JPH0533322B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to, for example, detecting the position of a sample such as a semiconductor substrate in a semiconductor manufacturing apparatus, or
The present invention relates to a position detection device suitable for focusing an autofocus mechanism linked to a microscope used for surface treatment.

[Conventional technology]

2. Description of the Related Art In semiconductor manufacturing processes and their inspection processes, microscopes are sometimes used to detect the condition and position of the surface of a semiconductor substrate (wafer), and to perform desired processing on the surface.

[Problem that the invention seeks to solve]

In such microscopes, focusing on a sample is done manually, and it is very troublesome to focus quickly and accurately, and it takes time to adjust the focus, and it is difficult to achieve sufficient accuracy. There were disadvantages such as not being able to obtain

Therefore, it is an object of the present invention to provide a position detection device that detects the position of a sample and the focal position with respect to the sample by using a part of the optical system of a microscope.

[Means for solving problems]

As illustrated in FIG. 1, the position detection device of the present invention includes a light source 5 that emits light 4 to be irradiated onto a sample 2 having a planar surface, and a light source 5 that receives the light emitted from the light source. a condensing means 8 that condenses light and focuses it near an arbitrary surface of the sample, and condenses and focuses the reflected light 10 from the surface of the sample; A plurality of slits 16 are formed near the connecting position and allow the reflected light to pass through, and by moving the slits in a direction perpendicular to the central optical path of the reflected light, the reflected light can be blocked or the reflected light can be blocked. A slit plate (optical interrupter 12) is provided to allow the reflected light to pass through the slit, and a slit plate (optical interrupter 12) is installed at a position spaced apart in the direction of movement of the slit across the center optical path on the light receiving side to allow the reflected light to pass through the slit. First and second photodetectors 14 that receive light
A, 14B, and calculation means for receiving each output of the first and second photodetectors and calculating the position of the sample based on the phase difference between the respective outputs.

[Effect]

In the above configuration, when the sample 2 is displaced in the direction of the optical axis 6, that is, when the sample 2 is at the position _S1 or _S2 displaced from the position _S0 , originally,
The focal point that should be set at position P ₀ at position S ₀ of sample 2 is apparently set at positions P ₁ and P ₂ .

Further, the reflected light 10 from the sample 2 is collected by a condensing means 8
The light passes through the objective lens constituting the transparent mirror body 18.
is reflected in a direction perpendicular to the direction of incidence of light 4,
The light enters the optical interrupters 14A and 14B through the slit 16.

In this case, the focus of the light 4 emitted from the light source 5
P ₀ is fixed, and by displacing the sample 2 in the direction of the optical axis 6 with respect to this focal point P ₀ , apparent focal points P ₁ and P ₂ are generated, which are obtained by reflection from the transparent mirror 18. On the optical axis 20 _{of the} reflected light 10, there are focal points _{Q 0 ,}
Q ₁ and Q ₂ are tied to their respective positions.

That is, at the focal point Q ₀ formed inside this slit 16, the reflected light 10 spreads out in a conical shape from this point to the side opposite to the incident side, so that it Installed photodetector 14
The light that has passed through the slit 16 is incident on A and 14B and detected.

In this case, even if the slit plate (light interrupter 12) moves, the light passing through the slit 16 spreads around the focal point _Q0 and enters the photodetectors 14A, 14B. Since the light incident time between the photodetectors 14B and 14B match and the output phases of the photodetectors 14A and 14B match, from the matching of the phases, the sample 2 is S ₀
It can be seen that it is located at

Furthermore, when the sample 2 is displaced below the focal point _P0 , that is, at the position _S1 , the focal point _Q1 appears at a position correspondingly displaced toward the incident side of the slit 16. Therefore, the reflected light 10 is
Since the light spreads from this focal point _Q1 toward the slit plate, the light passing through the slit 16 of the optical interrupter 12 fluctuates as the slit 16 moves. As a result, the position of the focus _Q1 and the slit 16
Due to the moving speed of
4A, the light enters the photodetector 14B after a certain delay time, and as the slit 16 moves,
After the incident on the photodetector 14A ends, the incident on the photodetector 14B ends after a certain delay time, so the delay time causes the photodetector 14A, 1 to
A phase difference is generated in the detection output of 4B, and from this phase difference, it can be known that the sample 2 is at the position _S1 .

Furthermore, when the sample 2 is displaced above the focal point P ₀ , that is, at the position S ₂ , the focal point of the reflected light 10 occurs at Q ₂ , and the photodetection is performed in the opposite relationship to that of Q ₁ . Output is generated in the devices 14A and 14B,
Since a phase difference is generated between the outputs, it can be determined from the phase difference that the sample 2 is at the position _S2 .

Note that the photodetector _14A ,
14B, _the light enters first.
The displacement in the optical axis direction can be quantitatively measured by the phase difference between the outputs of the photodetectors 14A and 14B.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

[First Embodiment] FIG. 2 shows a first embodiment of the focal position detection device of the present invention, in which the same parts as those of the focal position detection device shown in FIG. 1 are denoted by the same reference numerals.

In FIG. 2, the light source 5 includes, for example, He
−Ne laser tube is used. The light (laser) 4 generated from this laser tube is transmitted through the concave lens 24.
The beam then enters a beam expander 27 consisting of a convex lens 26, and the beam is expanded.

The light 4 that has passed through the beam expander 27 passes through a half mirror 28 as a transparent mirror, is focused by an objective lens 30, and focuses P ₀ on a point on the optical axis 6 of the sample 2. If the sample 2 has a mirror surface such as a silicon wafer, the reflected light from the surface is 10
is reflected by the half mirror 28 in the direction of the optical axis 20, which is perpendicular to the optical axis 6, and guided to the optical interrupter 12, which is a slit plate.

As shown in FIG. 3, this optical interrupter 12 has a plurality of slits 16 formed concentrically at regular intervals in a light shielding material plate, and a rotating shaft 32 of a motor 31 is attached to the center of the slits 16. , motor 31
is rotated at a constant speed in the direction of arrow A.

Further, on the back side of this optical interrupter 12, first and second photodetectors 14A and 14B that detect the reflected light 10 that has passed through the slit 16 are installed with the optical axis 20 in between. installed in the direction.

Each of the photodetectors 14A, 14B can be composed of a photoelectric conversion element, and on the output side thereof, a calculating means for determining a phase difference from the detection output and calculating the position is installed.

Based on the above configuration, its operation will be explained with reference to FIGS. 4 to 9.

FIG. 4 shows the relationship between the focal points Q ₀ , Q ₁ , Q ₂ connected to the optical axis 20 corresponding to the position on the optical axis 6 of the sample 2 and the reflected light 10 incident on the photodetectors 14A, 14B. It shows.

5 and 6 show the relationship between the displacement of the focal point position and the incidence of the reflected light 10 on the photodetectors 14A and 14B.

As shown in Q ₀ shown in Figure 4, the focus is on the optical interrupter 1.
2, the reflected light 10 is simultaneously incident on or blocked by the photodetectors 14A and 14B,
The detection signals are generated simultaneously. In this case, the seventh
A in the figure is the output signal of the photodetector 14A, B in FIG.
represent the output signals of the photodetector 14B, and as is clear from these output signals, there is no phase difference between the respective detection signals, so it can be seen that the sample 2 is at the position _S0 .

Next, as shown in A to C in FIG. 5, when the focus is at point _Q2 on the back side of the optical interrupter 12, as the optical interrupter 12 moves in the direction A, The reflected light 10 passing through the slit 16 is
As shown in A in the figure, after being detected by the photodetector 14A, it is detected by the photodetector 14B after a certain period of time, as shown in B in FIG. , as shown in FIG. 5C, after the photodetector 14A completes the photodetection, the photodetector 14B completes the photodetection after a certain period of time.

C and D in FIG. 8 show the output signals of the photodetectors 14A and 14B, and there is a phase difference t ₁ between these output signals.
has occurred, and the direction of displacement of the sample 2 and the amount of displacement thereof can be quantitatively known from this phase difference _t1 . In this case, the sample 2 is located above the focal point P ₀ .

Next, as shown in A to C in FIG. 6, when the focus is at point _Q1 on the front side of the optical interrupter 12, the optical Reflected light 10 is detected by detectors 14A and 14B.

E and F in FIG. 9 represent each photodetector 14A, 1
A phase difference t ₂ occurs between these output signals, and from this phase difference t ₂ it is possible to quantitatively know the direction of displacement of the focal point and the amount of displacement thereof. In this case, the focus is on the optical axis 6 above the sample 2.
tied on top.

Therefore, by moving the table on which the sample 2 is placed in the vertical direction of the optical axis 6 according to the phase difference, the sample 2 can always be placed at the position P ₀ .

[Second Embodiment] FIG. 10 shows a second embodiment of the focal position detecting device of the present invention, and the same parts as the focal position detecting device shown in FIGS. 1 and 2 are given the same reference numerals. be.

In FIG. 10, in this embodiment, the optical interrupter 1
An objective lens constituting the light condensing means 8 and a light condensing lens 34 as the light condensing means are installed on the incident side of the light beam 2.

Even if the condensing lens 34 is installed in this manner, the same effect can be expected.

[Third Embodiment] FIG. 11 shows a third embodiment of the focus position detection device of the present invention, and the same parts as the focus position detection device shown in FIGS. 1 and 2 are given the same reference numerals. be.

This example is implemented in the optical system of the microscope of the present invention.

In FIG. 11, light from an illumination light source 36 reaches the sample 2 from the objective lens 30 via a lens 37 and a half mirror 38. The sample 2 is thereby illuminated.

The light source 5 composed of a laser tube includes a lens 40,
42, half mirrors 44, 28, 38, and an objective lens 30 to reach the sample 2.

The reflected light (laser light) 10 from the sample 2 passes through the objective lens 30 and the half mirror 38, is reflected by the half mirror 28, is further reflected by the half mirror 44, and is transmitted from the lens 46 to the optical interrupter 12.
leading to. The optical interrupter 12 is rotated by a motor 48,
The reflected light 10 that has passed through the optical interrupter 12 reaches photodetectors 14A and 14B.

Then, the objective lens 30 and each half mirror 3
The light that has passed through the lenses 8 and 28 is guided in the direction indicated by arrow B via the imaging lens 50 and reaches an eyepiece (not shown).

According to this configuration, while observing the surface of the sample 2, the displacement of the focal point in the optical axis direction is detected, and the sample 2 is moved in the optical axis direction according to the displacement to automatically adjust the surface of the sample 2. You can set the focus on
The surface condition of the sample 2 can be accurately detected, measured, or photographed, and desired processing can be performed quickly and with high precision, for example, in semiconductor manufacturing processes and inspection processes.

〔Effect of the invention〕

As explained above, according to the present invention, the following effects can be obtained.

(a) The displacement of the sample in the optical axis direction can be detected accurately, and the reflectance of the sample does not affect the detection accuracy, so the detection accuracy can be improved.

(b) The position of the photodetector can be set arbitrarily, and detection errors due to the position do not occur, so high detection accuracy can be obtained.

(c) The uneven illuminance of the light source only affects the level of the detection signal of the photodetector, and does not affect the detection accuracy.

(d) The capture range of the focal position can be set widely by starting from the low magnification of the lens.

(e) The position of the sample along the optical axis and the direction of displacement can be easily determined.

(f) When the slit plate is composed of a light-shielding plate with multiple slits formed, even if there are irregularities in the size of the slits, the detection accuracy will not be affected and the detection accuracy can be improved. .

(g) Since the phase difference sensitivity is given by the value obtained by dividing the phase difference by the amount of displacement of the sample, when the focusing means, for example the objective lens, has a low magnification, the change in the phase difference with respect to the displacement of the sample is small, While the phase difference sensitivity becomes low, the capture range for capturing the focal position becomes wide. Also, when the objective lens has high magnification, the change in response to sample displacement becomes large, and the phase difference sensitivity becomes high, whereas the capture range increases. The narrower the lens becomes, and therefore the higher the magnification of the condensing means, the more accurate the focusing must be, and this requirement can be met.

(h) It has an extremely simple configuration, can be provided at low cost, and can be integrated into a microscope.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a position detecting device according to the present invention, FIG. 2 is an explanatory diagram showing a first embodiment of the position detecting device according to the present invention, and FIG. 3 is an explanatory diagram showing the positional relationship between an optical interrupter and a photodetector. FIGS. 4 to 6 are explanatory diagrams showing its operation. FIGS. 7 to 9 are explanatory diagrams showing the timing of generation and termination of the output signal of the photodetector. FIG. FIG. 11 is an explanatory diagram showing a second embodiment of the position detecting device of the invention, and FIG. 11 is an explanatory diagram showing a third embodiment of the position detecting device of the invention. 2...Sample, 4...Light, 5...Light source, 6,20
...Optical axis, 8...Condensing means, 10...Reflected light, 1
2... Optical interrupter (slit plate), 14A... 1st
photodetector, 14B... second photodetector, 16...
...Slit.

Claims (1)

[Scope of Claims] 1. A light source that emits light to be irradiated onto a sample whose surface is planar, and a light source that receives and condenses the light emitted from the light source, and focuses the light on any surface of the sample. a condensing means for concentrating and focusing the reflected light from the surface of the sample; and a condensing means for concentrating and focusing the reflected light from the surface of the sample; a slit plate in which a plurality of slits are formed, and the slits are moved in a direction perpendicular to the central optical path of the reflected light to block or pass the reflected light through the slits; first and second photodetectors that are installed at positions separated in the moving direction of the slit across a central optical path of the slit and receive the reflected light that has passed through the slit; and these first and second photodetectors 1. A position detection device comprising: calculation means for receiving each output of a device and calculating the position of the sample based on a phase difference between each output.