JPH0613287A - Alignment equipment - Google Patents

Abstract

PURPOSE:To improve the alignment precision of a TTR system, by changing the illumination positions of alignment lights which illuminate the diffraction grating mark on a reticle and the diffraction grating mark on a wafer, from two specified directions. CONSTITUTION:An illumination optical system has a 2 light flux frequency shifter which forms two coherent lights, a beam splitter 16 which divides each of the two light fluxes and forms a first and a second alignment lights, and parallel flat plates 15. The relative interval between the first and the second alignment lights is changed by the parallel flat plates 15. Thereby at least one out of the position where the first alignment lights (BMR1, BMR2) illuminate first diffraction gratings (RM1, RM2) from two specified directions and the position where the second alignment lights (BMW1, BMW2) illuminate the second diffraction gratings from two specified directions is changed. Thereby the magnification chromatic aberration of a projection lens in accordance with the change of chip size to be exposed is changed, and accurate illumination is made possible when the distance between alignment marks is changed, so that a signal of high S/N ratio can be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting the position of an object to be inspected by detecting a position detecting mark formed on the object to be inspected, and in particular, to form a predetermined exposure pattern. It is suitable for a position detection device of an exposure device that transfers a projection original plate such as a reticle (mask) that has been formed onto a wafer (substrate).

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. 2-133913 discloses a diffraction grating mark formed on a reticle by correcting an axial chromatic aberration of a projection optical system by using an objective lens of an alignment system as a double focus optical system. There is disclosed a technique of illuminating two coherent alignment lights from two predetermined directions on the RM and the diffraction grating mark WM formed on the substrate. This type of device illuminates two alignment light beams having different frequencies to each of the alignment grating marks (RM, WM) from predetermined two directions, and in the normal direction of each mark (RM, WM). This is a so-called heterodyne method in which the ± 1st-order diffracted light that is generated is photoelectrically converted to extract an optical beat signal, and for example, a relative positional deviation between the reticle and the wafer is detected by the phase difference of the optical beat signal from each mark. is there.

[0003]

The alignment system of the exposure apparatus as described above corrects the axial chromatic aberration of the projection optical system by the double focus optical system to obtain a TTR (through the reticle).
The system alignment is realized. Therefore, since the conjugate relationship between the reticle and the wafer can be maintained, highly accurate alignment is possible.

By the way, in recent years, even when the size of the chip to be exposed, that is, the size of one shot area is changed,
There is a long-felt need for a compatible alignment system. However, since the wafer mark is formed on the street line around each 1-shot area, if the size of the 1-shot area changes, the position of the alignment mark also changes accordingly. If you move it, you can deal with it.

However, although the projection optical system for transferring the reticle pattern onto the wafer is sufficiently corrected for chromatic aberration with respect to the exposure wavelength, it is sufficiently corrected for alignment light outside the exposure wavelength. Therefore, as the position of the alignment mark on the reticle changes, the position of the wafer mark shifts due to the influence of lateral chromatic aberration of the projection optical system. As a result, in the conventional alignment system, the illumination light flux from the alignment illumination optical system cannot accurately illuminate each of the alignment mark on the reticle and the alignment mark on the wafer. For this reason, there is a problem that the amount of the detected alignment light is significantly reduced and the alignment accuracy is adversely affected, and further, the alignment cannot be performed.

Therefore, the present invention solves the above problems,
It is an object of the present invention to provide an alignment apparatus capable of performing TTR type alignment with high accuracy even if the size of a chip to be exposed changes.

[0007]

In order to achieve the above object, the invention according to claim 1 is, for example, as shown in FIG.
When the pattern formed on the reticle R is transferred onto the substrate W (wafer) via the projection optical system PL, the first diffraction grating (RM ₁ , RM ₂ ) formed on the reticle R is predetermined. Illuminating the first alignment light (BM _R1 , BM _R2 ) coherent from the two directions and the second alignment light (coherent from the predetermined two directions to the second diffraction grating (WM ₁ ) formed on the substrate ( BM _W1 , B
M _W2 ) for illuminating the reticle R and the substrate W, and an alignment optical system for illuminating the reticle R and the substrate W, and an optical system for detecting each diffracted light from the first and second diffraction gratings. In the apparatus, the illumination optical system splits the two light flux generating means 11 for generating two coherent light beams and the two light fluxes from the two light flux generating means 11 to generate the first and second alignment lights. Light splitting means 1
6 and a luminous flux interval changing means 15 for changing the relative distance between the first and second alignment lights, and the luminous flux interval changing means 15 allows the relative distance between the first and second alignment lights. By changing the interval, the position where the first alignment light (BM _R1 , BM _R2 ) illuminates the first diffraction grating (RM ₁ , RM ₂ ) from two predetermined directions and the second alignment light (BM _W1 , BM _W2 ) is adapted to change at least one of the positions for illuminating the second diffraction grating (WM ₁ ) from predetermined two directions.

In order to achieve the above-mentioned object,
The invention according to item 2 is, for example, as shown in FIG.
The pattern formed on the substrate is projected through the projection optical system PL.
When transferring on W (wafer), shape on reticle R
First diffraction grating (RM ₁, RM₂) Prescribed
The first alignment light (B
M _R1, BM_R2) And is formed on its substrate
Second diffraction grating (WM₁) From two predetermined directions
Rent second alignment light (BM_W1, BM_W2)
Illuminating optical system and its first and second diffraction grating
A detection optical system for detecting each diffracted light, and a reticle R
Alignment device for performing relative alignment with the substrate W
At, the illumination optics are two coherent lights.
From the two-beam generating means and the two-beam generating means
The two luminous fluxes of
Light splitting means for generating a light
The step defines the relative spacing between the first and second alignment lights.
In order to change it, in the direction perpendicular to the optical axis of the illumination optical system
Movably provided, and moving the light splitting means
As a result, the first alignment light causes the first diffraction grating 2
Position illuminated from the direction and the second alignment light undergoes the second diffraction
Change one of the positions to illuminate the grid from two predetermined directions
It was done so.

[0009]

[Operation] According to the present invention, even if the size of the chip (one-shot area) to be exposed is changed, and the chromatic aberration of magnification of the projection optical system is changed, the diffraction grating mark RM on the reticle and the diffraction mark on the wafer are also changed. Since the illumination position of the alignment light that illuminates each of the lattice marks from two predetermined directions can be changed, the TTR method alignment can always be performed with high accuracy.

[0010]

1 is a plan view showing a schematic structure of a projection type exposure apparatus (stepper) equipped with a positioning device according to an embodiment of the present invention.
An apparatus having an R (Through The Reticle) type alignment system is shown as an example. In this embodiment, the objective lens 25 of the alignment system corresponds to the change of the chip size of the semiconductor element or the position change of the reticle mark due to the destruction of the wafer mark by various processes, as shown by A in FIG. , Drive control system 2 integrated with mirror 24
The objective lens 25 and the mirror 24 are integrally solidified in a holding metal 26. Further, in FIG. 1, a set of alignment systems (10
27), only the transparent windows RW _{1 to} RW ₄ (wafer marks WM ₁ to RW _{1 to} reticle alignment) are actually shown.
It is assumed that four sets of alignment systems are arranged corresponding to each WM ₄ ).

In FIG. 1, an illumination light source 1 such as an ultrahigh pressure mercury lamp or an excimer laser device is a g-line, i-line or K-line.
Exposure illumination light IL in the wavelength range that exposes the resist layer such as rF excimer laser light is generated, and the exposure light IL enters the illumination optical system 2 including an optical integrator (fly-eye lens) and the like. The illumination optical system 2 makes the luminous flux uniform,
The exposure light IL for which the speckle has been reduced reaches the dichroic mirror 5 via the mirror 3 and the main condenser lens 4. The dichroic mirror 5 vertically reflects the exposure light IL from the main condenser lens 4 downward and illuminates the reticle R with a uniform illuminance. here,
The dichroic mirror 5 is obliquely installed at an angle of 45 ° above the reticle R, has a reflectance of 90% or more with respect to the wavelength of the exposure light IL, and has a wavelength of the alignment illumination light (usually longer than the exposure light. ) Has a transmittance of 50% or more.

In the reticle R, four sets of alignment transparent windows RW _{1 to} RW ₄ (only RW ₁ and RW ₃ are shown) are provided in a light-shielding band (chrome layer) LSB surrounding the pattern area PA. Has been formed. The reticle R is placed on the reticle stage RS and positioned so that the center point of the pattern area PA coincides with the optical axis AX. The reticle stage RS is configured to be two-dimensionally movable in a horizontal plane by a drive motor 6, and has a movable mirror 7m that reflects a laser beam from a laser light wave interferometer (hereinafter referred to as an interferometer) 7 at its end. Is fixed. The interferometer 7 constantly detects the two-dimensional position of the reticle R with a resolution of, for example, about 0.01 μm. Initialization of the reticle R is performed by finely moving the reticle stage RS based on a mark detection signal from a reticle alignment system (not shown) that photoelectrically detects an alignment mark around the reticle.

The exposure light IL which has passed through the pattern area PA is incident on the projection lens PL which is telecentric on both sides, and the projection lens PL projects the projected image of the circuit pattern of the reticle R onto the wafer W on which a resist layer is formed. Projection (image formation) is performed by superimposing on one shot area above. On the wafer W, a wafer mark WM is formed at a position near the shot area in a fixed positional relationship. The projection lens PL is well corrected for chromatic aberration with respect to the wavelength (g-line, i-line, etc.) of the exposure light IL, and the reticle R and the wafer W are arranged so as to be conjugate with each other under the exposure wavelength.

The wafer W is placed on the wafer stage WS which is two-dimensionally moved by the step-and-repeat method by the drive motor 8, and when the transfer exposure of the reticle R onto one shot area on the wafer W is completed, Is stepped to the shot position. Wafer stage W
The two-dimensional position of S is 0.0, for example, by the interferometer 9.
A movable mirror 9m that is detected with a resolution of about 1 μm and reflects the laser beam from the interferometer 9 is fixed to the end of the wafer stage WS.

FIG. 4 shows an example of the pattern shape and arrangement of the reticle R used for the overlay exposure of the second and subsequent layers. The transparent windows RW _{1 to} RW are provided in the light-shielding band LSB surrounding the pattern area PA. ₄ is formed in the vicinity of the pattern area PA. Transparent windows RW ₁ and RW ₃ are reticle center R
Are provided facing each other on a line that passes through C and is parallel to the Y axis,
The transparent windows RW ₂ and RW ₄ are provided to face each other on a line passing through the center RC and parallel to the X axis. Further, the width of the light-shielding band LSB is set to a value of 1 / M times or more the width of the street line on the wafer (the projection magnification of the projection lens PL is M) or more,
Exposure light IL defined by a variable blind (not shown)
The illumination area IA of the pattern area PA and the transparent window RW ₁ to
RW ₄ (or only the transparent part RS ₁ described later may be used)
It is set to a size including a range, that is, a size that covers one shot area on the wafer and four street lines around the shot area.

[0016] Figure 5 is a there is shown an example of a specific configuration of the transparent window RW ₁ of the reticle R, the transparent window RW ₁ is rectangular transparent portion RS ₁ and the mark area MA _1, and MA ₂ Composed. The transparent portion RS ₁ allows the beams BM _w1 and BM _w2 for alignment to pass therethrough, and at the same time, the beams BM _w1 and BM _w1
The diffracted light (interference light BTL _W ) of a predetermined order at the wafer mark WM of BM _w2 is passed. Further, in the pair of beams BM _w1 and BM _w2 , the center BC of these beams can be displaced by Δ in the transparent portion RS ₁ (details will be described later). The mark areas MA ₁ and MA ₂ have a predetermined interval ΔD _R.
The diffraction grating-shaped reticle marks RM ₁ and RM ₂ (duty is 1: 1) are formed in each region at a pitch P _R.

Next, the TTR type alignment system of this embodiment will be described in detail with reference to FIG. 2A is a schematic configuration diagram in a non-measurement direction (Y direction), and FIG. 1B is a direction perpendicular to the paper surface of FIG. 1A, that is, a measurement direction (X direction). 2 is a schematic configuration diagram in FIG. In FIG. 2, the dichroic mirror 5 and the mirrors 18 and 24 in FIG. 1 are omitted to simplify the description.

As shown in FIG. 2, the laser light source 10 generates an alignment illumination light (laser beam) LB of linearly polarized light (for example, P polarized light), and this beam LB is a beam LB ₁ by a beam splitter (BS) 111. And beam LB ₂ . The illumination light LB is a laser beam having a wavelength range different from the wavelength range of the exposure light IL, and is, for example, a He-Ne laser having a wavelength of 633 nm that has almost no sensitivity to the resist layer.

Now, the beam LB reflected from BS111₁
Is the first acousto-optic modulator (AO) as a frequency shifter.
M) Beam LB incident on 113 and transmitted through BS 111
₂Is the second acousto-optic modulator via the reflection prism 112.
It is incident on the (AOM) 114. AOM113 has frequency f
₁High frequency signal SF₁Driven by the frequency f₁
Beam LB₁Is modulated. On the other hand, AOM114
Wave number f₁Beam LB ₁And the difference frequency with is Δf
Frequency f₂(f₂= F₁-Δf) high frequency signal SF
₂Driven by the same frequency f₂Beam LB
₂Is modulated.

The beams LB ₁ and LB ₂ modulated by the AOMs (114, 113) are condensed by the lens 12 and are incident on the beam splitter (BS) 13. In the BS 13, the beam LB ₁ is split into a beam LB ₁₁ and a beam LB ₁₂ having a frequency f ₁ , and the beam LB ₂ is split into a beam LB ₂₁ and a beam LB ₂₂ having a frequency f ₂ .

Here, the two beams LB ₁₂ (frequency f ₁ ) and LB ₂₂ (frequency f ₂ ) reflected by the BS 13 are the reference diffraction grating 14 arranged on the rear focal plane of the lens 12.
1 and the reference signal generating unit 13 (see FIG. 1) including the photoelectric detector 142. That is, the two beams LB ₁₂ and LB ₂₂ are incident on the reference diffraction grating 141 fixed on the apparatus from two different directions at a predetermined crossing angle and form an image (crossing). The photoelectric detector 142 has two sets of light receiving elements (or two-divided light receiving elements). For example, the 0th order light of the beam LB ₁₂ that has passed through the reference diffraction grating 141 and the + 1st order of the beam LB ₂₂ that travels coaxially therewith. The interference light with the folded light and the interference light with the −1st-order diffracted light of the beam LB ₁₂ and the 0th-order light of the beam LB ₂₂ traveling coaxially with the interference light are independently received (photoelectric conversion). The sinusoidal photoelectric signals corresponding to the intensities of these two interference lights are added by an amplifier (not shown), and the resulting photoelectric signal SR has a frequency proportional to the difference frequency Δf of the beams LB ₁₂ and LB ₂₂ , It becomes a beat signal. Here, the reference diffraction grating 14
The grating pitch of 1 is set to be equal to the pitch of the interference fringes formed by the beams LB ₁₂ and LB ₂₂ . The photoelectric detector 46 may receive the two interference lights on the same light receiving surface and output a photoelectric signal according to the intensity of the interference light added on the light receiving surface.

On the other hand, the two beams L passing through the BS 13
B ₁₁ (frequency f ₁ ) and LB ₂₁ (frequency f ₂ ) pass through the plane-parallel plate 15 and the beam splitter (BS) 16 receives 1
Two beams BM _W1 (frequency f ₁ ) and BM _W2 (frequency f ₂ ) are split in the transmission direction by the light splitting surface (optical path splitting surface) 16a of the BS 16 and are divided into _two in the reflection direction. Book beam BM _R1 (frequency f ₁ ) and beam B
M _R2 (frequency f ₂ ) is divided. After that, it was divided into 4
The beam of the book is the light splitting surface (optical path splitting surface) 16 of the BS 16.
Eject from each slope so that it is parallel to a.

This beam splitter 16 has two 2
The equilateral triangular prisms are joined to each other at their bottom surfaces, and a semi-transmissive surface as a light splitting surface 16a is formed on this joined surface. Here, as shown in FIG. 2A, the plane-parallel plate 15 has a rotation axis in the X-axis direction and is provided with a variable tilt angle, and the BS 16 has two beams LB.
_The light splitting surface (optical path splitting surface) 16a is provided so as to be parallel to the incident directions of ₁₁ (frequency f ₁ ) and LB ₂₁ (frequency f ₂ ). Therefore, when the tilt angle of the plane-parallel plate 15 is changed, the incident heights of the two beams LB ₁₁ and LB ₂₁ incident on the BS 16 are changed, and as a result, one set of the beams BM _R1 and BM split by the BS 16 is changed. It is possible to control the relative distance in the Y direction between _R2 and the other split beams BM _W1 and BM _W2 . Details of this will be described later.

Now, one set of beams BM _R1 and BM _R2 emitted from one slope of the BS 16 and the other set of beams BM _W1 and BM _W2 emitted from the other slope of the BS 16 are the lens 17 and the beam splitter. The objective lens 25 is reached via the (BS) 19. Then, one set of beam BM
The convergence angle of the objective lens 15 causes _R1 and BM _{R2 to} intersect at the focal plane HP at an intersection angle 2θ _R (an intersection angle 2 on the wafer, which will be described later).
After crossing once unconditionally determined) by theta _W, the pattern surface of the reticle R transparent window RW ₁ is separated, i.e. to irradiate the respective reticle mark RM _1, RM _2. still,
The focal plane HP (the rear focal plane of the objective lens 22) is almost conjugate with the wafer surface under the wavelength of the alignment illumination light LB, and the distance between the focal plane HP and the pattern surface of the reticle R is the projection lens PL. This corresponds to the axial color aberration amount ΔL. Therefore, the interval ΔD between the reticle marks RM ₁ and RM _2
R will be defined as ΔD _R = 2 · ΔL · tan θ _R (see FIG. 5).

On the other hand, the beam BM of the other set_W1, BM
_W2Is focused on the focal plane HP by the converging action of the objective lens 15.
Crossing angle 2θ_R(Crossing angle 2θ on the wafer described later_WBy
The transparent part RS₁Over
And the projection lens PL, and then a different image is formed on the wafer mark WM.
Crossing angle 2θ from 2 directions_WIncident at and image (cross)
It Well, beam BM_W1(Frequency f₁) And beam BM_W2
(Frequency f₂) Is the intersection angle 2θ _WIncident on the wafer mark WM
Then the beam BM_W1, BM_W2The spatial region where the
Inside an arbitrary plane (wafer surface) perpendicular to the optical axis AX,
Ehamark WM pitch P_W1 / N times (where N is
Pitch P)_f(In this embodiment, P_f= P _WFixed as / 2
Then, a one-dimensional interference fringe is created. this
The interference fringes appear in the pitch direction (X direction) of the wafer mark WM.
Beam BM_W1, BM_W2Move according to the difference frequency Δf of
(Flow), the speed V is V = Δf · P
_fIt is expressed by the relational expression. Also, the intersection angle 2θ_WIs Arai
Assuming that the wavelength of the illuminating light LB for light is λ,
It is set to satisfy.

[0026]

[Equation 1]

As a result, from the wafer mark WM, ± 1st-order diffracted light, which becomes a beat wavefront that periodically repeats the change in brightness and darkness due to the movement of the interference fringes, is generated, and these diffracted lights are coaxially combined to form the center of the entrance pupil Ep. It goes backward along the optical axis AX so as to pass through. These two diffracted lights have the same polarization component (p
Since they are polarized light components, they interfere with each other and the optical beat (interference light) B
It becomes TL _W, and passes through the projection lens PL, the transparent window RW ₁ of the reticle R, the objective lens 25, the BS 19, the condenser lens 20 and the mirror 22, and the first measurement signal generation unit 20 (FIG. 1).
Is incident on the photoelectric detector 230.

This photoelectric detector 230 produces a photoelectric signal corresponding to the interference light BTL _W , and this photoelectric signal has a sinusoidal AC signal corresponding to the cycle of the change in the brightness of the interference fringes, that is, a beat frequency with a frequency difference Δf. The optical beat signal SD _W is output to the phase detection system 29. On the other hand, beam B
M _R1, reticle mark RM ₁ that BM _R2 is irradiated, RM
The grating pitch P _{R of 2} is the beam BM _R1 at the focal plane HP,
According to the crossing angle 2θ _R of BM _R2 , it is defined as shown in the following Expression 2. However, M is the projection magnification of the projection lens PL.

[0029]

[Equation 2]

Therefore, the reticle mark RM₁Arises from
First-order diffracted light RL₁(Frequency f₁) And reticle mark RM₂
First-order diffracted light RL generated from₂(Frequency f₂) And the beam
BM _R1, BM_R2Objective lens 25, BS1
9 and the condenser lens 20, and the transmission type substrate
Second configured by the quasi-lattice plate 210 and the photoelectric detector 211
It is incident on the measurement signal creation unit 21 (FIG. 1).

The reference grating plate 210 is arranged on the rear focal plane (wafer conjugate plane) of the condenser lens 20, and the first-order diffracted lights RL ₁ and R from the reticle marks RM ₁ and RM ₂ are arranged.
L ₂ forms an image (intersection) on the reference lattice plate 210 from two different directions at a predetermined intersection angle. As a result, one-dimensional interference fringes flowing in the grating pitch direction are formed on the reference grating plate 210 corresponding to the frequency difference Δf.

In this way, each reticle mark RM₁, R
M₂First-order diffracted light RL from₁, RL ₂Is the reference grid plate 21
When incident on 0, due to this diffraction effect, ± 1 next time
Folding light is generated coaxially, and this interference light BTL_RIs a photoelectric detector
The light is received by 211. Interference from this photoelectric detector 211
Optical BTL_RThe photoelectric signal corresponding to the
A sinusoidal AC signal according to the cycle (optical frequency of beat frequency
Signal) SD_RAnd is output to the phase detection system 29.
It

Now, as shown in FIG. 1, the phase detection system 29
Is an optical beat signal SR as a reference signal created by the reference signal creation unit 14 and optical beat signals SD _W , SD _R created by the first measurement signal creation unit 23 and the second measurement signal creation unit 21.
Of the optical beat signals SD _W and SD _R , and the phase difference information is output to the main control system 28. The main control system 30 determines the reticle mark RM ₁ based on the phase difference information of the phase detection system 29.
The relative positional shift amount between the wafer mark WM and the wafer mark WM is calculated with high accuracy within a range of ± P _W / 4 of the grating pitch P _W. Further, the servo system 28, which interfaces both the interference systems 7 and 9, the drive motors 6 and 8, and the phase detection system 29 are collectively controlled, and the reticle R having a different size is used.
When the positions of the transparent windows (RW ₁ , RW ₂ ) are changed by replacing the transparent window (RW ₁ and RW ₂ ), the transparent windows (RW _1
1 、 RW ₂ ) Bar code BC containing information about the position of
The tilt angle of the plane-parallel plate 15 is controlled based on the detection signal from the barcode reader 31 for detecting and the magnification chromatic aberration information of the projection optical system stored in the memory unit in the main control system 30.

Now, the alignment operation of the reticle R and the wafer W by the alignment system having the above configuration will be briefly described. As shown in FIG. 2, one pair of beams BM _R1 and BM _R2 divided by the BS 16 is transmitted through the transparent window RW ₁
When the reticle marks RM ₁ and RM ₂ are irradiated, the first-order diffracted lights RL ₁ and RL ₂ are incident on the reference grating plate 210, and the photoelectric detector 211 receives the interference light BTL _R from the reference grating plate 210. and outputs the optical beat signal SD _R phase detection system 29. As a result, the phase detection system 29 causes the optical beat signal SR as the reference signal from the photoelectric detector 142.
The phase difference Φ _R with respect to is obtained and stored. At this time, the shift amount ΔX _R of the reticle R is calculated from the following equation.

[0035]

[Equation 3]

On the other hand, the other set of beams BM _W1 and BM _{W2 which} have passed through the transparent window RW ₁ irradiate the wafer mark WM,
The photoelectric detector 230 receives the interference light BT from the wafer mark WM.
L _W is received and the optical beat signal SD _W is detected by the phase detection system 2
Output to 9. The phase detection system 29 finds and stores the phase difference Φ _W with respect to the reference optical beat signal SR. At this time, the deviation amount ΔX _W of the wafer W is calculated from the following equation.

[0037]

[Equation 4]

The phase detection system 29 outputs the previously obtained phase differences Φ _R and Φ _W to the main control system 30, and the main control system 30 calculates the reticle R and the wafer from the following equation based on the phase difference information. An amount of positional deviation ΔX relative to W is calculated. However, M _AL
Is the projection magnification under the alignment wavelength of the projection lens PL, and the shift amount ΔX is a value on the wafer W.

[0039]

[Equation 5]

As a result, the main control system 30 uses the servo system 28 to finely move the reticle stage RS or the wafer stage WS so that the deviation amount ΔX becomes a constant value or zero, and the pattern area PA of the reticle R is moved. The projected image and the shot area on the wafer W are exactly matched.
At this time, the deviation amount ΔX is within a predetermined allowable range (for example, ± 0.
The exposure light IL is applied to the illumination area IA via the illumination optical system 2 when the exposure light IL falls within the range of 06 μm). Further, in the alignment, the servo system 29 is not used, and the reticle stage RS, so that the relative phase difference between the two optical beat signals obtained by the phase detection system 27 becomes zero.
Alternatively, the wafer stage WS may be servo-controlled. The phase detection system 29 does not use the reference optical beat signal SR, but uses the two optical beat signals SD _W and SD _R.
May be directly compared to obtain the relative phase difference.

Next, using FIG. 3 and FIG.
Window RW₁~ RW_FourTransparent when the position of is changed
Window RW₁Reticle mark (R
M₁, RM₂) Illuminating the beam (BM_R1, BM_R2)
And transparent part RS₁And the wafer lens via the projection lens PL.
WM₁For illuminating (BM_W1, BM_W2Between)
The distance adjustment will be described. 2 is an array of the present invention.
FIG. 7 is a principle view schematically showing a part of the ment system, and FIG.
Centers the optical axis Ax of the projection optical system PL with respect to the alignment light
Radial direction centered, that is, image height H and magnification of projection optical system PL
It is a figure which shows the correlation with the amount M of chromatic aberration. And
In FIG. 7, m₁Is the distance h from the reticle center RC₁of
Wafer mark WM at position₁Is projected under the alignment light.
The amount of chromatic aberration of magnification when backprojected by the shadow lens PL
Show, m₂Distance h from reticle center RC ₂At the position
Hammark WM₁Was back projected by the projection lens PL
The amount of lateral chromatic aberration is shown.

First, if the position of the transparent window RW ₁ for alignment changes as the reticle size (circuit pattern size) changes, the objective lens 25 is changed to the mirror 24 by the drive control system 27 as shown in FIG. It is understood that it is sufficient to move them in the A direction together. However, as described above, since the projection lens PL is not sufficiently corrected for chromatic aberration with respect to the alignment light, the transparent window RW
_The chromatic aberration of magnification of the projection optical system PL changes as the position of ₁ changes.

As shown in FIG. 7, the amount of lateral chromatic aberration of the projection lens PL gradually increases with distance from the optical axis Ax, and the transparent portion RS provided at a position h ₁ from the optical axis Ax of the projection lens PL. Wafer mark WM by _1
1 and the case where the wafer mark WM ₁ is observed by the transparent portion RS ₁ provided at the distance h ₂ from the optical axis Ax of the projection lens PL, the wafer mark WM is caused by the chromatic aberration of magnification of the projection lens PL. ₁ is Δm in the horizontal direction
It is shifted by (= m ₂ −m ₁ ).

As a result, as shown in FIG. 5, for example, the position of the image WMI ₁ of the wafer mark WM ₁ in the transparent portion RS ₁ shifts to the reticle center RC side as indicated by the dotted line, so that the area S indicated by the dotted line is formed. Light B for wafer position detection
Since only TL _W can be obtained, the detected interference light BTL _W
The amount of light is significantly reduced, and high-precision alignment becomes difficult.

Therefore, the relative distance between the beam for reticle mark irradiation (BM _R1 , BM _R2 ) and the beam for wafer mark irradiation (BM _W1 , BM _W2 ) is adjusted by the variation Δm of the chromatic aberration of magnification. There is a need. Therefore, in the embodiment according to the present invention, as shown in FIG. 3, two optical members provided in the alignment system, that is, a parallel plane plate 15 having a variable tilt angle and a light splitting surface (semi-transmission plane) parallel to the incident direction of the beam are used. The beam splitter 16 having a surface) allows the relative distance between the reticle mark irradiation beams (BM _R1 , BM _R2 ) for illuminating each alignment mark and the wafer mark irradiation beams (BM _W1 , BM _W2 ). I am adjusting.

Now, the plane parallel plate 15 is used for the beams LB ₁₁ and LB.
Assuming that the beam is set to be perpendicular to the incident direction of ₁₂ , the beams LB ₁₁ and LB ₁₂ pass through the plane parallel plate 15 as they are,
The light enters the slope of the beam splitter 16. After that, the beam is split into two by the semi-transmissive surface 16a of the beam splitter 16, and each inclined surface is emitted in parallel to the incident direction.

Next, when the plane parallel plate 15 is tilted by δ,
Beam LB passing through this₁₁, LB ₁₂Is indicated by the dotted line
The horizontal direction (paper direction), and finally the beam
The spacing between the beams of each set emitted from the liter 16 varies.
It Therefore, the tilt amount of the plane parallel plate 15 is set appropriately.
This allows each set of exiting beam splitter 16
Since the beam spacing can be adjusted appropriately, the projection lens
Reticle without being affected by lateral chromatic aberration of PL
Beam for mark irradiation (BM_R1, BM_R2) Is exactly
Kurumark (RM₁, RM₂) For wafer mark irradiation
Beam of (BM_W1, BM_W2) Is exactly the wafer mark WM
₂Each can be illuminated. Moreover, BEAMS
Reticle with equal optical path length by plitter 16
Beam for mark irradiation (BM_R1, BM_R2) And wafermers
Beam for irradiation (BM_W1, BM_W2) And can be split
Therefore, even if a light source with low coherence is used, it will be explained in this embodiment.
Even if you perform the alignment using the heterodyne method
High accuracy is guaranteed.

Here, the thickness of the plane parallel plate 15 is t,
The tilt angle of the plane-parallel plate 15 is δ, the refractive index of the plane-parallel plate 15 is n _P , the reference incident height of the beam entering the beam splitter 16 is d, the distance between the beams divided by the beam splitter 16 is D, The incident side and the exit side of the beam splitter 16 have an apex angle of 2θ (the beam splitter 16
When the angle of the inclined surface of the isosceles triangular prism that composes is θ), the height of the isosceles triangular prism that composes the beam splitter 16 is T, and the refractive index of the beam splitter 16 is n _BS , It is desirable to satisfy the condition shown in Formula 6.

[0049]

[Equation 6]

However, the sign of δ in equation 7 is positive when the plane-parallel plate 15 is tilted so that the incident height on the light splitting surface of the beam splitter 16 is low, and the incident height on the light splitting surface of the beam splitter 16 is positive. When the plane parallel plate 15 is tilted so that the value becomes low, the value is negative. Next, referring to FIG. 1, the beam for reticle mark irradiation (BM _R1 , B
M _R2 ) and beam for irradiating wafer mark (BM _W1 , B
The operation for adjusting the relative distance to M _W2 ) will be described.

Reticle R is loaded and reticle
Formed on the edge of the reticle R when placed on the stage RS
Bar code reader 31 with transparent bar code BC
RW ₁~ RW_FourRead the location information of this barcode
The reader 31 outputs this detection signal to the main control system 30.

As shown in FIG. 7, the main control system 30 has the first correlation of the magnification chromatic aberration amount M with respect to the image height H centered on the optical axis Ax of the projection optical system PL in the internal memory section.
The memory information and the second memory information of the correlation between the magnification chromatic aberration amount M and the correction angle (tilt amount) of the plane parallel plate 15 are stored in advance, and the first memory information and the detection signal from the bar code reader 31 are stored. And the transparent portions RS ₁ in the transparent windows RW _{1 to} RW _{4 with} respect to the reticle center RC.
After the amount of lateral chromatic aberration of the projection reticle PL at the center position of RS ₄ is determined, the amount of tilt of the plane parallel plate 15 is finally determined based on the second memory information.

The main control system 30 has a drive control system 32.
Is driven to tilt the plane-parallel plate 15 to set an appropriate tilt amount. At the same time as the operation of setting the tilt angle of the plane-parallel plate 15, the main control system 30 sets an appropriate position of the objective lens 25 so that the alignment system can detect the transparent windows RW _{1 to} RW ₄ of the reticle R. . If the main control system 30 determines that the objective lens 25 is not at a position where the transparent windows RW _{1 to} RW ₄ of the reticle R can be detected by the detection signal from the bar code reader 31, the drive control system 27 is driven to drive the objective lens 25. Also, the mirror 24 is moved in the A direction to set the objective lens 25 at an appropriate position.

With the above operation, the chromatic aberration of magnification of the projection reticle PL changes as the positions of the transparent windows RW _{1 to} RW ₄ of the reticle R change, and the wafer mark and the reticle mark when viewed on the reticle are changed. Even if the relative spacing changes, the beam (B
M _R1 , BM _R2 are exactly reticle marks (RM ₁ , RM
₂ ) is a beam for illuminating the wafer mark (BM _W1 , B
M _W2 ) can accurately illuminate the wafer mark WM ₂ . As a result, it can be seen that highly accurate alignment is always guaranteed even if the reticle size is different.

It should be noted that one of the beams (BM _W1 , B for irradiating the wafer mark) divided by the beam splitter 16 is used.
_Mw2 ) is provided with a scanning means such as a plane-parallel plate having a variable tilt angle or a vibrating mirror in the optical path of M _w2 ) and the scanning means scans the beam (BM _W1 , BM _W2 ) for wafer mark irradiation to detect the wafer mark. The position of the beam (BM _W1 , BM _W2 ) for irradiating the wafer mark may be set when the light intensity from the wafer mark detected by the photoelectric detector 230 becomes maximum.

Next, a modification of the embodiment shown in FIG. 2 will be briefly described with reference to FIG. In FIG.
Members having the same function shown in FIG. 2 are designated by the same reference numerals. The present embodiment is different from the embodiment shown in FIG. 2 in that polarization beamsplitters 160 and 190 are provided in place of the beam splitters 16 and 19, and the space between the plane-parallel plate 15 and the polarization beamsplitter 160 and between the polarization beamsplitters. The point is that a half-wave plate (P _{1 to} P ₃ ) is provided between the split optical paths of 160 and the lens 17.

These ½ wavelength plates (P _{1 to} P ₃ ) are rotatably provided, and by rotating these to adjust each optical axis, each photoelectric detector (210, 211) is adjusted.
Since it is possible to equalize the light amounts of the respective alignment lights detected by, highly accurate alignment becomes possible. Specifically, one of the beams (BM _W1 , BM _W2 ) for irradiating the wafer mark, which is split by the polarization beam splitter 160, passes through the projection lens PL twice, so that the light amount may be attenuated. For this reason, in order to equalize the light amounts of the light detected by the photoelectric detectors (210, 211), the light intensity of the wafer mark irradiation beams (BM _W1 , BM _W2 ) is set to the reticle mark irradiation beam (BM It is necessary to make it stronger than the light intensity of _R1 , BM _R2 ).

Therefore, if the half-wave plate P ₁ is rotated and its optical axis is adjusted, the polarization beam splitter 16
Beam for reticle mark irradiation divided by 0 (B
M _R1 , BM _R2 ) and beam for irradiating wafer mark (B
M _W1 , BM _W2 ) and the amount of light can be distributed at an appropriate ratio.
By rotating the two-wave plate (P ₂ , P ₃ ) and adjusting these optical axes, the beams (BM _W1 , B) for irradiating the wafer mark can be obtained.
M _W2 ) and beam for reticle mark irradiation (BM _R1 , BM
_Since it is possible to align the polarization plane with _R2 ), it is possible to perform efficient alignment mark illumination without causing a light amount loss in the polarization beam splitter 190.

As described with reference to FIGS. 1, 2 and 8, the plane parallel plate 15 is replaced with the beam splitters 16 and 160.
It is arranged on the incident side of the beam splitter, but instead of this, the exit side of the beam splitters 16 and 160 (the beam splitter 1
6, 160 and the objective lens 25 between the wafer mark irradiation beams (BM _W1 , BM _W2 ) and the reticle mark irradiation beams (BM _R1 , BM _R2 ) in the respective optical paths. Face plates may be respectively arranged, and the inclination angles of the two parallel plane plates may be changed independently.

Next, another embodiment will be described with reference to FIGS. 9 and 10. 9 and 10, members having the same functions as those in FIGS. 1 and 2 are designated by the same reference numerals.
This embodiment is different from the embodiment shown in FIGS. 1 and 2 in that
As shown in FIGS. 9 and 10, two sets of beams (one set of beam B
M _R1 , BM _R2 and the other set of beams BM _R1 , BM _R2 ). The tilt plane variable plane plate 15 that changes the relative distance between the beam and the beam splitter 16 itself is changed by the drive control system 32. It is a point that is provided so as to be movable in a direction perpendicular to.

As a result, in this embodiment, if the beam splitter 16 is moved by β in the direction perpendicular to the optical axis,
One set of beams B exiting the beam splitter 16
The distance between M _R1 and BM _R2 and the other set of beams BM _W1 and BM _W2 changes by 2β. In addition, as a result, the light splitting surface of the beam splitter 16 is fixed while fixing the positions at which the beams BM _R1 and BM _R2 that are transmitted and split through the light splitting surface of the beam splitter 16 irradiate the reticle marks RM ₁ and RM _2. It is possible to control only the position at which the beams BM _W1 and BM _W2 reflected by and splitting pass through the transparent window RS ₁ on the reticle.

Here, the reference incident height of the beam entering the beam splitter 16 is d, and the beam splitter 16
Is β, the distance between the beams divided by the beam splitter 16 is D, and the apex angles of the incident side and the exit side of the beam splitter 16 are 2θ (the beam splitter 16
When the angle of the inclined surface of the isosceles triangular prism that composes is θ), the height of the isosceles triangular prism that composes the beam splitter 16 is T, and the refractive index of the beam splitter 16 is n _BS , It is desirable to satisfy the condition shown in Expression 7.

[0063]

[Equation 7]

However, the sign of β in Equation 7 is positive when the beam splitter 16 is moved so that the incident height on the light splitting surface of the beam splitter 16 is low, and the incident height on the light splitting surface of the beam splitter 16 is positive. When the beam splitter 16 is moved so as to be low, the value is negative. The beam (L) is formed on the other slope (the left slope in the figure) of the beam splitter 16 shown in FIG.
B ₁₁ , LB ₂₁ ), the beams BM _W1 and BM _R2 fix the positions where the beams BM _W1 and BM _W2 pass through the transparent window RS ₁ on the reticle, while the beams BM _R1 and BM _{R2 move} to the reticle marks RM ₁ and
Only the position of irradiating RM ₂ can be controlled.

Further, if the optical system (10,111,112,113,114,12,13,141,142) above the beam splitter 16 is integrally movable so as to cross the right and left slopes of the beam splitter 16, one of the marks can be moved to two. Only the beam radiating in the direction can be selectively moved. As described above, in this embodiment, the beam splitter 1
With a simple configuration in which only 6 is moved, one beam split by the beam splitter 16 can be fixed while the position of the other split beam can be changed, so a greater effect can be expected.

[0066]

As described above, according to the present invention, even if the chromatic aberration of magnification of the projection lens changes as the size of the chip to be exposed changes, and the distance between the alignment marks changes, Since each alignment mark can be accurately illuminated, a signal with a good S / N ratio can be detected. Therefore, it is possible to realize an alignment apparatus which can always perform TTR type alignment with high accuracy.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a projection type exposure apparatus provided with an alignment apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of the alignment device shown in FIG.

FIG. 3 is a diagram for explaining the principle of adjusting the distance between the wafer mark irradiation beam and the reticle mark irradiation beam according to the embodiment of the present invention.

FIG. 4 is a diagram showing an example of a reticle pattern shape and mark arrangement.

FIG. 5 is a diagram showing a specific configuration of a transparent alignment window on a reticle.

6 is a diagram showing how alignment light is incident on a transparent alignment window on the reticle shown in FIG.

FIG. 7 is a diagram showing chromatic aberration of magnification of a projection lens with respect to alignment light.

FIG. 8 is a diagram showing a modification of the embodiment shown in FIG.

FIG. 9 is a diagram showing another modification of the embodiment shown in FIG.

FIG. 10 is a diagram showing another modification of the embodiment shown in FIG.

[Explanation of symbols for main parts]

10 ... Laser light source 11 ... Two-beam frequency shifter 12, 17, 20 ... Lens 14 ... Reference signal creation unit 15 ... Parallel plane plate 13, 15, 19 ... Beam splitter 21. .. Second measurement signal creation unit 22 ... First measurement signal creation unit 29 ... Phase difference detection system 30 ... Main control system 31 ... Bar code reader 27, 32 ... Drive control system RS・ ・ ・ Reticle stage WS ・ ・ ・ Wafer stage R ・ ・ ・ Reticle W ・ ・ ・ Wafer RW ₁ , RW ₂ , RW ₃ , RW ₄・ ・ ・ Transparent alignment windows WM ₁ , WW ₂ , WW ₃ , WW ₄ ... Wafer mark

Claims (4)

[Claims] 1. A first alignment that is coherent from two predetermined directions with respect to a first diffraction grating formed on the reticle when a pattern formed on the reticle is transferred onto a substrate via a projection optical system. An illumination optical system that illuminates light and illuminates second alignment light that is coherent to the second diffraction grating formed on the substrate from two predetermined directions, and the diffracted light from each of the first and second diffraction gratings. In the alignment apparatus for performing relative alignment between the reticle and the substrate, wherein the illumination optical system includes two light flux generation means for generating two coherent light beams, Relative distance between the first and second alignment light and the light splitting means for splitting the two light fluxes from the two light flux generation means to generate the first and second alignment lights, respectively. And changing the relative distance between the first and second alignment lights by the light flux interval changing means, so that the first alignment light causes the first diffraction grating to move. The position illuminated from two predetermined directions and the second alignment light are the second
A position detecting device characterized by changing at least one of a position where a diffraction grating is illuminated from two predetermined directions. 2. A first alignment that is coherent from predetermined two directions with respect to a first diffraction grating formed on the reticle when a pattern formed on the reticle is transferred onto a substrate via a projection optical system. An illumination optical system that illuminates light and illuminates second alignment light that is coherent to the second diffraction grating formed on the substrate from two predetermined directions, and diffracted light from each of the first and second diffraction gratings. In the alignment apparatus for performing relative alignment between the reticle and the substrate, wherein the illumination optical system includes two light flux generation means for generating two coherent light beams, The light splitting means splits the two light fluxes from the two light flux generating means to generate the first and second alignment lights, respectively, and the light splitting means includes the first and second alignment beams. Is provided so as to be movable in a direction perpendicular to the optical axis of the illumination optical system in order to change the relative distance between the first alignment light and the first alignment light. A position detecting device, wherein one of a position for illuminating one diffraction grating from two predetermined directions and a position for illuminating the second diffraction grating from the two predetermined directions by the second alignment light is changed. 3. The light flux interval varying means is composed of an optical member having a variable tilt angle provided between the two light flux generating means and the light splitting means, and the light splitting means is provided from the two light flux generating means. The first alignment light illuminates the first diffraction grating from two predetermined directions by changing the tilt angle of the optical member, which is composed of a light splitting prism having a light splitting surface parallel to each incident direction of two light fluxes. The alignment apparatus according to claim 1, wherein a distance between a position where the second alignment light is illuminated and a position where the second alignment light illuminates the second diffraction grating from two predetermined directions is variable. 4. The illumination optical system has a half-wave plate on the incident side of the light splitting means, and the light splitting prism is composed of a polarization splitting prism. Item 3. The alignment device according to item 3.