JPH05144702A - Position detector and fine pattern forming system employing position detector - Google Patents

Abstract

PURPOSE:To achieve focusing without moving the optical element in a rear surface detecting optical system by optically correcting error due to shift of focus in a rear surface detecting optical system caused by fluctuation of the thickness of wafer. CONSTITUTION:Focus of a rear surface position detecting optical system 27 shifts every time when the thickness of wafer 3 varies, and thereby focusing of a demagnification lens 22 onto the wafer 3 is performed through gap sensors 36, 23. The wafer 3 is mounted on XYZtheta tables 28, 30, 31 being driven through a drive unit 33. Position of a reticle 19 is measured through a position detecting optical system 21 and a signal is delivered to a system control unit 37. Position of the wafer 3 is measured through the rear surface detecting optical system 27 and a signal is delivered to the system control unit 37. The system control unit 37 calculates relative positional shift and commands the XYZtheta table drive unit 33 to move the wafer 3 to a desired position. Consequently, mechanical scanning is not required in the optical correction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor manufacturing method and apparatus, and more particularly to a pattern forming apparatus suitable for improving the alignment accuracy of an X-ray exposure apparatus, reduction projection exposure apparatus or electron beam drawing apparatus. Regarding how to use it.

[0002]

2. Description of the Related Art As a position detecting optical system which is not easily affected by a wafer process, there is backside detection for detecting the position of a mark provided on the backside of a wafer. This conventional backside detection is
As described in JP-A-63-224327, focusing on the mark on the back side of the sample is performed by moving some optical elements of the position detection optical system.

[0003]

Alignment accuracy higher than 0.1 μm is required for manufacturing devices of 0.35 μm rule or later. This accuracy is difficult to achieve in the conventional method of detecting the mark on the surface of the sample due to a detection error caused by uneven coating of the resist or damage to the mark. Against this background, Japanese Patent Publication No. 55-4
The method of detecting the back surface mark of the sample as described in Japanese Patent No. 6053 is effective.

When detecting the backside mark of such a sample, the exposure optical system is focused on the surface on which the circuit pattern on the surface is formed, as described in JP-A-63-224327. If the angle changes, the focus of the back surface detection optical system on the back surface of the sample shifts. For this reason, it is necessary to move a part of the optical element of the back surface detection optical system for focusing. With this operation, there is a problem that the reference position for position detection shifts and the position detection value becomes unstable.

An object of the present invention is to provide a highly-accurate and very simple ultra-small backside mark position detecting device capable of focusing without moving the optical element of the backside detection optical system,
Another object of the present invention is to provide a semiconductor manufacturing pattern forming apparatus using the position detecting apparatus.

[0006]

SOLUTION: A position detecting means depending on the inclination of a sample, a lens having a different focal position depending on a radial position in the meridional direction as an objective lens of the position detecting means, a sample holding means and its position measuring means, and a sample This is achieved by providing the fine movement means, the exposure or drawing means, and the mask or drawing data on which a desired pattern is formed.

[0007]

The position detection method for detecting the position of the mark 2 from the phase difference of the ± 1st order diffracted light among the diffracted light generated when the lattice-shaped marks on the wafer 3 are illuminated by the monochromatic light source will be described as an example. For example, it is assumed that the optical system has the configuration shown in FIG. When performing the back surface detection, it is important to reduce the detection error ε caused by the thickness of the wafer 3 as shown in FIG. This optical system can cancel the position detection error ε due to the inclination of the back surface of the wafer 3.

First, the position detection will be described. FIG. 5 schematically shows an optical system of a known roughness measuring instrument. This is APPLIED OPTICS Vol.20, No.
4 / p610. This basically uses a Nomarski interferometer. A light source 10 which emits two frequencies having slightly different wavelengths by linearly polarized light is used. The output beam is
It is divided into two by the beam splitter 15. One beam causes heterodyne interference by the analyzer 16a to detect a reference signal serving as a reference. The other beam enters the Wollaston prism 5. Here, the P-polarized light (ν ₁ ) and the S-polarized light (ν ₂ ) are separated and focused by the objective lens 3 into two points on the wafer surface. The light reflected from the sample surface passes through the objective lens 3 again and then enters the Wollaston prism 5. Here, the divided two frequencies are overlapped again to form one beam, which is guided to the analyzer 16b. Here, the analyzers 16b are adjusted to be at 45 ° with respect to the polarization plane of the tilt detection light 11. This causes heterodyne interference and obtains a detection signal. The reference signal and the detection signal have the same cycle. Therefore, when the sample 1 is tilted, the detection light 11a,
The optical path difference of 11b relatively changes, and the phase of the detection signal changes with respect to the reference signal.

FIG. 3 shows a structure in which the position of the back mark 2 can be detected by basically using this detection principle.
Similar to this detection method, the dual-frequency laser 10 illuminates the test surface. The two beams 11 illuminate the lattice-shaped mark 2 provided on the back surface. This beam 11 is P
It is divided into polarized light 11a and S polarized light 11b. Of the diffracted light generated at this time, the respective ± first-order lights 12ab and 13ab
Think only. The phases of these diffracted lights 12ab and 13ab change depending on the tilt and position of the back surface mark 2. This phase change is detected using the reference signal as a reference as shown in FIG. The detection lights 12 and 13 are made into parallel beams by the objective lens 1, and one of the two lights is selected by the polarization beam splitter 4 on the Fourier transform surface. These beams 13a and 12b are condensed by a condenser lens 6, a Wollaston prism 5b is placed at the intersection of these two beams to cause heterodyne interference, and they are detected by a photoelectric converter 7a. As shown in FIG. 4, when the mark position is δ, the mark pitch is P, the wavelength of the detection light is λ, and the deviation amount from the reference plane of the wafer 3 is t, the detected phase difference φ ₁ is

[0010]

[Equation 2]

[0011] At this time, if the inclination and the thickness of the wafer are d, the inclination of the wafer is θ, and the interval between the two beams 11 is 1, the error ε in the surface position due to this is

[0012]

[Equation 3]

[0013] here,

[0014]

[Equation 4]

[0015] At this time, P and l may be selected so that the phases caused by ε and t are equal. That is,

[0016]

[Equation 5]

It suffices if From the expressions (2), (3), (4) and (5), it is understood that the following expressions should be satisfied.

[0018]

[Equation 6]

From the above equation, for example, H is used as the detection light source 10.
e-Ne wavelength λ = 633 nm, sample 3 thickness d = 60
Assuming that 0 μm and the pitch P of the rear surface marks 2 = 6 μm,
Should be 63.3 μm. This l is determined by the beam separation angle ξ of the Wollaston prism 5a and the focal length f of the objective lens 1. That is, when the desired inter-beam distance 1 is known, it is determined by the following formula.

[0020]

[Equation 7]

A Wollaston prism having such a separation angle may be used.

Further, when processing wafers having different thicknesses by using this apparatus, the pitch P of the marks 2 may be determined based on the following equation obtained by modifying (Equation 6).

[0023]

[Equation 8]

As can be seen from (Equation 8), there is a proportional relationship between the thickness d of the wafer 3 and the mark pitch P. That is, when the wafers 3 having different thicknesses d are used, the pitch P of the marks 2 needs to be changed accordingly. Normally, in order to focus the exposure optical system on the front surface side on which the integrated circuit pattern is formed, as shown in FIG.
As shown in FIG. Since the amount of change in the wafer thickness d becomes the defocus amount Δf, it is sufficient to give the objective lens 1 spherical aberration that cancels the defocus amount Δf. For example, the focal length f of the objective lens 1 is 30 mm and the wafer thickness d is 600 μ.
The case where m is a designed value will be described. In general,
The diffraction angle of ± first-order diffracted light is expressed by the following equation.

[0025]

[Equation 9]

When the wafer thickness d is 500 μm, the defocus amount Δf is 100 μm. The pitch P of the marks 2 at this time is 5 μm from (Equation 8). The diffraction angle in this case can be calculated from (Equation 9). By substituting this into (Formula 10) shown below, the incident position of the diffracted light on the objective lens 1 in the meridional direction r can be known. (See Figure 1)

[0027]

[Equation 10]

Similarly, from (Equation 8), (Equation 9), and (Equation 10), it is understood that the objective lens 1 needs the spherical aberration shown in FIG. It can also be said that it is generally sufficient to give the objective lens 1 the spherical aberration represented by the following equation (Equation 1).

[0029]

[Equation 11]

By using the objective lens 1 having such spherical aberration, good focusing is possible even when the thickness of the wafer is different. The same effect can be obtained by using an optical element such as a prism having the same spherical aberration.

[0031]

EXAMPLE 1 An example of the present invention will be described in detail. The back surface detection optical system described in the section of action is used.

FIG. 7 shows an example in which the back surface detection alignment method is applied to a reduction projection exposure apparatus. Generally a reduction lens 22
Is mechanically fixed to a column (not shown), and since the back surface detection optical system 27 is fixed to the base 32, the focal position of the reduction lens 22 is always fixed. Therefore, the focus of the back surface position detection optical system 27 shifts each time the thickness of the wafer 3 changes. The present invention resides in a method for solving this problem when the above-mentioned back surface detection optical system 27 is used.

The reduction projection exposure apparatus illuminates a reticle 19 on which a pattern of an integrated circuit is drawn with an illumination optical system 17,
This is an apparatus for reducing and transferring onto the wafer 3 through the reduction projection lens 22. The exposure procedure is performed as follows. The focusing of the reduction lens 22 and the wafer 3 is performed by the gap sensor 3
Perform at 6 and 23. The gap sensors 36 and 23, which use air differential pressure, have a simple structure and can detect the position with high accuracy. Further, the wafer 3 has XYZθ tables 28, 3
It is placed on 0, 31 and can be moved to a desired position. The positions of the XYZθ tables 28, 30, 31 are measured by the laser length meter 25 and processed by the system control unit 37. Further, the XYZθ tables 28, 30, and 31 are
It is driven by the drive unit 33. The positions of the reticle 19 and the wafer 3 need to be accurately aligned relative to each other. The position of the reticle 19 is measured by the position detection optical system 21 and a signal is sent to the system control unit 37. The position of the wafer 3 is measured by the back surface detection optical system 27 and a signal is sent to the system control unit 37. Then, the system control unit 37 calculates the relative positional deviation amount, and XY
The Zθ table drive unit 33 is instructed to move the wafer 3 to a desired position. After that, the reticle 19 is illuminated to form a pattern on the photosensitive film on the wafer 3. At this time, if the objective lens 1 of the back surface detection optical system 27 having the spherical aberration described in the section of operation is used, the wafer 3
Good alignment accuracy can be achieved even when the thicknesses of the two are different.

<Second Embodiment> Next, a case where the present invention is applied to a reflection type projection exposure apparatus will be described with reference to FIG. The light generated from the exposure light source 40 is condensed by the illumination optical mirror 41 to illuminate the mask 42 on which the pattern is formed. The reflected light is reflected by the projection optical mirror group 44, 45, 46, 47.
And is illuminated by the photosensitive film on the wafer 3 to form a pattern. In the case of the reflection type optical system, since the entire surface of the mask 42 cannot be illuminated at one time, generally, the mask 42 and the wafer 3 are synchronously scanned and exposed as shown in FIG. Further, for the relative alignment between the masks 42 and the wafer 3, the back surface detection optical system 27 of the present invention is used as in the first embodiment. The alignment method is the same as in the first embodiment.

<Third Embodiment> The back surface position detecting optical system 27 of the present invention is also applicable to an electron beam exposure apparatus. This will be described with reference to FIG.

It is obvious that the method can also be applied to the alignment of the electron beam drawing apparatus.

As shown in FIG. 9, the drawing data storage unit 57.
The detector 27 is installed on the back surface of the wafer 3 of the electron beam drawing apparatus for forming a desired pattern on the wafer 3 by the electron gun 58 and the electron lens 59.

According to this embodiment, the alignment of the electron beam drawing apparatus can be performed with a higher precision than ever before.

[0039]

According to the present invention, the error due to the defocus of the back surface detection optical system due to the change in the thickness of the wafer (several hundred μm) is optically corrected. Therefore, there is no need for mechanical scanning for correction, which was required in the past, so that errors associated therewith can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory view of a lens of the present invention.

FIG. 2 is an explanatory diagram in which the lens of the present invention is applied to a position detection optical system.

FIG. 3 is an explanatory diagram of a back surface position detection optical system.

FIG. 4 is an explanatory diagram of a function of a back surface position detection optical system.

FIG. 5 is an explanatory view of a known roughness measuring machine.

FIG. 6 is an explanatory diagram showing a position example of a spherical aberration amount.

FIG. 7 is an explanatory diagram in which the present invention is applied to a reduction projection exposure apparatus.

FIG. 8 is an explanatory diagram in which the present invention is applied to a reflective reduction projection exposure apparatus.

FIG. 9 is an explanatory diagram in which the present invention is applied to an electron beam drawing apparatus.

[Explanation of symbols]

1 ... Objective lens, 2 ... Mark, 3 ... Wafer, 19 ... Reticle position detecting optical system, 27 ... Back surface position detecting optical system.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location 8831-4M 341

Claims (5)

[Claims] 1. A position detecting device for illuminating a lattice-shaped mark formed on a substrate with a monochromatic light source and receiving the diffracted light generated by a lens to detect the position of the substrate, which includes a lens having a predetermined spherical aberration. A position detecting device characterized by the above. 2. The position detecting device according to claim 1, wherein the lens is a single lens and is an axially symmetric aspherical lens. 3. The lens according to claim 1, which is a cemented or combined lens of two or more lenses, wherein the two or more lenses have different refractive indexes with respect to light emitted from the monochromatic light source. Position detection device. 4. The position detecting device according to claim 1, wherein
When the pitch of the grid-like marks is P, the wavelength of light emitted from the monochromatic light source is λ, the distance from the center of the lens in the meridional direction is r, and the focal length of the lens is f, a predetermined spherical aberration Δf is obtained. Substantially And position detection device. 5. A fine pattern forming apparatus comprising position detecting means for detecting a mark formed on the back surface of a substrate to detect the position of the substrate, and fine pattern forming means for forming a fine pattern on the front surface of the substrate. A fine pattern forming apparatus using the position detecting device according to claim 1 as the position detecting means.