 1 on which the silicon sample for which the lifetime measurement has been performed is placed moves downward, and another sample transfer tray 1 is arranged at the height where this tray was located. Subsequently, by sequentially repeating the steps of unloading and re-accommodating the trays shown in FIGS. 4(b) to 4(f) into the cassette, the lifetime measurement of the silicon samples respectively arranged on the plurality of sample transfer trays 1 in the cassette 3 can be performed.

[0035] By using the sample transfer tray, for example, as described above, a series of steps from loading to unloading the sample to be measured into the lifetime measurement device can be automated regardless of the shape and size of the sample to be measured, and the lead time of quality inspection can be shortened.

[0036] One aspect of the present invention relates to a disc-shaped tray made of resin, which has a notch groove on the outer edge of the disc shape, a recess on the sample placement surface, and a silicon sample cut out from a silicon ingot is placed in this recess. The details of such a sample transfer tray are as described above. The above sample transfer tray can be used for loading a sample into a lifetime measurement device and unloading the sample from the lifetime measurement device.

Example

[0037] Hereinafter, the present invention will be described based on examples. However, the present invention is not limited to the embodiments shown in the examples. In the following lifetime measurement, a μ-PCD device (model WT-2000) manufactured by Semilab was used as the lifetime measurement device.

[0038] [Fabrication of Sample Transfer Tray A (for Quadrilateral Circular Silicon Samples)] On one surface side of a 200 mm diameter disc-shaped flat plate made of PVC, a quarter-circular recess with a depth of 0.3 mm was formed so as to accommodate one quadrilateral circular silicon sample obtained by dividing a 300 mm diameter disc-shaped wafer into four parts. Thus, a sample transfer tray A having the recess shown in FIG. 1 was fabricated. In the sample transfer tray A, a notch was made at one location on the outer edge to form a notch groove so as to serve as a mark when placed in the lifetime measurement device.

[0039] [Fabrication of Sample Transfer Tray B (for Rectangular Silicon Samples)] On one surface side of a 200 mm diameter disc-shaped flat plate made of PVC, a recess with a depth of 0.3 mm was formed so as to accommodate one rectangular silicon sample cut from a quadrilateral circle obtained by dividing a 300 mm diameter disc-shaped wafer into four parts into a rectangular shape. Thus, a sample transfer tray B having the recess shown in FIG. 3 was fabricated. In the sample transfer tray B, a notch was made at one location on the outer edge to form a notch groove so as to serve as a mark when placed in the lifetime measurement device.

[0040] [Lifetime measurement example] Silicon blocks were cut out from four silicon ingots with different levels (referred to as "Level 1", "Level 2", "Level 3", and "Level 4"). Disk-shaped samples (sample wafers) were cut out from these silicon blocks. Specifically, silicon blocks were cut out from single-crystal silicon ingots grown by the CZ method, and these silicon blocks were sliced to obtain disk-shaped sample wafers. Then, mirror polishing was performed on the obtained sample wafers. Thus, sample wafers (p-type, main plane: <100>, diameter: 300 mm, resistivity: 10 - 12 Ωcm, [Oi]: 11 - 13×10 17 atoms / cm 3 , wafer thickness: 775 μm) were obtained from the silicon ingots of the above levels. After each sample wafer was divided into quadrants and washed with a 5 mass% HF aqueous solution (hydrofluoric acid), a horizontal furnace manufactured by ULVAC was used to grow an oxygen precipitation part, and heat treatment (oxygen precipitation treatment) was performed in a dry atmosphere at "780 °C, 3 hours" and "1000 °C, 16 hours" to give characteristics to the in-plane distribution of the lifetime. By the above heat treatment, an oxide film with a thickness of about 6000 angstroms was formed on the surface layer of the silicon sample, and the surface levels were passivated (passivation treatment). For each level, one of the quadrant-shaped silicon samples after the passivation treatment was placed in the recess of the sample carrier tray A while remaining quadrant-shaped. One of the other quadrant-shaped silicon samples was further cut off one side to form a rectangle and then placed in the recess of the sample carrier tray B. In the lifetime measurement automation system shown in FIG. 4, the unloading of each sample carrier tray from the cassette containing a plurality of sample carrier trays on which silicon samples of various levels and various shapes were placed, respectively, and the reloading into the cassette were sequentially performed. In the lifetime measurement device, after placing the sample carrier tray with the silicon sample on the measurement stage using the notch groove of the sample carrier tray as a mark, the placement area (shape: quadrant or rectangle) of the silicon sample on the placement surface of the sample carrier tray was detected by the infrared sensor of the measurement probe, and the detected placement area was specified as the measurement target area. A laser beam and microwaves were irradiated onto the surface of the silicon sample located in the measurement target area on the placement surface of the sample carrier tray, and the lifetime of the silicon sample was measured by detecting the microwaves reflected from the sample surface with a microwave detector. Specifically, lifetime map measurement with a 2 mm pitch in the plane was performed. FIG. 6 is a lifetime map obtained for silicon samples (quadrant or rectangle) of levels 1 to 4. As described above, by using the sample carrier tray, it has become possible to continuously automate the lifetime measurement of silicon samples of various shapes.

Industrial Applicability

[0041] One aspect of the present invention is useful in the field of manufacturing single crystal silicon wafers. By automating the quality inspection of inspection samples, the lead time can be shortened, the workload of workers can be reduced, and as a result, the wafer production yield can be improved. This enables an improvement in the productivity and quality of products, enables meeting more demand, and improves the productivity of the entire semiconductor industry. Thus, one aspect of the present invention can contribute to the promotion of economic growth (development goal: SDGs8).

Claims

1. A sample placement step of placing a silicon sample cut out from a silicon ingot on a sample placement surface of a sample transfer tray outside a lifetime measurement device; A tray loading step of placing the sample transfer tray on which the silicon sample is placed on a measurement stage inside the lifetime measurement device; A lifetime measurement step of measuring the lifetime of the silicon sample by irradiating light on the surface of the silicon sample and detecting the reflected light of the light; A tray unloading step of unloading the sample transfer tray on which the silicon sample is placed after the lifetime measurement outside the lifetime measurement device; A lifetime measurement method comprising the above steps.

2. The sample transfer tray has a recess on the sample placement surface, In the sample placement step, the silicon sample is placed in the recess. The lifetime measurement method according to Claim 1.

3. After the tray loading step, further comprising a measurement target area specifying step of specifying a measurement target area by detecting a placement area of the silicon sample on the sample transfer tray inside the lifetime measurement device, In the lifetime measurement step, the lifetime of the silicon sample is measured by irradiating light on the surface of the silicon sample located in the measurement target area and detecting the reflected light of the light. The lifetime measurement method according to Claim 1.

4. In the measurement target area specifying step, the placement area of the silicon sample is detected by irradiating infrared rays toward the sample placement surface on which the silicon sample is placed and detecting the reflected light of the infrared rays. The lifetime measurement method according to Claim 3.

5. The sample transfer tray has a notch groove at the outer edge. The lifetime measurement method according to Claim 1.

6. The sample transfer tray is a resin tray. The lifetime measurement method according to Claim 1.

7. Further comprising a cassette preparation step of preparing a cassette in which a plurality of sample transfer trays with silicon samples placed on the sample placement surface are accommodated at intervals in the height direction, In the tray loading step, one sample transfer tray with a silicon sample placed on the sample placement surface is taken out from the cassette and placed on the measurement stage inside the lifetime measurement device. The lifetime measurement method according to claim 1, wherein in the tray unloading step, after the lifetime measurement, the sample carrier tray on which the silicon sample is placed is unloaded outside the lifetime measurement device and rearranged in the cassette.

8. The sample carrier tray has a recessed portion on the sample placement surface, In the sample placement step, the silicon sample is placed in the recessed portion, After the tray loading step, the method further includes a measurement target area specifying step of specifying a measurement target area by detecting a placement area of the silicon sample on the sample carrier tray within the lifetime measurement device. In the lifetime measurement step, the lifetime of the silicon sample is measured by irradiating light onto the surface of the silicon sample located in the measurement target area and detecting the reflected light of the light. In the measurement target area specifying step, the placement area of the silicon sample is detected by irradiating infrared rays toward the sample placement surface on which the silicon sample is placed and detecting the reflected light of the infrared rays. The sample carrier tray has a notch groove on the outer edge, The sample carrier tray is a resin tray, The lifetime measurement device includes an infrared sensor, and in the measurement target area specifying step, the placement area of the silicon sample is detected by the infrared sensor. The method further includes a cassette preparation step of preparing a cassette in which a plurality of sample carrier trays with silicon samples placed on the sample placement surface are accommodated at intervals in the height direction. In the tray loading step, one sample carrier tray with a silicon sample placed on the sample placement surface is taken out from the cassette and placed on a measurement stage in the lifetime measurement device. The lifetime measurement method according to claim 1, wherein in the tray unloading step, after the lifetime measurement, the sample carrier tray on which the silicon sample is placed is unloaded outside the lifetime measurement device and re-accommodated in the cassette.

9. A resin disc-shaped tray, The disc shape has a notch groove on the outer edge, A sample carrier tray having a recessed portion on the sample placement surface and having a silicon sample cut out from a silicon ingot placed in the recessed portion.

10. The outer shape of the recessed portion is substantially the same as the outer shape of the silicon sample. The tray for sample transfer according to claim 9.

11. The resin is polyvinyl chloride, polytetrafluoroethylene, or polyether ether ketone. The tray for sample transfer according to claim 9 or 10.

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