JP3611724B2 - Pattern inspection apparatus and pattern inspection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pattern inspection technique for inspecting a pattern formed on a sample by irradiating a sample with a focused charged particle beam and detecting and imaging a signal obtained from the sample in correspondence with a beam irradiation position. In particular, while deflecting the convergent beam in one direction, the sample stage is continuously moved in the direction crossing the scanning direction, and the signal obtained from the sample is detected in correspondence with the beam irradiation position. In the pattern inspection technique for inspecting the pattern by the scanned image obtained in step (1), the present invention relates to a pattern inspection technique that is effective for correcting the positional deviation of the inspection area accompanying the continuous movement of the stage and performing the inspection with high accuracy.
[0002]
[Prior art]
In general, inspecting a pattern formed on the surface of a sample involves irradiating the sample with a particle beam or light beam that can detect this pattern, and detecting the signal obtained from the sample due to this. Is done. The most typical example is SEM pattern inspection using a scanning image (hereinafter referred to as SEM image) of secondary electrons obtained by a scanning electron microscope (hereinafter referred to as SEM).
[0003]
Since the SEM image can image the surface shape of a sample with high resolution, attempts to use it for the inspection of circuit patterns on a semiconductor wafer have been actively made in recent years. In manufacturing a semiconductor integrated circuit device, a circuit pattern is formed on a semiconductor wafer by a deposition process, a lithography process, an etching process, or the like of a conductive material or a hardly conductive material. Since the quality of the circuit pattern formed on the semiconductor wafer greatly affects the productivity such as the manufacturing yield of the semiconductor integrated circuit device, the circuit pattern on the semiconductor wafer is used in the manufacturing process of the semiconductor integrated circuit device. Inspection is important.
[0004]
Today, with the high integration of semiconductor integrated circuit devices, circuit patterns formed on semiconductor wafers are rapidly miniaturized. For this reason, attention has been focused on a method using an SEM having a higher resolution than a conventionally used optical inspection apparatus as a circuit pattern inspection means.
[0005]
As a technology related to this, for example, Japanese Patent Laid-Open No. 5-258703 discloses a method and system for inspecting an X-ray mask or a pattern formed on a conductive substrate equivalent thereto using an SEM. ing.
[0006]
JP-A-59-160948 discloses that an electron beam is deflected in one direction, and a stage on which a semiconductor wafer is placed is continuously moved in a direction perpendicular thereto to generate an SEM image. Means for using and inspecting a circuit pattern at high speed is disclosed.
[0007]
Furthermore, Japanese Patent Laid-Open No. 63-218803 discloses a technique for precisely controlling the electron beam irradiation time on a semiconductor wafer at the time of image acquisition to reduce the influence of charge-up and gradation drift of the semiconductor wafer on image quality. Means for improving the reliability and sensitivity of SEM images used for inspection are disclosed.
[0008]
[Problems to be solved by the invention]
In today's semiconductor integrated circuit device manufacturing technology field, semiconductor wafers are becoming larger in size in line with the above-described miniaturization of circuit patterns. Therefore, inspection of a circuit pattern is required to inspect a wider area with higher resolution. For this purpose, it is essential to speed up the inspection.
[0009]
In pattern inspection using both electron beam scanning and stage continuous movement, it is necessary to correct the displacement of the inspection region caused by the rotation angle (azimuth) error when the wafer is placed on the stage. In this correction, the position angle of the inspection region is corrected by obtaining a rotation angle error of the wafer from two alignment marks on the wafer and performing control for correcting the rotation angle error on the deflecting device.
[0010]
When pattern inspection using both electron beam scanning and continuous stage movement is performed by a single stage electron beam scanning apparatus, both the deflection of the electron beam and the position correction accompanying the stage movement must be performed by a single stage deflection apparatus. Don't be. However, in order to perform position correction with a single stage deflection device, the deflection sensitivity of the deflection device (deflection sensitivity is the applied voltage applied to the deflection device) from the viewpoint that the deflection region of the electron beam must be wide. (It is a value indicating how many angle electron beams are deflected with respect to the current).
[0011]
As the deflection sensitivity is improved, the problem of image quality degradation (deflection noise) due to electrical noise of the deflection device itself becomes serious. Accordingly, there is a limit to the range in which the position of the inspection area can be corrected with a single stage deflection apparatus, and there is a problem that the position cannot be corrected in the case of pattern inspection of a large wafer.
[0012]
SUMMARY OF THE INVENTION An object of the present invention is to realize a pattern inspection that does not cause image quality deterioration due to deflection noise while performing position correction of a region to be inspected along a continuous stage movement in a SEM pattern inspection of a stage continuous movement method. That is.
[0013]
[Means for Solving the Problems]
In the present invention, in order to solve the above-mentioned problem, pattern inspection is performed by a deflecting device composed of two stages. The two-stage deflection device includes, for example, a main deflection device for deflecting the electron beam at a high speed and a narrow range and an auxiliary deflection device for deflecting the electron beam at a low speed and a wide range for the purpose of correcting the position of the inspection area. Consists of.
[0014]
That is, according to one embodiment of the present invention, a charged particle generator, a stage on which a sample on which a pattern is formed can be placed, and a first charged particle beam from the charged particle generator are used as the sample. A converging device that converges upward, an auxiliary deflection device that deflects the first charged particle beam, a main deflection device that deflects the first charged particle beam that has passed through the auxiliary deflection device in one direction, and the stage A stage driving device that moves in a direction crossing the one direction within the stage surface, a detector that detects second charged particles generated from the sample by the first charged particle beam irradiation to the sample , and the detection And an image generation device for acquiring an image corresponding to the region of the sample scanned by the first charged particle beam based on a signal from the measuring device, and calculating an installation deviation angle α ° of the sample with respect to the one direction Equipment Further, the auxiliary deflecting device is intended for the scanning region by the main deflecting device and the sample that increases or decreases with the movement of the stage, which occurs due to the installation deviation angle α ° of the sample. The first charged particle beam is deflected in synchronism with the movement of the stage so as to cancel the positional deviation from the inspected region .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described using an example in which an electron beam generator is used as a charged particle generator.
[0016]
FIG. 2 is a block diagram of a position correction control mechanism according to the present invention. In FIG. 2, the mirror 1 includes an electron beam generator 2, a blanking device 34, a fixed aperture 35, an auxiliary deflection device 24, a main deflection device 26, It is comprised by the convergence apparatus 5 and the detection apparatus 8.
[0017]
The sample chamber section 14 includes the sample 11 (including the alignment mark 23), the stage 10, the stage driving device 15, and the laser interferometer 18.
[0018]
The position correction control unit 19 includes a position correction control computer 20, a blanking circuit 31, a main deflection device control circuit 27, an auxiliary deflection device control circuit 25, and a convergence device control circuit 22.
[0019]
Before starting the pattern inspection, the sample 11 is scanned with the electron beam 9, and the detection device 8 detects the alignment mark 23 based on the generated secondary electrons 12. From the detected secondary electron signal 12 and the coordinate value obtained from the laser interferometer 18, the position correction control computer 20 determines the position setting error of the sample 11 with respect to the stage 10, that is, the sample 11 with respect to the reference direction on the stage 10. And the amount of displacement X and Y of the sample 11 with respect to the reference point on the stage 10 are calculated.
[0020]
After the inspection is started, the position correction control computer 20 sends a signal to the stage driving device 15 to inspect an appropriate area from the coordinates of the inspection area start point sent from the laser interferometer 18 and the sample deviation amounts X and Y. To control the stage 10.
[0021]
Further, from the coordinates of the inspection area start point sent from the laser interferometer 18 and the value of the rotation angle α of the sample, the position correction control computer 20 allows the auxiliary deflection apparatus to inspect the inspection area properly during the inspection. Signals are sent to the control circuit 25 and the convergence device control circuit 22 to control the auxiliary deflection device 24 and the convergence device 5.
[0022]
In the position correction control of the present invention, a deflection device having a small deflection sensitivity is used as a main deflection device that deflects an electron beam at high speed, and a deflection device having a large deflection sensitivity and a deflection aberration is less affected by an auxiliary deflection device that follows the movement of the electron beam. By using each apparatus, it is possible to perform stage position correction control over a wide range with high accuracy while minimizing the influence of electrical noise.
[0023]
FIG. 1 is a diagram showing an apparatus configuration according to an embodiment of the present invention.
[0024]
In FIG. 1, a mirror 1 includes an electron generator 2, a beam alignment device 33, for example, a converging device 3 comprising a magnetic lens system, a blanking device 34, a fixed aperture 35, eg, an auxiliary deflection device 24 comprising a magnetic field deflection system, A main deflection device 26 composed of an electrostatic deflection system, for example, a converging device 5 composed of a magnetic lens system, an ExB deflection device 6 and a reflection plate 7 are constructed.
[0025]
Here, the electron generator 2 includes a Schottky field emission electron source 36, a suppressor electrode 37, a lead electrode 38, a first anode electrode 39, and a second anode electrode 40.
[0026]
The detection device unit 28 includes a detection device 8 including a semiconductor detector, and an AD conversion unit 29 including an AD conversion substrate at 100 MHz. The detection device unit 28 can apply a high voltage to attract secondary electrons to the detection device.
[0027]
The sample chamber section 14 includes a stage 10 on which the sample 11 including the alignment mark 23 is placed, a stage driving device 15, and a laser interferometer 18.
[0028]
The position correction control unit 19 includes a position correction control computer 20, a blanking circuit 31, an auxiliary deflection device control circuit 25, a main deflection device control circuit 27, and a convergence device control circuit 22. The electron beam 9 generated by the electron generator 2 is once crossed over by the converging device 3 (formed in the vicinity of the fixed aperture 35 in FIG. 1), then deflected at high speed by the main deflecting device 26 and converged. The apparatus 5 focuses on the sample 11.
[0029]
Here, the beam alignment device 33 is used to adjust the optical axis of the electron beam 9. The blanking device 34 is used to deflect the electron beam 9 and block the electron beam 9 with the fixed aperture 35 when it is not desired to irradiate the sample 11 with the electron beam 9. The blanking device 34 is blanked at high speed by the position correction control computer 20 and the blanking circuit 31 in order to realize high-speed electron beam scanning in only one direction by the main deflection device 26 during pattern inspection. It is possible to be controlled in this way.
[0030]
As described above, the auxiliary deflection device 24 is used for position correction control in conjunction with the movement of the stage 10. The sample 11 is fixed on the stage 10. Further, a deceleration voltage (hereinafter referred to as a retarding voltage) for decelerating the primary electron beam 9 from the electron beam generator 2 can be applied to the sample 11 by the power source 46. The sample 11 moves two-dimensionally with respect to the mirror body 1 as the stage 10 moves in the plane of the stage 10 by the stage driving device 15. The movement of the stage 10 is controlled by the stage driving device 15.
[0031]
Here, among the moving directions of the stage 10, the moving direction perpendicular to the scanning direction of the primary electron beam 9 is referred to as “continuous moving direction”, and the moving direction parallel to the scanning direction of the primary electron beam 9 is referred to as “feeding direction”. . The secondary electrons 12 generated from the sample 11 are accelerated by the retarding electric field, separated from the primary electron beam 9 by the ExB deflecting device 6 in which the magnetic field is superimposed on the electric field, and collide with the reflecting plate 7. Secondary electrons 12 generated from the reflecting plate 7 are detected by the detection device 8 to which a high voltage is applied.
[0032]
The analog signal based on the secondary electrons 12 is converted into a digital signal by the AD converter 29, and then sent to the grounded image generating device 13 through the optical fiber cable 30. The acquisition of the SEM image is performed by using both the deflection of the electron beam 9 and the continuous movement of the stage 10.
[0033]
Regarding the position correction control, an alignment mark (not shown) on the sample 11 is scanned with the electron beam 9 before the pattern inspection is started, and the generated secondary electrons 12 are detected by the detection device 8. The position correction control computer 20 calculates the rotation angle α ° of the sample 11 and the shift amounts X and Y of the sample 11 from the detected secondary electron signal and the coordinate value obtained from the laser interferometer 18.
[0034]
After the inspection is started, the position correction control computer 20 sends a signal to the stage driving device 15 to inspect a desired area from the coordinates of the inspection area start point sent from the laser interferometer 18 and the sample deviation amounts X and Y. To control the stage 10.
[0035]
Further, from the coordinates of the inspection area start point sent from the laser interferometer 18 and the value of the rotation angle α of the sample, the position correction control computer 20 allows the auxiliary deflection apparatus to inspect the inspection area properly during the inspection. Signals are sent to the control circuit 25 and the convergence device control circuit 22 to control the auxiliary deflection device 24 and the convergence device 5.
[0036]
The movement of the stage 10 in the position correction control will be described with reference to FIG. The stage 10 is at a constant speed (for example, 5 to 8 mm / sec) and ends from the start point 42 in the continuous movement direction defined above (that is, the direction perpendicular to the scanning locus 48 of the electron beam 9 indicated by the arrow in FIG. 3). After moving to 43, the feed is again returned to the starting point 42 in the continuous movement direction, and at the same time, a predetermined amount (feed amount S) is sent in the defined feed direction (that is, the direction perpendicular to the continuous movement direction).
[0037]
Here, the feed amount S of the stage is controlled to be S = D / cos α, where D is the width of the stripe-shaped pattern 50 drawn on the sample 11 by scanning the electron beam 9.
[0038]
On the other hand, simultaneously with the continuous movement of the stage 10, the primary electron beam 9 is scanned while sequentially moving the starting point of scanning by an amount corresponding to the rotation angle α of the wafer with the same deflection width as the feed amount S of the entire stage.
[0039]
The present invention includes a charged particle generator 2, a stage 10 on which a pattern-formed sample 11 can be placed, and a convergence device 5 that converges a first charged particle beam 9 from the charged particle generator 2 onto the sample 11. A main deflection device 26 that deflects the first charged particle beam 9 in one direction, an auxiliary deflection device 24 that deflects the first charged particle beam 9, and a stage 10 crossing the one direction in the stage surface. A stage driving device 15 that moves in a moving direction, a detection device 8 that detects a second charged particle beam 12 generated from the sample 11 by irradiation of the sample 11 with the first charged particle beam 9, Based on the signal, an image generating device 13 that generates an image corresponding to the region of the sample 11 scanned by the first charged particle beam 9 and an installation deviation angle α ° of the sample 10 with respect to the reference direction of the stage 10 are set. A device 20 for calculating The offset of the scanning region by the main deflection device 26 and the intended region to be inspected in the sample 11 which is increased or decreased with the movement of the stage 11 generated due to the installation deviation angle α ° of the sample 11 is offset. Thus, the first charged particle beam 9 is deflected by the auxiliary deflection device 24 in synchronization with the movement of the stage 10.
[0040]
In the embodiment of the present invention, a quadrupole magnetic deflecting device is used as the auxiliary deflecting device 24. However, since the auxiliary deflecting device 24 deflects an electron beam in a wide range, image quality is deteriorated due to deflection aberration. There is a fear. As the auxiliary deflection device 24, a multipolar magnetic field deflection device and a multipolar electrostatic deflection device can be used. Of course, their use does not impair the effectiveness of the present invention.
[0041]
Example 1
One specific embodiment of the present invention using the apparatus of FIG. 1 will be described with reference to the drawings. FIG. 4 explains the outline of the pattern inspection by the position correction control of the present invention. In FIG. 4, assuming that the substrate 11 is rotated by α ° with respect to the feed direction of the stage 10 and fixed on the stage 10, the pattern 41 to be inspected on the substrate 11 is in the feed direction of the stage 10. On the other hand, it is fixed by rotating α °.
[0042]
When α is small, the main deflection device 26 (see FIG. 1) deflects the electron beam 9 at a high speed by a constant width (D / cos α) in the same direction as the feed direction of the stage 10.
[0043]
On the other hand, the auxiliary deflection device 24 has a scanning region and an intention of the main deflection device 26 that increase with continuous movement of the stage 10 because the pattern 41 is fixed by rotating by α ° with respect to the feed direction of the stage 10. In order to correct the positional deviation of the region to be inspected, the electron beam 9 is deflected so that a scanning region 50 in which the locus 48 of the electron beam 9 is corrected is formed as shown in FIG. FIG. 6 shows the relationship between the deflection signals in the auxiliary deflection device 24 and the main deflection device 26 at this time.
[0044]
As shown in FIG. 6A, the main deflection device 26 has a deflection signal waveform period of 10 μsec when the sampling number of one line is 1000 at a sampling frequency of 100 MHz.
[0045]
On the other hand, as shown in FIG. 6B, the auxiliary deflecting device 24 gradually adds a deflection voltage corresponding to the rotation angle of the pattern every 10 μsec every time the main deflecting device 26 deflects one line. . By performing this process during pattern inspection, position correction control is performed.
[0046]
(Example 2)
Another specific embodiment of the present invention using the apparatus of FIG. 1 will be described with reference to the drawings. In the case of the first embodiment, the main deflection device 26 deflects the electron beam 9 in the same direction as the feed direction of the stage 10. However, when the pattern rotation angle α ° of the pattern 41 to be inspected on the substrate 11 with respect to the feed direction of the stage 10 is large, the deflection width D / cos α of the main deflection device 26 becomes large, and the pattern inspection speed is increased. It is disadvantageous.
[0047]
In this case, this problem can be solved by providing the main deflection device 26 itself with a function of correcting the rotation error of the wafer. FIG. 5 illustrates an outline of pattern inspection by position correction control according to the present invention when a rotation error correction function is added to the main deflection device 26 itself.
[0048]
In FIG. 5, the pattern 41 to be inspected on the substrate 11 is fixed by being rotated by α ° with respect to the stage moving direction.
[0049]
When α is large, the main deflecting device 26 deflects the electron beam 9 at a constant scanning width D at a high speed in a direction rotated α ° with respect to the stage feed direction.
[0050]
On the other hand, in the auxiliary deflection device 24, as in the first embodiment, the main deflection device 26 increases with the continuous movement of the stage 10 because the pattern 41 is rotated and fixed by α ° with respect to the feed direction of the stage 10. As shown in FIG. 5, the electron beam 9 is deflected so as to form a scanning region 50 in which the locus 48 of the electron beam 9 is corrected.
[0051]
In the above embodiments, an electron beam generator is used as the charged particle generator, but the present invention is not limited to this, and it goes without saying that an ion beam generator can be used. .
[0052]
【The invention's effect】
As described above, according to the present invention, position correction control over a wide range can be performed with high accuracy while minimizing the influence of electrical noise in pattern inspection using both deflection of charged particle beams and continuous stage movement. become.
[0053]
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a configuration of an embodiment of the present invention.
FIG. 2 is a block diagram for explaining an outline of a position correction control mechanism in the present invention.
FIG. 3 is a diagram for explaining stage movement in position correction control;
FIG. 4 is a diagram for explaining an outline of pattern inspection by position correction control according to the present invention.
FIG. 5 is a diagram for explaining an outline of pattern inspection by position correction control according to the present invention;
FIG. 6 is a diagram for explaining a relationship between deflection signal waveforms of a main deflection device and an auxiliary deflection device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Mirror body, 2 ... Electron generator, 3 ... Convergence apparatus, 4 ... Deflection apparatus, 5 ... Convergence apparatus, 6 ... ExB deflection apparatus, 7 ... Reflection plate, 8 ... Detection apparatus, 9 ... Electron beam, 10 ... Stage 11 ... Sample, 12 ... Secondary electron, 13 ... Image generating device, 14 ... Sample chamber, 15 ... Stage driving device, 16 ... Start point of pattern inspection, 17 ... End point of pattern inspection, 18 ... Laser interferometer, 19 DESCRIPTION OF SYMBOLS ... Position correction control part, 20 ... Position correction control computer, 21 ... Deflection device control circuit, 22 ... Convergence device control circuit, 23 ... Alignment mark, 24 ... Auxiliary deflection device, 25 ... Auxiliary deflection device control circuit, 26 ... Main deflection 27: main deflection device control circuit, 28: detection device unit, 19: AD conversion unit, 30: optical fiber cable, 31: blanking circuit, 32: movable diaphragm, 33: beam alignment device, 34: blank 35 ... fixed aperture, 36 ... Schottky field emission electron source, 37 ... suppressor electrode, 38 ... extraction electrode, 39 ... first anode electrode, 40 ... second anode electrode, 41 ... pattern, 42 ... stage continuous Start point of movement, 43 ... End point of continuous stage movement.

Claims (6)

A charged particle generator; a stage on which a sample on which a pattern is formed can be placed; a converging device that converges a first charged particle beam from the charged particle generator on the sample; and the first charged particle beam. An auxiliary deflection device that deflects the first charged particle beam that has passed through the auxiliary deflection device in one direction, and a stage that moves the stage in a direction crossing the one direction within a stage surface The first charged particle beam based on a drive device, a detector that detects second charged particles generated from the sample by the first charged particle beam irradiation to the sample , and a signal from the detector An image generation device that acquires an image corresponding to the region of the sample scanned by the device, a device that calculates an installation deviation angle α ° of the sample with respect to the one direction, and the auxiliary deflection device includes: Sample In order to cancel out the positional deviation between the scanning area by the main deflection device and the intended inspection area in the sample, which is caused by the installation deviation angle α °, and increases or decreases with the movement of the stage. A pattern inspection apparatus for deflecting the first charged particle beam in synchronization with movement of a stage . The pattern inspection apparatus according to claim 1 , wherein the one direction intersects the moving direction of the stage at an angle of ( 90 ° −α °) . 2. The pattern inspection apparatus according to claim 1 , wherein the auxiliary deflection device is a device that performs low-speed deflection and a wide range of deflection, and the main deflection device is a device that performs high-speed deflection and a narrow range of deflection. to pattern inspection apparatus. 2. The pattern inspection apparatus according to claim 1 , wherein the stage driving device includes means for moving the stage also in the one direction . 2. The pattern inspection apparatus according to claim 1 , wherein the detection device includes a semiconductor detection device. No. generated from charged particle generator 1 A step of focusing the charged particle beam by a focusing device and the auxiliary deflection device 1 A step of deflecting the charged particle beam and a main deflection device 1 A step of deflecting the charged particle beam in one direction, a step of moving the sample stage in a direction crossing the one direction within a stage surface by a stage driving means, and the step of applying the first to the sample 1 Generated from the sample by irradiation of charged particle beam 2 And detecting the charged particles of the first and second signals based on a signal from the detection device. 1 A step of generating an image corresponding to the region of the sample scanned by the charged particle beam of the sample, and an installation deviation angle α of the sample with respect to the one direction ゜ And the step of deflecting the charged particle beam by the auxiliary deflecting device is increased or decreased with the movement of the sample stage, which occurs due to the sample misalignment angle. The first synchronizer is synchronized with the movement of the stage so as to cancel out the positional deviation between the scanning area by the main deflection device and the intended inspection area in the sample. 1 A pattern inspection method comprising: deflecting a charged particle beam of the first particle by the auxiliary deflection device.

Images