JPH1089913A - Device for detecting surface position - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the position of sample surface accurately even when the sample surface is inclined by selecting an incident optical axis according to angle of inclination, allowing light reflecting from the sample surface to enter an optical detecting means securely, thereby detecting it. SOLUTION: Illuminating optical systems 4A, 4B and 4C are provided with light sources 5A, 5B and 5C for illumination, mirrors 6A, 6B and 6C, lenses 7A and 7B, etc. Light which enters and reflects on a sample surface 3 is formed on the light reception surface of an optical position detector 14 through a formation lens 12 for detection. The detector 14 inputs to an optical axis selection device 11 a signal corresponding to the position of the sample surface 3. An inclination measuring system for measuring an angle of inclination on the sample surface and an optical axis selection device 11 constitute a light axis selection means, which selects one incident optical axis from 3 incident optical axes. Even when an angle of inclination of a sample varies from 0 degree to 60 degrees, a reflection light from either of 3 incident optical axes enters the detector 14, so that this detector can correspond to the change of inclination of sample from 0 to 60 degrees.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a height position of a sample surface in a microscope such as a scanning electron microscope (SEM) for observing a fine morphology of the sample or a semiconductor manufacturing apparatus such as an electron beam exposure apparatus. The present invention relates to a surface position detecting device that performs

[0002]

2. Description of the Related Art In a sample inspection apparatus such as a scanning electron microscope, it is effective when the position of a sample surface of a semiconductor wafer or the like is accurately positioned on a focal plane of an inspection means (for example, an electron optical system). Observation is possible.

Conventionally, a so-called optical lever type focus position detection method as shown in FIG. 9 has been known as a surface position detection device for measuring the height position of a sample surface. This is because light emitted from the light source S is focused into a spot by the lens L1, and
The portion of the sample surface T located near the focal point of the sample inspection device D is obliquely irradiated, and the reflected light is imaged on the light receiving surface of the optical position detector PSD (Position Sensitive Device) by the lens L2. Of the incident position is determined. Then, the deviation ΔS of the incident position and the deviation ΔZ of the height of the sample surface are determined.
10 has a relationship as shown in FIG. 10, and the deviation ΔZ of the height of the sample surface can be obtained from the deviation ΔS of the incident position.

[0004]

However, in the conventional focus detection method using the optical lever, the following problem arises because the incident light on the sample surface T enters the sample surface T obliquely.

That is, as in a scanning electron microscope, the sample surface may be inclined for a certain inspection purpose.
When the sample surface is tilted in this manner, the reflection angle becomes twice as large as the tilt angle, so that the light reflected on the sample surface T tends to deviate from the optical axis of the light receiving optical system having the optical position detector PSD.

For example, the angle θy at which the sample surface T is inclined is
Assuming that the angle is 60 degrees, the reflection angle of the reflected light in the θy direction (inclination angle around the y axis) is 2θy in principle of the optical lever type.
= 120 °. As a result, the inclination angle θy of the sample surface T
Is changed in the range of 0 ° ≦ θy <60 °, the aperture ratio NA is set to sin (2
θy) = sin (120 °). However, in reality, NA is sin (0 °) ≦ NA.
It can be obtained only in the range of ≦ sin (90 °). Therefore, the reflected light on the sample surface exceeding this cannot be received, and the focus position cannot be detected.

In particular, when determining the focal position of an inspection device such as a scanning electron microscope, the distance between the tip of the eyepiece of the inspection device and the sample surface is a very small gap of about several mm. In general, the angle of incidence of the incident light on the sample surface must be increased, and when the sample surface is tilted, the incident light in the area of the irradiation spot on the surface to be inspected is increased. The height difference between the reflection points and the change in the reflection characteristics become remarkable, causing a decrease in the position resolution of the optical position detector, making it impossible to perform linear and clear position measurement.
The detection accuracy of the optical position detector is greatly reduced.

As described above, in the conventional method for measuring the height of the sample surface, for example, when the method is used for detecting the focus position of a scanning electron microscope, when the sample surface is tilted for inspection, In other words, the reflected light deviates from the optical position detector and the reflected light cannot be detected, or the reflection efficiency on the sample surface deteriorates, and the detection accuracy decreases, and the height position of the sample surface cannot be measured. There was a problem.

[0009] An object of the present invention is to provide a method in which even if the sample surface is inclined,
It is an object of the present invention to provide a surface position detecting device capable of reliably measuring the height position of a sample surface.

[0010]

In order to achieve the above object, the present invention provides a method of irradiating a surface of a test object with light,
In a surface position detecting device that receives reflected light of the light on the surface of the test object and detects the surface position of the test object from the received light, the test object is detected in a three-dimensional space of X, Y, and Z. Holding the surface of the test object around the Y axis at an angle 0 to θma.
A stage system configured to be tiltable up to x, and having a plurality of incident optical axes for obliquely entering light toward the surface of the test object, among the plurality of incident optical axes, one selected from An illumination optical system that causes light to enter the surface of the test object from an incident optical axis; and a position of the surface of the test object that detects light incident from the illumination optical system and reflected by the surface of the test object. And a light axis selecting means for selecting one of the plurality of incident optical axes based on an output result of the light detecting means. .

According to the above configuration, an incident optical axis through which light enters the test object is appropriately selected according to the inclination angle of the stage system. For example, when three incident optical axes are provided: a first incident optical axis, a second incident optical axis, and a third incident optical axis, the first incident optical axis is selected when the inclination angle of the stage system is small. However, when the inclination angle is slightly increased, the second incident optical axis is selected, and when the inclination angle is further increased, the third incident optical axis is selected. As a result, the reflected light on the surface of the test object surely enters the light detecting means and is detected, so that the position of the surface of the test object can be accurately measured.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. A surface position detecting device according to the present invention includes a stage system that holds a sample as an object to be inspected in a three-dimensional space of X, Y, and Z, and tilts the surface of the sample around a Y axis, and a surface of the sample. A plurality of incident optical axes for incident light obliquely toward the illuminating optical system, and an illumination optical system for causing light to enter the sample surface from one of the plurality of incident optical axes, and an incident optical axis of the illumination optical system. A light detection optical system that detects light reflected on the sample surface and outputs a signal corresponding to the position of the sample surface, and one of a plurality of incident optical axes in the illumination optical system based on an output result of the light detection optical system. And an optical axis selection device that selects

FIG. 1 shows a schematic configuration of a surface position detecting device according to the present invention. A stage system is provided in a three-dimensional space of x-axis, y-axis, and z-axis which are orthogonal to each other, and a sample such as a semiconductor wafer is mounted on the stage system. In FIG. 1, the surface of the sample is indicated by reference numeral 3. The stage system is configured to be tiltable around the y axis, and the sample surface 3 also tilts with the tilt of the stage system. In FIG. 1, the sample surface when the inclination angle is 0 degree is represented by 3A, the sample surface when the inclination angle is 20 degrees is represented by 3B, the sample surface when the inclination angle is 40 degrees is represented by 3C, and the sample surface when the inclination angle is 60 degrees is represented by 3C. I have. Note that the maximum tilt angle of the stage system is θmax.

Above the sample surface 3, an inspection apparatus 2 in a semiconductor manufacturing apparatus such as a scanning electron microscope (SEM) or an electron beam exposure apparatus is provided. The inspection apparatus 2 is a scanning electron microscope or an electron beam exposure apparatus. Etc. are held by the main body. In practice, when the inspection apparatus 2 is mounted on, for example, a scanning electron microscope, the distance between the tip of the eyepiece of the inspection apparatus 2 and the sample surface 3 is about several mm.

Normally, the sample surface 3 is not inclined, and the direction perpendicular to the sample surface 3 at that time coincides with the z-axis. The focus detection direction of the inspection device 2 also matches the z-axis direction. The sample is set so that it can be tilted around the y-axis in the range of 0 ° ≦ θy <90 °, and the sample surface 3 is tilted in the direction around the y-axis at the time of inspection by the inspection device 2 and depending on the case. I am getting it.

On the side of the inspection device 2, there are provided illumination optical systems 4A to 4C of a so-called optical lever type oblique incidence type focus position detecting device.
And a light detection optical system 10 are provided. Illumination optical system 4A
Is composed of an illumination light source 5, a lens 6 and a slit 7, and the other two illumination optical systems 4B and 4C are omitted in the figure, but have the same configuration as the illumination optical system 4A.

FIG. 2 is a view of the sample surface 3 of FIG. 1 as viewed from the inspection apparatus 2 side, and shows the arrangement relationship of the illumination optical systems 4A to 4C and the light detection optical system 10. In FIG. 1, the sample surface 3
Is represented by a rectangle, but in FIG. 2, the sample surface 3 is represented by a circle and an ellipse in order to clearly show the case where the sample surface 3 is inclined (the circle is the sample surface when the inclination angle is 0 degree). And the ellipse is the sample surface when the tilt angle is 60 degrees).

Next, the illumination optical system will be described. There are a plurality of incident optical axes, and these optical axes are arranged at positions where light is incident toward the focal position of the electron optical system. In the present embodiment, three incident optical axes are provided, and the direction of each optical axis is (φy, φz) = (0,
30), (−20, 30) and (−40, 30).
Here, φy represents an angle between a straight line which is an image when the incident optical axis is projected on the XY plane and the X axis, and φz represents an angle between the incident optical axis and the XY plane. Hereinafter, these three lines are referred to as a first incident optical axis, a second incident optical axis, and a third incident optical axis, respectively. In FIGS. 1 and 2, the first incident optical axis is the optical axis of the illumination optical system 4A, and the second incident optical axis is the illumination optical system 4B.
And the third incident optical axis corresponds to the optical axis of the illumination optical system 4C.

The direction cosine of the incident optical axis is (α, β, γ), and the direction cosine of the reflected light of the incident light on the sample surface is (α ′, β ′, γ ′). Also, as shown in FIG.
The angle formed by the component of the incident optical axis parallel to the XY plane with the y-axis, the angle formed by the incident ray with the xy plane (φy, φz), and the angle formed by the component of the output optical axis parallel to the XY plane with the y-axis , And the angle between the emitted light and the xy plane is (φy ′, φz ′), and the inclination angle of the sample surface is θ. Then, Figure 3
Thus, the following equation (1) is derived.

[0020]

(Equation 1) Equation (2) shows the direction cosine of the sample surface inclined by θ.

(Equation 2) The input / output angle i is as follows: cos i = αλ + βμ + γν = −α · sin θ + γ · cos θ (3)

From the above equations (1) to (3), the direction cosine of the emitted light beam is as follows.

(Equation 3) When the above equations are put together, the following equation (4) can be derived.

(Equation 4) The following equation (5) holds for the outgoing light beam.

(Equation 5) Here, the direction of the optical axis of the incident light beam (φy, φz) = (0, 3)
0), (−20, 30), (−40, 30), the inclination angle θ of the sample surface is 0 °, 20 °, 40 °.
The change in the emission direction of the emission optical axis at the angles of 60 ° and 60 ° is obtained.

First, when (φy, φz) = (0, 30), that is, when the first incident optical axis is used, if the sample stage is tilted from 0 ° to 60 °, the direction of the emitted light beam Cosine (α ', β', γ '), and φy' and φz '
Changes as shown in Table 1. FIG. 4 is a graph of Table 1.

[0023]

[Table 1] Next, when (φy, φz) = (− 20, 30), that is, when the second incident optical axis is used, if the sample stage is inclined from 0 ° to 60 °, the direction cosine of the outgoing light beam is obtained. (Α ′, β ′, γ ′), and φy ′ and φz ′ change as shown in Table 2. FIG. 5 is a graph of Table 2.

[0024]

[Table 2] Further, when (φy, φz) = (− 40, 30), that is, when the third incident optical axis is used, if the sample stage is inclined from 0 ° to 60 °, the direction cosine of the outgoing light ray ( α ′, β ′, γ ′) and φy ′ and φz ′ are shown in Table 3.
It changes like FIG. 6 is a graph of Table 3.

[0025]

[Table 3] As can be seen from Tables 1 to 3, when the tilt angle of the stage is changed from 0 to 60 degrees, the direction of the reflected optical axis also changes greatly. For example, paying attention to Table 1, the direction of the reflected light when the tilt angle of the stage is 0 degree (0, 0.866, 0.5)
And the reflected light when the stage tilt angle is 60 degrees (-0.4
33, 0.866, -0.25), the reflection direction differs by about 60 degrees. Therefore, in an electron microscope having a stage that can be tilted up to 60 degrees, if an attempt is made to perform focus detection with one incident optical axis and one light detection optical system, the NA of the light detection optical system is at least 0.5. That is all you need to do. However, such a large NA optical system cannot be installed with an electron microscope in which the distance between the electron optical system and the sample is short. Therefore, in the present invention, in order to selectively use the plurality of incident optical axes according to the inclination angle of the stage, an NA.
A wide range of detection is possible even with a small detection optical system.

FIG. 7 shows an example of an optical axis selecting means for selecting one incident optical axis from the first incident optical axis, the second incident optical axis, and the third incident optical axis. That is, the illumination optical system 4
Each of A to 4C has a light source for illumination 5A to 5C and a mirror 6
A to 6C, lenses 7A to 7C (lens 7c is not shown)
Are provided, and the illumination light sources 5A to 5C and the mirror 6A are further provided.
6A to 6C, shutters 8A to 8C are provided. Solenoids 9A to 9C are connected to the shutters 8A to 8C, and the solenoids 9A to 9C are connected to the optical axis selecting device 11 respectively.
Is electrically connected to The shutters 8A to 8C are driven by solenoids 9A to 9C, and emit light sources 5A to 5C for illumination.
The sample surface 3 is irradiated with light of 5C or shielded. FIG. 7 shows a state where only the light from the illumination optical system 4B is irradiated to the sample surface 3, and the light from the illumination optical systems 4A and 4C is shielded.

FIG. 8 is a view of FIG. 7 viewed from the direction B, and shows a case where the sample surface 3 is horizontal and a case where the sample surface 3 is inclined by 60 degrees. Although not shown, a tilt measuring system is provided for measuring the tilt angle of the sample surface. In the present embodiment, the tilt measuring system and the optical axis selecting device 11 constitute an optical axis selecting unit. doing.

Next, the light detection optical system will be described. As shown in FIG. 7, the light detection optical system 10 includes a detection imaging lens 12, a mirror 13, a light position detector 14 including a light receiving element such as a PSD, and the like. Light incident from the illumination optical system and reflected by the sample surface 3 is transmitted to the detection imaging lens 1.
2 forms an image on the light receiving surface of the optical position detector 14. Then, the light position detector 14 detects the light reflected on the sample surface 3 and outputs a signal corresponding to the position of the sample surface 3. The output signal from the optical position detector 14 is input to the optical axis selection device 11.

The direction of the optical axis of the light detection optical system 10 is such that the reflected light from any of the three incident optical axes is transmitted to the optical position detector 14 even when the inclination angle of the sample changes from 0 ° to 60 °. It is better to match the direction of incidence. Therefore, the direction of the optical axis of the light detection optical system 10 varies depending on the arrangement direction of the three incident optical axes of the illumination optical system. However, in this embodiment, the incident optical axes are arranged as described above. For example, the direction of the optical axis of the light detection optical system 10 is (−20, 20),
When designed so that light beams in the range of −40 ≦ φy ′ ≦ 0 and −0 ≦ φz ′ ≦ 40 are incident (that is, when the NA of the photodetection optical system is about 0.34), from 0 to 60 degrees Can respond to the change in the tilt angle of the sample.

Then, the arrival position of the reflected light is detected, and whether or not the observation position is at the focal position is detected from the arrival position and the measurement result of the above-described tilt measurement system.

Incidentally, the light position detector 14 may be, for example, a photodiode for detecting the amount of reflected light on the sample surface 3, and the shift ΔS of the incident position may be obtained from the difference in the amount of light. good.

With the above configuration, even if the sample surface 3 is inclined,
Even when the sample surface 3 is not tilted, the position of the sample surface 3 in the z direction can be detected stably and with high accuracy. Further, for the lens of the light detection optical system 10, for example, even when θmax = 60 °,
The NA is at most NA = sin (30 °) = 0.
5, which makes the optical design easier.

Next, the operation of the surface position detecting device having the above configuration will be described. First, when a switch (not shown) of the detection device main body is turned on, an operation of detecting the position of the sample surface is started, and the optical axis selection device 11 sends a shutter release signal to, for example, the solenoid 9A. In response to this, the solenoid 9A opens the shutter 4A for a predetermined time. Thereby, a light beam is incident on the sample surface 3 from the first incident optical axis.

The same is repeated for the second and third incident optical axes. Then, in each case, it is determined whether or not any signal is output from the optical position detector 14. As can be seen from FIGS. 4 and 5, when the first incident optical axis is used, the reflected light is incident on the optical position detector 14 when the inclination angle θ is 45 degrees or less, but is not incident otherwise. When the second incident optical axis is used, the reflected light enters the optical position detector 14 when the inclination angle θ is equal to or greater than 15.3 degrees, but does not enter when the inclination angle θ is less than 15.3 degrees. further,
When the third incident optical axis is used, the reflected light is incident on the optical position detector 14 when the inclination angle θ is 24.1 degrees or more,
Otherwise, it does not enter.

Therefore, a method for selecting one of the first, second, and third incident optical axes can be determined as follows. (1) When the light is incident on the optical position detector regardless of the incident optical axis, the first incident optical axis is selected. (2) If the light is incident on the first and second incident optical axes, it is incident on the optical position detector, but if it is off the third incident optical axis, the first incident optical axis is selected. (3) If the light is incident on the first and third incident optical axes, it is incident on the optical position detector, but if it is off the second incident optical axis, the first incident optical axis is selected. (4) When the light is incident on the second and third incident optical axes, the light is incident on the optical position detector, but when the incident light deviates from the first incident optical axis, the second incident optical axis is selected. (5) When the light is incident on the first incident optical axis, the light is incident on the optical position detector, but when the incident light deviates from the second and third incident optical axes, the first incident optical axis is selected. (6) When the light is incident on the second incident optical axis, the light is incident on the optical position detector. However, when the incident light deviates from the first and third incident optical axes, the second incident optical axis is selected. (7) When the light is incident on the third incident optical axis, the light is incident on the optical position detector. However, when the incident light deviates from the first and second incident optical axes, the third incident optical axis is selected.

The above selection method is merely an example. For example, the third incident optical axis may be selected in the case of (1), and the second incident optical axis may be selected in the case of (2). May be selected.

In the above example, the light is once incident on all of the first, second, and third incident optical axes, and then an appropriate incident optical axis is selected. If light enters one of the light position detectors when the light is incident on any one of them, the incident optical axis may be selected immediately.
In this way, it is not necessary to make light incident on another incident optical axis, and the work of surface position detection can be performed efficiently.

It is assumed that the output from the optical position detector 14 becomes zero as a result of projecting on the first incident optical axis and gradually changing the tilt angle of the sample. In this case, a zero signal has been transmitted to the optical axis selecting device 11, and the optical axis selecting device 11 receives the signal and sequentially drives the solenoids 4B and 4C. Thereby, the incident light is sequentially turned on from the second and third incident optical axes. Then, when light is incident on the second and third incident optical axes, the optical axis selecting device 11 determines whether or not there is an output from the optical position detector 14. Then, the incident optical axis having the output is selected, the solenoid of the incident optical axis is driven, light is emitted from the light source of the optical axis toward the sample, and focus detection is continuously performed. When there is output from both the second and third incident optical axes, the second or third incident optical axis is used.

Similarly, the projection was performed on the second incident optical axis, and the inclination angle of the sample was gradually changed.
When the output from 4 becomes zero, the first and third incident optical axes are sequentially turned on, and the optical axis having the output from the optical position detector 14 is selected. used. In addition,
When there is output from both the first and third incident optical axes, the first or third incident optical axis is used.

Similarly, the light is projected on the third incident optical axis, and the inclination angle of the sample is gradually changed.
When the output from 4 becomes zero, the first and second incident optical axes are sequentially turned on, and the optical axis having the output from the optical position detector 14 is selected. used. first,
When there is output from either of the second incident optical axes, the first or second incident optical axis is used.

In the above-described embodiment, the first, second, and third incident optical axes are sequentially turned on to determine whether or not incident light is incident on the photodetector. Although selected, the present invention is not limited to this, for example, from the output of the tilt sensor provided in the stage system,
Under the inclination angle, an optical axis selecting device may determine which incident optical axis is preferable, and the optical axis may be selected based on the result.

In the above-described embodiment, the case where the number of incident optical axes is three has been described as an example. However, the number of incident optical axes may be two, and the NA of the light detection optical system is reduced. Instead, 4
More than two incident optical axes may be used. Further, when there are two suitable optical axes, the one having the larger light amount may be selected.

[0043]

As described above, according to the present invention,
Since a plurality of incident optical axes are selected by the optical axis selecting means, focus detection can be easily performed even when the sample is greatly inclined.

Further, even when the inclination angle is changed during the observation, the incident optical axis is automatically switched, so that the operation can be facilitated.

Furthermore, since the NA of the light detection optical system can be reduced, the optical design is easy.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a surface position detection device.

FIG. 2 is a plan view showing an arrangement relationship between an illumination optical system and a light detection optical system.

FIG. 3 is a diagram showing directions of an incident light beam and a reflected light beam on an inclined sample surface.

FIG. 4 is a diagram showing a change in the direction of reflection of reflected light on the sample surface when the sample surface is sequentially inclined with φy = 0 °.

FIG. 5 is a diagram illustrating a change in the direction of reflection of reflected light on the sample surface when the sample surface is sequentially inclined with φy = 20 °.

FIG. 6 is a diagram showing a change in the direction of reflection of reflected light on the sample surface when the sample surface is sequentially inclined with φy = 40 °.

FIG. 7 is a perspective view showing a schematic configuration of a surface position detecting device according to the present invention.

FIG. 8 is a diagram viewed from a direction B in FIG. 7;

FIG. 9 is a diagram illustrating the principle of a conventional surface position detecting device.

FIG. 10 is a diagram showing a relationship between a shift in the incident position of the conventional surface position detecting device and a shift in the height of the sample surface.

[Explanation of symbols]

 2 Detector 3 Sample surface 4A-4C Illumination optical system 5A-5C Illumination light source 8A-8C Shutter 9A-9C Solenoid 10 Light detection optical system 11 Optical axis selection device 14 Optical position detector

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Noriyuki Ishibashi 1 Toshiba R & D Center, Komukai-ku, Kawasaki City, Kanagawa Prefecture (72) Inventor Norio Uchida Komukai, Koyuki-ku, Kawasaki City, Kanagawa Prefecture No. 1, Toshiba Town Inside Toshiba R & D Center

Claims (2)

[Claims] 1. A method for irradiating a surface of a test object with light,
In a surface position detecting device that receives reflected light of the light on the surface of the test object and detects a surface position of the test object from the received light, the test object is detected in a three-dimensional space of X, Y, and Z. A stage system configured to hold and incline the surface of the test object from the angle 0 to θmax around the Y axis, and a plurality of incident optical axes for obliquely incident light toward the surface of the test object. And an illumination optical system for causing light to enter the surface of the test object from a selected one of the plurality of incident optical axes, and an illumination optical system for causing the test object to enter from the illumination optical system. Light detecting means for detecting light reflected on the surface and outputting a signal corresponding to the position of the surface of the test object; one of the plurality of incident optical axes based on an output result of the light detecting means And a light axis selecting means for selecting a position. 2. The surface position detecting device according to claim 1, wherein the optical axis selecting means is a signal indicating that the signal from the light detecting means has detected the reflected light on the surface of the test object. Selects an incident optical axis incident on the light detecting means at that time.