JP6288515B2 - Evaluation method and measurement method - Google Patents

Description

  The present invention relates to a method for evaluating a measurement position deviation of a measuring instrument that measures characteristics such as a thickness of a film formed on the surface of a wafer, and a method for measuring film characteristics using the measuring instrument.

  High integration of silicon semiconductor devices is progressing remarkably, and higher quality of the silicon wafer itself of the substrate on which the devices are formed is demanded more severely. In other words, as the circuit pattern becomes finer with higher integration, in the device active region where the device on the wafer is formed, crystal defects such as dislocations that cause an increase in leakage current and a decrease in carrier lifetime and Reduction and removal of metal impurities is more strictly required than ever before. In response to such a demand, an epitaxial wafer in which an epitaxial layer free from crystal defects is grown on the wafer has been developed and is often used in the manufacture of highly integrated devices.

  The thickness of the epitaxial layer of a silicon wafer is generally measured by FTIR (Fourier Transform Infrared) (for example, see Patent Document 1). In this method, the film thickness of the epitaxial layer is measured from the difference in impurity concentration between the wafer and the epitaxial layer using infrared light irradiated on the wafer surface.

JP 2009-302133 A

  Conventionally, according to the quality standard of the epitaxial wafer, the area within 5 mm from the outer peripheral edge of the epitaxial wafer was not used for manufacturing the semiconductor device as the outer peripheral exclusion area, but recently, the flatness defined by the quality standard has become stricter, There is a demand for an epitaxial wafer that is flat to the outer periphery and has no irregularities.

  Furthermore, the requirement for the outer periphery exclusion area in quality standards has become stricter, and the outer periphery exclusion area has been gradually reduced. As a result, it is the mainstream to make the outer periphery excluded area within 2 mm from the outer peripheral edge, and it is necessary to satisfy the required flatness for the outer peripheral portion other than the outer periphery excluded area. As a result, the measuring instrument is also required to have tighter measurement position accuracy.

  As a measurement management method of the FTIR measuring instrument, calibration is performed using reflected laser intensity values at several points in the surface of the wafer. This is suitable for evaluating and calibrating the inclination of the measuring instrument and the wafer, but is insufficient for evaluating and calibrating a minute measurement position shift of the measuring instrument.

  The present invention has been made in view of such circumstances, a method capable of evaluating a minute measurement position deviation of a measuring instrument that measures film characteristics such as film thickness, and a film capable of improving the accuracy of the measurement position of film characteristics. It is an object to provide a method for measuring characteristics.

  In order to solve the above problems, the present inventor conducted various tests, and as a result of intensive studies, the wafer was normally charged, the film thickness was measured in a predetermined angular direction with each of 180 ° reversal charging, and the same measurement was performed. It has been found that the measurement position deviation of the measuring instrument can be easily detected by taking the difference in film thickness at the points. Furthermore, it has been found that there is a certain correlation between the film thickness distribution at the outer periphery of the wafer and the detection sensitivity of the measurement position deviation of the measuring instrument.

The present invention has been completed based on the above findings. That is, the evaluation method of the present invention includes a first measurement step in which a measurement point is selected from points within a surface of a wafer having a film formed on the surface, and the characteristics of the film at the measurement point are measured with a measuring instrument. ,
After rotating the wafer around a rotation axis perpendicular to the surface of the wafer at an angle different from that in the first measurement step, the measurement instrument is configured to perform the measurement in the coordinate system set for the measurement instrument. A second measurement step for measuring the characteristic at the same measurement point as the first measurement step;
An evaluation step for evaluating a measurement position shift of the measuring device based on a comparison between the measurement value obtained in the first measurement step and the measurement value obtained in the second measurement step;
It is characterized by including.

  According to the present invention, two measurement steps, a first measurement step and a second measurement step, are performed, and in these two measurement steps, the same measurement point is measured while the circumferential direction of the wafer is measured. The angle (angle around the rotation axis perpendicular to the wafer surface) is varied. At this time, if there is no measurement position deviation of the measuring instrument, the measurement values obtained in the two measurement steps are the same. On the other hand, when there is a measurement position shift of the measuring instrument, the measuring instrument intends to measure the same measuring point, but in fact, in the second measuring step, the measurement is shifted from the measuring point of the first measuring step. A point will be measured. That is, when there is a measurement position deviation of the measuring device, a deviation occurs between the measurement value obtained in the first measurement process and the measurement value obtained in the second measurement process. Therefore, in the evaluation process, a minute measurement position shift of the measuring device can be evaluated by comparing the two measured values.

  In the present invention, it is preferable that in the second measuring step, the wafer is charged in a state rotated by 180 ° around the rotation axis from the time of the first measuring step. In this way, in the second measurement process, the measurement position shift of the measuring instrument can be easily reflected in the measurement value of the second measurement process by reversing the wafer from the time of the first measurement process. Therefore, the measurement position shift of the measuring instrument can be evaluated with high sensitivity.

In the present invention, the characteristic is a film thickness,
In the first measurement step and the second measurement step, at least the film thickness at the outer peripheral portion of the wafer is measured,
In the evaluation step, the measurement of the measuring instrument is performed based on a comparison between the measurement value in the outer peripheral portion obtained in the first measurement step and the measurement value in the outer peripheral portion obtained in the second measurement step. It is preferable to evaluate the positional deviation. At this time, when the average film thickness in the range of 3 mm to 5 mm from the outer peripheral edge of the film is d and the amount of change in the film thickness in the range is Δd, Δd / d is 0.1% or more. preferable.

  According to this, since the change in film thickness is usually larger at the outer peripheral part of the wafer than at the inner part of the wafer, the measurement position deviation of the measuring instrument can be reduced by measuring at least the film thickness of the outer peripheral part. It can be easily reflected in the measurement value of the second measurement step. Therefore, the measurement position shift of the measuring instrument can be detected with high sensitivity. In particular, by using a wafer having a film thickness distribution Δd / d in the outer peripheral portion of 0.1% or more, even a minute measurement position deviation can be detected with high sensitivity.

In the present invention, in the first measurement step and the second measurement step, respectively, along the first direction and the other along one of two orthogonal straight lines among straight lines passing through the in-plane of the wafer. Measuring the in-plane distribution of the characteristic in at least two directions of the second direction,
In the evaluation step,
Based on the comparison between the measured value in the first direction obtained in the first measuring step and the measured value in the first direction obtained in the second measuring step, the measuring device in the first direction Evaluate measurement position deviation, and
Based on the comparison between the measured value in the second direction obtained in the first measuring step and the measured value in the second direction obtained in the second measuring step, the measuring device in the second direction It is preferable to evaluate the measurement position deviation. At this time, one of the first direction and the second direction can be a direction along a straight line passing through the notch of the wafer.

  According to this, since the measurement position deviations in the two orthogonal directions are evaluated, the measurement position deviation can be evaluated in any direction on the two-dimensional plane.

  Further, in the present invention, the characteristic is a film thickness, and in the evaluation step, a measured value in the outer peripheral portion of the wafer obtained in the first measurement step and the outer circumference obtained in the second measurement step. It is possible to obtain a difference between measured values in the unit and evaluate the direction and amount of measurement position deviation of the measuring device based on the difference. According to this, since the direction and amount of the measurement position deviation are obtained, the measurement position of the measuring instrument can be easily corrected.

  In the present invention, the characteristic is a film thickness, and the measuring device is a film thickness measuring device based on the FTIR method. Thereby, the measurement position shift of the film thickness measuring device can be evaluated.

  At this time, the thickness of the film is preferably 0.3 μm or more and 100 μm or less, more preferably 1 μm or more and 100 μm or less. In the FTIR method, the internal measurement results are affected by reflection from the outermost surface up to a depth of 0.3 μm. As a result, the interface position where the impurity concentration difference cannot be detected accurately. Therefore, the detection limit of the film thickness by the FTIR method is about 0.3 μm. Further, the film thickness of the wafer is preferably 1 μm or more in order to accurately detect the interface position of the impurity concentration. Further, when an epitaxial wafer having a film thickness of 100 μm or more is produced, a by-product is deposited between the susceptor and the wafer sticks on the susceptor, and the wafer cannot be taken out frequently. Therefore, the film thickness of the wafer is preferably 100 μm or less.

  The measurement method of the present invention uses the evaluation method of the present invention, a correction step of correcting the measurement position of the measurement device based on the evaluation result of the evaluation step, and the measurement device whose measurement position is corrected in the correction step. And a post-correction measuring step for measuring the characteristics of the wafer. According to this, it is possible to perform film characteristic measurement with improved measurement position accuracy.

It is the figure which showed schematic structure of the film thickness measuring device. It is the flowchart which showed the procedure of the method of evaluation of the measurement position shift of the measuring device of this invention, and a film thickness measurement. It is the figure which showed the mode of the film thickness measurement of the X direction in normal preparation. It is the figure which showed the mode of the film thickness measurement of the Y direction in normal preparation. It is the figure which showed the mode of the film thickness measurement of the X direction in reverse preparation. It is the figure which showed the mode of the film thickness measurement of the Y direction in reverse preparation. It is the figure which showed the difference of 1) the film thickness of a normal preparation, 2) the film thickness of reverse preparation, and 3) those film thicknesses of a X direction with a notch down. It is the figure which showed the difference of 1) the film thickness of normal preparation, 2) film thickness of reversal preparation, 3) those film thicknesses with a notch down. It is the figure which showed the difference of 1) the film thickness of a normal preparation, 2) the film thickness of reversal preparation, and 3) the film thickness of a reverse preparation in the X direction with the notch after a measuring device position adjustment down. It is the figure which showed the difference of 1) the film thickness of a normal preparation, 2) the film thickness of reversal preparation, 3) with the notch after a measuring device position adjustment downward. It is the figure which showed the variation | change_quantity of the film thickness difference in an outer peripheral part with respect to the positional offset amount of a measuring device for every film thickness distribution.

  Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, the present invention is applied to the film thickness measurement of a silicon epitaxial wafer (hereinafter sometimes simply referred to as a wafer) in which a silicon single crystal thin film (epitaxial layer) is formed on the surface of a silicon substrate by vapor phase growth. An example will be described. FIG. 1 shows a schematic configuration of a film thickness measuring instrument 1 (hereinafter simply referred to as a measuring instrument) used in the present invention. The measuring instrument 1 includes a load port 2, a robot hand 3, an aligner 4, and a measuring unit 5.

  The load port 2 is an apparatus for attaching a container in which a wafer whose thickness is to be measured is accommodated and taking the wafer into the measuring instrument 1 from the container. The robot hand 3 includes a hand unit 31 that grips a wafer by suction and an arm unit 32 that can be moved to each unit in the measuring instrument 1 by connecting the hand unit 31 to the tip. The robot hand 3 (hand unit 31) also serves as a measurement stage on which a wafer is placed when the film thickness is measured by the measurement unit 5.

  The aligner 4 positions the wafer before the wafer is transferred to the measuring unit 5. Specifically, the aligner 4 rotates the wafer while applying an infrared laser to the wafer, for example, and measures and corrects how many times the wafer is displaced with respect to the notch position and how much in the X and Y directions. be able to. If an orientation flat (orientation flat) is formed on the wafer, positioning can be performed with reference to the orientation flat. When the wafer is transferred, the wafer can be transferred in the same position and in the same direction on the robot hand 3 through such an aligner 4.

  The measurement unit 5 is a part that measures the film thickness of the epitaxial layer formed on the surface of the wafer by the FTIR method. Here, the FTIR method irradiates the main surface of the wafer with infrared light, detects reflected light reflected on the surface of the epitaxial layer and reflected light reflected on the interface between the epitaxial layer and the substrate, This is a method of calculating the film thickness of the epitaxial layer by measuring the optical path difference of the reflected light. Therefore, the measurement unit 5 calculates the film thickness by measuring the space portion in which the wafer is arranged, the irradiation unit that irradiates the wafer with infrared light, the detector that detects each reflected light, and the optical path difference of the reflected light. It consists of parts.

  The conventional procedure of film thickness measurement by the measuring instrument 1 will be described. First, the wafer is horizontally held from the load port 2 by the robot hand 3, and the wafer is conveyed to the aligner 4. Next, the aligner 4 positions the wafer. At this time, the position of the wafer is corrected so that, for example, the notch is positioned in the 12 o'clock direction when viewed from the center of the wafer.

  Next, the positioned wafer is gripped by the robot hand 3 and conveyed to the measuring unit 5 while maintaining the positioned state. At this time, when the position of the notch is corrected by the aligner 4 in the 12 o'clock direction, the wafer is transferred so that the position of the notch is held in the 12 o'clock direction. Hereinafter, the conveyance (preparation) to the measurement unit 5 with the notch positioned in the 12 o'clock direction is referred to as normal preparation. Further, for example, the initial transfer position of the wafer in the measurement unit 5 is determined so that the center of the wafer is located at the origin set in advance in the measurement unit 5. For this reason, the robot hand 3 transports the wafer to the initial transport position by numerical control.

  Next, a measurement point for measuring the film thickness is selected from a point in the plane of the wafer, and the film thickness at the measurement point is measured by the measurement unit 5. For example, a plurality of measurement points along the diameter direction of the wafer are selected excluding the outer periphery exclusion region (for example, a region within 2 mm from the outer periphery of the wafer). For example, when the diameter of the wafer is 200 mm and the coordinates of the wafer center are zero, the film thickness is measured over a coordinate range of −98 mm to +98 mm excluding the outer peripheral exclusion region. Further, as described above, the robot hand 3 also serves as a measurement stage on which the wafer is placed in the measurement unit 5. Therefore, the robot hand 3 remains on the robot hand 3 when measuring the film thickness. Moves in the X direction and the Y direction, so that the film thickness can be measured at an arbitrary measurement point.

  By the way, the wafer conveyance position to the measurement part 5 by the robot hand 3 may shift | deviate. For example, when the initial transfer position of the wafer in the measurement unit 5 is shifted, a deviation occurs between the origin O in the coordinate system set in the measurement unit 5 and the center O ′ of the wafer W as shown in FIG. 3. Due to this shift, a shift occurs in the measurement position of the film thickness. That is, as shown in FIG. 3, an actual film thickness measurement range 102 (for example, a coordinate range of −98 mm to +98 mm in the coordinate system of the measurement unit 5) and a desired film thickness measurement range 101 (for example, in the wafer plane). A deviation (in the case of FIG. 3, a deviation Δx in the X direction) occurs in the range of −98 mm to +98 mm.

  Therefore, in the present invention, the presence / absence, deviation amount, and deviation direction of the measurement position of the measuring instrument 1 are evaluated, the measurement position of the measuring instrument 1 is corrected based on the evaluation result, and the corrected measuring instrument 1 is used. To measure the film thickness. Hereinafter, details of the measurement position deviation evaluation and film thickness measurement method of the measuring instrument 1 will be described. FIG. 2 is a flowchart showing the procedure of the method.

First, an epitaxial wafer for evaluation of measurement position deviation is prepared (S1). At this time, in the FTIR method, it is necessary to reflect light at the interface between the substrate and the epitaxial layer. Therefore, it is necessary that the substrate and the epitaxial layer have a difference in impurity concentration detectable by the FTIR method. Specifically, the substrate is preferably p ++ type or p + type, and the epitaxial layer is preferably p− type. Here, the p ++ type means a low resistance having an impurity concentration of about 10 ¹⁹ atoms / cm ³ and a resistance value of 10 (mΩ · cm) or less. The p + type means an impurity concentration of about 10 ¹⁸ atoms / cm ³ and a resistance value of about 10 to 100 (mΩ · cm). The p-type means an impurity concentration of about 10 ¹⁵ atoms / cm ³ and a resistance value of 0.1 (Ω · cm) or more. The impurity doped in the substrate and the epitaxial layer is boron (B) or the like. The diameter of the wafer is not particularly limited, but here, a wafer having a diameter of 200 mm is prepared.

  Further, the larger the film thickness change at the outer peripheral portion of the wafer, the more effective the detection of the measurement position deviation of the measuring instrument 1. Specifically, when the average film thickness at the outer peripheral part (range from 3 mm to 5 mm from the outer peripheral edge) of the wafer is d and the film thickness change amount within that range is Δd, the film thickness distribution Δd / d of the outer peripheral part is 0. It is preferable to prepare a wafer on which an epitaxial layer of 1% or more is formed. When the film thickness distribution is 0.1% or more, when the difference between the measured values of the film thickness obtained by normal preparation and reverse preparation described later is taken at the same measurement point, The amount of change in the difference increases, and as a result, a minute measurement position shift can be detected with high sensitivity. On the other hand, when the film thickness distribution is less than 0.1%, the change amount of the film thickness difference at the same measurement point is small, and it is difficult to detect a minute measurement position shift.

  Furthermore, the thickness of the epitaxial layer is preferably 0.3 μm or more, preferably 1 μm or more and 100 μm or less. As described above, the detection limit of the film thickness by the FTIR method is about 0.3 μm, and in the case of a film thickness of 100 μm or more, the by-product deposited between the susceptor and the wafer causes the wafer on the susceptor. This is in consideration of sticking.

  Next, the wafer prepared in S <b> 1 is normally charged with the aligner 4 (the notch is set at 12 o'clock), and the robot hand 3 sets the wafer at a predetermined initial transfer position in the measurement unit 5 ( S2). When the wafer is viewed from the upper side, the coordinate value increases from the left side to the right side when the notch is viewed downward. The X axis, which is a coordinate axis extending left and right through the origin, and the upper side from the lower side A coordinate system that is determined by the Y axis, which is a coordinate axis extending vertically through the origin, is set such that the coordinate value increases as the distance increases. Then, the film thickness measurement in the direction along the X axis (X direction) and the direction along the Y axis (Y direction) in the coordinate system is performed by the measurement unit 5 (S2). When the position of the notch is 0 °, the Y direction is the 0 ° direction and the X direction is the 90 ° direction.

  Here, FIG. 3 shows a state (measurement range, etc.) of film thickness measurement in the X direction in normal preparation. 3 shows a wafer W in which the notch 10 is set in the 12 o'clock direction, and an X axis (coordinate axis facing the left direction in FIG. 3) whose coordinate value increases toward the left side in FIG. In S2, as the film thickness measurement in the X direction, the film thickness is measured at predetermined intervals along the X axis, for example, over a coordinate range of −98 mm ≦ X coordinate ≦ + 98 mm. In FIG. 7, the results of film thickness measurement in the X direction in normal charging (film thickness change with respect to the X coordinate) are illustrated by rhombus plot lines.

  As described above, when the deviation in the X direction occurs between the origin O of the measurement unit 5 and the center O ′ of the wafer W due to the deviation of the initial transfer position of the wafer, the actual film thickness measurement range 102 is assumed. It deviates from the existing film thickness measurement range 101 by Δx. FIG. 3 shows an example in which a deviation Δx occurs on the plus side in the X direction.

  FIG. 4 shows the state of film thickness measurement (measurement range, etc.) in the Y direction during normal preparation. 4 shows the wafer W in which the notch 10 is set in the 12 o'clock direction and the Y axis (the coordinate axis facing downward in FIG. 4) whose coordinate value increases toward the lower side of FIG. In S2, as the film thickness measurement in the Y direction, the film thickness is measured at predetermined intervals along the Y axis, for example, over a coordinate range of −98 mm ≦ Y coordinate ≦ + 98 mm. In FIG. 8, the results of film thickness measurement in the Y direction in normal charging (film thickness change with respect to the Y coordinate) are illustrated by rhombus plot lines.

  Also in FIG. 4, the actual film thickness measurement range 104 is assumed to be different from the assumed film thickness measurement range 103 due to a deviation in the Y direction between the origin O of the measurement unit 5 and the center O ′ of the wafer W. It shows that it is shifted by Δy. FIG. 4 shows an example in which a deviation Δy is generated on the negative side in the Y direction. The step S2 corresponds to the first measurement step of the present invention.

  Next, the wafer whose film thickness has been measured in S2 is transferred from the measuring unit 5 to the aligner 4 by the robot hand 3 (S3). Then, the orientation of the wafer is reversed in the aligner 4. That is, the wafer is positioned (notch alignment) so that the notch is positioned in the 6 o'clock direction by rotating the wafer by 180 ° around a rotation axis perpendicular to the surface of the wafer. After that, the robot hand 3 sets (inverts) the wafer from the aligner 4 to the initial transfer position of the measuring unit 5 (the same position as the initial transfer position of S2). And the coordinate system similar to S2, that is, when viewed from the notch down, the coordinate value increases to the right as it goes to the right and the X axis extends to the left and the coordinate from which the coordinate value increases as it goes upward. Set the coordinate system determined by. This coordinate system is a coordinate system obtained by rotating the coordinate system of S2 by 180 ° around the origin, in other words, a coordinate system in which the plus and minus of each coordinate value of the coordinate system of S2 is reversed. In the coordinate system, the film thickness is measured at the same coordinate point (measurement point) as S2 (S3). That is, the film thickness is measured in the 90 ° direction (X direction) and 0 ° direction (Y direction) with the notch being 0 °.

  Here, FIGS. 5 and 6 show the state of film thickness measurement (measurement range, etc.) in the reverse preparation, FIG. 5 shows the film thickness measurement in the X direction, and FIG. 6 shows the film thickness measurement in the Y direction. ing. 5 and 6, since the wafer W is reversely charged, the notch 10 is set at a position reversed from the normal charge (position in the 6 o'clock direction). Since the X direction and the Y direction are set based on the position of the notch 10, the X direction in FIG. 5 is opposite to the X direction in FIG. 3, and the Y direction in FIG. 6 is the Y direction in FIG. The opposite direction.

  If the wafer transfer position is shifted in the same direction and by the same amount between the normal preparation and the reverse preparation, the measurement position deviation is opposite to the deviation direction of the measurement position in the normal preparation when measuring the film thickness in the reverse preparation. Occur. That is, the film thickness measurement in the X direction in FIG. 5 indicates that the actual film thickness measurement range 105 is deviated by Δx from the assumed film thickness measurement range 101, but in FIG. In contrast to the occurrence on the plus side in the X direction, in FIG. 5, the deviation Δx occurs on the minus side in the X direction. Similarly, the film thickness measurement in the Y direction in FIG. 6 shows that the actual film thickness measurement range 106 deviates from the assumed film thickness measurement range 103 by Δy, but FIG. 4 shows a deviation Δy. Is generated on the negative side in the Y direction, whereas in FIG. 6, the deviation Δy is generated on the positive side in the Y direction.

  As described above, when there is a measurement position deviation, the film thickness measurement in the normal charge and the film thickness measurement in the reverse charge are actually the same as the coordinates of the measuring instrument 1, but in reality, different measurement points on the wafer. Measuring the film thickness. In FIGS. 7 and 8, the results of film thickness measurement in the X direction and the Y direction in the reverse charging are illustrated by Δ plot lines. As shown in FIG. 7 and FIG. 8, if there is a measurement position shift, a difference occurs between the measured value THK of the film thickness in the normal preparation and the measured value THK of the film thickness in the reverse preparation. The difference is large at the outer periphery of the wafer where the change is large. The step S3 corresponds to the second measurement step of the present invention.

  Next, a difference ΔTHK between the measurement value THK1 obtained in S2 and the measurement value THK2 obtained in S3 at the same measurement point (same coordinate) is obtained (S4). At this time, the difference ΔTHK may be obtained by subtracting the measured value THK2 of S3 from the measured value THK1 of S2, or the difference ΔTHK may be obtained by subtracting the measured value THK1 of S2 from the measured value THK2 of S3. 7 and 8, the film thickness difference ΔTHK between the rhombus plot line and the Δ plot line is obtained. In FIGS. 7 and 8, the film thickness difference ΔTHK (the value obtained by subtracting the measured value THK2 of S3 from the measured value THK1 of S2) is indicated by a plot line of ◯. As indicated by the plot lines, if there is a measurement position shift, the film thickness difference ΔTHK increases at the wafer outer periphery (X and Y coordinates are in the range of about ± 95 mm to 98 mm). Further, since the film thickness change with respect to the position change is small in the inner part of the wafer, the film thickness difference ΔTHK is small even if there is a measurement position shift.

  Next, the measurement position deviation is evaluated based on the film thickness difference ΔTHK obtained in S4 (S5). Specifically, the measurement position deviation in the X direction is evaluated based on the film thickness difference THK in FIG. 7, and the measurement position deviation in the Y direction is evaluated based on the film thickness difference THK in FIG. More specifically, for example, if the absolute value of the film thickness difference ΔTHK is smaller than a predetermined threshold value at all measurement points, it is evaluated that there is no measurement position deviation. If even one measurement point is larger than the threshold value, the measurement position deviation is detected. Evaluate that there is. In both cases of FIGS. 7 and 8, since the film thickness difference ΔTHK in the outer peripheral portion is large, it is evaluated that there is a measurement position shift in each of the X direction and the Y direction.

  In FIG. 7, the film thickness difference ΔTHK in the outer peripheral portion where the X coordinate is plus side (X = + 100 mm) is a large value on the negative side, whereas the outer peripheral portion where the X coordinate is minus side (X = The film thickness difference ΔTHK in the vicinity of −100 mm is a large value on the plus side. In FIG. 8, the film thickness difference ΔTHK in the outer peripheral portion where the Y coordinate is positive (around Y = + 100 mm) is a large value on the positive side, whereas the outer peripheral portion where the Y coordinate is negative (Y = −100 mm). The film thickness difference ΔTHK in the vicinity) is a large value on the negative side. In S5, the direction of the measurement position deviation is evaluated based on the positive or negative tendency of the film thickness difference ΔTHK in the outer peripheral portion.

  Specifically, in the case of FIG. 7, since the film thickness difference ΔTHK in the outer peripheral portion on the plus side of the X coordinate is a negative value, the normal charge is more in the X direction than the reverse charge. The film thickness is measured near the plus side (see FIGS. 3 and 5). When this is considered in the direction of deviation of the actual film thickness measurement range 102 with respect to the assumed film thickness measurement range 101 at the time of normal preparation in FIG. 3, it is evaluated that the deviation direction is the positive direction of the X axis. be able to. That is, it can be evaluated by the robot hand 3 that the wafer is initially transferred to a position close to the plus side in the X direction during normal preparation.

  In the case of FIG. 8, since the film thickness difference ΔTHK at the outer peripheral portion where the Y coordinate is positive is a positive value, the normal charging is closer to the negative side in the Y direction than the reverse charging. Thus, the film thickness is measured (see FIGS. 4 and 6). If this is considered in the direction of deviation of the actual film thickness measurement range 104 with respect to the assumed film thickness measurement range 103 at the time of normal preparation in FIG. 4, the deviation direction is evaluated to be the negative direction of the Y axis. be able to. That is, it can be evaluated by the robot hand 3 that the wafer is initially transferred to a position closer to the minus side in the Y direction during normal preparation.

  To summarize the above deviation direction evaluation, for example, when the outer peripheral portion where the film thickness difference ΔTHK is a negative value is the positive side of the X coordinate and the Y coordinate (in the case of FIG. 7), On the other hand, it is evaluated that the wafer is initially transferred to a position close to the plus side in the X direction or the Y direction. On the contrary, when the outer peripheral portion where the film thickness difference ΔTHK is a negative value is the negative side of the X coordinate and the Y coordinate (in the case of FIG. 8), the X direction or the Y direction with respect to the assumed initial transport position. It is evaluated that the wafer is initially transferred to a position closer to the minus side of the wafer. This is because when the film thickness difference ΔTHK in the outer peripheral portion (X, Y = + 100 mm vicinity) where the X coordinate or Y coordinate is positive is a negative value, the wafer is positioned closer to the positive side in the X direction or Y direction. When the film thickness difference ΔTHK is a positive value, it is synonymous with evaluating that the wafer is initially transported to a position closer to the minus side in the X direction or the Y direction.

  Furthermore, since the film thickness difference ΔTHK increases as the measurement position shift amount increases, in S5, the measurement position shift amount is evaluated based on the film thickness difference ΔTHK. Specifically, the deviation amount of the measurement position in the X direction is evaluated based on the film thickness difference ΔTHK in the X direction shown in FIG. More specifically, for example, the amount of change in the outer peripheral portion of the film thickness difference ΔTHK in FIG. 7 is obtained. This amount of change corresponds to the value of the difference in film thickness at points 201 and 202 located at the ends of the measurement points. In this case, the amount of change is about 0.06 μm. Then, the amount of deviation in the X direction is evaluated based on the obtained amount of change. For example, in order to set the change amount of the film thickness difference (about 0.06 μm) to 0, the measurement points on the outer periphery in normal charging (diamond points in FIG. 7) and the measurement points on the outer periphery in reverse charging ( It is evaluated how many points in FIG. Then, the amount of deviation of the measurement position in the X direction can be obtained by multiplying the number of deviations of the obtained measurement points by the pitch (interval) of the measurement points on the outer periphery. For example, assuming that the number of deviations of the measurement points is about 2.5 and the pitch of the measurement points on the outer periphery is 1 mm, the deviation amount is about 2.5 mm.

  The amount of deviation of the measurement position in the Y direction is also evaluated in the same manner as the amount of deviation in the X direction. That is, the amount of deviation in the Y direction is evaluated based on the amount of change in the outer peripheral portion of the film thickness difference ΔTHK in FIG. 8 (corresponding to the value of the film thickness difference at the end measurement points 203 and 204). Specifically, by evaluating how many points in the Y direction the measurement points on the outer peripheral part in the normal preparation and the measurement points on the outer peripheral part in the reverse preparation are shifted in the Y direction, the difference in film thickness is evaluated. By multiplying by the pitch of the measurement points in the section, the amount of deviation in the Y direction can be obtained. For example, when the number of deviations of the measurement points is about 1 and the pitch of the measurement points on the outer periphery is 1 mm, the amount of deviation is about 1 mm. After all, when the measurement position deviation is evaluated based on FIGS. 2 and 3, it can be evaluated that there is a measurement position deviation of about +2.5 mm in the X direction and about −1 mm in the Y direction.

  Note that the relationship between the amount of change in the outer peripheral portion of the film thickness difference ΔTHK and the amount of deviation of the measurement position may be examined in advance, and the amount of deviation may be evaluated based on the relationship. Steps S4 and S5 correspond to the evaluation step of the present invention.

  As described above, by performing the steps S1 to S5, the shift amount and the shift direction of the measurement position of the measuring instrument 1 can be easily evaluated.

  Next, the measurement position of the measuring instrument 1 is corrected based on the measurement position shift evaluation result (the shift amount and shift direction of the measurement position) obtained in S5 (S6). Specifically, for example, the initial transfer position of the wafer by the robot hand 3 is corrected in the direction opposite to the deviation direction of the obtained measurement position by the amount of deviation of the obtained measurement position. As a result, the wafer can be transported to a position where the origin of the measuring unit 5 and the center of the wafer coincide. Note that step S6 corresponds to the correction step of the present invention.

  Thereafter, the thickness of the wafer is measured using the corrected measuring instrument 1 (S7). This film thickness measurement is the same as the film thickness measurement in the normal preparation of S2. As a result, it is possible to obtain a measured value of the film thickness with good measurement position accuracy, and more accurately evaluate the shape of the outer peripheral portion of the epitaxial wafer. Note that step S7 corresponds to the post-correction measurement step of the present invention.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples of the present invention, but the present invention is not limited thereto.

Example 1
The steps S1 to S4 in FIG. 2 are performed using an epitaxial wafer having a diameter of 200 mm, that is, 1) normal preparation, and 2) film thickness in the X direction and Y direction are measured by 180 ° inversion preparation, and the difference between the same measurement points. Asked. At the time of measurement, measurement was performed at a 1 mm pitch from the outer periphery 95 mm to 98 mm. The results are shown in FIGS. Based on the results of FIG. 7 and FIG. 8, the step S5 of FIG. 2 was carried out to evaluate the measurement position deviation. The notch is down and about 2.5 mm in the X direction and about −1 mm in the Y direction. There was a measurement position shift.

  Next, after adjusting each measurement position based on the positional deviation amount and the positional deviation direction of the obtained measuring instrument, the positional deviation amount and the deviation direction of the measuring instrument were obtained again under the same conditions as described above. FIG. 9 shows the film thickness of the normal charge, the film thickness of the reverse charge, and the difference ΔTHK between the film thicknesses in the X direction. FIG. 10 shows the film thickness of the normal charge, the film thickness of the reverse charge, and the difference ΔTHK between the film thicknesses in the Y direction. As shown in FIG. 9 and FIG. 10, the position is improved with no notch downward and almost no displacement in the X and Y directions (the film thickness difference ΔTHK is almost zero).

(Example 2)
In order to investigate how the film thickness distribution on the outer periphery of the wafer affects the detection of the measurement position deviation, the following experiment was conducted.

  An epitaxial wafer was prepared on a P ++ substrate having a thickness of 4 μm and a thickness distribution of 5 mm to 3 mm from the outer periphery thereof adjusted to 0.40%, 0.18%, 0.10%, 0.03%. The position of the measuring device was shifted by 0.3 mm, 0.5 mm, 1.0 mm, and 2.0 mm, and the positional deviation of the measuring device was evaluated for each epitaxial wafer by the procedure shown in FIG. Table 1 and FIG. 11 show the evaluation results. Specifically, Table 1 indicates whether or not a position shift is detected for each position shift amount and each film thickness distribution by using ◯ and X. FIG. 11 shows the change amount of the film thickness difference in the outer peripheral portion with respect to the positional deviation amount of the measuring device for each film thickness distribution.

  As shown in Table 1, in the epitaxial wafer having the outer peripheral film thickness distribution of 0.1% or more, the positional deviation amount could be detected in the range of the positional deviation amount of 0.3 mm to 2 mm. This is because when the outer peripheral film thickness distribution is 0.1% or more (Examples 2-1, 2-2, 2-3), as shown in FIG. This is because even a positional deviation amount of 2 is a somewhat large value. On the other hand, in the epitaxial wafer (Example 2-4) in which the film thickness distribution of the outer peripheral part is 0.03%, since the change in the film thickness of the outer peripheral part is small, a positional deviation of 0.5 mm or less cannot be detected well. .

  From the results of Example 1 (FIGS. 7 to 10), it was confirmed that the present invention is effective in evaluating the positional deviation of the measuring device. Further, from the results of Example 2 (Table 1 and FIG. 11), it is found that an epitaxial wafer having a film thickness distribution of 0.1% or more at the outer peripheral portion is effective for evaluating the positional deviation of the measuring instrument of the present invention. It was.

  As described above, according to the present embodiment, since the measurement position deviation is evaluated by comparing the film thicknesses of the normal preparation and the reverse preparation, a minute measurement position deviation can be accurately detected. In the film thickness measurement by reversal charging, the wafer is reversed by 180 ° from the normal charging, so that a film thickness reflecting a positional shift in the direction opposite to the positional shift direction in the normal charging can be obtained. Thereby, the film thickness difference between the normal preparation and the reverse preparation can be increased, and the measurement position deviation in the measurement direction (X direction or Y direction) can be easily detected.

  Further, in this embodiment, measurement position deviations in two orthogonal directions (X direction and Y direction) are evaluated, so that any measurement position deviation in the two-dimensional plane can be detected. . Moreover, in this embodiment, since the X direction and the Y direction are determined based on the notch, the same measurement point can be easily measured by the normal preparation and the reverse preparation.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention. For example, in the above embodiment, the measurement position deviation of the measuring device is evaluated using a silicon epitaxial wafer, but the evaluation may be performed using an epitaxial wafer other than silicon.

  Moreover, although the said embodiment demonstrated the example which evaluated the measurement position shift | offset | difference of 2 directions by measuring the film thickness difference of 2 directions of a X direction and a Y direction, in addition to or instead of a X direction and a Y direction, it replaced. The film thickness difference in other directions (for example, a 45 ° direction or a 135 ° direction with the notch being 0 °) may be measured. By measuring the film thickness difference in other directions in addition to the X direction and the Y direction, the detection accuracy of the measurement position deviation can be improved.

  In the above-described embodiment, in the second measurement step performed following the normal charge film thickness measurement, the film thickness measurement was performed by reversing the wafer rotated 180 ° from the normal charge. Alternatively, the film thickness may be measured at the same measurement point as in the normal preparation while the wafer is rotated at an angle of 90 degrees (for example, 90 °). Also in this case, if there is a measurement position deviation, a difference occurs between the film thickness obtained in the second measurement step and the film thickness of the normal preparation, so that the measurement position deviation can be detected based on the difference.

  Further, in the above embodiment, the film thickness measurement of the normal preparation and the reverse preparation has also measured the film thickness of the wafer inner part in addition to the outer peripheral part of the wafer, but there is a measurement position deviation in the wafer inner part. However, since it is difficult for the film thickness difference to be generated between the normal preparation and the reverse preparation, the film thickness difference only at the outer peripheral portion may be obtained by measuring the film thickness only at the outer peripheral portion. As a result, the measurement position deviation can be more easily evaluated. Further, the film thickness may be measured only at one point in the outer peripheral portion (for example, a point of X = 98 mm, a point of Y = 98 mm). As a result, the measurement position deviation can be more easily evaluated.

  In the above-described embodiment, an example in which the robot hand also serves as a measurement stage, which is a wafer placement unit in the measurement unit, has been described. However, the present embodiment is used for evaluation of measurement position deviation of a measuring instrument provided with a measurement stage separately from the robot hand. The invention may be applied.

  Moreover, although the said embodiment demonstrated the example which applied this invention to the position shift evaluation of the film thickness measuring device based on FTIR method, even if it applies this invention to the film thickness measuring device based on systems other than FTIR method good. Further, the present invention may be applied to measurement position deviation evaluation of a measuring instrument that measures the characteristics of the epitaxial layer other than the film thickness (for example, an index (for example, Front-ZDD) that correlates with the surface roughness of the epitaxial layer).

DESCRIPTION OF SYMBOLS 1 Film thickness measuring instrument 2 Load port 3 Robot hand 4 Aligner 5 Measuring part 10 Notch

Claims (11)

A first measurement step of selecting a measurement point from points within the surface of the wafer having a film formed on the surface, and measuring the characteristics of the film at the measurement point with a measuring instrument;
After rotating the wafer around a rotation axis perpendicular to the surface of the wafer at an angle different from that in the first measurement step, the measurement instrument is configured to perform the measurement in the coordinate system set for the measurement instrument. A second measurement step for measuring the characteristic at the same measurement point as the first measurement step;
An evaluation step for evaluating a measurement position shift of the measuring device based on a comparison between the measurement value obtained in the first measurement step and the measurement value obtained in the second measurement step;
The evaluation method characterized by including.   2. The evaluation method according to claim 1, wherein in the second measurement step, the wafer is charged in a state of being rotated by 180 ° around the rotation axis from the time of the first measurement step. The characteristic is film thickness,
In the first measurement step and the second measurement step, at least the film thickness at the outer peripheral portion of the wafer is measured,
In the evaluation step, the measurement of the measuring instrument is performed based on a comparison between the measurement value in the outer peripheral portion obtained in the first measurement step and the measurement value in the outer peripheral portion obtained in the second measurement step. The evaluation method according to claim 1, wherein the positional deviation is evaluated.   The average film thickness in a range of 3 mm to 5 mm from the outer peripheral edge of the film is d, and Δd / d is 0.1% or more, where Δd is the amount of change in film thickness in the range. 3. The evaluation method according to 3. In the first measurement step and the second measurement step, at least in a first direction along one of two orthogonal lines out of straight lines passing through the plane of the wafer and in a second direction along the other, respectively. Measure the in-plane distribution of the characteristics in two directions,
In the evaluation step,
Based on the comparison between the measured value in the first direction obtained in the first measuring step and the measured value in the first direction obtained in the second measuring step, the measuring device in the first direction Evaluate measurement position deviation, and
Based on the comparison between the measured value in the second direction obtained in the first measuring step and the measured value in the second direction obtained in the second measuring step, the measuring device in the second direction The evaluation method according to claim 1, wherein the measurement position deviation is evaluated.   6. The evaluation method according to claim 5, wherein one of the first direction and the second direction is a direction along a straight line passing through the notch of the wafer. The characteristic is film thickness,
In the evaluation step, a difference between a measurement value at the outer peripheral portion of the wafer obtained in the first measurement step and a measurement value at the outer peripheral portion obtained in the second measurement step is obtained, and based on the difference The evaluation method according to claim 1, wherein the direction and amount of measurement position deviation of the measuring device are evaluated. The characteristic is film thickness,
The evaluation method according to claim 1, wherein the measuring instrument is a film thickness measuring instrument based on the FTIR method.   The evaluation method according to claim 8, wherein the film has a thickness of 0.3 μm or more and 100 μm or less.   The evaluation method according to claim 8, wherein the thickness of the film is 1 μm or more and 100 μm or less. The evaluation method according to any one of claims 1 to 10,
A correction step of correcting the measurement position of the measuring device based on the evaluation result of the evaluation step;
A post-correction measurement process that measures the characteristics of the wafer using the measuring instrument whose measurement position has been corrected in the correction process;
A measurement method comprising:

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