JP2002157969A - Sample evaluating device using electron beam and method of manufacturing semiconductor device by using this device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an aberration even if a visual field is wide by improving an objective lens in a sample evaluating device of multibeams. SOLUTION: Electrodes 21, 23 and 25 for constituting the objective lens are grounded, and lens power is divided into a front stage and a rear stage by grounding of an intermediate electrode 23. Voltage is independently impressed between the electrodes 21 and 22, and between the electrodes 24 and 25, and the front stage and rear stage power can be independently adjusted. The front stage power is used for forming an image of a main electron beam on the optical axis in the central vicinity of the rear stage power, and the rear stage power is used for forming the final image on a surface of a wafer. A reducing lens of this sample evaluating device is adjusted so that an intermediate image forming surface M is positioned in the center of the front stage power. Since the rear stage power is used for forming the image and the front stage power is used to control a main beam of light to pass through the optical axis in the central vicinity of the rear stage power, the main beam of light is not diffused so that even when the visual field is widened, a distortion aberration can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for evaluating a sample using an electron beam, and more particularly to an apparatus for evaluating a sample which is characterized by an electrostatic lens provided in the apparatus. The present invention also relates to a semiconductor device manufacturing method including a step of evaluating a semiconductor wafer during and after processing using such a sample evaluation apparatus.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor wafer sample evaluation apparatus, an SEM (scanning electron microscope) is generally used to detect a defect such as a contact failure and a line width. In an SEM, a primary electron beam is radiated in the form of a spot onto a surface to be observed, that is, a detection region of a wafer, which is a sample, and secondary electrons emitted thereby are accelerated and taken out and received by a detector. Pixel data is obtained by detecting the amount of electrons. By scanning the primary electron beam two-dimensionally on the surface of the wafer,
Image data of the entire detection area is obtained.

[0003]

However, the SEM
In the above, as described above, the detection area on the wafer is set to 2
Since it is necessary to perform dimensional scanning, it takes a relatively long time to obtain image data of all pixels in the detection area. On the other hand, in a defect inspection of a semiconductor device, it is required to improve a throughput so as to substantially match a processing speed of a wafer processing apparatus.
Therefore, when the SEM is used for defect inspection of a semiconductor device or the like, a desired throughput cannot be obtained, and it takes a long time to manufacture a semiconductor device including a wafer evaluation process. In view of such non-high-speed characteristics of the SEM, attempts have been made to obtain image data of the inspection area at a high speed by using a multi-beam electron optical system instead of the SEM. However, even in this case, various technical problems remain unsolved, and therefore, the use of the multi-beam electron optical system instead of the SEM for the evaluation such as the defect inspection of the semiconductor device is It was said to be difficult.

[0004] One of the technical problems of the multi-beam electron optical system
First, there is a problem that aberration is increased when a wide field of view is to be obtained. That is, a simple Einzel lens is generally used for an objective lens used in a multi-beam electron optical system. In this case, aberrations increase, and it is difficult to obtain a wide field of view. In addition,
Even if a simple Einzel lens is used, if one image is formed using two such lenses, it is possible to suppress the deterioration of aberration to some extent. However, in this case, since the number of beams cannot be increased, it is difficult to realize a desired high speed in a defect inspection or the like.

The reason why the number of beams cannot be increased is as follows. When performing multi-beam imaging using an electrostatic lens, a lens having a short focal length f may be simply arranged at f + dz (dz ≦ f) behind the wafer surface as a sample or an intermediate imaging surface. However, in an electrostatic lens, when the applied voltage is increased, the electric field intensity in the lens is increased, so that f is shortened. However, by increasing the applied voltage, the applied voltage at which a potential barrier higher than the energy of the incident charged particles is formed is reduced. Then, reflection occurs and the lens does not function. In addition, in the case of the same applied voltage, the small lens can shorten the focal length f. However, even if an attempt is made to reduce the distance between adjacent electrodes constituting the lens in order to reduce the size of the lens, the distance between the electrodes is naturally limited in view of the dielectric strength. In addition, a small lens having a narrow paraxial region has a problem that aberration is bad for a wide field of view. Therefore, it has been extremely difficult to form an electrostatic lens having a short focal length f while preventing deterioration of aberration.

The present invention has been made in view of such conventional problems, and a first object of the present invention is to achieve good aberration and a multi-beam even when the field of view is wide. An object of the present invention is to provide a sample evaluation device using an electrostatic lens. A second object of the present invention is to provide a method for manufacturing a semiconductor device while inspecting a semiconductor device in process using a sample evaluation apparatus which achieves the first object.

[0007]

In order to achieve the above-mentioned first object, according to the present invention, a sample is irradiated with a primary electron beam and secondary electrons emitted from the sample are detected. In a sample evaluation apparatus for obtaining image data of a sample, an electrostatic lens including five or more electrodes is used as an objective lens, and at least one or more primary optical systems that irradiate the sample with a plurality of primary electron beams; At least one or more secondary optical systems for guiding secondary electrons to at least one or more detectors, wherein the primary optical system separates a plurality of primary electron beams from each other by a distance greater than the distance resolution of the secondary optical system. It is characterized in that it is configured to irradiate a position.

[0008] In the sample evaluation apparatus described above, the electrostatic lens is preferably configured so that the center electrode at the center is divided into a front stage and a rear stage to divide the lens power. At least one of the rear part is composed of four or more electrodes including the center electrode, and by changing the voltage applied to these electrodes, the front part or the rear part,
Alternatively, the center positions of both lens powers can be adjusted independently. Further, in one embodiment of the electrostatic lens, at least one electrode other than the center electrode among the electrodes constituting the front stage is a multipole electrode having four or more quadrupoles. Thus, the deflection angle due to the lens power of the front stage can be made different, and astigmatism in the pupil space can be corrected. The present invention also provides a semiconductor device manufacturing method including a step of evaluating a semiconductor wafer using the above-described sample evaluation apparatus.

[0009]

FIG. 1A is a schematic diagram showing an optical system of a sample evaluation apparatus using an electron beam according to an embodiment of the present invention. In FIG. 1, an electron beam emitted from an electron gun 1 is focused by a condenser lens 2 to form a crossover at a point 4. Below the condenser lens 2, a first multi-aperture plate 3 having a plurality of openings is arranged, thereby forming a plurality of primary electron beams. Each of the formed primary electron beams is reduced by the reduction lens 5 and projected onto a point 15. After focusing at the point 15, the objective lens 7
Focuses on the wafer 8 as a sample. The plurality of primary electron beams from the first multi-aperture plate 3 are deflected by a deflector 19 disposed between the reduction lens 5 and the objective lens 7 so as to simultaneously scan the surface of the wafer 8. Incidentally, reference numeral 20 denotes an XY stage on which the wafer 8 is placed and moves in the xy plane.

In order to prevent curvature of field between the reduction lens 5 and the objective lens 7 from occurring, the first multi-aperture plate 3, as shown in FIG. Are arranged, and the points projected on the x-axis have an equal interval. A plurality of points of the wafer 8 are irradiated with the plurality of focused primary electron beams, and the secondary electron beams emitted from the plurality of irradiated points are attracted by the electric field of the objective lens 7 to be narrowly focused. And EXB separator 6
And input to the secondary optical system. The image formed by the secondary electron beam is focused on a point 16 closer to the objective lens 7 than the point 15. This is because the plurality of primary electron beams each have energy of about 500 eV on the surface of the wafer 8, whereas the secondary electron beam has energy of only several eV.

The secondary optical system has magnifying lenses 9 and 10, and the secondary electron beam passing through these magnifying lenses forms an image on a second multi-aperture plate 11. Then, the light passes through the plurality of openings of the second multi-aperture plate and is detected by the plurality of detectors 12. Note that, as shown in FIG. 1B, the plurality of openings of the second multi-aperture plate 11 and the plurality of openings of the first multi-aperture plate 3 are arranged in front of the detector 12. It corresponds to one to one. Each of the detectors 12 converts the received secondary electron beam into an electric signal representing its intensity. The electric signal from each detector 12 is amplified by an amplifier 13 and then converted into image data in an image processing device 14. A scanning signal for deflecting the primary electron beam from the deflector 19 is also supplied to the image processing device 14, whereby the image processing device 14 obtains image data representing an image of the surface of the wafer 8. . By comparing the obtained image data with the standard pattern, a defect of the wafer 8 can be detected. Further, the pattern to be evaluated on the wafer 8 is moved to the vicinity of the optical axis of the primary optical system by registration, The line width of the pattern on the wafer 8 can be measured by taking out the line width evaluation signal by scanning the line and appropriately correcting the signal.

The primary electron beam passing through the opening of the first multi-aperture plate 3 is focused on the surface of the wafer 8, and the secondary electron beam emitted from the wafer 8 is imaged on the detector 12. At this time, it is preferable to take care so as to minimize the influence of three aberrations, distortion, field curvature and field astigmatism caused by the primary optical system. If the minimum value of the interval between the irradiation positions of the plurality of primary electron beams is separated by a distance larger than the aberration of the secondary optical system, crosstalk between the plurality of beams can be eliminated.

FIG. 2 shows in detail a first embodiment of the electrostatic lens constituting the objective lens 7 shown in FIG.
In FIG. 2, (a) shows an electrode arrangement of the electrostatic lens, and (b) and (c) show an optical lens system equivalent to the electrostatic lens shown in (a). In FIG. 2, 2
1 to 25 are electrodes, and the electrodes 21, 23, and 25 are grounded. The electrode 23 constitutes an intermediate electrode, and the lens power is divided into a front stage and a rear stage by grounding the electrode. That is, the electrodes 21 and 22 are the first and second electrodes (first and first electrodes and second electrode) forming the former part, and a voltage is applied between these electrodes.
Reference numerals 25 and 25 denote first and second electrodes (second-stage first and second electrodes) constituting the second-stage power, and a voltage is applied between these electrodes.

As described above, since the intermediate electrode 23 is grounded, the lens power can be controlled independently of the front-stage power and the rear-stage power around the intermediate electrode 23. In other words, the former-stage power is controlled by the voltage applied between the former-stage second electrode 22 and the grounded first-stage first electrode 21, and the voltage is applied between the latter-stage first electrode 24 and the grounded latter-stage second electrode 25. The post-stage power can be controlled by the applied voltage. The first-stage power is used to form an image of the main electron beam on the optical axis near the center of the second-stage power, and the second-stage power is used to form a final image on the surface of the wafer 8. Further, the intermediate image plane M
The reduction lens 5 of the sample evaluation apparatus in FIG.

The equivalent lens system shown in FIG. 2 (b) shows the state of the light beam when the former stage power is not used, and the solid line shows the principal light beam. The light rays form an image on the intermediate image plane M, but as shown in the figure, the chief rays are diverging slightly.
The principal ray forms an image behind the center of the lens (principal point = node) by the lens corresponding to the subsequent first electrode 24. Therefore, pincushion distortion occurs. this is,
This corresponds to a case where a conventional Einzel lens is used alone. FIG. 2C shows a situation in which the voltage of the front-stage second electrode 22 is controlled so that the principal ray intersects the optical axis at the center of the lens corresponding to the rear-stage first electrode 24. . In this case, since the chief ray forms an image almost at the center of the post-stage power, not only the distortion is almost corrected, but also the paraxial region of the post-stage power is used, so that coma and chromatic aberration of magnification are considerably reduced. Is done.

As described above, in the electrostatic lens of the first embodiment shown in FIG. 2, since the lens powers of the front part and the rear part can be controlled independently, for example, the lens power of the rear part is controlled. It is used for imaging, and can be used to control the front lens power so that the principal ray passes through the optical axis near the center of the rear lens power. As a result, the principal ray does not diffuse, so that distortion can be reduced even when the field of view is widened. That is,
In general, in a system in which a principal ray is imaged at the front node of the lens system (coincides with the principal point when the refractive index of all the rear surfaces of the lens system is the same), no distortion occurs, and The distortion becomes a barrel type image formed on the object surface, and a pin-shaped type image formed on the image surface side. Therefore, if a field lens is arranged at an intermediate image forming position and its power is controlled to adjust the principal ray incident on the image forming lens, distortion can be reduced.

This is applied to an electrostatic lens. Under conditions where no distortion occurs, the center (principal surface) of the imaging lens
In the vicinity, principal rays of all angles of view are concentrated. Therefore, even when a small electrostatic lens having a smaller paraxial region than the conventional imaging lens is used, various aberrations can be suppressed well. Further, with a small electrostatic lens, the shortest focal length can be shortened, so that lower aberrations can be realized. In this way, by controlling the principal ray with the field lens (corresponding to the lens power of the front stage), aberrations can be reduced even when a small electrostatic lens for imaging is used, even when the field of view is widened. And a multi-beam can be obtained.

FIGS. 3A and 3B respectively show in detail second and third embodiments of the electrostatic lens that can be employed as the objective lens 7 (FIG. 1). The second embodiment is different from the first embodiment shown in FIG.
An electrode (first-stage third electrode) 22 ′ is added, and the front-stage portion includes four electrodes including the center electrode 23. Third
The third embodiment is different from the first embodiment in that a third electrode (later third electrode) 24 ′ is added to the latter part, and the latter part is composed of four electrodes including the center electrode 23. In the electrostatic lens according to the second embodiment shown in FIG. 3A, the voltage applied to the front-stage second electrode 22 and the voltage applied to the front-stage third electrode 22 ′ are independently controlled. As a result, the magnitude of the former-stage power and the center position thereof can be independently adjusted.

Therefore, by controlling the reduction lens 5 of the sample evaluation apparatus of FIG. 1, the intermediate imaging position 15 can be changed, and the magnification by the reduction lens 5 can be changed. Then, the center position of the former stage power is set to the intermediate image plane position M
As described with reference to FIG. 2, while maintaining the relationship, the pre-stage power is adjusted by changing the voltage applied to the pre-stage first electrode, and the chief ray is imaged substantially at the center of the post-stage power. By doing so, it is possible to perform a zoom action for continuously changing the magnification of the image while keeping the aberration small.

In the electrostatic lens according to the third embodiment shown in FIG. 3B, the voltage applied to the second electrode 24 and the voltage applied to the third electrode 24 'are changed independently. This makes it possible to independently adjust the magnitude of the post-stage power and the center position thereof. Since the change in the position of the center of the post-power corresponds to the change in the position of the imaging lens, the zooming operation for continuously changing the magnification of the image with the intermediate image plane position M fixed is performed. It can be carried out. In this case, it is a matter of course that the former-stage power is changed with the movement of the center of the latter-stage power, and the principal ray is controlled so as to always form an image at almost the center of the latter-stage power. By doing so, it is possible to perform the imaging operation while keeping the aberration small.

In the electrostatic lens according to the second embodiment, the number of electrodes at the front stage may be four or more. Third
Also in the electrostatic lens according to the embodiment, the number of electrodes at the rear stage may be four or more. In addition, if both the center position of the former stage power and the center position of the latter stage power can be controlled, the magnification can be changed with a corresponding degree of flexibility.
More preferably, the number is equal to or more than the number.

FIG. 4 shows in detail a fourth embodiment of the electrostatic lens that can be employed as the objective lens 7 (FIG. 1). 4A shows the arrangement of the electrodes of the electrostatic lens, and FIG. 4B shows the equivalent lens system. In the fourth embodiment, the quadrupole electrode 2 is used as the former second electrode 22 in the first embodiment shown in FIG.
6 is used. Like the sample evaluation device in Fig. 1,
When the EXB separator 6 is used, the inclination of the principal ray on the intermediate image plane M behind the EXB separator 6 differs in the direction orthogonal to the optical path section, and astigmatism in the pupil space cannot be avoided. That is, assuming an xyz orthogonal three-dimensional coordinate system in which the optical axis is the z-axis, the intermediate imaging plane M is an xy plane, and the aberration is corrected in the intermediate imaging plane M. Light rays ((b) of FIG. 4)
(Solid line) differs between the x direction and the y direction.

Therefore, it is necessary to deflect θ1 in the x direction and θ2 in the y direction in order to concentrate each of them at the center of the post-stage power. Therefore, each of the quadrupole electrodes 6 can obtain a different deflection angle for each pole. Such a voltage is applied. However, since θ1> θ2, it is necessary to apply a voltage to the quadrupole electrode 26 so that the lens power is stronger in the x direction than in the y direction.
Is shown in As shown in FIG. 5, a main voltage V1 as the imaging power and a voltage V2 for astigmatism adjustment (V1>V2>).
0) is superimposed so that the applied voltage in the x direction is increased. As a result, chief rays having different inclinations can be imaged together at the center of the post-stage power, and various aberrations can be corrected.

As described above, in the electrostatic lenses of the first to fourth embodiments, it is preferable that the center position of the former-stage power substantially coincides with the intermediate imaging plane. That is, in order to focus the principal ray on the optical axis near the center of the post-stage power, it is generally necessary to adjust the lens system placed in front of the electrostatic lens simultaneously with the pre-stage power. If the center position of the former power is set to be approximately the intermediate image plane, the chief ray can be focused on the optical axis near the center of the latter power only by adjusting the former power.
Adjustment is simplified. The fact that the center position of the former stage power is “substantially coincides with the intermediate imaging plane” means that it is not necessary to exactly match the center position with the intermediate imaging plane. This means that a position having a predetermined tolerance from the intermediate imaging plane may be used. The permissible error is determined according to design conditions and the like.

Next, a method for manufacturing a semiconductor device according to the present invention will be described. The semiconductor device manufacturing method of the present invention
The above-described sample evaluation apparatus is used in a semiconductor device manufacturing method described below with reference to FIGS. 6 and 7. As shown in FIG. 6, the semiconductor device manufacturing method is roughly divided into a wafer manufacturing step S1 for manufacturing a wafer, a wafer processing step S2 for performing necessary processing on the wafer, and a mask required for exposure. It comprises a mask manufacturing step S3, a chip assembling step S4 for cutting out chips formed on the wafer one by one to make them operable, and a chip inspection step S5 for inspecting completed chips. Each of these steps
It includes several sub-steps.

Among the above-mentioned steps, a step that has a decisive effect on the manufacture of the semiconductor device is a wafer processing step. This means that in this process, a designed circuit pattern is formed on a wafer, and a memory or M
This is because many chips that operate as PUs are formed.
As described above, it is important to evaluate the processing state of the wafer performed in the sub-process of the wafer processing process which affects the manufacture of the semiconductor device. The sub-process will be described below.

First, a dielectric thin film serving as an insulating layer is formed, and a metal thin film for forming a wiring portion and an electrode portion is formed. The thin film is formed by CVD, sputtering, or the like. Next, the formed dielectric thin film and metal thin film, and the wafer substrate are oxidized, and using the mask or reticle created in the mask manufacturing process S3,
In a lithography process, a resist pattern is formed. Then, the substrate is processed according to a resist pattern by dry etching technology or the like, and ions and impurities are implanted. Thereafter, the resist layer is peeled off, and the wafer is inspected. Such a wafer processing step
This process is repeated for a required number of layers, and a wafer before being separated for each chip in the chip assembling step S4 is formed.

FIG. 7 is a flowchart showing a lithography step which is a sub-step of the wafer processing step of FIG. As shown in FIG. 6, the lithography process includes a resist coating process S21, an exposure process S22, a developing process S23, and an annealing process S24. In the resist application step S21, a resist is applied on the wafer on which the circuit pattern is formed by using CVD or sputtering, and in the exposure step S22, the applied resist is exposed. Then, in a developing step S23, the exposed resist is developed to obtain a resist pattern, and in an annealing step S24, the developed resist pattern is annealed and stabilized. These steps S21 to S21
S24 is repeatedly executed by the required number of layers.

In the method of manufacturing a semiconductor device according to the present invention, not only a process in the middle of processing but also a chip inspection process S5 for inspecting a completed chip by using the sample evaluation apparatus described with reference to FIGS. By using, even in the case of a semiconductor device having a fine pattern, an image with reduced distortion and blur can be obtained.
Wafer defects can be reliably detected. In addition, the processing apparatus in which the defect inspection apparatus is arranged in the vicinity may be any processing apparatus as long as it performs processing requiring evaluation.

[0030]

As described above, in the present invention, a sample evaluation apparatus having a multi-beam configuration with good throughput is used, and an electrostatic lens used as an objective lens in the apparatus is composed of a plurality of electrodes. These electrodes are divided into a front part and a rear part which can be controlled independently.
Therefore, the rear part can be used as an imaging lens, and the front part can be used to control the chief ray to pass through the optical axis near the center of the lens power of the rear part, so that the entire shape can be used. , The principal ray is not diffused, the distortion can be reduced even when the field of view is widened, and a multi-beam image can be formed.

In the electrostatic lens, the focal length can be continuously changed by changing at least one of the center position of the front lens power and the center position of the rear lens power. Further, by configuring at least one electrode other than the center electrode of the electrostatic lens as a multipole electrode having four or more quadrupoles, the x direction and the y direction
The deflection angle due to the lens power of the front stage can be made different depending on the direction, and astigmatism in the pupil space can be corrected. Furthermore, if the center of the lens power of the front part of the electrostatic lens is arranged so as to be almost at the intermediate image plane, the chief ray can be emitted near the center of the lens power of the rear part only by adjusting the lens power of the front part. The image can be formed on the axis, and the adjustment is simplified.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing one embodiment of a sample evaluation apparatus using a multi-beam according to the present invention.

FIG. 2 is an explanatory view showing a first embodiment of an electrostatic lens constituting an objective lens provided in the sample evaluation apparatus according to the present invention shown in FIG.

FIGS. 3A and 3B are second and third electrostatic lenses constituting an objective lens included in the sample evaluation apparatus according to the present invention shown in FIG.
It is explanatory drawing which shows Example of this.

FIG. 4 is an explanatory view showing a fourth embodiment of the electrostatic lens constituting the objective lens provided in the sample evaluation apparatus according to the present invention shown in FIG.

FIG. 5 is an explanatory diagram showing a relationship between voltages applied to quadrupole electrodes provided in the electrostatic lens of the fourth embodiment shown in FIG.

FIG. 6 is a flowchart of a method for manufacturing a semiconductor device by applying the sample evaluation apparatus according to the present invention.

FIG. 7 is a flowchart showing a lithography step which is a sub-step of the wafer processing step shown in FIG. 6;

Continued on the front page (72) Inventor Hiroshi Nishimura 3-2-2, Marunouchi, Chiyoda-ku, Tokyo Nikon Corporation (72) Inventor Muneki Hamashima 3-2-2, Marunouchi, Chiyoda-ku, Tokyo Nikon Corporation (72) Inventor Nakasuji Mamoru, Ebara Meister Co., Ltd., 11-1, Haneda Asahi-cho, Ota-ku, Tokyo (72) Inventor Shinji Noji 11-1, Haneda Asahi-cho, Ota-ku, Tokyo In Ebara Corporation (72) Inventor Toru Satake 11-1 Haneda-cho, Haneda, Ota-ku, Tokyo F-term in Ebara Corporation (reference) 2G001 AA03 AA10 BA07 CA03 DA06 DA09 DA10 EA04 FA01 GA05 GA09 JA02 JA07 JA11 KA03 KA20 LA11 PA11 4M106 AA01 AA10 AA11 AA12 BA02 CA39 DB02 DB04 DB05 DB07 DB12 DJ02 DJ04 DJ18 DJ20 5C033 CC02 CC06 UU02 UU08

Claims (4)

[Claims] 1. A sample evaluation apparatus for irradiating a sample with a primary electron beam and detecting secondary electrons emitted from the sample to obtain image data of the sample, comprising: five or more electrodes. At least one or more primary optical systems that irradiate a sample with a plurality of primary electron beams using an electrostatic lens as an objective lens, and at least one or more secondary optical systems that guide secondary electrons to at least one or more detectors The primary optical system is configured to irradiate a plurality of primary electron beams to positions separated from each other by a distance greater than the distance resolution of the secondary optical system. 2. The sample evaluation apparatus according to claim 1, wherein the electrostatic lens is divided into a front part and a rear part by a center electrode at a center part to divide the lens power, and At least one of the rear part is composed of four or more electrodes including a central electrode, and by changing the voltage applied to these electrodes, the center position of the front part, the rear part, or both lens powers is independent. A sample evaluation device characterized by being configured to be adjustable. 3. The sample evaluation device according to claim 1, wherein at least one electrode other than the center electrode is a multipole electrode having four or more poles among the electrodes constituting the front stage. A sample evaluation device, characterized in that: 4. A method for manufacturing a semiconductor device, comprising the step of evaluating a semiconductor wafer by using the sample evaluation apparatus according to claim 1. Description: .