JP4288744B2 - Inspection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inspection method for inspecting a surface layer of a sample using an electron beam, and more particularly to an inspection method for inspecting a surface layer of a sample on which an integrated circuit is formed.
[0002]
[Prior art]
As is well known, an integrated circuit is formed on a single semiconductor substrate in a state where a large number of circuit elements are interconnected. In such an integrated circuit, a contact hole for connecting the diffusion region of the semiconductor substrate and the wiring layer and a number of via holes for connecting the wiring layers of the multilayer wiring are formed in the insulating layer on the semiconductor substrate. Has been. These contact holes and via holes are usually formed in the insulating layer using well-known photolithography and etching processes.
[0003]
For example, when forming the contact hole, it is desirable that the etching process be terminated when the insulating layer is completely removed and the semiconductor substrate is exposed through the insulating layer.
However, since the etching process is simultaneously performed on a large number of contact holes, in some contact holes, a part of the insulating layer to be removed may remain at the bottom, and the semiconductor substrate may not be completely exposed.
[0004]
An integrated circuit having such a defective contact hole is a defective product that does not operate normally.
Conventionally, in order to inspect a large number of contact holes formed in an insulating layer on a semiconductor substrate, cross-sectional observation by destructive inspection and surface observation by a scanning electron microscope (SEM) have been performed.
[0005]
According to SEM, it is possible to selectively capture only images of normal contact holes that are completely open to the bottom among the contact holes formed in the insulating layer. Furthermore, a defective contact hole can be determined by comparing the captured image with a template image.
[0006]
Surface observation by SEM utilizes the fact that the charge-up state during electron beam irradiation differs between a normal contact hole and a defective contact hole, and the amount of secondary electrons emitted from the sample varies depending on the charge-up state. .
[0007]
[Problems to be solved by the invention]
By the way, in order to reduce the opening defect at the time of forming the contact hole, it can be considered to increase the amount of over-etching in the etching process. However, overetching damages the semiconductor substrate.
[0008]
For this reason, it is desirable that the overetching amount be set to a value that can completely open as many contact holes as possible and that can minimize damage to the semiconductor substrate.
When setting an appropriate overetching amount, among the many contact holes formed with a certain amount of overetching, it is inspected over the entire surface whether it is a normal contact hole that is completely open to the bottom, and this inspection result is used in the manufacturing process. It is necessary to provide feedback.
[0009]
However, in the conventional cross-sectional observation described above, since the sample must be destroyed, the inspection efficiency is poor, and a full inspection of the sample cannot be expected.
In the surface observation by the SEM, the diameter of the electron beam irradiated from the electron gun is sufficiently narrowed down by the electron optical system, and the surface of the sample is scanned with the spot-focused electron beam. There is a problem that the throughput is slow to do.
[0010]
Therefore, in the present situation, it is only possible to inspect whether or not the contact hole is completely opened to the bottom.
On the other hand, in the case of a via hole formed in an insulating layer on a semiconductor substrate, a barrier layer (e.g., on the underlying wiring layer is prevented in order to prevent the material (e.g., aluminum) of the underlying wiring layer from adhering to the inner wall of the via hole during the etching process. TiN) is often laminated.
[0011]
Therefore, when such a via hole is formed, the etching process must be completed with the barrier layer left so that the underlying wiring layer is not exposed.
For this reason, after the etching process is finished, there is a demand to inspect whether a barrier layer to be left at the bottom of a large number of via holes remains properly or whether the underlying wiring layer is exposed by removing the barrier layer.
[0012]
However, in the surface observation by the SEM described above, it cannot be distinguished whether the bottom of the via hole is a barrier layer or a base wiring layer. At present, there is no device that can handle the material inspection of the bottom of the via hole.
An object of the present invention is to provide an inspection method capable of non-destructively inspecting a surface layer of a sample on which an integrated circuit is formed using an electron beam.
[0013]
[Means for Solving the Problems]
  BookInventionOne aspectIs an inspection method for inspecting a surface layer of a sample, and includes a step of irradiating the sample with a planar electron beam, and a step of imaging a secondary beam generated from the sample on a predetermined surface, Based on the fact that the imaging conditions for imaging the secondary beam on the predetermined surface differ depending on the charged state of the surface layer by irradiation of the electron beam, and the charged state corresponds to the physical characteristics of the surface layer. In this case, at least one of the structure and the material is discriminated.
[0014]
  in this way,In one embodiment of the present inventionThen, the electron beam is shaped into a plane and irradiated onto the sample. At this time, the surface layer of the sample in the irradiation region is in the same charged state for each portion having common physical characteristics. Since the imaging condition of the secondary beam varies depending on the charged state of the surface layer, when the imaging condition is set so that the secondary beam generated from a part of a certain physical characteristic A forms an image on a predetermined surface, another physical characteristic The secondary beam generated from the portion B does not form an image on a predetermined plane.
[0015]
That is, only the secondary beam from the portion having the common physical characteristics of the surface layer can be selectively imaged on the predetermined surface. Further, by changing the setting of the imaging condition, the secondary beam that forms an image on the predetermined surface can be switched to one generated from another physical characteristic portion of the surface layer. As a result, at least one of the structure and material of the surface layer can be determined.
[0016]
  Furthermore, since a two-dimensional image corresponding to a portion having a common physical property of the sample in the irradiation area is projected as it is onto a predetermined surface, the portion having the same physical property is scanned without scanning the sample surface with an electron beam. Corresponding two-dimensional images can be captured at once. Therefore,One embodiment of the present inventionAccording to the method, the surface layer of the sample can be inspected at high speed without destruction.
[0021]
  One embodiment of the present inventionIsBy detecting the height variation of the sample and changing the voltage applied to the electron optical system that forms an image of the secondary beam on a predetermined surface according to the height variation, the imaging state of the electron optical system is changed. And a maintaining step.
  Thus, according to one aspect of the invention,Even if the sample height fluctuates, imagingStatusCan be kept constant. Therefore, even when the sample itself is warped or undulated, a two-dimensional image corresponding to a portion having a common physical property (conduction state) of the surface layer can be selectively captured sequentially from a plurality of regions of the sample. It becomes possible to inspect the entire surface layer.
[0022]
  According to one embodiment of the present invention,An apparatus used for realizing the inspection method can be configured easily and inexpensively.
[0023]
  In addition, since the above two-dimensional image can be selectively captured sequentially from a plurality of regions of the sample while moving the sample in a plane orthogonal to the height direction, it is possible to enhance the entire surface inspection of the sample. Can be done with throughput.
One embodiment of the present invention includesThere are a step of capturing an image based on a secondary beam imaged on a predetermined surface, and a step of comparing each captured image with respect to a plurality of regions in the sample where the same pattern is formed.May.
[0024]
  in this way,One embodiment of the present inventionThen, it is possible to infer good / bad pattern formation only by comparing a plurality of captured images with each other and without comparing with a template image.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0026]
  Figure1 is a configuration diagram of an inspection apparatus 10 used for realizing the inspection method of the present embodiment.
  The inspection apparatus 10 includes a primary column 21, a secondary column 22, and a chamber 23. Of these, the primary column 21 is attached obliquely to the side surface of the secondary column 22. A chamber 23 is attached to the lower part of the secondary column 22.
[0027]
The primary column 21, the secondary column 22, and the chamber 23 are connected to an evacuation system (not shown), and are evacuated by a turbo pump of the evacuation system to maintain an internal vacuum state.
Here, the configuration of the primary column 21, the secondary column 22, and the chamber 23 will be described.
[0028]
[Primary column]
An electron gun 24 that accelerates and emits electrons is arranged inside the primary column 21. The cathode of the electron gun 24 is a lanthanum hexabolite (LaB) that can extract a large current with a rectangular cathode.₆) Is used.
[0029]
In addition, a primary optical system 25 having a three-stage configuration is disposed inside the primary column 21 on the optical axis of an electron beam (hereinafter referred to as “primary beam”) emitted from the electron gun 24. Each stage of the primary optical system 25 is configured by a quadrupole (or octupole) electrostatic lens (or electromagnetic lens) that is asymmetric about the rotation axis.
For example, when each stage of the primary optical system 25 is an electrostatic lens composed of four cylindrical rods 1 to 4 as shown in FIG. 2, the opposing cylindrical rods (1 and 3, 2 and 4) are equal to each other. A voltage characteristic that is set to a potential and opposite to each other (+ Vq for 1 and 3 and −Vq for 2 and 4) is given. Such an electrostatic lens, like a so-called cylindrical lens, causes focusing and divergence of the primary beam on the long axis (X axis) and the short axis (Y axis) of the rectangular cathode.
[0030]
Therefore, according to the primary optical system 25, by optimizing the lens voltage of each electrostatic lens, the section of the primary beam is shaped into an arbitrary shape (rectangular shape, elliptical shape, etc.) without losing emitted electrons. can do. FIG. 2 shows a case where the primary beam has a rectangular cross section.
Further, a primary column control unit 45 for controlling the lens voltage of each electrostatic lens of the primary optical system 25 and controlling the acceleration voltage Vac of the electron gun 24 is connected to the primary column 21 (FIG. 1). Further, the primary column control unit 45 is connected to the CPU 43.
[0031]
〔Chamber〕
As shown in FIG. 1, a stage 27 on which the sample 28 is placed and a Z sensor 26 that detects the height of the surface of the sample 28 are installed inside the chamber 23.
Among these, a stage control unit 49 is connected to the stage 27. The stage control unit 49 drives the stage 27 in the XY directions, and outputs an XY position signal corresponding to the XY position of the stage 27 to the CPU 43.
[0032]
Note that a predetermined retarding voltage Vr (described later) is applied to the stage 27.
Further, as shown in FIG. 3, the Z sensor 26 is disposed on a light emitting element 51 that emits light toward the surface (sample surface 28 a) of the sample 28 and an optical path of light emitted from the light emitting element 51. It comprises a collimator lens 52, a condensing lens 53 disposed on the optical path of light reflected by the sample surface 28a, and a two-divided detector 54. Incidentally, the two-divided detector 54 has two light receiving portions 54a and 54b as shown in FIG.
[0033]
In such a Z sensor 26 (FIG. 3), the reflected light L1 from the sample surface 28a is incident on different positions of the two-divided detector 54 in accordance with the height (Z position) of the sample surface 28a. FIG. 3 shows a state in which the reflected light L1 from the sample surface 28a is incident on the positions a, b, and c of the two-divided detector 54 when the Z position of the sample surface 28a is Z1, Z2, and Z3. FIG. 4 shows the positional relationship between the reflected light L1 and the light receiving parts 54a and 54b.
[0034]
The two-divided detector 54 receives the reflected light L1 at each of the light receiving portions 54a and 54b, and outputs a difference signal based on the difference in the amount of received light. Incidentally, this difference signal corresponds to the incident position (a, b, c) of the reflected light L1 in the two-divided detector 54, that is, the Z position (Z1, Z2, Z3) of the sample surface 28a.
The Z sensor 26 is connected to a Z sensor control unit 47 (FIG. 1). The Z sensor control unit 47 drives the Z sensor 26, acquires a difference signal from the two-divided detector 54, and sends a Z position signal corresponding to the Z position of the sample surface 28a to the CPU 43 based on the difference signal. Output.
[0035]
The CPU 43 stores a reference value for the Z position of the sample surface 28a. Therefore, the CPU 43 obtains the difference between the detected Z position of the sample surface 28a and the reference value based on the Z position signal from the Z sensor control unit 47, and detects the height ΔZ of the sample surface 28a.
In addition, although the 2 division detector was shown as the detector 54, it is not restricted to this, You may use a 4 division detector. Alternatively, the Z position and the inclination of the sample surface 28a may be detected by using a multi-point AF system that multi-measures the emitted light and measures at multiple points.
[0036]
[Secondary column]
As shown in FIG. 1, the secondary column 22 has a cathode lens 29, a numerical aperture 30, a Wien filter 31, a second filter on the optical axis of a secondary beam (described later) generated from the sample 28. A lens 32, a field aperture 33, a third lens 34, a fourth lens 35, and a detector 37 are arranged.
[0037]
  Among these, the cathode lens 29 is composed of three electrodes 29a, 29b, and 29c, as shown in FIG. 5, for example. In this case, the voltage VCL is applied to the first electrode 29a and the second electrode 29b from the bottom of the cathode lens 29 (sample 28 side), and the third electrode 29c is set to zero potential..
[0038]
The cathode lens 29 is connected to a cathode lens control unit 50 (FIG. 1) that controls the voltage VCL applied to the electrodes 29a and 29b.
The numerical aperture 30 corresponds to an aperture stop and determines the aperture angle of the cathode lens 29. The shape is a thin film plate made of metal (Mo or the like) having a circular hole.
[0039]
The numerical aperture 30 is arranged so that the opening is the focal position of the cathode lens 29. For this reason, the numerical aperture 30 and the cathode lens 29 constitute a telecentric electron optical system.
The Wien filter 31 is a deflector that acts as an electromagnetic prism and satisfies the Wien condition (E = vB, where v is the velocity of charged particles, E is an electric field, B is a magnetic field, and E⊥B). Only the charged particles (for example, secondary beam) can go straight, and the trajectory of other charged particles (for example, primary beam) can be bent.
[0040]
The second lens 32, the third lens 34, and the fourth lens 35 are all rotationally symmetric lenses called unipotential lenses or einzel lenses, and are each composed of three electrodes (see FIG. 7). . In each lens, the lens action is usually controlled by setting the outer two electrodes to zero potential and changing the voltage applied to the center electrode.
[0041]
A field aperture 33 is disposed between the second lens 32 and the third lens 34. This field aperture 33 limits the field of view to the required range, similar to the field stop of an optical microscope.
The detector 37 (FIG. 1) includes an FCP (fiber optic) having an MCP (microchannel plate) 38 for accelerating and multiplying electrons, a fluorescent screen 39 for converting an electron image into an optical image, and an optical relay lens (not shown). Plate) 40 and a CCD camera 41 for picking up an optical image.
[0042]
Incidentally, the optical relay lens of the FOP 40 reduces the optical image on the fluorescent screen 39 to about 1/3 and projects it on the imaging surface of the CCD camera 41. The FOP 40 is not limited to the fiber optic plate, and may be an optical relay lens system.
Further, the CCD camera 41 reads out signal charges based on the captured optical image, for example, every 1/30 seconds.
[0043]
An image processing unit 42 is connected to the detector 37. The image processing unit 42 A / D converts the signal charge from the CCD camera 41, stores it in an internal VRAM, creates image information, and outputs it to the CPU 43.
Further, the secondary column 22 includes a secondary column control unit for controlling the lens voltages of the second lens 32, the third lens 34, and the fourth lens 35 and for controlling the electromagnetic field applied to the Wien filter 31. 46 is connected.
[0044]
The secondary column control unit 46, the image processing unit 42, and the cathode lens control unit 50 are connected to the CPU 43.
A CRT 44 is connected to the CPU 43. The CPU 43 displays an image on the CRT 44 based on the image information output from the image processing unit 42. Further, the CPU 43 transfers the image information to the memory.
[0045]
Next, the trajectories of the primary beam and the secondary beam in the inspection apparatus 10 configured as described above will be described in order.
[Primary beam]
As shown in FIG. 5, the primary beam from the electron gun 24 is incident on the central portion of the Wien filter 31 obliquely while receiving the lens action of the primary optical system 25. FIG. 5 shows the trajectory of electrons emitted in the X-direction cross section of the rectangular cathode and the electron trajectory emitted in the Y-direction cross section.
[0046]
The primary beam incident on the Wien filter 31 has its trajectory bent by the deflection action of the Wien filter 31 and reaches the opening of the numerical aperture 30. Here, by setting the lens voltage of the primary optical system 25, the primary beam forms an image at the opening of the numerical aperture 30.
The primary beam imaged at the opening of the numerical aperture 30 is irradiated onto the sample surface 28 a via the cathode lens 29. Here, since the numerical aperture 30 and the cathode lens 29 constitute a telecentric electron optical system, the primary beam that has passed through the cathode lens 29 becomes a parallel beam. As a result, the sample beam 28a is irradiated with the primary beam vertically and uniformly. That is, Koehler illumination called an optical microscope is realized.
[0047]
Further, since the retarding voltage Vr is applied to the stage 27 on which the sample 28 is placed, a negative electric field is formed between the electrode 29a of the cathode lens 29 and the sample 28 with respect to the primary beam. Is done. Therefore, the primary beam that has passed through the cathode lens 29 is decelerated until it reaches the sample surface 28a. For this reason, destruction of the sample 28 is prevented.
[0048]
The unnecessary electron beam scattered in the inspection apparatus 10 is prevented from reaching the sample surface 28 a by the numerical aperture 30. For this reason, contamination of the sample 28 is prevented.
By the way, the primary beam irradiation area 24A on the sample surface 28a is shaped by controlling the lens voltage to the primary optical system 25, and has a rectangular shape, for example, as shown in FIG.
[0049]
As described above, the sample 28 placed on the stage 27 of the inspection apparatus 10 is irradiated with the planar primary beam. The sample 28 positioned in the primary beam irradiation region 24A is charged up according to the conduction state of the surface layer and the acceleration voltage Vac of the primary beam (details will be described later).
In addition, light emitted from the light emitting element 51 of the Z sensor 26 described above is incident on the sample 28 located in the irradiation region 24A. Thereby, the height variation ΔZ of the sample surface 28 a in the irradiation region 24 </ b> A is detected based on the output from the Z sensor 26.
[0050]
[Secondary beam]
When the sample 28 is irradiated with the primary beam, a secondary beam composed of at least one of secondary electrons, reflected electrons, and backscattered electrons is generated from the sample 28 in the irradiation region 24A (FIG. 7). .
This secondary beam has two-dimensional image information of the irradiation region 24A. Since the primary beam is irradiated perpendicularly to the sample surface 28a as described above, the secondary beam has a clear image with no shadow.
[0051]
Here, since the retarding voltage Vr is applied to the stage 27 on which the sample 28 is placed, a positive electric field is formed with respect to the secondary beam between the sample 28 and the electrode 29a of the cathode lens 29. Is done. Therefore, the secondary beam generated from the sample 28 is accelerated toward the cathode lens 29.
[0052]
  The secondary beam is focused by the cathode lens 29, passes through the numerical aperture 30, travels straight without being subjected to the deflection action of the Wien filter 31, and passes through the second lens 32 to the surface of the field aperture 33. (Hereinafter referred to as “reference surface 33a”).
[0053]
By changing the electromagnetic field applied to the Wien filter 31, only electrons having a specific energy band (for example, secondary electrons, reflected electrons, or backscattered electrons) can be selected and passed from the secondary beam. it can.
The secondary beam that has passed through the field aperture 33 is repeatedly focused and diverged by the third lens 34 and the fourth lens 35 that are arranged in the subsequent stage, and is re-imaged on the detection surface of the detector 37.
[0054]
Thus, the secondary beam generated from the sample 28 forms an image once by the cathode lens 29 and the second lens 32, and then forms an image once by the third lens 34 and the fourth lens 35 ( 3 times in total). The third lens 34 and the fourth lens 35 may be combined to perform one image formation (total two image formation).
As described above, the image formation of the secondary beam generated from the sample 28 is not performed by the cathode lens 29 alone, but is performed together with the second lens 32, so that the occurrence of lens aberration can be suppressed.
[0055]
The field aperture 33, together with the third lens 34 and the fourth lens 35 in the subsequent stage, blocks unnecessary secondary beams to prevent the detector 37 from being charged up or contaminated. The numerical aperture 30 plays a role of suppressing lens aberration of the second lens 32 to the fourth lens 35 in the subsequent stage with respect to the secondary beam.
[0056]
As described above, the secondary beam generated from the sample 28 and re-imaged on the detection surface of the detector 37 is accelerated and multiplied when passing through the MCP 38 in the detector 37, and converted into light by the phosphor screen 39. The Then, the light from the fluorescent screen 39 forms an image on the imaging surface of the CCD camera 41 via the FOP 40.
The third lens 34 and the fourth lens 35 are lenses for enlarging and projecting the intermediate image obtained on the reference surface 33a. Therefore, the two-dimensional image of the irradiation region 24A on the sample surface 28a is enlarged and projected on the detection surface of the detector 37.
[0057]
Further, the two-dimensional image (secondary beam image) of the irradiation area 24A projected on the detection surface of the detector 37 is converted into an optical image on the fluorescent screen 39, and then the imaging surface of the CCD camera 41 via the FOP 40. Is projected as it is. The projected image is displayed on the CRT 44 via the image processing unit 42 and the CPU 43 (FIG. 1).
[0058]
By the way, in the above-described inspection apparatus 10, whether or not the secondary beam (FIG. 7) generated from the sample 28 forms an image on the reference surface 33 a is determined by the potential difference Vsc between the sample 28 and the cathode lens 29. Assume that the secondary beam from the sample 28 forms an image on the reference surface 33a when the potential difference Vsc is maintained at a certain value Vsc0. Therefore, when the potential difference Vsc deviates from the constant value Vsc0, the secondary beam from the sample 28 does not form an image on the reference surface 33a.
[0059]
The apparatus parameters related to the potential difference Vsc are the applied voltage VCL to the cathode lens 29 and the distance WD from the sample surface 28a to the lower end portion (end portion on the sample 28 side) 29d of the cathode lens 29. The combination of the applied voltage VCL and the distance WD corresponds to the “imaging condition” in the claims.
The potential difference Vsc is related to the above-described device parameters (applied voltage VCL, distance WD) as well as the charge-up state of the surface layer of the sample 28. Details will be described later.
[0060]
Incidentally, among the above device parameters, when the distance WD changes, the change in the potential difference Vsc based on the change in the distance WD can be corrected by adjusting the voltage VCL applied to the cathode lens 29.
[0061]
Accordingly, when the charge-up state of the surface layer of the sample 28 is constant, even if the distance WD changes, the potential difference Vsc is maintained at the constant value Vsc0 by adjusting the applied voltage VCL, and the secondary beam from the sample 28 is maintained. Can be imaged on the reference surface 33a.
For such focus control, an adjustment amount of the applied voltage VCL with respect to the change amount of the distance WD is previously given to the CPU 43 as a control table. The control table is preferably set to lens conditions such that the imaging magnification does not change even when the applied voltage VCL is changed.
[0062]
The change in the distance WD occurs when the height fluctuation ΔZ of the sample surface 28a occurs during the XY movement of the stage 27. Further, the height variation ΔZ of the sample surface 28a is caused by warpage or undulation of the sample 28 itself, an inclination generated when the sample 28 is attached to the stage 27, an inclination of the stage 27 itself, or an up-and-down movement of the stage 27.
The CPU 43 detects the height variation ΔZ of the sample surface 28a based on the output (Z position signal) from the Z sensor control unit 47, obtains the amount of change in the distance WD, and based on the control table. An adjustment amount of the applied voltage VCL is set, and an applied voltage signal is output to the cathode lens control unit 50.
[0063]
Next, a method for inspecting the surface layer of the sample 28 using the above-described inspection apparatus 10 (FIGS. 1 to 7) will be described with two specific examples of the sample 28 to be inspected.
The inspection method of the present embodiment is an apparatus parameter (applied voltage) for forming an image of the secondary beam from the sample 28 on the reference plane 33a in accordance with the charge-up state generated in the surface layer of the sample 28 by irradiation of the primary beam. VCL, distance WD) are different, and the fact that this charge-up state corresponds to the conduction state of the surface layer of the sample 28 is utilized. According to this inspection method, it is possible to distinguish between a conductive portion and an insulating portion formed on the surface layer of the sample 28.
[0064]
Here, the first sample 28 to be inspected will be described. As shown in FIG. 8, the sample 28 has a large number (10 in FIG. 8) of contact holes 63, 63,.
These many contact holes 63, 63,... Are formed using an insulating layer 62 (for example, SiO 2) on the silicon (Si) substrate 61 shown in FIG.₂Layer).
[0065]
Therefore, in the contact holes 63, 63,..., The insulating layer 62 is completely removed and the Si substrate 61 is exposed through the insulating layer 62 as shown in FIG. Not only the contact hole 63a but also a defective contact hole 63b in which a part of the insulating layer 62 to be removed remains at the bottom as shown in FIG.
[0066]
The bottom of the normal contact hole 63a (FIG. 10A) where the Si substrate 61 is exposed is referred to as an “exposed portion 61a”. A part of the insulating layer 62 remaining at the bottom of the defective contact hole 63b (FIG. 10B) is referred to as “residual portion 62a”.
Therefore, when inspecting a large number of contact holes 63, 63,... Formed in the insulating layer 62 of the sample 28, the sample 28 is irradiated with a primary beam. At this time, it is preferable to set the acceleration voltage Vac of the primary beam to a value at which the insulating layer 62 of the sample 28 is easily charged up.
[0067]
When the primary beam is irradiated, the normal contact hole 63a is not charged up as shown in FIG. This is because the bottom part is the exposed part 61a (that is, the conduction part).
On the other hand, the defect contact hole 63b is charged up as shown in FIG. 11B when the primary beam is irradiated. This is because the bottom portion is the remaining portion 62a (that is, the insulating portion).
[0068]
Here, normal contact holes 63a (exposed portions 61a) that are not charged up and defective contact holes 63b (remaining portions 62a) that are charged up are mixed in the primary beam irradiation region 24A. Suppose that
At this time, the potential difference Vsc between the sample 28 in the irradiation region 24A and the cathode lens 29 partially changes depending on the charge-up state of the sample 28 in the irradiation region 24A. In other words, the potential difference Vsc between the remaining portion 62a and the cathode lens 29 is deviated from the potential difference Vsc between the exposed portion 61a and the cathode lens 29 by ΔVsc.
[0069]
Therefore, when the device parameters (applied voltage VCL, distance WD) are set such that the potential difference Vsc between the exposed portion 61a and the cathode lens 29 is maintained at a constant value Vsc0 (for example, applied voltage VCL = VCL1). , Distance WD = WD1), and the potential difference Vsc between the remaining portion 62a and the cathode lens 29 deviates from the constant value Vsc0.
[0070]
At this time, as shown in FIG. 12, the secondary beam generated from the exposed portion 61a of the sample 28 forms an image on the reference surface 33a, but the secondary beam from the remaining portion 62a does not form an image on the reference surface 33a. As a result, only the image corresponding to the exposed portion 61a (normal contact hole 63a) is clearly displayed on the CRT 44. FIG. 14 shows an example of an image corresponding to the exposed portion 61a (normal contact hole 63a).
[0071]
On the other hand, when the setting of the apparatus parameters (applied voltage VCL, distance WD) is changed so that the potential difference Vsc between the remaining portion 62a and the cathode lens 29 is maintained at a constant value Vsc0 (for example, applied voltage VCL = VCL2). (≠ VCL1), distance WD = WD1), and the potential difference Vsc between the exposed portion 61a and the cathode lens 29 deviates from the constant value Vsc0.
[0072]
At this time, as shown in FIG. 13, the secondary beam generated from the remaining portion 62a of the sample 28 forms an image on the reference surface 33a, but the secondary beam from the exposed portion 61a does not form an image on the reference surface 33a. As a result, only the image corresponding to the remaining portion 62a (defective contact hole 63b) is clearly displayed on the CRT 44. FIG. 15 shows an example of an image corresponding to the remaining portion 62a (defective contact hole 63b).
[0073]
Incidentally, the device parameters (applied voltage VCL1, distance WD1) when the image of the exposed portion 61a (normal contact hole 63a) is clearly displayed and the image of the remaining portion 62a (defective contact hole 63b) are clearly displayed. The difference from the device parameters (applied voltage VCL2, distance WD1) at this time corresponds to the deviation ΔVsc of the potential difference Vsc based on the charge-up amount of the remaining portion 62a.
[0074]
As described above, according to the inspection method of the present embodiment, a clear image (for example, FIG. 14) of the exposed portion 61a (normal contact hole 63a) that is not charged up, and the remaining portion 62a (defect that is charged up). A clear image (for example, FIG. 15) of the contact hole 63b) can be displayed separately by changing the setting of the apparatus parameters (applied voltage VCL, distance WD).
[0075]
As a result, among the many contact holes 63, 63,... Formed in the sample 28 (FIG. 8), a normal contact hole 63a (FIG. 10A) and a defective contact hole 63b (FIG. 10B) are obtained. ).
Further, the image of the exposed portion 61a (normal contact hole 63a) or the image of the remaining portion 62a (defective contact hole 63b) existing in the sample 28 located in the irradiation region 24A can be captured in a lump. Therefore, the contact hole inspection of the sample 28 can be performed at high speed without destruction.
[0076]
Furthermore, according to the inspection method of the present embodiment, a plurality of samples 28 are moved by moving the stage 27 XY while constantly managing the height variation ΔZ of the sample surface 28a based on the output from the Z sensor 26 described above. In order from the regions 65A, 65B,... (FIG. 16), only the image corresponding to the exposed portion 61a (normal contact hole 63a) or only the image corresponding to the remaining portion 62a (defective contact hole 63b) is captured. Can do.
[0077]
For example, the region 65A of the sample 28 is first positioned in the irradiation region 24A, the apparatus parameters are set to the applied voltage VCL = VCL1, and the distance WD = WD1, and the exposed portion 61a (normal contact) present in the region 65A is set. Assume that the image of the hole 63a) is captured (state shown in FIG. 12). At this time, the potential difference Vsc between the exposed portion 61a and the cathode lens 29 is kept at a constant value Vsc0. Even if the remaining portion 62a (defect contact hole 63b) exists in the region 65A, the image cannot be captured.
[0078]
After that, when the region 65B (FIG. 16) is positioned in the irradiation region 24A by the XY movement of the stage 27, the height variation ΔZ of the sample surface 28a occurs, and the distance WD has changed from WD1. (The state shown in FIGS. 17A and 18A). In this case, even if the applied voltage VCL = VCL1 does not change, a change in the potential difference Vsc based on the change in the distance WD occurs, so the potential difference Vsc between the exposed portion 61a and the cathode lens 29 deviates from the constant value Vsc0. Thus, the secondary beam from the exposed portion 61a does not form an image on the reference surface 33a. As a result, even if the exposed portion 61a (normal contact hole 63a) exists in the region 65B, the image cannot be captured.
[0079]
However, in the above-described inspection apparatus 10, even if the distance WD changes due to the height variation ΔZ of the sample surface 28a, the change in the potential difference Vsc based on the change in the distance WD can be corrected by adjusting the applied voltage VCL. it can.
For this reason, even when the height variation ΔZ of the sample surface 28a occurs, the potential difference Vsc between the exposed portion 61a and the cathode lens 29 can be kept at a constant value Vsc0. At this time, the secondary beam from the exposed portion 61a forms an image on the reference surface 33a as shown in FIGS. 17 (b) and 18 (b).
[0080]
Therefore, a clear image of the exposed portion 61a (normal contact hole 63a) can be captured also in the region 65B (FIG. 16) as in the case of the region 65A.
[0081]
As described above, according to the inspection method of the present embodiment, the height fluctuation ΔZ of the sample surface 28a is managed and the change in the potential difference Vsc based on the change in the distance WD is corrected, while the plurality of regions 65A, 65B,... (FIG. 16) are sequentially positioned in the irradiation region 24A (that is, the sample surface 28a is scanned with a planar primary beam), thereby the die 65 on which the predetermined pattern is formed on the sample 28 is entirely exposed. The contact hole can be inspected over the entire area.
[0082]
As a result, it is possible to capture a clear image of all the exposed portions 61a (normal contact holes 63a) existing in the die 65.
Similarly, with respect to the remaining portion 62a (defect contact hole 63b), by scanning the sample surface 28a with the primary beam while managing the height variation ΔZ of the sample surface 28a, all of the remaining in the die 65 are also detected. A clear image of the remaining portion 62a (defective contact hole 63b) can be captured.
[0083]
The device parameters (applied voltage VCL, distance WD) set at this time are the same as the device parameters (applied voltage VCL, distance WD) at the time of image capture of the exposed portion 61a (normal contact hole 63a). A difference ΔVsc in potential difference Vsc based on the charge-up amount of the remaining portion 62a of 63b is different.
In the inspection method of the present embodiment, since the sample surface 28a is scanned with the planar primary beam, the entire surface inspection (image capture) of the die 65 can be performed with high throughput.
[0084]
Here, usually, a plurality of dies 65, 65,... In which the same pattern is formed are arranged on the sample 28 (FIG. 19).
According to the inspection method of this embodiment, the entire surface inspection of the plurality of dies 65, 65,... Can be performed with high throughput, and the sample 28 can be inspected over the entire surface.
[0085]
The image of the exposed portion 61a (normal contact hole 63a) or the image of the remaining portion 62a (defective contact hole 63b) with respect to the entire surface of the sample 28 obtained as a result is used to appropriately set the overetching amount when forming the contact hole. , Very useful information.
Further, in the actual sample 28, among the many contact holes 63, 63,... Existing in each die 65, the number of normal contact holes 63a is overwhelmingly larger than the number of defective contact holes 63b. Many.
[0086]
Therefore, by changing the setting of the apparatus parameters (applied voltage VCL, distance WD), it can be estimated which of the two captured images is the normal contact hole 63a image or the defective contact hole 63b image.
Further, the sample surface 28a is scanned with the primary beam while managing the height variation ΔZ of the sample surface 28a, and the captured images of the plurality of dies 65, 65,. Also, it can be estimated that the common part of the image is the normal contact hole 63a and the non-common part is the defective contact hole 63b.
[0087]
Next, the second sample 28 to be inspected will be described. As shown in FIG. 20, the second sample 28 has a large number (10 in FIG. 20) of via holes 74, 74,.
These many via holes 74, 74,... Are formed using an insulating layer 73 (for example, SiON) on the barrier layer 72 (for example, TiN layer) shown in FIG.₂Layer). The barrier layer 72 is laminated on the base wiring layer 71 in order to prevent the material (for example, aluminum) of the base wiring layer 71 from adhering to the inner wall of the via hole 74 during the etching process.
[0088]
Therefore, when such a via hole 74 is formed, the etching process must be completed with the barrier layer 72 left so that the underlying wiring layer 71 is not exposed.
[0089]
However, in the large number of via holes 74, 74,..., The insulating layer 73 is completely removed and the barrier layer 72 is exposed through the insulating layer 73 as shown in FIG. In addition to the via hole 74a, a defective via hole 74b in which the barrier layer 72 to be left is removed from the bottom as shown in FIG. 22B is also included.
[0090]
The barrier layer 72 left at the bottom of the normal via hole 74a (FIG. 22A) is referred to as “residual portion 72a”. The bottom of the defective via hole 74b (FIG. 22B) where the underlying wiring layer 71 is exposed is referred to as an “exposed portion 71a”.
Therefore, when inspecting a large number of via holes 74, 74,... Formed in the insulating layer 73 of the sample 28, the sample 28 is irradiated with a primary beam. At this time, it is preferable to set the acceleration voltage Vac of the primary beam to a value at which the barrier layer 72 of the sample 28 is easily charged up.
[0091]
When the primary beam is irradiated, the normal via hole 74a is charged up as shown in FIG. This is because the bottom portion is the remaining portion 72a (that is, the insulating portion).
On the other hand, the defective via hole 74b is not charged up as shown in FIG. 23B when the primary beam is irradiated. This is because the bottom portion is the exposed portion 71a (that is, the conduction portion).
[0092]
Therefore, as in the case of the contact hole 63 described above, by changing the setting of the device parameters (applied voltage VCL, distance WD), an image of the remaining portion 72a (normal via hole 74a) being charged up, and the charge The image of the exposed portion 71a (defective via hole 74b) that is not up can be captured separately.
[0093]
As a result, among the large number of via holes 74, 74,... Formed in the sample 28 (FIG. 20), normal via holes 74a (FIG. 22A) and defective via holes 74b (FIG. 22B) are formed. Can be distinguished. That is, the material at the bottom of the via holes 74, 74,.
In addition, since the image of the remaining portion 72a (normal via hole 74a) or the image of the exposed portion 71a (defective via hole 74b) can be captured at once, the via hole inspection of the sample 28 can be performed at high speed without destruction. it can.
[0094]
Further, the height fluctuation ΔZ of the sample surface 28a is always managed by the output from the Z sensor 26, and the sample surface 28a is scanned with the primary beam, so that the remaining portion 72a ( It is also possible to capture an image of a normal via hole 74a) or an image of an exposed portion 71a (defect via hole 74b) that is not charged up.
[0095]
In addition, the entire surface inspection of a plurality of dies of the sample 28 can be performed with high throughput, and the sample 28 can be inspected via holes over the entire surface.
The image of the remaining portion 72a (normal via hole 74a) or the image of the exposed portion 71a (defective via hole 74b) with respect to the entire surface of the sample 28 obtained as a result is very important for appropriately setting the overetching amount when forming the via hole. Valid information.
[0096]
In the above-described embodiment, the example in which the remaining portion 62a (FIG. 11) of the defective contact hole 63b and the remaining portion 72a (FIG. 23) of the normal via hole 74a are charged to a negative charge has been shown. Varies depending on the energy of the primary beam (acceleration voltage Vac) and may be charged up to a positive charge. The inspection method of the present embodiment can be executed regardless of the charge-up polarity.
[0097]
Furthermore, in the above-described embodiment, the case where the contact hole 63 and the via hole 74 are inspected after the etching process is described as an example. However, the inspection can be similarly performed after the contact hole 63 and the via hole 74 are filled with tungsten. it can.
[0098]
In the above-described embodiment, an example has been described in which when the distance WD changes due to the height variation ΔZ of the sample surface 28a, the change in the potential difference Vsc based on the change in the distance WD is corrected by adjusting the applied voltage VCL. However, the change in the potential difference Vsc can also be corrected by driving the stage 27 in the Z direction to restore the height of the sample surface 28a.
[0099]
Furthermore, in the above-described embodiment, the example in which the change in the potential difference Vsc based on the change in the distance WD is corrected by adjusting the applied voltage VCL to the cathode lens 29 has been described, but the applied voltage to the second lens 32 is described. Also, it may be used for adjustment. Even if only the voltage applied to the second lens 32 is adjusted, the change in the potential difference Vsc can be corrected.
[0100]
Further, in the above-described embodiment, the example in which the primary beam irradiation area 24A is fixed and the stage 27 is driven to scan the primary beam on the sample surface 28a has been described, but the configuration is not limited thereto. For example, if the deflector is arranged on the optical axis of the primary beam in the primary column 21 and the trajectory of the primary beam can be deflected by controlling the voltage applied to the deflector, irradiation is performed. By moving the region 24A on the sample surface 28a and stopping the stage 27, the primary beam can be scanned on the sample surface 28a.
[0101]
In the above-described embodiment, the oblique incidence type Z sensor 26 is used to match the irradiation area 24A and the detection position of the height fluctuation ΔZ, but the irradiation area 24A and the detection position of the height fluctuation ΔZ match. It is also possible to always manage the height fluctuation ΔZ of the sample surface 28a by using a Z sensor (for example, TTL detection method) that is not performed.
Furthermore, before the sample is detected by the electron beam, the height variation may be detected on the entire surface of the sample, and a focus control amount map for the entire surface of the sample may be created in advance. In addition, for example, an optical microscope may be disposed at a position adjacent to the electron beam axis at this time, and the height variation of the sample may be detected by the optical microscope. Further, the height variation may be detected by first detecting the height variation roughly at several points of the sample and compensating for other data blank portions by interpolation processing.
[0102]
In the above-described embodiment, the example in which the focus control is performed using the control table given in advance to the CPU 43 has been described. However, the present invention is not limited to this. It may be calculated.
Furthermore, in the above-described embodiment, an example in which the electron optical system (primary optical system 25) of the primary column 21 and the electron optical system (second lens or the like) of the secondary column 22 are joined by the Wien filter 31 has been described. The inspection method of the present invention can also be applied to an independent configuration.
[0103]
【The invention's effect】
  As explained above,BookAccording to the invention, the surface layer of the sample can be inspected nondestructively simply and at high speed only by selectively setting the imaging condition of the secondary beam. Therefore, the inspection of the surface layer of the sample can be performed over the entire surface, and a very useful inspection result can be fed back to the manufacturing process. As a result, appropriate process conditions can be reliably set even if the process margin is reduced due to the increase in the device structure accompanying the miniaturization of the integrated circuit.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an inspection apparatus 10 according to an embodiment.
2 is a diagram showing a configuration of a primary optical system 25. FIG.
3 is a diagram illustrating a Z sensor 26. FIG.
4 is a diagram illustrating a Z sensor 26. FIG.
FIG. 5 is a diagram showing a trajectory of a primary beam.
FIG. 6 is a diagram illustrating a primary beam irradiation region 24A.
FIG. 7 is a diagram showing a trajectory of a secondary beam.
8 is a plan view illustrating a first sample 28. FIG.
9 is a cross-sectional view illustrating a first sample 28. FIG.
10 is a cross-sectional view illustrating a contact hole formed in a sample 28. FIG.
11 is a cross-sectional view illustrating a charge-up state of a contact hole formed in a sample 28. FIG.
12 is a diagram for explaining an imaging state of a secondary beam generated from a specimen 28. FIG.
13 is a diagram for explaining an imaging state of a secondary beam generated from a sample 28. FIG.
FIG. 14 is a diagram illustrating an example of a captured image.
FIG. 15 is a diagram illustrating an example of a captured image.
FIG. 16 is a diagram showing a plurality of inspections of a sample.
FIG. 17 is a diagram illustrating an imaging state of a secondary beam generated from a sample.
18 is a diagram for explaining an imaging state of a secondary beam generated from a sample 28. FIG.
19 shows a plurality of dies of a sample 28. FIG.
FIG. 20 is a plan view illustrating a second sample 28. FIG.
21 is a cross-sectional view illustrating a second sample 28. FIG.
22 is a cross-sectional view illustrating a via hole formed in a sample 28. FIG.
23 is a cross-sectional view illustrating a charge-up state of a via hole formed in a sample 28. FIG.
[Explanation of symbols]
10 Inspection equipment
21 Primary column
22 Secondary column
23 Chamber
24 electron gun
25 Primary optics
26 Z sensor
27 stages
28 samples
29 Cathode lens
30 New Menal Aperture
31 Vienna Filter
32 Second lens
33 Field aperture
33a Reference plane
34 Third lens
35 4th lens
37 Detector
38 MCP
39 phosphor screen
40 FOP
41 CCD camera
42 Image processing unit
43 CPU
44 CRT
45 Primary column control unit
46 Secondary column control unit
47 Z sensor control unit
49 Stage control unit
50 Cathode lens control unit
51 Light emitting device
52 Collimator lens
53 Condensing lens
54 Divided detector
61 Silicon substrate
62,73 Insulating layer
63 Contact hole
71 Underlying wiring layer
72 Barrier layer

Claims (2)

An inspection method for inspecting a surface layer of a sample, the step of irradiating the sample with a planar electron beam;
Forming a secondary beam generated from the sample on a predetermined plane,
The imaging condition for imaging the secondary beam on the predetermined surface varies depending on the charged state of the surface layer by irradiation of the electron beam, and the charged state corresponds to the physical characteristics of the surface layer. Based on at least one of the structure and material of the surface layer ,
Detecting the height variation of the sample;
Maintaining an imaging state of the electron optical system by changing a voltage applied to the electron optical system that forms an image of the secondary beam on the predetermined surface according to the height fluctuation;
An inspection method characterized by comprising: The inspection method according to claim 1 ,
Capturing an image based on a secondary beam imaged on the predetermined surface;
And a step of comparing the images captured for a plurality of regions where the same pattern is formed in the sample with each other.

Images