JP2796347B2 - Projection exposure method and apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure method and an apparatus for projecting and exposing a mask pattern on a substrate to be exposed.

[Conventional technology]

In a conventional projection exposure apparatus for projecting and exposing a circuit pattern formed on a mask on a substrate to be exposed such as a semiconductor wafer,
The means for detecting the inclination of the substrate to be exposed is formed by directing the light emitted from the laser diode 2 shown in FIG. The two-dimensional position detector 20 irradiates the wafer 4 from above and detects the position of the reflected light.

A measuring device for measuring the distance (height) and inclination of a general object is not limited to an optical multi-layer structure object and is shown in FIG. 9 as a second known example in Japanese Patent Application Laid-Open No. Sho 62-218802. . In this known example, the light is incident perpendicularly with respect to the inclination, and is obtained by the second light receiver similarly to the first known example, and the distance (perpendicular to the surface of the DUT 6) is 60 ° by the first optical path 9 and the incident angle is 60 °. The spot irradiated at about で is imaged on the first detector, and is obtained from the imaged position.

[Problems to be solved by the invention]

The above-mentioned prior art discloses a pattern formed in a thin film structure on a wafer surface such as a semiconductor wafer, and a photoresist 1 formed thereon.
When applied to an object coated with a thickness of about 1 μm, the irradiation light not only reflects on the surface of the object to be measured, but also refracts and enters the inside of the layer structure, and the light reflected on the underlayer reappears on the surface again. , And is superimposed on the light reflected on the uppermost surface. At this time, the light reflected by the uppermost surface and the light reflected by the base surface interfere with each other, and the interference intensity greatly changes with a minute change in the thickness of the film and the incident angle of the irradiation light. When irradiating obliquely as in the distance detecting systems of FIGS. 8 and 9, as shown in FIG. 4, the distribution of reflected light from the measured object is different from the distribution at the time of incidence (eg, Gaussian distribution). In addition, the distribution varies depending on the layer structure of the object to be measured and the optical constants of the substances constituting the layer structure. As a result, an offset is generated in the measurement data every time the object to be measured is different, and it is difficult to accurately measure an absolute value. In addition, in the inclination detection of FIG. 9, irradiation is performed vertically,
If the inclination and height detection are applied to a semiconductor exposure apparatus or a semiconductor pattern inspection apparatus, the exposure optical system or the detection optical system and the irradiation optical system overlap, and the configuration of the optical system becomes difficult.

The occurrence of the measurement error due to the interference of the optical multilayer object described above becomes a serious problem particularly when the inclination and the height of the surface of the object to be measured are measured by the interference method. In the case of the interference method, the slope and phase of the wavefront of the reflected light are obtained from the interference fringes generated by the light reflected on the surface of the object and the reference light, and this represents the inclination and height of the object. But in the case of multi-layer structures,
As shown in FIG. 4, when the light is incident on the DUT at a normal incident angle of about 0 to 85 °, the light reflected on the surface of the multilayer structure object and between the respective layers inside the multilayer structure interferes, and the light immediately after the reflection of the DUT is reflected. The amplitude and phase greatly change depending on the thickness of each layer and the change depending on the location. As a result, an interference fringe obtained by superimposing the reference light does not have an accurate sine waveform, and a large error occurs.

An object of the present invention is to solve the above-mentioned conventional problems and to accurately measure at least one of the inclination and the height of a substrate to be exposed having a layer structure such as a semiconductor wafer, regardless of the structure or optical characteristics of the substrate to be exposed. It is an object of the present invention to provide a projection exposure method and apparatus capable of projecting and exposing a submicron fine pattern on a substrate to be exposed.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, there is provided an exposure optics for projecting a pattern formed on a mask by irradiating an exposure light onto a mask serving as an original image onto a substrate to be exposed. System means, irradiating means for irradiating irradiation light at an incident angle of 85 degrees or more at a position or near the place where the surface of the substrate to be exposed is projected and imaged, and the surface of the substrate to be exposed which is irradiated by the irradiation means Detecting means for detecting the reflected light reflected, calculating means for calculating the inclination and / or height of the substrate to be exposed based on the light reflected on the surface of the substrate to be detected detected by the detecting means; and And a correcting means for correcting the inclination and / or height of the substrate to be exposed based on the calculated result. Further, in the projection exposure method, irradiation is performed by irradiating irradiation light emitted from a light source different from the exposure light onto the surface of the substrate to be exposed at an angle of 85 ° or more with respect to the surface of the substrate to be exposed. The reflected light of the irradiation light reflected on the surface of the substrate is detected, the inclination and / or height of the substrate to be exposed is calculated based on the detected reflected light, and the inclination and / or of the substrate to be exposed is calculated based on the calculated result. A method of correcting the height and irradiating exposure light through a mask to the substrate to be exposed whose tilt and / or height has been corrected is adopted.

(Operation)

S-polarized light amplitude of light incident on the object to be measured, P-polarized light with respect to A _s, When A _p, the amplitude R _s of the light reflected and refracted at the surface of the object of the refractive index n, R _p and D _s, D _p is given by the following equation with respect to the incident angle θ and the refraction angle (sin = sin θ / n).

For S-polarized light, the angle of incidence is 0 ° to 60 °, and for P-polarized light, from 0 ° to 75 °, the transmitted light is larger than the surface reflected light,
Reflected light from the boundary of the underlying multilayer structure causes large-amplitude interference with the surface reflected light. When the angle of incidence is from the above value to about 85 °, the amplitude of the surface reflected light becomes larger, but this is an insufficient condition for performing accurate measurement. The reasons are as follows. Refraction angle light amplitude A which is incident at an incidence angle θ, as shown in FIG. 3, is refracted at an amplitude D, when reflected by the amplitude reflectance R _b at the base, the amplitude of the reflected light D · R _b
Becomes Here, assuming that the amplitude of the incident light A is 1, D becomes the amplitude transmittance. Thus the light reflected by the base passes through the surface amplitude becomes R _b D ^2. On the other hand, the light incident with the amplitude A (= 1) is reflected by the surface and the amplitude becomes R. Where R and D
R _s-polarized light of the incident light is in the S or P, D _s and R _p, when expressed by D _p (1) to (4) below is satisfied. Light reflected from the surface R ₀
Light R ₁ reflected by the underlying Unlike thin thickness d of the layer, the light of the complex amplitude A _R shown as a result in the following equation.

Here, λ is the wavelength of light used for measurement. It can be seen that the phase of A _R changes from even (5) with respect to a slight change in thickness d of the film shown in FIG. 3 (a change of one digit of a length of the wavelength). Therefore, the relationship between the incident angle θ and R and D is as shown in FIGS. 5 and 6 for the S and P polarized lights, respectively. To make it easier to understand from this graph, the first component of the equation (5) that becomes a noise component If the amplitude ratio R _b · D ² / R of the second term with respect to the term is obtained, the degree of error exerted on the measurement can be evaluated. Therefore, the worst case is considered when R _b = 1, and D ²
FIG. 7 shows the results obtained with respect to the incident angle θ and the two polarized lights. Since D ² / R is a noise (error) component in various detection methods, to keep this value at 5% or less
It turns out that the incident angle must be 85 ° or more. Also S
If the light is incident in the polarized state, the noise is further reduced. To keep the above value at 5% or less, as can be seen from FIG. It is required from.

The method of reflecting twice on the surface of the ratio measurement object improves the inclination and height detection sensitivity as described above, and enables highly accurate measurement.

In the detection by the interference method, the reflected light from the ground surface is superimposed on the interference pattern and disturbs the pitcher phase of the interference fringes. However, as described above, this effect is almost eliminated by incidence of 85 ° or more and further using S-polarized light. Becomes possible,
Highly accurate detection becomes possible. Further, by setting the optical path of the reference light used for the interference measurement to be substantially the same as the optical path of the measurement light, stable and high-precision measurement hardly affected by the measurement environment such as the fluctuation of air is realized.

When the above-described tilt and height measurement method is applied to a semiconductor exposure apparatus, there is no spatial interference with the exposure optical system, and the tilt and height of the exposed portion of the wafer can be detected with high precision as described above. Therefore, it is possible to control the tilt and height of the wafer from these detection values, precisely align the wafer surface with the exposure image forming surface, and print the submicron pattern accurately over the entire exposure area. It becomes possible.

〔Example〕

FIG. 1 shows an embodiment of the present invention. FIG. 1 detects the inclination of an exposure area of a wafer in an exposure state of a semiconductor exposure apparatus. 81 is an exposure illumination system, 9 is a reticle, 8 is a reduction exposure lens, and the pattern of the reticle 9 is exposed on the wafer 4. At this time, the surface of the photoresist applied to the wafer surface is not necessarily flat due to the undulation of the wafer, uneven thickness, the flatness of the wafer chuck, and the like. Therefore, the laser light emitted from one semiconductor laser is converted into a narrow parallel beam by the collimating lens 11, and is applied to the exposure area on the resist surface of the wafer via the mirror 13.
It is incident at an incident angle of ゜ or more. The reflected light is mirror 210,
The light is focused on the optical position detector 3 'by the focusing lens 20,
The light condensing position is detected. If the exposure area is inclined by α, the specularly reflected light is inclined by 2α, so that if the focal length of the condenser lens is f, the focal spot of the optical position detector is shifted by 2αf. Therefore, the detected signal is sent to the processing circuit 5 'to drive the tilt mechanism equipped with the wafer chuck, so that the photoresist surface on the wafer is controlled to coincide with the reticle pattern image surface. At this time, if the semiconductor laser is arranged so that the semiconductor laser emission light 161 'is incident on the wafer surface as S-polarized light, more accurate tilt detection can be performed as described above. In the embodiment shown in FIG. 1, the optical position detector 3 'is of a type that detects both the x and y directions, and one detection system can determine the inclination in two directions.

In FIG. 1, a second detection system is provided in a direction perpendicular to the paper, and x
And the inclination in the y direction may be separately detected. The light source is not limited to a semiconductor laser as long as it can irradiate the wafer with light having relatively high directivity.

FIG. 2 shows an embodiment of the present invention, and the same reference numerals as those in FIG. 1 denote the same components. The light emitted from the semiconductor laser 1 is incident angle
The light enters the wafer at an angle of 85 ° or more, and a light source image is formed in the exposure area on the wafer by the condenser lens 11 ′. The reflected light is condensed on the optical position detector 3 "by the mirror 210 and the lenses 21 and 22. If the wafer surface is at the resist pattern image forming position of the exposure optical system, the light is located at the center of the optical position detector 3". If it is shifted vertically, it will be shifted left and right from the center of the light position detector 3 ". Therefore, if the detection signal of the light position detector 3" is sent to the processing circuit 5 'and the drive of the wafer upper and lower tables is controlled, the correct focus is always obtained. It becomes possible. If the polarization of the laser beam is incident on the wafer surface as S-polarized light, the height of the photoresist surface can be determined more accurately.

FIG. 10 shows an embodiment of the present invention, and the same part numbers as those in FIG. 1 represent the same parts. The parallel light obtained by the collimator lens 11 passes through the beam splitter 19 'and is incident on the photoresist surface of the wafer at an incident angle of 85 ° or more, for example, 87 °. The specularly reflected light is incident on the plane mirror 14 almost perpendicularly, and the reflected light is specularly reflected again on the photoresist surface, reflected by the beam splitter 19 'and condensed on the light position detector 3' by the condensing lens 20, The position of the focused spot is detected. As shown in FIG.
When the polarization is set to 16 _s , D _s ² / R _s becomes as shown in FIG.
0.0065, that is, 0.65%, and the light 1621 almost entering the photoresist becomes negligible. Even if the underlayer is uneven as shown in FIG. 11, it is hardly affected at all, and it remains parallel light. Reflect specularly. Therefore, a sharp spot light having a high light condensing degree is obtained at the light position detector 3 '. Further, in this embodiment, as shown in FIG. 12, the light is vertically reflected by the plane mirror 14 and re-enters the wafer.
When the light is tilted by α, the light finally returning to the optical position detector is tilted by 4α, so that the light position can be detected with twice the sensitivity as compared with the embodiment of FIG. This results in S /
For both N and sensitivity, it is possible to detect a tilt which is much better than before.

FIG. 13 shows one embodiment of the present invention, and the same reference numerals as those in FIG. 2 denote the same components. The condensed beam obtained by the condensing lens 11 'is almost condensed at the irradiation position A on the wafer. Incident angle is 85
゜ or more. The specularly reflected light is collimated by the collimator lens 141 and is incident on the plane mirror 14 almost perpendicularly. The reflected light passes through almost the same optical path as the outward path, and is almost condensed on the wafer,
The light is reflected again, passes through the beam splitter 12, and is condensed.
The light is condensed on the light position detector 3 "by 22. In FIG. 14, the surface (reflection surface Σ) 4 of the wafer shown by a solid line is a dotted line 4 '.
The position of the focal point near the wafer when changing to (reflection surface Σ) is described. Consider the case where light is condensed at point A when the reflection surface is Σ for both the forward path and the return path. When the reflection surface is Σ ', the Σ' surface becomes a mirror surface, and point A on the outward path forms a mirror image at point A '. The light exiting from the point A 'is converged on the return path A "by the lens 141 plane mirror 14. At the condensing point, Σ' becomes a mirror surface and a mirror image of the point A 'is formed on A. Therefore, it is as if A were from the return path. The light is incident on the condensing lens 22 as the light exits from the light source, and the light is condensed on the light position detector 3 ″ at the image position of A. Assuming that the distance between Σ and Σ ′, that is, both the vertical movement of the wafer is Δh, AA ′ = AA ″ = 2Δh AA = AA ′ + A′A = 4Δh (6), and the position of the light emitting point on the return path is the displacement amount of the wafer. 4 times (4
Δh) shift (see FIG. 14). As a result, a displacement amount twice as large as that in the embodiment shown in Fig. 2 is detected by the optical position detector 3 ". As a result, height detection with high sensitivity and high S / N becomes possible.

FIG. 15 is a diagram showing an embodiment of the present invention. The same numbers as those in FIG. 1 represent the same items. The light emitted from the coherent light source 1 such as a laser is converted into parallel light 15 by the collimator lens 11 and enters the prism 10. Prism 10 separates incident light 15 into two parallel beams 16 and 17. The two parallel beams have a fixed angle θ ₀ −θ ₁ so as to overlap at zero point. One of the parallel beams 16 is incident on the wafer at an incident angle θ ₁ , and the other is a reference beam, which is θ _{0 with} respect to a vertical line set on the wafer.
It proceeds without irradiating the wafer at an angle of (> 90 °). The parallel beam 16 reflected by the wafer is incident on the plane mirror 14 almost perpendicularly, re-enters the wafer, traces the outward path in reverse, is reflected by the beam splitter 12, becomes a parallel beam after passing through the lenses 21 and 22, and becomes a one-dimensional sensor. 3 is incident. On the other hand, the reference light directly enters the plane mirror 14 from the point 0 almost perpendicularly, follows the outward path after reflection, and also enters the one-dimensional sensor 3 to generate interference fringes with one of the beams reflected by the wafer. I do. The pinhole 23 and the wedge glass 26 are arranged on the return path of the light reflected by the wafer. Pinhole 23 is also in the reference optical path,
It plays a role in removing noise light reflected on the back surface of the optical component. On the other hand, the wedge glass 26 refracts the light reflected by the wafer to form an image of the wafer irradiation position on the one-dimensional sensor and overlaps with the reference light.
On the one-dimensional sensor, an interference fringe having an intensity as shown by a solid line in FIG. 16 with respect to the sensor array direction X is detected. When the wafer is tilted by Δθ around the wafer irradiation position (X = 0) as shown by the dotted line, the detected interference fringe becomes as shown by the dotted line in FIG. That is, although the intensity at X = 0 hardly changes, it changes from the stripe pitch P to P ′. That is, the relationship between the pitch P and the inclination Δθ is obtained from the equation (8) from the equation (7) because the interference fringe intensity I (X) is given by the equation (7).

In the above equation (7), M is the magnification at which the irradiation position on the wafer is imaged on the one-dimensional sensor, but it is assumed that the wedge angle of the wedge glass is 0 degree for simplicity (there is no wedge glass). Case).

The second term in cosine of equation (7) is that the wafer surface is ΔZ
This indicates the change of the interference fringe when it changes, and as shown in FIG. 17, when the wafer surface changes by Δz, the pitch of the interference fringe does not change and the phase shifts. Therefore, in the present embodiment, the interference fringes obtained by the one-dimensional sensor 3 are sent to the processing circuit 5, where the pitch and phase of the interference fringes are obtained, whereby the height and inclination of the wafer surface can be obtained simultaneously. Also in this embodiment it is also possible to take the incident angle theta ₁ to 87-89 degrees, S
If polarized light is used as the irradiation light, the inclination and the height can be accurately obtained without being affected by the underlying multilayer structure, as is clear from FIG. Further, in this embodiment, the reference light passes through almost the same optical path as the wafer irradiation light, and the optical components used are all common except for the reflection on the wafer surface, so that they are hardly affected by air fluctuations and the like. Stable measurement can be realized.

〔The invention's effect〕

As described above, according to the present invention, it is possible to accurately measure the inclination or height of an optical multilayer object such as a wafer having various multilayer structures in a semiconductor circuit manufacturing process without being affected by the multilayer structure. , It is possible to accurately execute the tilt control for focusing and alignment of the wafer surface to the image forming surface in the semiconductor exposure apparatus, 0.8 μm or less,
In particular, a high NA _i- line reduction exposure apparatus used for exposure of a line width circuit pattern of less than 0.5 μm or less, accompanied by a shallow depth of focus expected to occur in an excimer laser reduction exposure apparatus,
It has a very remarkable effect on the reduction of the exposure focus margin.

[Brief description of the drawings]

1 and 2 are each a device configuration diagram showing an embodiment of the present invention, FIG. 3 is a diagram for explaining the principle of the present invention, FIG. 4 is a diagram for explaining a conventional problem, and FIG. FIG. 7 to FIG. 7 are characteristic diagrams for explaining the principle and effect of the present invention, FIG. 8 and FIG. 9 are diagrams for explaining the prior art, and FIG. 10 is a configuration diagram showing another embodiment of the present invention. , FIGS. 11 and 12 are views for explaining the embodiment of FIG. 10, FIG. 13 is a block diagram showing another embodiment of the present invention, and FIG. FIG. 15 is a diagram for explaining the embodiment, FIG. 15 is a configuration diagram showing still another embodiment of the present invention, and FIGS. 16 and 17 are diagrams for explaining the embodiment shown in FIG. . 1 ... light source, 11 ... collimating lens, 11 '... condensing lens, 20 ... condensing lens, 21, 22, ... lens, 13, 14, 210
… Mirror, 16, 19… half mirror, 3… one-dimensional sensor, 3 ′, 3 ″… optical position detector, 4… wafer, 5,
5 'processing circuit, 7 stage, 8 reduction exposure lens, 81 illumination system, 9 reticle.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-113706 (JP, A) JP-A-56-101112 (JP, A) JP-A-60-136311 (JP, A) JP-A-62 140419 (JP, A) JP-A-61-74338 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 21/027 G03F 9/00 G01B 11/26 G01B 11/02

Claims (11)

(57) [Claims] An irradiation light emitted from a light source different from the exposure light onto the surface of the substrate to be exposed is irradiated onto the surface of the substrate to be exposed at an angle of 85 ° or more, and the substrate is exposed by the irradiation. Detecting the reflected light of the irradiation light reflected on the surface of,
The inclination and / or height of the substrate to be exposed is calculated based on the detected reflected light, and the inclination and / or height of the substrate to be exposed is corrected based on the calculated result, and the inclination and / or height is calculated. A projection exposure method, comprising irradiating the corrected exposure substrate with exposure light via a mask. 2. The irradiation light emitted from a light source different from the exposure light is S-polarized on the surface of the substrate to be exposed, and the S-polarized irradiation light is incident on the surface of the substrate at an angle of 82 degrees or more. Irradiating, detecting the reflected light of the irradiating light reflected on the surface of the substrate to be exposed by the irradiation, calculating the inclination and or height of the substrate to be exposed based on the detected reflected light, A projection exposure method comprising: correcting the tilt and / or height of the substrate to be exposed based on the calculated result; and irradiating the substrate with corrected tilt and / or height with exposure light through a mask. Method. 3. A radiation light emitted from different light sources and exposure light exposed substrate surface, wherein the D ² / R when the amplitude of the illumination light reflected and refracted at the exposed substrate surface and R and D 0.
05 and below, the incident light is irradiated to the surface of the substrate to be exposed and irradiated, and the reflected light of the irradiation light reflected by the surface of the substrate to be exposed by the irradiation is detected, and based on the detected reflected light, Calculating the inclination and / or height of the substrate to be exposed, correcting the inclination and / or height of the substrate to be exposed based on the calculated result, and correcting the inclination and / or height to the substrate to be exposed. A projection exposure method, comprising irradiating exposure light through a mask. 4. Exposing a pattern having a width of 0.5 μm or less on the substrate to be exposed by irradiating the substrate with the corrected inclination and / or height with exposure light through the mask. The projection exposure method according to claim 1, wherein: 5. The method according to claim 5, wherein the reflected light is incident on the surface of the substrate to be exposed again, the reflected light of the reflected light due to the incident light is detected, and the substrate to be exposed is detected based on the detected reflected light of the reflected light. 5. The projection exposure method according to claim 4, wherein the inclination and / or height of the projection exposure is calculated. 6. An exposure optical system means for irradiating exposure light onto a mask serving as an original image to project a pattern formed on the mask onto a substrate to be exposed to form an image, and Irradiation means for irradiating irradiation light at an incident angle of 85 degrees or more at or near a position where the image is projected and formed, and detection means for detecting reflected light irradiated by the irradiation means and reflected on the surface of the substrate to be exposed Calculating means for calculating the inclination and / or height of the substrate to be exposed based on the light reflected by the surface of the substrate to be detected detected by the detecting means; and calculating the tilt based on the result calculated by the calculating means. A projection exposure apparatus comprising: a correction unit configured to correct a tilt and / or a height of an exposure substrate. 7. An exposure optical system means for irradiating exposure light to a mask serving as an original image to project a pattern formed on the mask onto a substrate to be exposed to form an image, and Irradiation means for irradiating S-polarized irradiation light at an incident angle of 82 degrees or more at or near the position where the image is projected and formed, and detecting reflected light irradiated by the irradiation means and reflected on the surface of the substrate to be exposed Detecting means to calculate the inclination and / or height of the substrate to be exposed based on the light reflected on the surface of the substrate to be detected detected by the detecting means; and And a correcting means for correcting the inclination and / or height of the substrate to be exposed. 8. An exposure optical system means for irradiating exposure light onto a mask serving as an original image to project a pattern formed on the mask onto a substrate to be exposed to form an image, and The amplitude of the irradiation light reflected and refracted on the substrate surface at or near the position where the image is projected and formed is represented by R and D.
Irradiating means for irradiating the surface of the substrate by irradiating the substrate so that D ² / R is 0.05 or less, and detecting the reflected light irradiated by the irradiating means and reflected on the surface of the substrate to be exposed Detecting means, calculating means for calculating the inclination and / or height of the substrate to be exposed based on the light reflected on the surface of the substrate to be detected detected by the detecting means, and based on the result calculated by the calculating means. A projection exposure apparatus comprising: a correction unit configured to correct a tilt and / or a height of the substrate to be exposed. 9. By irradiating exposure light to the substrate whose inclination and / or height has been corrected through the mask,
9. The projection exposure apparatus according to claim 6, wherein a pattern having a width of 0.5 [mu] m or less is exposed on the substrate. 10. The irradiating means irradiates parallel light onto the substrate surface, and calculates the inclination of the substrate to be exposed by the calculating means based on the reflected light of the parallel light detected by the detecting means. The projection exposure apparatus according to claim 9, wherein: 11. The irradiating means irradiates a focused light onto the substrate surface, and calculates the height of the substrate to be exposed by the calculating means based on the reflected light of the focused light detected by the detecting means. The projection exposure apparatus according to claim 9, wherein: