JP3222214B2 - Target surface position detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a target surface position detecting device for detecting a position of a target surface with respect to a focal position of a main optical system.

[0002]

2. Description of the Related Art In a conventional optical device, the position of a surface (target surface) of an object is detected by a position detecting device (position detecting optical system), and the position of the main optical system with respect to the target surface is detected. There is something. For example, when an electronic circuit is constructed on a wafer (object) using photographic technology or after the construction, the position of the surface (object surface) of the wafer is detected by a position detecting device. In some cases, the surface of the wafer is observed / measured or surface-treated with a main optical system.

As a position detecting device used in this type of optical device, as shown in FIG. 3, an object is irradiated with a focus detecting device (focus detecting optical system) different from the main optical system, and a target surface is irradiated. , Or a TTL type as shown in FIG. Hereafter, this 2
The two types will be described.

(1). Focus position detector separate from the main optical system
[Focal Position Detection Optical System] (FIG. 3) FIG. 3 shows an example in which a scanning type focus position detection device, that is, a focus position detection optical system 2 is provided separately from the main optical system 1 by an optical lever system. . 1a is an objective lens of the main optical system 1.

The focus position detecting optical system 2 includes a light source 3 for emitting a point-like or linear light beam, a scanning mirror 4, an illumination lens 5,
It comprises a light receiving lens 6, a light sensor 7 such as a line sensor or a PSD. A point-like or linear illumination light beam from the light source 3 is projected on an object 8 via an illumination lens 5 while being scanned by a scanning mirror 4, and is imaged on an object surface 8 a of the object 8. , A secondary light source image is formed on the target surface 8a.

On the other hand, the secondary light source image is enlarged by the light receiving lens 6 and projected on the light receiving sensor 7, and the light receiving sensor 7 outputs a detection signal. Then, by calculating the position of the center of gravity of the secondary light source or the light amount distribution based on the output signal from the light receiving sensor 7, the position of each part of the target surface 8a can be known.

At this time, even if the height of the target surface 8a partially fluctuates up and down due to unevenness, and the amount of reflected light of the secondary light source image formed in the fluctuating portion fluctuates, the center of gravity of the secondary light source or By knowing the light amount distribution, the position of the fluctuation part can be known. There is a fixed type that does not perform scanning without using the scanning mirror 4.

[0008]

In order to achieve this object, a main optical system for inspecting or measuring the target surface through an objective lens facing the target surface, and a point light source or a light source from a light source. While scanning the linear light beam through the scanning means,
The scanned light beam is passed through the objective lens through an objective lens.
Scanning and projecting onto the target surface from a first direction inclined with respect to the optical axis of the objective lens, and the speed of light from a secondary light source image formed on the target surface by the scanning with respect to the optical axis of the objective lens.
Through the objective lens is taken out from the second direction inclined an optical subsystem for guiding the light receiving sensor Te, receiving
Position to detect the position of the target surface based on the signal from the sensor
In the position detecting device, an optical system for making a light beam scanning position of the scanning unit and a pupil position of the objective lens conjugate is a position detecting device of a target surface provided between the scanning unit and the pupil position. It is characterized by the following.

The position detecting optical system 11 is composed of a main optical system 10
And a common optical member objective, that is, a lens 10a and a beam splitter 10b. In this position detection optical system 11, a point-like or linear light beam from a light source 12 of an illumination system is projected and formed on a target surface 8a of a target object 8 via a projection auxiliary lens 13, a beam splitter 10b, and an objective lens 10a. Thus, a secondary light source image is formed on the target surface 8a.

In addition, this secondary light source image is
0a, the beam splitter 10b, is adapted to be projected imaged on the same light receiving sensor 15 and the light receiving sensor -7 through the light receiving auxiliary lens 14 of the light receiving system. Then, by calculating the position of the center of gravity of the secondary light source or the light amount distribution based on the output signal from the light receiving sensor 15, the position of each part of the target surface 8a can be known.

[0011]

In order to perform high-precision measurement and inspection, an objective lens having a large NA (lens numerical aperture) of a lens and a high resolution capable of transmitting light having a short wavelength is used. Must. The objective lens of high resolution has a shallow depth of focus, so that it is necessary to perform high-precision focusing.

However, when an external focus position detecting optical system 2 as shown in (1) is used, the relative position between the focus position detecting optical system 2 and the objective lens 1a changes due to a temperature change. The measurement accuracy changes because the focal position between the objective lens 1a and the illumination lens 5 of the focal position detection optical system 2 is shifted, or the focal position of the objective lens 1a is shifted from the focal position of the illumination lens 5 due to temperature and pressure. Is not preferred. Further, in the type (1), a change in measurement accuracy occurs due to replacement of the objective lens 1a.

Such a change in measurement accuracy can be prevented by using a TTL type focus position detecting device using the objective lens 10a as shown in (2). Further, from the viewpoint of the arrangement of the focus position detection optical system, a TTL type focus detection device is desirable.

In addition, when there is a portion having a different reflectance on the target surface 8a of the object 8, a fixed optical lever type focus detection device having a focus detection position as shown in FIG. Therefore, it is desirable to use a scanning type.

However, since the pupil of the main optical system 10 in (2) is located in or near the objective lens 10a, a deflecting device cannot be provided near the objective lens 10a. When deflected away from the pupil, the light source 12
The principal ray of the projection light beam from the object moves on the pupil of the objective lens 10a.

The movement of the projection light beam on the pupil position changes the incident angle α with respect to the target surface 8a. The magnification of the vertical fluctuation amount of the height in each part of the target surface 8a and the magnification of the movement amount of the secondary light source image on the target surface 8a is 2Δβtanα (Δ is the vertical movement amount of the test surface, β is the objective lens 10a The optical magnification of the light receiving system, α, is the angle of incidence shown in FIG. 4).

If the incident angle α changes, the detection magnification also changes, making accurate focus detection difficult. Moreover, since the reflectance of the target surface 8a changes from the incident angle α, it is desirable that the incident angle α on the target surface 8a be constant for accurate measurement. When the light beam moves on the pupil at the time of scanning, the light beam must always enter the objective lens 10a. However, in this case, the average incident angle α to the target surface 8a becomes small, As can be seen from the equation, the detection magnification decreases. Further, in the case of a general substance, the smaller the incident angle is, the lower the reflectivity is, so that the accuracy of focus detection is further reduced.

In view of the above, it is desirable to constitute a TTL type optical lever type target surface position detecting device in which a light beam does not move on a pupil even when scanning.

In view of the above, an object of the present invention is to provide an optical lever type target position detecting device of a TTL type, in which a light beam does not move on a pupil even when it is scanned. It is.

[0020]

In order to achieve this object, a main optical system for inspecting or measuring the target surface through an objective lens facing the target surface, and a point light source or a light source from a light source. While scanning the linear light beam through the scanning means,
The scanned light beam is projected onto the target surface through the objective lens from a first direction inclined with respect to the optical axis of the objective lens, and a secondary image formed on the target surface by the scanning is formed. A sub optical system that takes out a light beam from the light source image from a second direction inclined with respect to the objective lens optical axis and guides the light beam to the light receiving sensor via the objective lens, and determines the position of the target surface based on a signal from the light receiving sensor. In a position detecting device for detecting, a position detecting device for a target surface, wherein an optical system for conjugate a light beam scanning position of the scanning unit and a pupil position of the objective lens is provided between the scanning unit and the pupil position. It is characterized by having.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

[First Embodiment] FIG. 1 shows a first embodiment of the present invention.

The optical device shown in FIG.
a, a main optical system 10 including a beam splitter 10b, other optical members (not shown), etc., and a TTL type optical lever type position detecting optical system, that is, a sub optical system (position detecting device).
11 The sub optical system 11 has an optical member objective, that is, a lens 10a and a beam splitter 10b, which are common to the main optical system 10.

In the sub optical system 11, the light source 1 of the illumination system
The point-like or linear light flux from the projection auxiliary lens 1
3. Projection image formation on a target surface (test surface) 8a of the target object 8 via a scanning mirror 21 (scanning means), an optical system 22 such as a beam expander including lenses 22a and 22b, a beam splitter 10b, and an objective lens 10a. Thus, a secondary light source image is formed on the target surface 8a. This optical system 2
Numeral 2 makes the scanning mirror 21 conjugate with the pupil position 23 of the objective lens 10a.

Moreover, this secondary light source image is
0a, beam splitter 10b, scanning mirror 21, optical system 2
2. The image is projected and formed on the light receiving sensor 15 via the light receiving (image forming) auxiliary lens 14 of the light receiving system.

Then, by calculating the position of the center of gravity of the secondary light source or the light amount distribution based on the output signal from the light receiving sensor 15, the position of each part of the target surface 8a can be known.

By the way, in the optical lever type focus position detecting device, a detection error increases at a boundary between portions of the target surface 8a having different reflectivities, that is, at a boundary where the reflectivity changes. However, with the above configuration, the scanning mirror 21 is scanned, the secondary light source image of the light source 12 is moved on the target surface 8a, the position where focus detection is performed is changed, and the average position of the target surface 8a is determined. As a result, a detection error at the boundary between portions having different reflectances on the target surface 8a can be significantly reduced.

If the scanning mirror 21 can be arranged at the pupil position 23 of the objective lens, the light beam from the light source 12 does not move on the pupil position 23 even when scanning, but the pupil position 23 of the objective lens 10a is usually Since it is inside the lens 10a or near the objective lens 10a, it is difficult to arrange the scanning mirror 21 at the pupil position 23. Further, disposing the scanning mirror 21 between the beam splitter 10b that separates from the main optical system 10 and the objective lens 10a shields a part of the opening viewed from the main optical system 10, and as a result, The performance of the main optical system 10 will be reduced. In addition, objective lens 1
It is also impossible to dispose the beam splitter 10b between 0a and the pupil position 23 of the objective lens 10a because the interval is small or small.

Therefore, by providing the optical system 22 for projecting the scanning mirror 21 to the pupil position 23 of the objective lens 10a,
The scanning mirror 21 and the pupil position 23 are conjugated as described above. Thus, even when the light beam from the light source 12 is scanned by the scanning mirror 21, the light beam does not move on the pupil position 23. Usually, since the objective lens 10a of the inspection optical system is telecentric toward the object 8, even if the light beam from the light source 12 scans, the incident angle α to the object surface 8a does not change.

Further, the reflection angle on the target surface 8a is also β (α =
Since there is no change in β), the luminous flux reflected on the target surface 8a also returns to the position directly opposite to the pupil position 23 at the time of incidence. This light beam passes through the optical system 22 in the opposite direction again, and forms an image on the light receiving sensor 15 by the auxiliary lens 14 for image formation.

When the target surface 8a partially moves up and down due to unevenness or inclination, the light source 12 projected on the target surface 8a is observed as a movement of the secondary light source in the horizontal direction when observed from the objective lens 10a. Since this is enlarged and projected on the light receiving sensor 15 by the optical system 22 and the auxiliary lens 14, the movement of the secondary light source image on the target surface 8 a is the movement of the secondary light source image on the light receiving sensor 15. The light receiving sensor 15 may be a light sensor such as a line sensor or a sensor indicating the center of gravity of light such as a PSD.
By processing the output of No. 5, it is possible to detect the movement of the focal point. When scanning is performed in this manner, the secondary light source image on the light receiving sensor 15 also moves. This can be dealt with by taking the time average of the output of the light receiving sensor 15.

Since the focus position detecting optical system of the present embodiment shares the objective lens 10a of the main optical system 10, even if the focal position of the objective lens 10a changes due to an environmental change or the like, the main optical system 10 and the main optical system 10 are not changed. There is no difference in focal position. In addition, with this configuration, the image plane is divided into the main optical system 10 and the sub optical system 11
Are the same, the size of the spot of the secondary light source on the target surface 8a does not change even if the light beam from the light source 12 is scanned by the scanning mirror 21. As a result, target surface 8
a is less likely to be affected by the difference in reflectance.

Further, at the focus position detection position of the present embodiment,
Since the light beam from the light source 21 is scanned and moved by the scanning mirror 21 and the output signal from the light receiving sensor 15 is averaged, a focus detection error due to a partial change in reflectance is also reduced.

Further, the addition of the optical system 22 does not change the incident angle α even when scanning, so that the focus position detection accuracy does not change, and an accurate focus can be obtained only by performing a simple time averaging process. It can be detected. The sensitivity is proportional to tan α, but since the incident angle α does not change during scanning, α can be increased to the limit allowed by the numerical aperture of the objective lens and the thickness of the light beam used in auto focus. In other words, the focus can always be detected with the maximum sensitivity, and the reflectivity of the object 8 also increases when the incident angle α increases, so that the amount of light increases, and the reflectivity is constant because the incident angle α is constant. Therefore, focus detection with higher precision can be performed.

As a scanning means for changing the focus detection position to the left and right or the like instead of the scanning mirror 21, there is a method using an acousto-optic element. Although the optical system 22 is an expander in FIG. 1, the scanning mirror 21 is conjugated to the pupil position 23, and the light source 12 is connected to the target surface 8a through the objective lens 10a.
It is not necessary to be an expander as long as the conjugate relationship can be formed so as to form an image.

[Second Embodiment] FIG. 2 shows a second embodiment of the present invention.

FIG. 2 shows an embodiment in which the scanning mirror 21 shown in FIG. In this embodiment, although the scanning mirror 21 is large, there is an advantage that the secondary light source image does not move on the light receiving sensor 15 even when the light beam from the light source 12 is scanned by the scanning mirror 21.

In this case, not the position where the light beam hits the scanning mirror 21 but the position 31 where the deflected light beam intersects the light beam before being deflected is set as the deflection position, and the position 31 and the objective lens 1
The pupil position 23 of 0a is conjugated.

[0039]

The TTL type focus detection device is provided with a scanning mechanism and the deflection position thereof is conjugate with the pupil position of the objective lens, so that it is resistant to environmental changes and the reflectance of the test object changes. This also enables highly accurate focus detection.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing a first embodiment of an optical system according to a target surface position detecting device of the present invention.

FIG. 2 is a schematic explanatory view showing a second embodiment of the optical system according to the target surface position detecting device of the present invention.

FIG. 3 is an explanatory diagram showing an example of an optical system of a conventional target surface position detecting device.

FIG. 4 is an explanatory diagram showing another example of the optical system of the conventional target surface position detecting device.

[Explanation of symbols]

 8 Target Object 8a Target Surface (Test Surface) 10 Main Optical System 10a Objective Lens 11 Sub Optical System 12 Light Source 15 Light Receiving Sensor 21 Scanning Mirror (Scanning Means) 22 Optical System 23 Pupil Position

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-53-91754 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B 11/00-11/30 102 G01C 3 / 00-3/32 H01L 21/027

Claims (1)

(57) [Claims] 1. A main optical system for inspecting or measuring the target surface via an objective lens facing the target surface, and scanning a point-like or linear light beam from a light source via a scanning unit. At the same time, the scanned light beam is scanned and projected on the target surface from the first direction inclined with respect to the optical axis of the objective lens via the objective lens, and is imaged on the target surface by the scanning. A sub-optical system that takes out a light beam from the secondary light source image from a second direction inclined with respect to the objective lens optical axis and guides the light beam to the light receiving sensor via the objective lens, based on a signal from the light receiving sensor. In a position detection device for detecting a position, an optical system for conjugate a light beam scanning position of the scanning unit and a pupil position of the objective lens is provided between the scanning unit and the pupil position. Subject to Position detecting device.