JP2698446B2 - Interval measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an interval measuring apparatus for measuring an interval between two objects with high accuracy, for example, in a semiconductor manufacturing apparatus, measuring an interval between a mask and a wafer, This is suitable for controlling to a predetermined value.

2. Description of the Related Art Conventionally, in a semiconductor manufacturing apparatus, the distance between a mask and a wafer is measured by an interval measuring device or the like, and controlled so as to be a predetermined distance, and then the pattern on the mask surface is exposed on the wafer surface. Transcribed. As a result, highly accurate exposure transfer is performed.

FIG. 12 is a schematic view of an interval measuring device proposed in Japanese Patent Application Laid-Open No. 61-111402. And is focused on a point P _S between the mask M and the wafer W and arranged opposite, the mask M and the wafer W to the light beam by the lens L1 of the second object as the first object in the drawing.

In this case the light beam is respectively reflected by the mask M surface and on the wafer W surface, a point P _W on the screen S surface through the lens L2, the being focused projected to P _M. The distance between the mask M and the wafer W focal point P _W of the light beam on the screen S surface is measured by detecting the distance between the P _M.

(Problems to be Solved by the Invention) However, the apparatus shown in FIG.
Are parallel to each other, the distance between the two can be measured correctly. However, if one of them is inclined, for example, the mask M is inclined as shown by a dotted line and becomes non-parallel, the incidence of the light beam on the screen surface S the point is to change from the point P _M to the point P _N, it becomes a cause of measurement error.

The present application has been made in view of the above-mentioned drawbacks of the conventional example, and has as its object to provide an interval measuring apparatus that always enables highly accurate interval measurement.

(Means for Solving the Problems) The present invention provides a method for changing the distance between the first object and the second object.
High precision interval measurement is always possible by using two light beams that change position in the opposite direction.

As shown in an embodiment described later as a specific example, a first object and a second object provided with a mask and a physical optical element corresponding to a wafer are arranged to face each other, and a light beam is incident on the physical optical element on the first object. Then, after the light deflected in a predetermined direction by the physical optical element is reflected by the second object surface, the light is guided onto the light receiving means surface, and by detecting the incident position of the light on the light receiving means surface, When calculating the distance between the first object and the second object,
The distance between the first object and the second object is determined using two sets of physical optical elements having a wavefront conversion function in which the directions of movement of the light flux positions on the light receiving surface corresponding to the increase and decrease of the distance are opposite to each other. .

In the first measurement system, for example, when the distance increases, the light beam position on the detection surface moves to the right, and in the second measurement system, when the distance increases or decreases, the light beam position on the detection surface moves to the left. Set the optical system so that

If the optical system is set so that the absolute value of the amount of movement on the detection surface with respect to the interval between them is the same, when the wafer corresponding to the second object is inclined, the movement on the detection surface corresponding to the inclination The amount can be the same, including the direction.

That is, the moving amount corresponding to the interval is opposite in direction in the first and second measurement systems, and the moving amount corresponding to the inclination is the same. Therefore, if the difference between the movement amounts of the first system and the second system is calculated, the movement amount corresponding to the inclination is canceled, and only the movement amount corresponding to the interval is measured with twice the sensitivity.

(Embodiment) FIG. 1 is a schematic view of an optical system according to an embodiment when the present invention is applied to an apparatus for measuring the distance between a mask and a wafer in a semiconductor manufacturing apparatus, and FIG. It is a perspective view.

In this figure, 1,1 'is a light beam from, for example, a He-Ne laser or a semiconductor laser; 2,2' is a first object, for example, a mask; 3,3 'is a second object, for example, a wafer;
Wafer 3 are opposed to each other at a distance d ₀ as shown in Figure 2 and. Reference numerals 4 and 4 ', 5 and 5' denote first and second physical optical elements provided on a part of the surface of the mask 2, respectively. The physical optical elements 4, 4 ', 5, and 5' It consists of a zone plate and the like. Reference numerals 7, 7 'denote condensing lenses, the focal length of which is fs.

Numerals 8 and 8 'denote light receiving means, which are arranged at the focal positions of the condenser lenses 7, 7' and are composed of a line sensor, a PSD, etc., and detect the position of the center of gravity of the incident light beam in the sensor plane.

Here, the center of gravity of the luminous flux is a point in the luminous flux cross section at which the integral value becomes a zero vector when the value obtained by multiplying the position vector of each point in the cross section by the light intensity at that point is integrated over the entire cross section. However, as another example, the position of a point where the light intensity reaches a peak may be detected.

Reference numeral 9 denotes a signal processing circuit which determines the center of gravity of the light beam incident on the light receiving means 8, 8 'using the signals from the light receiving means 8, 8', and as described later, the distance between the mask 2 and the wafer 3 d ₀
Is calculated.

Reference numeral 10 denotes an optical pickup, which has a condenser lens 7, a light receiving means 8, and a signal processing circuit 9 as required.
The mask 2 and the wafer 3 are relatively movable.

The upper and lower two measurement systems shown in FIG. 1 constitute a system symmetrical with respect to a straight line equidistant from the optical axes of both light projection systems on the paper. Since the configuration is almost the same, a detailed description will be given below based on the system below.

In this embodiment, the light flux 1 from the semiconductor laser LD
(Wavelength λ = 830 nm) is perpendicularly incident on a point A on a first Fresnel zone plate (hereinafter abbreviated as FZP) 4 on the mask 2. Then, a diffracted light of a predetermined order diffracted at an angle θ ₁ from the first FZP 4 is converted into a point B (C) on the wafer 3 surface.
Is reflected by Among them, the reflected light 31 is the reflected light and the reflected light when the wafer 3 is located at the position P1 close to the mask 2.
32 is a reflected light when the wafer 3 is from the position P1 at a distance d _G only displaced position P2.

Next, the reflected light from the wafer 3 is converted to the second light on the first object 2 surface.
At the point D (E at the position P2) on the FZP5 surface.

The second FZP 5 has an optical function of changing the exit angle of the output diffracted light according to the incident position of the incident light beam.

And (62 when the position P2) is guided to the light receiving unit 8 on the surfaces of via the condenser lens 7 to a second predetermined order diffracted light 61 diffracted by an angle theta ₂ from FZP5.

Then, the incident light beam on the surface of the light receiving means 8 at this time
The distance between the mask 2 and the wafer 3 is calculated using the barycentric position of 61 (62 for the position P2).

In this embodiment, the first and second FZPs 4, 5 provided on the mask 2 surface are provided.
Are constituted by known pitches set in advance, and the diffraction angles θ _{1 at} FZP4 of the diffracted light of a predetermined order (for example, ± 1st order) of the light beam incident thereon and the diffraction angle θ _{2 at} the predetermined incident position of FZP5 are It is required in advance.

Next, a method for determining the distance between the mask 2 and the wafer 3 will be described with reference to the optical path diagram shown in FIG.

Incident light 1 is incident on the upper incident side physical optic element 4 mask 2 is diffracted to - [theta] ₁ direction at point A. Now, when the wafer 3 g ₀ had from the mask 2 to the position of Giyatsupu g _0, the diffraction light is reflected by the point C, is diffracted at a point E on the Masukumen second upper exit side physical optic element 5 again, the light receiving system It is arranged so as to advance in the optical axis direction. That is, E passes through the point F at the distance f _M
Is set to the point A interval -d.

When the gap between the mask 2 and the wafer 3g is an arbitrary g, the light 61 is reflected at the point B, and diffracted so as to always pass through the F at the point D of the physical optical element 5 regardless of g. Become. Further, the wafer 3g is inclined by beta at point B, if becomes light 61 _beta through the F _beta point diffracted by the D _beta point reflected the physical optic element 5 at point B, the relational expression shown below Holds,
The angle θ between the light emitted from the physical optical element 5 and the optical axis of the light receiving system
_2β is the gap g ₀ , g, the emission angle of the incident side physical optical element 4 −
θ ₁ , the focal length f _{M of the} output-side physical optical element 5 and the wafer 3
It is determined by the slope β of β.

If you take the direction of the angle and length as shown in the figure, The change in the angle of incidence / emission at the point E due to the inclination is: 2β ′ = cos θ ₁ 2β (3) On the other hand, d = −2g ₀ tan θ ₁ , and d _M2 = d + 2g tan θ ₁ = 2 (g−g ₀ ) tan θ ₁ ... (4) When tan θ _2β is obtained from the above (1), (2), (3), and (4), Now consider the movement S ₁ of Supotsuto on the sensor surface, However, β≪1 and tan (Cβ) Cβ.

From equation (6), if the wafer is not tilted, the spot movement S ₁ is And the gap change amount Δg Move on the light receiving means surface at the magnification of. Now, f _S =
If 60 mm, f _M = 1 mm, tan θ ₁ = 1, the magnification Q = 60,
For a change of 1 μm between the mask 2 and the wafer 3 per 1 μm, the luminous flux on the light receiving means 8 moves by 60 μm.
If a PSD having a position resolution of 0.3 μm is used as the light receiving means 8, it is possible in principle to measure the distance between the mask 2 and the wafer 3 with a resolution of 0.005 μm.

More specifically, the surface gap g _R is known by measuring other distance detecting means, for example, by previously focusing on the mask and the wafer with an optical microscope through a mask and measuring the amount of raising and lowering the lens barrel of the microscope. The mask and the wafer are irradiated with a light beam by this apparatus, and the light beam incident position on the sensor surface at this time is stored as a reference position, and the deviation of the spot position from the reference position at the time of detecting the interval is obtained. the distance by obtaining the deviation Δg from g _R of the current mask, the wafer spacing is substituted into the S ₁ (6) 'expression is measured.

Here, considering the effect on the wafer inclination β, the gap measurement error amount at the wafer inclination β, that is, the error gap amount εg can be obtained from the equation (6) in terms of the gap. Β is 10 ^-4 rad for proximity type semiconductor exposure equipment
The degree is considered to be the maximum, and since g is usually 100 μm or less, if β = 10 ⁻⁴ rad, g = 100 μm, As shown in FIG. 1, the error due to such tilt is constituted by two optical systems of upper and lower systems, and the effects of the wafer tilt β are set so as to be opposite to each other. Is detected by the signal processing circuit 9 based on the signals from the light receiving means 8 and 8 ', and the interval is detected based on the amount of movement of the spot. This is described in detail below.

In the system shown in FIG. 1 as previously obtained, the movement S ₁ ′ of the spot on the light receiving means surface is as follows.

Here, the incident position as shown in FIG. 4 constitutes shifted by k, if tilted β in Giyatsupu g ₁ of the system under the difference in Giyatsupu _{is, g 1 '-g 1 = {} g 1 tan (−θ ₁ ) + k−g ₁ ′ tan (θ ₁ )｝ tanβ Therefore, When the difference ΔS of the movement of the spot on the sensor surface is obtained, As can be seen by comparing Equations (6) and (7),
In the embodiment shown in FIG. 1, the average gap at two measurement points can be evaluated with twice the sensitivity as compared with one system. In other words, when there is no wafer tilt, the difference in spot movement is The magnification of the variation of the spot on the light receiving means surface with respect to the variation of the gap, that is, the sensitivity θ is Becomes In this case, an interval is obtained by subtracting the difference between the amounts of displacement of the respective centers of gravity from the reference position obtained as described above for each sensor into ΔS. F _S as before
= 30 mm, f _M = 1 mm, tan θ ₁ = 1, θ = 120 times, and the mask 2 and the wafer 3 are in principle with a resolution of 0.0025 μm.
Can be measured. The effect on the wafer inclination β (error gap amount ε'g) is obtained from the equation (7). As before, β = 10 ^-4 rad, g = 100 μm, If k = 1000 μm, εg ′ = − 0.000008 [μm], which is sufficiently small and can be ignored. Since the difference in the amount of movement of the spot by the two optical systems corresponds to the change in the space between the mask and the wafer and is hardly affected by the inclination of the wafer, the difference in the amount of movement of the spot can be determined with high accuracy. Gaps fluctuation measurement becomes possible.

5A and 5B show a second embodiment according to the present invention, wherein FIG. 5A is a view showing the arrangement of physical optical elements on a mask surface, and FIG. 5B is a view showing a schematic arrangement of an optical system. The two measurement systems are shared, and the physical optical elements (incident marks) 4, 4 'on the incident side are adjacent to each other, and the incident light from the same light projecting system is 1, 1'. , 'projecting light and to, physical optic element on the output side (outgoing mark) 5,5' 4 receives light emitted 62 _{P1 from, 62 P2, 62 P1 ',} 62 P2' to a condenser lens 7, light receiving means 8 to detect. Mask 2,
In the present embodiment, when measuring between the gap positions P ₁ and P ₂ between the wafers 3, the position P ₁ where the measurement range of the gap is the minimum is P _1.
At this time, the spot positions on the detection surface 8 by the two systems are set so as to coincide with each other. Supotsuto position at the position of the companion no P ₂ is changed as S _2, S ₂ 'to Giyatsupu fluctuations, it can be performed by measuring both the Supotsuto interval as in the first embodiment the measurement.

More specifically, the surface gap g _R is known by measuring other distance detecting means, for example, by previously focusing on the mask and the wafer with an optical microscope through a mask and measuring the amount of raising and lowering the lens barrel of the microscope. The apparatus irradiates a light beam to the mask and the wafer, stores the spot interval on the sensor surface at this time as a reference interval, detects the spot interval when measuring the interval, and determines the deviation from the reference interval by (7). ) 'is substituted into equation [Delta] S, the mask, the deviation from g _R of the wafer spacing Δ
The interval measurement is performed by calculating g.

6A and 6B show a third embodiment according to the present invention, wherein FIG. 6A is a view showing the arrangement of alignment marks on a mask surface, and FIG. 6B is a view schematically showing an optical path.

The two systems of marks are arranged adjacent to each other in the direction orthogonal to the direction in which the beam moves due to the gap variation. The measurement system, measurement sensitivity, and the like are the same as in the above-described embodiment.

FIG. 7 shows a fourth embodiment according to the present invention in which two systems of marks are superposed.

FIG. 8 shows a mark on the incident side according to a fifth embodiment of the present invention.
Only 4, 4 'are arranged in an overlapping manner.

FIG. 9 shows a sixth embodiment according to the present invention, in which the mark 4 on the incident side is formed of a linear lattice parallel to the incident surface, and the ± 1st-order diffracted lights are diffracted in directions symmetrical with respect to the incident surface, and the output marks 5 , 5 '. (A) shows a projection optical path in the plane of incidence, (b) shows a plane projection optical path parallel to the mask, and (c) shows a mark arrangement diagram.

FIG. 10 shows a seventh embodiment of the present invention, in which (a) shows a mark arrangement diagram and (b) shows an outline of an optical path diagram. In this embodiment, after the incident light 1 is diffracted by the incident mark 4 and reflected by the wafer 3, the light is split into two diffracted lights 62, 62 ″ by the output marks 5, 5 ″ on the mask 2, and is received by the light receiving lens 7. The light is condensed, and the position of the spot light is shifted by the sensor 8 below S ₁ -S ₁ ″.
Is used to measure the gap between the mask 2 and the wafer 3. In this case, the exit mark 5 the description as well as the outgoing beam center is designed to pass through the point F of the distance f _M to the light receiving system from the mask 2, but from the output marks 5 "emitted light beam center mask 2 It is designed to diverge from a point F ″ at the same distance on the wafer side as a starting point.

The gap between the mask 2 and the wafer 3 and the movement of the spot light on the light receiving means surface in the latter system will be described with reference to FIG. 11, including the inclination of the wafer.

Incident light 1 is incident on the upper incident side physical optic element 4 mask 2 is diffracted to - [theta] ₁ direction at point A. Now, when the wafer 3g ₀ is at the position of the gap g ₀ , the diffracted light is reflected at the point C, is diffracted again at the point E on the exit side physical optical element 5 ′ on the mask surface 2, and is reflected by the light receiving system. An arrangement that proceeds in the axial direction is adopted.

If the diffraction point on the emission-side physical optical element 5 ″ when the wafer 3 moves to the gap g is D ″, the direction of a straight line passing through the point F ″ on the optical axis of the light receiving system (the optical axis and −θ ₂ ″). (Tilted direction)
Will be diffracted.

Here, if the wafer surface 3g is inclined by beta, exit side physical optic element 5 "diffraction points on the D _beta", and the "direction of the straight line passing through the (optical axis and - [theta] _2.beta" F _beta inclined direction) Diffracted to

These relationships are expressed by the following equations using the parameters shown in FIG.

The change in the angle of incidence at point E due to the inclination of the wafer is as follows: 2β ″ = cos θ ₁ 2β (13) Since d = −2 g ₀ tan θ _{1 in} one direction, dM ₂ = d + 2 g tan θ ₁ = 2 (g−g ₀ ) tan θ ₁ (14) When tan θ _2β ″ is obtained from the above equations (11) to (14), Considering the spot movement S ₁ ″ on the sensor surface, Assuming that Here, if two systems are set so that f _M ″ = −f _M , From the above, the difference S ₁ −S ₁ ″ of the amount of movement on the sensor surface of the light receiving system is obtained from the equations (6) and (17). If there is no wafer tilt β, equation (18) is And the gap change amount Δg, Will move on the sensor surface at the magnification of. This would be twice as sensitive as a single system.

Next, the effect on the inclination β of the wafer will be considered. (18) If Giyatsupu converted error ε _β "by the β of the formula ^{β = 10 -4 rad, g =} 100μm, if _{tanθ 1 = 1, ε β "} = 10 -4 × 100 × 2 = 0.02 [μm] , and the negligible sufficiently small.

〔The invention's effect〕

As described above, the tilt amount of the wafer is corrected and the interval measurement sensitivity is increased by using two sets of light beams in which the moving directions of the light beam positions on the light receiving surface corresponding to the increase and decrease of the interval are opposite to each other. And high-precision interval measurement can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of an optical system according to a first embodiment of the present invention. FIG. 2 is an explanatory diagram of a light beam incident on the mask and the wafer in FIG. FIG. 3 and FIG. 4 are detailed optical path diagrams for calculating an interval measurement amount in FIG. FIG. 5 is a schematic view of a second embodiment according to the present invention. FIG. 6 is an optical path diagram near a mark and mark arrangement of a third embodiment according to the present invention. 7 and 8 are mark arrangement diagrams of the fourth and fifth embodiments according to the present invention. FIG. 9 is an optical path diagram near a mark and a mark arrangement diagram of a sixth embodiment according to the present invention. FIG. 10 is a schematic view of a seventh embodiment according to the present invention. FIG. 11 is a detailed optical path diagram for calculating an interval measurement amount in FIG. FIG. 12 shows a conventional example. DESCRIPTION OF SYMBOLS 1 ... Projected light beam 2 ... Mask 3 ... Wafer 4 ... Incident mark 5 ... Outgoing mark 7 ... Light receiving lens 8 ... Sensor 9 ... Signal processing circuit 10 ... Optical pickup 61 , 62 …… Emission beam

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-74815 (JP, A) JP-A-2-167412 (JP, A) JP-A-63-159705 (JP, A) JP-A-63-159705 184004 (JP, A)

Claims (1)

(57) [Claims] An apparatus for detecting a distance between a first object and a second object, comprising: light source means for emitting light in the direction of the first object or the second object; and a first light receiving surface; First, the light is deflected by the first object and the second object, is incident on the first light receiving surface, and changes in a certain direction in accordance with a change in the distance between the first object and the second object. A first detector for detecting a position of the light beam incident on the first light receiving surface; and a second light receiving surface, the second light receiving surface being emitted from the light source means and deflected by a first object and a second object. And the incident position on the second light receiving surface of the second light beam whose incident position changes in a direction opposite to the first light beam according to a change in the distance between the first object and the second object is detected. Based on the detection results of the first detection means and the second detection means, Means for measuring the distance between one object and the second object, wherein the detection performs an interval measurement that is not affected by a tilt change between the first object and the second object. apparatus.