JP2000056211A - Scanning type probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a cantilever or probe and sample to quickly and automatically approach from separated state to close distance by calculating the quantity of deviation between a sample surface or cantilever back and focal position of an optical system. SOLUTION: In the state of separating the probe from the sample, the sample is driven toward the cantilever by a three-dimensional(3D) stage, and the next measuring point is moved to just under the probe (S73). Two peaks of light intensity are detected, a distance (x) between them is found and that distance is compared with a prescribed value (y) (S74 and S76). At such a time, on the condition of x>y, the cantilever is made close to the sample by a 3D scanner (S75) and the comparison between (x) and (y) is performed again. When the distance (x) gets smaller than (y) by the approach of the cantilever to the sample, namely, on the condition of x<=y, the approach of the probe to the sample due to an auto focus mechanism is finished and while monitoring the deflection of the cantilever as performed by an ordinary scanning type probe microscope, the probe automatically approaches by the 3D scanner (S77).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus mechanism for bringing a cantilever closer to a sample surface in a scanning probe microscope.

[0002]

2. Description of the Related Art In a conventional scanning probe microscope, the cantilever and the sample are approached to a certain distance while visually monitoring the optical microscope attached to the scanning probe microscope. When the above-described process is not performed, a long distance is approached over time while monitoring the bending of the cantilever.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a scanning probe microscope in which a cantilever or a probe and a sample are quickly and automatically approached from a state of being far apart to a very short distance.

[0004]

According to a first aspect of the present invention, there is provided an optical system comprising a light source, a slit, a photodetector, and an optical system. Light emitted from the slit is transmitted to the sample surface and the back surface of the cantilever by the optical system. An autofocus mechanism for irradiating and reflecting the light, and making the reflected light incident on the position of the photodetector to obtain a spot, wherein the spot shape from the sample surface and the cantilever back surface, the sample surface or the cantilever back surface and the An autofocus mechanism that calculates the shift amount by utilizing the change due to a shift from the focal position of the optical system, and a drive mechanism that closes the gap between the cantilever and the sample surface based on the shift amount, Equipped "scanning probe microscope. When the displacement becomes smaller than the predetermined value, the rough approach operation of the cantilever to the sample surface is completed.

[0005]

FIG. 1 is a schematic configuration diagram of a scanning probe microscope having an autofocus mechanism according to an embodiment of the present invention. This scanning probe microscope comprises a cantilever 1 having a deflection detecting function and a three-dimensional scanner 2.
, A support 3, an autofocus optical system 4, a three-dimensional stage 5, a wafer loader 6, a frame 7, and a table 8.
The cantilever 1 has a probe near the tip, and the bending of the cantilever 1 is detected by using the fact that the resistance value of the boron-doped portion on the cantilever changes due to the bending. The autofocus optical system 4 has the structure shown in FIG. 2, and the light from the objective lens is focused on the cantilever and the sample from the objective lens 17 on the thin three-dimensional scanner 2. The light reflected on the sample surface and the back surface of the cantilever is focused on the line sensor 25 by the cylindrical lens 24. 3D stage 6
Is a stage corresponding to a 12-inch wafer, and the entire surface of the 12-inch wafer can be observed by the scanning probe microscope of the present embodiment. Also, the three-dimensional stage 5 has a z
Although the stroke in the direction is 10 mm, the stroke in the z direction is not limited to this, and a scanning probe having a mechanism for driving the three-dimensional scanner 2 and the cantilever 1 in the z direction by a coarse movement mechanism. It may be a microscope. The wafer loader 6 has a wafer pre-alignment function, and can load a wafer with an accuracy of about 1 μm.
It can be set on the dimension stage 5. Hereinafter, a method for causing the cantilever to approach the sample using the autofocus mechanism of the present invention will be described. FIG. 2 is a schematic configuration diagram of the autofocus optical system. Light from the LED 11 is collected by the lens 12, and a part of the light passes through the slit 13. The light that has passed through the slit 13 is converted into parallel light by a lens 14, half of the light is blocked by a light-shielding plate 15, reflected by a half mirror 16, and further focused by an objective lens 17 on a sample surface 18. The light reflected on the sample surface 18 passes through the objective lens 17 and the half mirror 16 and is then focused on the photodetector 20 by the lens 19. Reference numerals 21, 22, and 23 indicate the shapes of light at the slit 13, the sample surface 18, and the photodetector 20, respectively. When the sample surface 18 coincides with the focal point of the objective lens 17 (18b)
In the photodetector 20, light (2
3b) is irradiated. On the other hand, when the sample surface 18 is closer to the objective lens 17 than the focal point (18c), the blurred light (23c) is applied to the photodetector 20. Here, when the light-shielding plate 15 is not provided, the reflected light from the sample surface 18 shifted from the focal point is
Although it becomes a light shape that is blurred both up and down with respect to 23b,
Due to the presence of the light-shielding plate 15, the component reflected from the sample surface 18c, which is blurred upward, is cut off to form a shape 23c. On the other hand, when the sample surface 18a is farther than the focal point of the objective lens 17, the light shape is 23a, which is shifted upward. This makes it possible to know from the signal of the photodetector 20 which of the sample surfaces 18 is deviated from the focal point of the objective lens 17. Also, the degree of blur increases as the focus deviates, so that the amount of defocus can be known at the same time. Here, it is also possible to use a line sensor 25 as the photodetector 20 and irradiate the line sensor 25 with light focused in a specific direction by the cylindrical lens 24. In this case, the light shape 23a on the photodetector 20;
The lines 23b and 23c are compressed in the horizontal direction as indicated by 26a, 26b and 26c, respectively, and are irradiated on the line sensor 25. Next, an embodiment of the present invention will be described with reference to FIGS. 3 and 4. In FIGS. 3 and 4, a region irradiated with light from a slit on a sample surface or a cantilever is called a “slit light region”. FIG. 3 is a schematic diagram illustrating the principle of the autofocus of the present invention. FIG. 3A is a plan view showing the cantilever 31 and the slit light region 32 irradiated to the sample surface 18. Cantilever 31 and sample surface 1
8 is not on the same plane. The slit light area 32 is shown in FIG.
As shown in (a), the y direction is sufficiently long and the x direction is slightly smaller than the width of the cantilever. FIG. 3 (b)
Indicates the shape of light applied to the photodetector 20 when the autofocus system is focused on the sample surface. The spot 33 is a spot of light corresponding to the reflected light on the sample surface 18, but is focused on the photodetector 20 without being blurred because it is in focus. On the other hand, the spot 34 is a spot of light corresponding to the reflected light on the back surface of the cantilever 31, but the cantilever 31 is focused on the objective lens 1 with respect to the focus.
The spot is shifted to the right because it is on the seventh side. Here, the spot has a triangular shape because the cantilever 31 is inclined with respect to the sample surface 18.
This is because the spot near the root of the cantilever is further defocused and the spot is shifted to the right. Here, in FIG. 3, the light spot is shifted at the detector position to the right when the reflecting surface is closer to the objective lens than the focal point, and to the left when the reflecting surface is farther than the objective lens. FIG. 3C shows a state in which a cylindrical lens 24 is inserted between the lens 19 and the photodetector 20 and the line sensor 2 is inserted.
5 is a light spot when light is collected. The cylindrical lens 24 has power only in one direction, whereby the light spot as shown in FIG. 3B is condensed in the vertical direction to have the shape shown in FIG. 3C. Spot 3
Reference numeral 5 denotes a spot 33 in which the spot 33 is contracted in the vertical direction by a cylindrical lens, and corresponds to the reflected light from the sample. The spot 36 is obtained by contracting the spot 34 in the vertical direction, and is a spot corresponding to light reflected from the back surface of the cantilever 31. A line 38 in FIG. 3D represents an intensity distribution of light applied to the line sensor 37, A is a light intensity peak corresponding to the reflected light on the sample surface, and B is a light intensity peak on the back surface of the cantilever 31. Is the peak of the light intensity corresponding to the reflected light. FIG. 3 (e)
The shape of light emitted to the photodetector 20 when the autofocus system is focused on the back of the cantilever 31 is shown. The spot 39 is a light spot corresponding to the reflected light on the sample surface, and the spot is shifted to the left because the sample surface is on the opposite side of the objective lens with respect to the focal point. on the other hand,
The spot 40 is a light spot corresponding to the reflected light on the back surface of the cantilever 31, and is focused almost without blurring because the light is in focus. Here, the spot 40 has the shape shown in FIG. 3E because the cantilever 31 is attached slightly obliquely. FIG. 3F shows a light spot when a cylindrical lens 24 is inserted between the lens 19 and the photodetector 20 and light is collected on a line sensor 25 of the photodetector. The spot 41 is obtained by reducing the spot 39 in the vertical direction by a cylindrical lens, and is a spot corresponding to the reflected light from the sample. The spot 42 is a spot 40
Are spots corresponding to the light reflected from the back of the cantilever 31. A line 44 in FIG. 3G represents an intensity distribution of light applied to the line sensor 43, C is a light intensity peak corresponding to the reflected light on the sample surface, and D is a back surface of the cantilever 31. Is the peak of the light intensity corresponding to the reflected light. here,
The interval between A and B in FIG. 3 (d) or FIG. 3 (g)
Is longer when the distance between the cantilever and the sample is longer and shorter when the distance between the cantilever and the sample is shorter. For this reason, the positional relationship between the cantilever and the sample can be known from the interval between the two light intensity peaks corresponding to the reflected light from the sample surface and the back surface of the cantilever. Therefore, by bringing the cantilever closer to the sample while monitoring this interval, it becomes possible to make the cantilever approach a very close distance to the sample. Hereinafter, a case where there are two slits, one for irradiating the back surface of the cantilever with light and the other for irradiating the sample surface with light, will be described with reference to FIG. FIG. 4A is a plan view illustrating a state in which all light in the slit light region 52 is reflected on the back surface of the cantilever 51 and all light in the slit light region 53 is reflected on the sample surface. FIG. 4B shows the shape of light emitted to the photodetector 20 when the autofocus system is focused on the sample surface. The spot 54 is a light spot corresponding to the light reflected on the sample surface, and is focused on the photodetector 20 without being blurred because it is in focus. On the other hand, the spot 55 is a light spot corresponding to the reflected light on the back surface of the cantilever 51, but the spot is shifted downward because the cantilever 51 is on the objective lens 17 side with respect to the focal point. Here, in FIG. 4, it is assumed that the light spot is shifted at the detector position downward when the reflecting surface is closer to the objective lens than the focal point, and upward when the reflecting surface is farther than the objective lens. FIG. 4 (c)
Inserts a cylindrical lens 24 between the lens 19 and the photodetector 20, and detects the line sensor 2 as a photodetector.
5 is a light spot when light is collected. The cylindrical lens has power only in one direction, so that the light spot as shown in FIG. 4B is condensed in the horizontal direction to have the shape shown in FIG. 4C. The spot 56 is obtained by contracting the spot 54 in the lateral direction by a cylindrical lens, and is a spot corresponding to the reflected light from the sample. The spot 57 is obtained by contracting the spot 55 in the horizontal direction, and is a spot corresponding to light reflected from the back of the cantilever 51. Line 5 in FIG. 4 (d)
Reference numeral 9 denotes an intensity distribution of light applied to the line sensor 58, E denotes a light intensity peak corresponding to the reflected light on the sample surface, and F denotes light corresponding to the reflected light on the back surface of the cantilever 51. Intensity peak. Since the sample surface is focused, the peak E of the light intensity coincides with the position E0 corresponding to the slit light region 53. On the other hand, on the back surface of the cantilever 51, the peak F of the light intensity is shifted downward from the position F 0 corresponding to the slit light region 52 because it is closer to the objective lens than the focal point. FIG. 4E shows the state of FIG.
It is the same schematic diagram as. FIG. 4F shows the shape of light emitted to the photodetector 20 when the autofocus system is focused on the back of the cantilever. Spot 60
Is a light spot corresponding to the reflected light on the sample surface, and the spot is shifted upward because the sample surface is on the opposite side of the objective lens with respect to the focal point. On the other hand, the spot 61 is a spot of light corresponding to the reflected light on the back surface of the cantilever 51, and is focused almost without blurring because it is in focus. FIG. 4G shows a light spot when a cylindrical lens 24 is inserted between the lens 19 and the photodetector 20 and light is collected on a line sensor 25 of the photodetector. The spot 62 is obtained by contracting the spot 60 in the lateral direction by a cylindrical lens, and is a spot corresponding to the reflected light from the sample. Also, spot 63
Is a spot corresponding to the light reflected from the back of the cantilever 51, which is obtained by shrinking the spot 61 in the horizontal direction.
A line 65 in FIG. 4H represents the intensity distribution of the light applied to the line sensor 64, G is the peak of the light intensity corresponding to the reflected light on the sample surface, and H is the back of the cantilever 51. Is the peak of the light intensity corresponding to the reflected light. Since the back of the cantilever 51 is focused, the peak H of the light intensity coincides with the position H0 corresponding to the slit light region 52. On the other hand, since the sample surface is on the opposite side of the focus from the objective lens, the peak G of the light intensity is shifted upward from the position G0 corresponding to the slit light region 53. When the focus is on the sample, the difference between the peak of the reflected light from the back of the cantilever and the position corresponding to the slit light region 52 indicates the distance between the cantilever and the sample. Therefore, while maintaining the peak of the reflected light from the sample surface at the position corresponding to the slit light region 53, that is, while focusing on the sample, the position of the peak of the reflected light from the back of the cantilever and the position corresponding to the slit light region 52 are maintained. Move the cantilever closer to the sample until the deviation from the value decreases to a certain value. This allows the cantilever to be very close to the sample. It is also possible to monitor the deviation between the peak of the reflected light from the sample surface and the position corresponding to the slit light region 53 by focusing on the back surface of the cantilever.

[First Embodiment] An autofocus process in the first embodiment will be described below with reference to FIGS. 3 and 5. FIG. In the flowchart of FIG. 5, when one image measurement is completed (Step 71), the probe is retracted by 10 μm from the 12-inch silicon wafer as the sample by the three-dimensional scanner (Step 72). The three-dimensional scanner of this embodiment has a stroke of 15 μm in the z direction.
The stroke in the m and xy directions is 50 μm. In a state where the probe is separated from the sample, the sample is driven with respect to the cantilever by the three-dimensional stage, and the next measurement point is moved immediately below the probe (step 73). Here, it is assumed that the focus of the autofocus system is fixed on the sample surface. Two light intensity peaks, eg, FIG.
A and B in FIG. 3C or C and D in FIG. 3F are detected, and a distance x between them is obtained (step 74). Next, the distance x is compared with a predetermined value y (step 7).
6). At this time, if x> y, the cantilever is brought closer to the sample by the three-dimensional scanner (step 75), and x and y are compared again. When the distance x becomes smaller than the predetermined value y due to the cantilever approaching the sample, that is, when x ≦ y, the approach of the probe to the sample by the autofocus mechanism is terminated, and the normal scanning probe is used. As in a microscope, the cantilever is automatically approached by a three-dimensional scanner while monitoring the bending of the cantilever (step 77). Here, the focus of the auto focus is made variable, the center of gravity of the light detected by the line sensor is obtained, and the focus of the auto focus is changed, so that the center of gravity is set at a point corresponding to the slit light area 32 at the center of the detector. A structure may be employed in which the focus of the autofocus system is always feedback controlled so as to match.

[Second Embodiment] An autofocus process in the second embodiment will be described below with reference to FIGS. 4A to 4D and FIG. In the flowchart of FIG. 6, when one image measurement is completed (Step 8)
1) The probe is retracted by 100 μm from a 12-inch silicon wafer as a sample by a three-dimensional scanner (step 82). The three-dimensional scanner of this embodiment has a stroke in the z direction of 150 μm and a stroke in the xy direction of 50 μm. In a state where the probe is separated from the sample, the sample is driven with respect to the cantilever by the three-dimensional stage to move the probe to the next measurement point (step 83). Next, the focus of the autofocus system is made to coincide with the sample surface. That is, the peak E of the reflected light from the sample surface
Is the slit light area 5 when the sample surface is in focus.
The focus of the autofocus system is adjusted so as to coincide with the peak position E0 of the light from No. 3 (step 84). In this state, the peak F of the reflected light from the back of the cantilever
The deviation L1 from F0 is obtained (step 85), and the deviation L1 is compared with a predetermined value α (step 86). Here, when the deviation amount is larger than the predetermined value α, 3
The cantilever is moved closer to the sample by the dimensional scanner (step 87), and the deviation L1 is compared with the predetermined value α again. When the displacement L1 becomes smaller than the predetermined value α due to the approach of the cantilever to the sample, that is, when L1 ≦ α, the approach of the probe to the sample by the autofocus mechanism is terminated, and normal scanning is performed. As in the case of a probe microscope, the cantilever is automatically approached by a three-dimensional scanner while monitoring the bending of the cantilever (step 88).

[Third Embodiment] An autofocus process in the third embodiment will be described below with reference to FIGS. 4 (e) to 4 (h) and FIG. In the flowchart of FIG. 7, when one image measurement is completed (step 9).
1) The probe is withdrawn by 5 μm from a 12-inch silicon wafer as a sample by a three-dimensional scanner, and a 5-mm sample is further withdrawn from the probe by a three-dimensional stage (step 92). In the present embodiment, it is not necessary to retreat the probe more largely by the three-dimensional scanner, so that there is an advantage that the driving amount of the three-dimensional scanner in the z direction can be small. In a state where the probe is separated from the sample, the sample is driven with respect to the cantilever by the three-dimensional stage to move the probe to the next measurement point (step 93). Next, the focus of the autofocus system is made to coincide with the back of the cantilever. That is, the autofocus system focuses so that the peak H of the reflected light from the back surface of the cantilever coincides with the peak position H0 of the light from the slit light region 52 when the back surface of the cantilever is focused (step 94). . Here, in the following process, feedback control is performed so that the focus of the autofocus system always coincides with the back of the cantilever. In this state, the deviation L2 of the peak G of the reflected light from the sample surface from G0 is obtained (step 9).
5) The deviation L2 is compared with a predetermined value β (step 96). Here, when the deviation is larger than the predetermined value β, the sample is made to approach the probe by the three-dimensional stage (step 97), and the deviation L2 is compared with the predetermined value β again. When the displacement L2 becomes smaller than the predetermined value β due to the cantilever approaching the sample, that is, when L2 ≦ β, the approach of the probe to the sample by the autofocus mechanism is terminated, and the normal As in a scanning probe microscope, the cantilever is automatically approached by a three-dimensional scanner while monitoring the bending of the cantilever (step 98).

[0009]

According to the present invention, the cantilever (probe) and the sample can be quickly and automatically approached from a state where they are far apart to a very short distance.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a scanning probe microscope having an autofocus mechanism according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an autofocus optical system according to an embodiment of the present invention.

FIG. 3 is a schematic diagram for explaining the principle of the autofocus mechanism according to the first embodiment of the present invention.

FIG. 4 is a schematic diagram for explaining the principle of an autofocus mechanism according to second and third embodiments of the present invention.

FIG. 5 is a flowchart illustrating a cantilever approaching step according to the first embodiment of the present invention.

FIG. 6 is a flowchart illustrating a cantilever approaching step according to a second embodiment of the present invention.

FIG. 7 is a flowchart showing a step of approaching a cantilever according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 31, 51 Cantilever 2 3D scanner 3 Support 4 Autofocus optical system 5 3D stage 11 LED 12, 14, 19 Lens 13 Slit 15 Light shield 16 Half mirror 17 Objective lens 18 Sample surface 20 Photodetector 21, 22, 23, 26 Light shape 24 Cylindrical lens 25, 37, 43, 58, 64 Line sensor 32, 52, 53 Slit light area 33-36 39-42 54-57 60-63 Light spot A-H Light peak

Continued on the front page F term (reference) 2F065 AA06 CC00 DD00 GG07 HH05 JJ02 LL08 LL28 PP22 2F069 AA17 BB40 DD30 GG07 HH09 MM38 2H051 AA11 BA25 BA33 BA34 BA37 CB05 CB07 CB11 CB22 CB28 CC04 CC06 CC13 CE02

Claims (4)

[Claims] 1. A light source, a slit, a photodetector, and an optical system. The light emitted from the slit is irradiated to the sample surface and the back of the cantilever by the optical system and reflected, and the reflected light is reflected by the photodetector. An autofocus mechanism that obtains a spot by being incident on a position, utilizing that the shape of the spot from the sample surface and the back of the cantilever changes due to a shift between the sample surface or the back of the cantilever and the focal position of the optical system. A scanning probe microscope, comprising: an autofocus mechanism for calculating the shift amount by using a driving mechanism for shortening the distance between the cantilever and the sample surface based on the shift amount. 2. The scanning probe microscope according to claim 1, wherein a line sensor is used as the photodetector, and a cylindrical lens that focuses a spot on the line sensor is added to the optical system. 3. The device according to claim 1, wherein a slit light region irradiated on the sample surface and the back surface of the cantilever is narrower than a width of the back surface of the cantilever, and is sufficient to irradiate both the back surface of the cantilever and the sample surface. A scanning probe microscope having a size. 4. The device according to claim 1, wherein two slits are provided, and light emitted from one of the slits is applied to the sample surface, and light emitted from the other is applied to the back surface of the cantilever. Scanning probe microscope.