JPH116714A - Method for detecting height of sample surface and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure the height of an object by obliquely irradiating the surface of a measured object with light having relatively higher directivity so that the angle of incidence of the main light beam thereof exceeds a specified value. SOLUTION: Light emitted from a semiconductor laser 1 is admitted into a wafer 4 at an angle of incidence of 85 deg. or the more to form an image of a light source with a condenser lens 11' within an exposure area on the wafer. The reflected light is condensed onto a light position detector 3" by a mirror 210 and lenses 21 and 22. When the surface of the wafer is at a resist pattern imaging position in an exposure optical system, the light stays at the center of the light position detector 3", when it deviates vertically, it shifts horizontally from the center of the light position detector 3", and a detection signal of the light position detector 3" is sent to a processing circuit 5 to allow accurately focusing constantly by driving and controlling upper/lower wafer moving tables. When it is so arranged that the polarized light of a laser light is admitted into the surface of the wafer by S polarization, the height of the surface of a photoresist can be accurately determined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for optically detecting the height of a sample surface.

[0002]

2. Description of the Related Art A conventional device for detecting the inclination of a surface of a semiconductor wafer or the like is disclosed in Japanese Patent Application Laid-Open No. 61-170605, which is a first known example, in which light emitted from a laser diode 2 shown in FIG. The directional beam is applied to the wafer 4 from above, and the reflected light is detected by the two-dimensional position detector 20.

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

[0004]

The above prior art is applied to a pattern formed in a thin film structure on a wafer surface such as a semiconductor wafer, or a pattern in which a photoresist is applied thereon with a thickness of 1 to several μm. Irradiation light is not only reflected on the surface of the object to be measured, but also refracted and enters the inside of the layer structure, and the light reflected on the underlayer passes through the surface again and is superimposed on the light reflected on the top surface described above. Is done. 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 film thickness and the incident angle of the irradiation light. When the light is obliquely irradiated as in the systems for detecting the distance in FIGS. 8 and 9, the distribution of the reflected light from the object to be measured is different from the distribution at the time of incidence (for example, Gaussian distribution) as shown in FIG.
In addition, the distribution varies depending on the layer structure of the object to be measured and the optical constants of the materials 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, the irradiation is performed vertically, but if the inclination and height detection are applied to a semiconductor exposure apparatus or a semiconductor pattern inspection apparatus, the exposure optical system and the detection optical system overlap with the irradiation optical system, The configuration of the optical system becomes difficult.

[0005] The occurrence of measurement errors due to the interference of the optical multilayer object described above becomes a serious problem particularly when measuring the inclination or height of the surface of the object to be 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. However, in the case of a multi-layered structure, as shown in FIG. 4, when the light is incident on the measured object at a normal incident angle of about 0 to 85 °, the light reflected between the surfaces of the multi-layered structure and between the layers inside the multi-layered structure interferes. The amplitude and phase of light immediately after the reflection of an object greatly changes 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,
It is an object of the present invention to provide a method and apparatus for detecting the height of a sample surface, which can accurately measure the height of an object such as a semiconductor wafer regardless of the structure and optical characteristics of the object to be measured.

Another object of the present invention is to make it easy to mount the apparatus on an exposure apparatus or an inspection apparatus.

[0008]

In order to achieve the above object, in the present invention, light having a relatively high directivity is applied to the surface of an object to be measured so that an incident angle of a principal ray of the light is 85 ° or more. Irradiate diagonally. When the incident angle is 85 ° or more, the ratio of the amplitude of the reflected light to the amplitude of the incident light becomes smaller as shown in FIGS. 5 and 6, most of the light is reflected on the surface, and the light entering the interior becomes slightly. Further, when the amplitude of the irradiated light is S-polarized, the reflection on the surface is further increased, and the incident angle of the principal ray may be 82 ° or more.

The direction of the regular reflection of the irradiation light incident on the object to be measured is 2α with respect to the inclination α of the object to be measured. When the specularly reflected light is reflected almost vertically, returned to the original optical path, and made incident again on the device under test, the specularly reflected light becomes 4α as shown in FIG. That is, an inclination four times the inclination of the object to be measured occurs in the specularly reflected light.

Further, in the present invention, when interference is used as a method for detecting the inclination or height, the amplitude and phase of the specularly reflected light are increased by increasing the reflection on the surface, as opposed to the conventional problem using the above-described interference method. It almost represents the surface information, and is not affected by the thickness of the inner layer or the pattern step.

The amplitude of light incident on the object to be measured is S-polarized light,
Assuming that AS and AP are P-polarized light, the amplitudes RS and RP and DS and DP of the light reflected and refracted on the surface of the object having the refractive index n are: incident angle θ and refraction angle ψ (sinψ = sin θ / n) It is given by the following equation.

[0012]

(Equation 1)

[0013]

(Equation 2)

[0014]

(Equation 3)

[0015]

(Equation 4)

For S-polarized light, the transmitted light is larger than the surface reflected light from 0 ° to 60 ° for the incident angle of 0 ° to 75 ° for P-polarized light, and the surface reflected light is larger than the reflected light from the boundary of the underlying multilayer structure. Interference with light having large amplitude occurs. When the incident angle 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.

As shown in FIG. 3, light having an amplitude A incident at an incident angle θ is refracted at a refraction angle ψ and an amplitude D, and is reflected at a base with an amplitude reflectance Rb, the amplitude of the reflected light becomes D · Rb. Become.
Here, assuming that the amplitude of the incident light A is 1, D becomes the amplitude transmittance. Therefore, when the light reflected by the base passes through the surface, its amplitude becomes Rb · D ² . On the other hand, the light incident with the amplitude A (= 1) is reflected by the surface and the amplitude becomes R. Here, R and D are expressed by RS, DS and RP, DP depending on whether the polarization of the incident light is S or P, and the above (Equation 1) to (Equation 4) hold. The light R0 reflected by the surface and the light R1 reflected by the base overlap when the thickness d of the layer is small, resulting in light having a complex amplitude AR represented by the following equation.

[0018]

(Equation 5)

Here, λ is the wavelength of light used for measurement.

It can be seen from FIG. 3 that even if the thickness d of the film shown in FIG. 3 changes slightly (change in the length one order of magnitude below the wavelength), the phase of AR changes from (Equation 5). Therefore, the relationship between the incident angle θ and R and D is as shown in FIG. 5 and FIG. 6 for S and P polarized light, respectively. By obtaining the amplitude ratio Rb · D ² / R of the second term, it is possible to evaluate the degree of an error exerted on the measurement. So, in the worst case, Rb =
Considering the case of 1, the ratio D ² / R to the incident angle θ, and 2
FIG. 7 shows the results obtained for two polarized lights. Since D ² / R is a noise (error) component in various detection methods, it can be seen that in order to keep this value at 5% or less, the incident angle must be 85 ° or more. If the light is incident in the S-polarized state, the noise is further reduced.
As can be seen from (Equation 1) and (Equation 2), it is sufficient that the angle should be 82 ° or more.

The method of reflecting twice on the surface of the object to be measured 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 pitch and phase of the interference fringes. The influence can be eliminated, and highly accurate detection can be performed. 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 measuring method is applied to a semiconductor exposure apparatus, there is no spatial interference with the exposure optical system, and
Moreover, since the tilt and height of the exposed portion of the wafer can be detected with high accuracy as described above, the tilt and height of the wafer are controlled based on the detected values, and the surface of the wafer is formed on the exposure image forming surface. The submicron pattern can be precisely printed over the entire exposure area.

[0024]

FIG. 1 shows an embodiment of the present invention. FIG. 1 is for detecting 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,
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 incident on the resist surface of the wafer and at an exposure angle of 85 ° or more via the mirror 13. The reflected light is condensed on the light position detector 3 'by the mirror 210 and the condensing lens 20, and the 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 becomes possible as described above. In the embodiment of 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 may be provided in a direction perpendicular to the plane of the drawing to separately detect inclinations in the x and y directions. 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. The same reference numerals as those in FIG. 1 denote the same parts. The light emitted from the semiconductor laser 1 is incident on the wafer at an incident 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 collected 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, it is shifted to the center of the optical position detector 3 ''. By sending the detection signal 3 '' to the processing circuit 5 'and controlling the drive of the wafer upper and lower tables, correct focusing can always be performed. 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 reference numerals as those in FIG. 1 denote the same parts. The parallel light obtained by the collimator lens 11 is converted into a beam splitter 19 '.
And incident on the photoresist surface of the wafer at an incident angle of 85 ° or more, for example, 87 °. The specularly reflected light is a plane mirror 14
, And the reflected light is specularly reflected again at the photoresist surface, reflected by the beam splitter 19 ′, and condensed on the optical position detector 3 ′ by the condenser lens 20, and the position of the condensed spot is detected. Is done. When the incident angle on the wafer is 87 ° and the S-polarized light is 16S as shown in FIG. 11, DS2 / RS is 0.0065, that is, 0.6 as shown in FIG.
5%, light 162 almost entering the photoresist
1 becomes negligible, and although the underlying layer is uneven as shown in FIG. 11, the influence is hardly affected at all, and the light is specularly reflected as parallel light. 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. Therefore, when the wafer is tilted from 4 to 4 'by .alpha., The light finally returning to the optical position detector Is inclined by 4α, and the light position can be detected with twice the sensitivity as compared with the embodiment of FIG. As a result, it is possible to detect a tilt which is very excellent in both S / N and sensitivity as compared with the related art.

FIG. 13 shows an embodiment of the present invention. The same reference numerals as those in FIG. 2 denote the same parts. The condensed beam obtained by the condensing lens 11 'is almost condensed at the irradiation position A on the wafer. The incident angle is 85 ° or more. The specularly reflected light is collimated by the collimating lens 141 and is incident on the plane mirror 14 almost perpendicularly. The reflected light passes through substantially the same optical path as the outward path, is substantially condensed on the wafer, is reflected again, passes through the beam splitter 12, and is condensed on the optical position detector 3 '' by the condensing lens 22. FIG. 14 illustrates the position of the condensing point near the wafer when the surface (reflection surface Σ) 4 of the wafer indicated by the solid line changes to the dotted line 4 ′ (reflection surface Σ). 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 emitted from the point A 'is condensed on the return path A''by the lens 141 plane mirror 14. This condensing point becomes a mirror surface of Σ ′ and forms a mirror image of the A ″ point at A ′ ″. Accordingly, from the return path, the light enters the condenser lens 22 as if the light exits from A '''', and the light is focused on the image position of A '''' on the light position detector 3 ''. If the distance between Σ and Σ ', that is, the amount of vertical movement of the wafer is Δh,

[0030]

(Equation 6)

Then, the light emitting point position on the return path is shifted by four times (4Δh) the displacement amount of the wafer (see FIG. 14). As a result, a displacement amount twice as large as that in the embodiment of 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. FIG.
The same numbers indicate the same items. 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 θ0−θ1 so as to overlap at zero point. One of the parallel beams 16 is incident on the wafer at an incident angle θ1, and the other is reference light, which travels without irradiating the wafer at an angle of θ0 (> 90 °) with respect to a perpendicular to the wafer.

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,
After passing through and, it becomes a parallel beam and enters the one-dimensional sensor 3. On the other hand, the reference light directly enters the plane mirror 14 almost perpendicularly from the point 0, follows the reverse path after reflection, and also enters the one-dimensional sensor 3 to generate an interference fringe with one of the beams reflected by the wafer. I do.

A pinhole 23 and a wedge glass 26 are arranged on the return path of the light reflected by the wafer. The pinhole 23 is also in the reference optical path and plays a role of removing noise light reflected on the back surface of the optical component. Wedge glass 2
Numeral 6 refracts the light reflected from 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 in the sensor array direction X is detected. Wafer irradiation position (X
= 0), and the wafer is inclined by Δθ as shown by the dotted line, the detected interference fringes become 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 slope Δθ is given by the following equation (7), where the intensity I (X) of the interference fringes is given by:
From this equation, it is obtained by (Equation 8).

[0035]

(Equation 7)

[0036]

(Equation 8)

In the above (Equation 7), M is the magnification at which the irradiation position on the wafer is imaged on the one-dimensional sensor. For the sake of simplicity, it is assumed that the wedge angle of the wedge glass is 0 ° (wedge). Without glass).

The second term in cosine of (Equation 7) represents a change in interference fringes when the wafer surface changes by ΔZ.
As shown in FIG. 17, when the wafer surface changes by .DELTA.Z, the pitch of the interference fringes 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 interference fringe pitch and phase can be obtained.
The height and inclination of the wafer surface are determined simultaneously.
Further, in this embodiment, the incident angle θ1 can be set to 87 to 89 degrees, and if S-polarized light is used for the irradiation light, as is apparent from FIG. The height can be determined accurately. 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 also common except for the reflection on the wafer surface, so that they are hardly affected by air fluctuations and the like. A stable measurement can be realized.

[0039]

As described above, according to the present invention, the inclination or height of an optical multilayer object such as a wafer having various multilayer structures in a semiconductor circuit manufacturing process can be accurately measured without being affected by the multilayer structure. It is possible to accurately execute the focus control in the semiconductor exposure apparatus and the tilt control for adjusting the wafer surface to the image forming surface,
A high NAi line reduction exposure apparatus used for exposure of a line width circuit pattern of 0.8 μm or less, especially around 0.5 μm or less,
In response to the decrease in exposure focus margin due to the shallow depth of focus expected to occur in excimer laser reduction exposure equipment,
It has a very remarkable effect.

[Brief description of the drawings]

FIG. 1 is an apparatus configuration diagram showing one embodiment of the present invention.

FIGS. 2A and 2B are device configuration diagrams each 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 illustrating a conventional problem.

FIG. 5 is a characteristic diagram illustrating the principle and effect of the present invention.

FIG. 6 is a characteristic diagram illustrating the principle and effect of the present invention.

FIG. 7 is a characteristic diagram illustrating the principle and effect of the present invention.

FIG. 8 is a diagram for explaining a conventional technique.

FIG. 9 is a diagram for explaining a conventional technique.

FIG. 10 is a configuration diagram showing another embodiment of the present invention.

FIG. 11 is a view for explaining the embodiment in FIG. 10;

FIG. 12 is a view for explaining the embodiment in FIG. 10;

FIG. 13 is a configuration diagram showing still another embodiment of the present invention.

FIG. 14 is a view for explaining the embodiment shown in FIG. 13;

FIG. 15 is a configuration diagram showing still another embodiment of the present invention.

FIG. 16 is a view for explaining the embodiment shown in FIG. 14;

FIG. 17 is a view for explaining the embodiment shown in FIG. 14;

[Explanation of symbols]

1: light source, 11: collimating lens, 1
1 ': condenser lens, 20: condenser 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, 9: reticle.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI G03F 9/02 G03F 9/02 H01L 21/66 H01L 21/66 P

Claims (13)

[Claims] 1. The method according to claim 1, wherein the surface of the sample is 8
Light is irradiated at an incident angle of 5 degrees or more, an image of the sample surface at the position where the light is irradiated is formed on a detector, and the formed image of the sample surface is detected by the detector. Detecting the height of the sample surface based on the detected image of the sample surface. 2. The surface of the sample has a height of 8
Irradiating light at an incident angle of 5 degrees or more, collecting reflected light from the surface due to the irradiation on a detector, detecting the collected reflected light with the detector, and detecting the detected reflected light Detecting the height of the sample surface based on the following formula: 3. The method according to claim 1, wherein the light applied to the surface of the sample is a laser beam. 4. A sample surface is irradiated with S-polarized light at an incident angle of not less than 82 degrees with respect to a normal direction of the surface, and an image of the sample surface at a position where the light is irradiated is detected by a detector. A sample, wherein the image of the sample surface formed on the sample is detected by the detector, and the height of the sample surface is detected based on the detected image of the sample surface. Surface height detection method. 5. The surface of the sample has a height of 8 with respect to the normal direction of the surface.
Irradiating S-polarized light at an incident angle of 2 degrees or more, collecting reflected light from the surface due to the irradiation on a detector, detecting the collected reflected light with the detector, A method for detecting the height of the sample surface, comprising detecting the height of the sample surface based on the detected reflected light. 6. A place on the sample surface where the light is irradiated,
The method for detecting the height of a sample surface according to any one of claims 1, 2, 4, and 5, wherein the method is made of a material transparent to the light. 7. A mounting means for mounting a sample, and an irradiating means for irradiating a surface of the sample mounted on the mounting means with light at an incident angle of 85 degrees or more with respect to a normal direction of the surface. Detecting means for detecting an image of the sample surface at a position irradiated with light by the irradiating means; and calculating a surface height based on a signal of the image detected by the detecting means. Means for detecting the height of the sample surface. 8. A mounting means for mounting a sample, and irradiating means for irradiating a surface of the sample mounted on the mounting means with light at an incident angle of 85 degrees or more with respect to a normal direction of the surface. A light collecting means for collecting reflected light of light illuminated on the surface of the sample by the irradiation means; a detecting means for detecting the reflected light collected by the light collecting means; and a detecting means for detecting the reflected light. Surface height calculating means for calculating the height of the sample surface based on the signal of the reflected light. 9. The height of the sample surface according to claim 7, wherein the irradiating means has a laser light source unit, and irradiates the sample surface with laser light emitted from the laser light source unit. Detection device. 10. A mounting means for mounting a sample, and a surface of the sample mounted on the mounting means, the surface of which is 82 mm normal to the surface.
Irradiating means for irradiating S-polarized light at an incident angle of not less than degrees, a detecting means for detecting an image of the sample surface at a position irradiated with light by the irradiating means, and an image of the image detected by the detecting means. And a surface height calculating means for calculating the height of the sample surface based on the signal. 11. A mounting means for mounting a sample, and a surface of the sample mounted on the mounting means, the surface of which is 82 mm normal to the surface.
Irradiating means for irradiating S-deflected light at an incident angle of not less than degree, condensing means for condensing reflected light of the light irradiated on the surface of the sample by the irradiating means, and condensing light by the condensing means A detecting means for detecting the detected reflected light, and a surface height calculating means for calculating a height of the sample surface based on a signal of the reflected light detected by the detecting means. Surface height detector. 12. The apparatus according to claim 7, wherein said detecting means has an image detector for detecting an image.
2. The apparatus for detecting the height of a sample surface according to any one of 1 to 1 above. 13. The apparatus according to claim 12, wherein said image detector is a one-dimensional sensor.