JPH02280313A - Detection of inclination or height of optical multiplier object, device therefor and projection aligner - Google Patents

Abstract

PURPOSE:To measure an inclination or a height of an object to be measured by irradiating irradiation light to the object at an incident angle of 85 deg. or more and by detecting information of reflected light. CONSTITUTION:A pattern of reticule 9 is expressed on a wafer 4 through a reduction exposure lens 8 by an exposure illumination system 81. A plane surface is not always acquired because of waviness of a wafer with a photoresist surface which is applied to a surface of the wafer 4, irregularities in thickness, flatness of a wafer chuck, etc. Laser light which is projected from a semiconductor laser 1 is injected through a collimator lens 11 and a mirror 13 into an aligning region of a resist surface of the wafer 4 at an incident angle of 85 deg. or more. Reflected light is converged on an optical position detector 3' by a mirror 210 and a condenser lens 20, and a condensing position is detected. A detected signal is sent to a treatment circuit 5', a tilt mechanism whereon a wafer chuck is mounted is driven, and a photoresist surface on the wafer is controlled to match a reticule pattern image surface.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method and apparatus for optically detecting the inclination or height of an optical multilayer object such as a wafer, and further relates to a projection apparatus using this method and apparatus. Related to exposure equipment.

[Conventional technology]

A conventional inclination detection device for an optical multilayer structure object such as a semiconductor wafer uses a lens 14 to detect light emitted from a laser diode 2 shown in FIG. The beam becomes directional and the wafer 4
The beam is irradiated from above, and the position of the reflected light is detected by a two-dimensional position detector 20.

Furthermore, the distance (height) and inclination measuring device for general objects, not limited to optical multilayer structure objects, is shown in the second known example, JP-A-62-218802, shown in Fig. 9. . In this known example, the inclination is perpendicular, and the first
The distance #it (in the direction perpendicular to the object to be measured 6) is determined by the second light receiver as in the known example of An image is formed on the device and determined from the position of the image.

[Problem to be solved by the invention]

The above conventional technology uses a pattern formed in a thin film structure on the surface of a wafer such as a semiconductor wafer, or a photoresist layer formed on the pattern.
When applied to a coating with a thickness of ~ several μm, the irradiated light not only reflects on the surface of the object to be measured, but also refracts and enters the layered structure, and the light reflected from the base layer becomes 11 ) and the surface, and is superimposed on the light reflected at the top surface of -1-. At this time, the light reflected from the underlying surface interferes with each other, and the interference intensity changes greatly with minute changes in the thickness of the film and the angle of incidence of the irradiated light. When irradiating from an oblique direction as in the distance detection systems shown in Figures 8 and 9, the distribution of reflected light from the object to be measured differs from the distribution at the time of incidence (e.g. Gaussian distribution), as shown in Figure 4. Furthermore, the distribution differs depending on the layer structure of the object to be measured and the optical constants of the substances that make up the object.

As a result, an offset occurs in the measurement data each time the object to be measured changes, making it difficult to accurately determine the absolute value Mi11.

In addition, in the tilt detection shown in Figure 9, the irradiation is performed vertically, but when trying to apply tilt and height detection to semiconductor exposure equipment or semiconductor pattern inspection equipment, the exposure optical system, detection optical system, and irradiation optical system overlap. , the configuration of the optical system becomes difficult.

The occurrence of measurement errors due to the interference of the optical multilayer object described above becomes a significant problem, especially when measuring the inclination or height of the surface of the object to be measured using the interference method. In the case of the interference method, the inclination and phase of the wavefront of the reflected light are determined from the interference fringes generated by the light reflected from the surface of the object to be measured and the reference light, and this represents the inclination and height of the object to be measured. However, in the case of a multilayer structure, when the light is incident on the object to be measured at a normal incident angle of about 0 to 85'', as shown in Figure 4, the light reflected from the surface of the multilayer structure object and between each layer inside the object interferes. The amplitude and phase of the light immediately after it is reflected from the measurement object changes greatly depending on the thickness of each layer and its location.As a result, the interference fringes obtained by superimposing the reference light do not have an accurate sine waveform, resulting in large errors. Resulting in.

An object of the present invention is to solve the above-mentioned conventional problems, and to be able to accurately measure at least one of the inclination and height of an object made of a semiconductor wafer homolayer structure, regardless of the structure and optical characteristics of the object to be measured. An object of the present invention is to provide a method and apparatus for detecting the inclination or height of an optical multilayer object.

Another object of the present invention is to facilitate implementation in an exposure device or an inspection device.

[Means to solve the problem]

In order to achieve the above object, in the present invention, relatively highly directional light is emitted obliquely onto the surface of an object to be measured having a multilayer structure such as a wafer so that the incident angle of the principal ray is 85@ or more. irradiate. When the angle of incidence is 85° or more, the ratio of the amplitude of the reflected light to the amplitude of the incident light becomes small, as shown in Figures 5 and 6, and most of the light is reflected from the surface, and only a small amount of light enters the interior. It becomes slight. Furthermore, when the amplitude of the irradiated light is made S-polarized, the reflection on the surface becomes even greater.

The direction of specular 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 this specularly reflected light is reflected almost perpendicularly, returned to the original optical path, and incident on the object to be measured again, the specularly reflected light becomes 4α as shown in FIG. In other words, the specularly reflected light has an inclination that is four times the inclination of the object to be measured.

When using interference, the problem with conventional interferometry described above is that by increasing the reflection at the surface, the amplitude and phase of the specularly reflected light mostly represent surface information, and the thickness of the internal layer It is no longer affected by the sheath pattern step.

[For production]

Covered! I What is the amplitude of light incident on a constant object as ΔS for S-polarized light and P-polarized light? Let AP be the amplitude RSt Rp of light reflected and refracted on the surface of an object with refractive index n and 1) s, l
)P is the angle of incidence θ, and the angle of refraction is p(sinp=sinθ/n
) is given by the following formula.

From 0'' to about 75 degrees, the transmitted light is larger than the surface reflected light, and the reflected light from the boundary of the underlying multilayer structure causes interference with a large amplitude with the surface reflected light. The amplitude of the surface reflected light becomes larger up to about 85 degrees from the value, but this is an insufficient condition to carry out accurate jl estimation.The reason for this is shown below.As shown in Figure 3. Light with an amplitude A that is incident at an incident angle O is refracted at a refraction angle f and an amplitude equal to the amplitude, and is reflected by the substrate with an amplitude reflectance R4, and the amplitude of this reflected light becomes D-Rb.Here, the amplitude of the incident light A is ] is the amplitude transmittance. Therefore, when the light reflected from the base passes through the surface, its amplitude becomes Rt,D''.On the other hand, the light incident with amplitude A (=1) is reflected by the surface. Its amplitude is R. Here, R and ■) are I<s, Ds and 1 depending on whether the polarization of the incident light is S or P.

1] If expressed as P, the above equations (1) to (4) hold true. The light Rn reflected on the surface and the light R1 reflected on the F ground overlap when the H width d of the layer is small, resulting in light having a complex amplitude AR expressed by the following equation.

For S-polarized light, the incident angle is O'' to 60''. For P-polarized light, the following is a blank space, where λ is the wavelength of the light used for measurement. It can be seen from equation (5) that the phase of the AR changes even with a slight change in the film thickness d (a change in length one digit below the wavelength) shown in FIG. Therefore, the relationship between the incident angle θ and R and D is as shown in Figs. 5 and 6 for S and P polarized light, respectively, and to make it easier to understand from this graph, it becomes a noise component (
5) Amplitude ratio Rh-D2/R of the second term to the first term of the equation
By determining , it is possible to evaluate the degree of error that will affect the measurement.

Therefore, consider the case where R1=1 as the worst case, and D”
FIG. 7 shows /R determined for the incident angle θ and for the two polarized lights. I) Since 2/R becomes a noise (error) component in various detection methods, it can be seen that in order to keep this value below 5%, it is necessary to set the incident angle to 85" or more. Also, the S polarization state It can be seen from FIG. 7 that the noise becomes even smaller if the light is incident at .

As described above, the method of reflecting the light twice on the surface of the object to be measured improves the detection sensitivity of the inclination and height, and enables highly accurate measurement.

In addition, in detection using interferometry, the reflected light from the underlying surface is superimposed on the interference pattern and disturbs the pitcher phase of the interference fringe.
By using the above-mentioned incidence and by using S-polarized light, it is possible to almost eliminate this effect as mentioned above.
Highly accurate detection becomes possible. Furthermore, by making the optical path of the reference light used for this interference measurement almost the same as that of the measurement light, it is possible to achieve stable and high-precision measurement that is almost unaffected by the measurement environment such as air fluctuations. Achieve your goals.

When the above-mentioned method for measuring the inclination and height is applied to a semiconductor exposure apparatus, there is no spatial interference with the exposure optical system, and the inclination and height of the foggy part of the wafer can be detected with high precision as described above. From this detected value, the wafer's tilt and height can be controlled to precisely align the wafer's surface with the exposure image plane.

It becomes possible to accurately print a submicron pattern over the entire exposed area.

〔Example〕

An embodiment of the present invention is shown in FIG. 1 below. FIG. 1 shows a method for detecting the inclination of an exposed area of a wafer in an exposed 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 onto the wafer 4. At this time, the surface of the photoresist applied to the wafer surface is not necessarily flat due to undulations of the wafer, uneven thickness, flatness of the wafer chuck, and the like. Therefore, the laser light emitted from the semiconductor laser 1 is made into a narrow parallel beam by the collimating lens 11,
The reflected light, which is incident on the resist surface of the wafer and the exposed area through the mirror 1:3 at an incident angle of 85'' or more, is transmitted to the optical position detector 3' by the mirror 210 and the condensing lens 20.
The light is focused on the top and the focused position is detected. Exposure area is α
If it is tilted, the specularly reflected light is tilted by 2α, so if the focal length of the condenser lens is taken as the focal length, the focal spot of the optical position detector will be shifted by 2α. Therefore, the detected signal is sent to the processing circuit 5', which drives a tilt mechanism equipped with a wafer chuck, and is controlled so that the photoresist on the wafer is aligned with the image plane of the reticle pattern.

At this time, if the semiconductor laser is arranged so that the semiconductor laser emitted light 161' is incident on the wafer as S-polarized light, more accurate tilt detection can be performed as described above. In the embodiment of FIG. 1, the optical position detector 3' is χ.

7. It is a type that detects in both directions, and the inclination in two directions can be determined with one detection system.

In FIG. 1, a second detection system may be provided in a direction perpendicular to the plane of the drawing, and the inclinations in the X and y directions may be detected separately.

Further, the light source is not limited to a semiconductor laser as long as it can irradiate the wafer with relatively highly directional light.

FIG. 2 shows an embodiment of the present invention, and the same numbers as in FIG. 1 represent the same parts. The light emitted from the semiconductor laser 1 has an incident angle of 8
5" or more, and a light source image is formed in the exposure area on the wafer by the condensing lens 11'. The reflected light is transmitted to the optical position detector 3 by the mirror 210 and lenses 21 and 22.
If the wafer surface is at the resist pattern imaging position of the exposure optical system, the light is focused on the optical position detector 3''.
If the wafer is shifted vertically, it will shift left or right from the center of the optical position detector 3'', so if the detection signal of the optical position detector 3'' is sent to the processing circuit 5' and the wafer upper and lower tables are driven and controlled, correct focusing can be achieved at all times. It becomes possible. If the polarization of the laser beam is configured to be incident on the wafer as S-polarized light, it becomes possible to more accurately determine the height of the photoresist surface.

FIG. 10 shows one embodiment of the present invention, and the same part numbers as in FIG. 1 represent the same parts. The parallel light obtained by the collimating lens 11 passes through the beam splitter 19',
The light is incident on the photoresist surface of the wafer at an incident angle of 85° or more, for example 87°.

The specularly reflected light enters 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 sent to the optical position detector 3 by the condensing lens 20.
′, and the position of the focused spot is detected. If the incident angle to the wafer is 87'' and the S polarization is 16s as shown in FIG. 11, D s2 as shown in FIG.
/ RS is 0.0065, that is, 0.65%, which means that even if the underlying layer is uneven, as shown in Figure 11, it is hardly affected by it and remains parallel light. reflect specularly. Therefore, a sharp spot light with a high degree of convergence can be obtained on the optical position detector 3'. Furthermore, in this embodiment, the 12th
As shown in the figure, the light is vertically reflected by the plane mirror 14 and enters the wafer again, so if the wafer is tilted from 4 to 4' by α, the light that finally returns to the optical position detector will be tilted by 4α. .

It becomes possible to detect the optical position with twice the sensitivity as compared to the embodiment shown in FIG. As a result, it becomes possible to detect a tilt that is much superior in terms of S/N and sensitivity compared to conventional methods.

FIG. 13 shows an embodiment of the present invention, and the same numbers as 21F+ represent the same items. The condensed beam obtained by the condensing lens 11' is at the irradiation position 1 of the wafer. ! Most of the light is focused at iA. The angle of incidence is 85° or more. The specularly reflected light is made into parallel light by the collimating 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, is almost focused on the wafer, is reflected again, and is sent to beam splitter 1.
2, and is focused by the condensing lens 22 onto the optical position detector 3''.
The position of the focal point near the wafer when the reflective surface Σ) 4 changes to 4' (reflective surface Σ) indicated by a dotted line is explained.

When the reflecting surface is Σ, let's consider the case where light is focused on point A on both the outward and return trips.0When the reflecting surface is Σ', the Σ' surface becomes a mirror surface, and point A on the outward trip creates a mirror image at point A'. The light emitted from this point A' is passed through the lens 141 and the plane mirror 14, and on the return trip, the light is
At this focal point, Σ' becomes a mirror surface and creates a mirror image of point A'' at A''.Therefore, from the return trip, it appears as if A'''
The light is emitted from the condenser lens 22 and is focused on the optical position detector 3'' at the image position A'''. Σ and Σ
If the distance of ', that is, the vertical movement direction of the wafer is Δh, then AA"=AA"=2,6h AA"'=AA'+A'A"'=4Δh...
6), and the light emitting point position on the return trip is shifted by four times the displacement of the wafer (4Δh) (see Fig. 14).
''. As a result, height detection with high sensitivity and high S/N is possible.

FIG. 15 is a diagram showing an embodiment of the present invention. The same numbers as in FIG. 1 represent the same items. Light emitted from a coherent light source 1 such as a laser becomes parallel light 15 by a collimator lens 11 and enters a prism 1o. Prism 10 receives incident light 1
5 into two parallel beams 16 and 17. These two parallel beams are set at a constant angle to each other so that they overlap at the 0 point.
-θ is attached. One of the parallel beams 16 is incident on the wafer at an incident angle θ, and the other is a reference beam that travels at an angle of On (>9°) with respect to a perpendicular to the wafer without irradiating the wafer. The parallel beam 16 reflected by the wafer enters the plane mirror 14 almost perpendicularly, enters the wafer again, follows the outward path in the reverse direction, is reflected by the beam splitter 12, and then enters the lens 21.
After passing through and 22, it becomes a parallel beam and enters the -dimensional sensor 3. On the other hand, the reference light directly enters the plane mirror 14 almost perpendicularly from the 0 point, and after reflection follows the outward path in the reverse direction, similarly generating interference fringes with the -dimensional sem. 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 located in the reference optical path and plays the role of removing noise light reflected from the back surface of the optical component.

On the other hand, the wedge glass 26 refracts the light reflected by the wafer, thereby forming an image of the wafer irradiation position on the -dimensional sensor and overlapping the reference light. - On the dimensional sensor, the 181st! ! J
Intensity interference fringes as shown by the solid line are detected. When the wafer is tilted by 70° as shown by the dotted line around the wafer irradiation position vi (X=O), the detected interference fringe is the 16th
It will look like the dotted line in the figure. That is, the intensity at X=0 hardly changes, but changes from the stripe pitch P to P'. That is, since the intensity I (X) of the interference fringe is given by the equation (7), the relationship between the pitch P and the inclination Δθ can be determined from the equation (8).

Hereinafter, the margin λ coslj, ·ΔZ) ,,,(7)
λ In the above equation (7), M is the magnification for imaging the irradiation position on the wafer on a one-dimensional sensor, but for the sake of simplicity, the wedge angle of the wedge glass is assumed to be 0 degrees (the wedge angle is 0 degrees). if not).

In addition, the second term in cos and ins of equation (7) represents the change in interference fringes when the wafer changes by 6Z, and as shown in Figure 17, when the wafer changes to 7Z'&, interference occurs. The pitch of the fringes does not change, but the phase shifts. Therefore, in this 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 determined, thereby simultaneously determining the height and inclination of the wafer. Furthermore, in this embodiment, it is possible to set the incident angle θ1 to 87 to 89 degrees, which makes it possible to accurately determine the inclination and height without being affected by the underlying multilayer structure.

In addition, in this example, the reference light passes through almost the same optical path as the wafer irradiation light, and the optical components used are all the same except for reflection from the wafer, so it is hardly affected by air fluctuations, etc. It is possible to achieve a stable 8 (resolution).

〔Effect of the invention〕

As explained 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 made of various multilayer structures during the semiconductor circuit manufacturing process without being affected by the multilayer structure. .

It is now possible to accurately perform tilt control for focusing and aligning the wafer to the imaging plane in semiconductor exposure equipment, and it is possible to accurately control the inclination for focusing and aligning the wafer to the imaging plane. To cope with the decrease in exposure focus margin due to the shallow depth of focus that is expected to occur with high NA i-line reduction fog light equipment and excimer laser reduction exposure equipment used for exposure of

[Brief explanation of drawings]

Fig. 1 ν Fig. 2 is a device configuration diagram showing one 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 the conventional problem, Fig. 5 7 to 7 are characteristic diagrams for explaining the principles and effects of the present invention, FIGS. 8 and 9 are diagrams for explaining the prior art, and FIG. 10 is a configuration showing another embodiment of the present invention. figure. Figures 11 and 12 are diagrams for explaining the embodiment of Figure 10, Figures 1:3 are configuration diagrams showing another embodiment of the present invention, and Figure 14 is similar to Figure 13. FIG. 15 is a configuration diagram showing another embodiment of the present invention, and FIGS. 16 and 17 are diagrams for explaining the embodiment shown in FIG. 14. be. 1... Light source, 11... Collimating lens, 11'.
・・Condensing lens, 20 ・・Condensing lens, 21.22・
...Lens, 13,14,210...Mirror, 16.
1ri...half mirror 3...-dimensional sensor, 3',
:3″...Optical position detector, 4...Wafer, 5,5'
...Processing circuit, 7... Stage, 8... Reduction exposure lens, 81... Illumination system, 9... Liticle. Is it too late? Otsu 11 year old son-in-law is Issakimurahi 6 warm! 21st - Medihime l ± 0 member - (Shugeki extinguishing firmness 塙躬 0 ) 5 I5+ e 5z Iez k N Second country/θθ 躬/Δ η Indication of procedural amendments Heisei/Showa 1st year patent application no. No. 100026 amendment person 1f case Patent applicant name (51Q + Co., Ltd. Ritsu Seisakusho Rijinsho's target drawings I light = 7jfr, 3'' leakage)吃 tons゛ 9 thousand km 27.221. Eyebrow L heather 5 processing circuit 7
Stage 8 Reducing exposure lens 11 Collimation 1-no-Z / 3 Mirror 2 o Rakusen-zu Figure 1 Figure 2 Figure 2 Shima! 3 Compilation! 4 Volume/7 Figure

Claims (1)

[Claims] 1. A method for detecting inclination or height from information on reflected light of light irradiated onto an object to be measured, characterized in that the incident angle of the irradiated light is 85 degrees or more. A method of detecting the inclination or height of an object. 2. The method for detecting the inclination or height of an optical multilayer object according to claim 1, wherein the irradiation light uses linearly polarized light consisting only of an S-polarized component. 3. The specularly reflected light is reflected almost perpendicularly by a fixed plane mirror and irradiated onto the object to be measured again, and only the specularly reflected light is extracted to detect the inclination or height of the object to be measured. A method for detecting the inclination or height of an optical multilayer object according to claim 1. 4. An optical system characterized in that the specularly reflected light is caused to interfere with a fixed reference beam that is coherent with the specularly reflected light, and the inclination is detected from the pitch of this interference information, and the height information is detected from the pitch and phase. A method for detecting the inclination or height of a multilayered object. 5. Inclination or height detection of an optical multilayer object according to claim 4, wherein the reference light is configured to pass through substantially the same optical path as the irradiation light and specularly reflected light that are caused to interfere with the reference light. Method. 6. The light source and the light emitted from the light source are applied to the surface of the object to be measured which has an optical multilayer structure, so that the angle of incidence of the principal ray is 85
irradiation means for making the light enter the object at a temperature of at least 100°C, a detection means for detecting information about the light specularly reflected by the object to be measured, and a processing circuit for deriving the inclination or height of the object to be measured from the signal obtained by the detection means. An optical multilayer object tilt or height detection device characterized by comprising: 7. The optical multilayer object inclination or height detection device according to claim 6, wherein the light source or the irradiation means includes S-polarization means for converting the light irradiated onto the object to be S-polarized into S-polarization. 8. The light source and the light emitted from the light source are applied to the surface of the object to be measured which has an optical multilayer structure, and the angle of incidence of the principal ray is 85.
irradiation means that causes the light to enter at an angle of at least 100 degrees, a reflective irradiation means that reflects the light specularly reflected by the object to be measured almost vertically and irradiates it onto the object to be measured, and detects information on the light that is specularly reflected again by the object to be measured. What is claimed is: 1. An optical multilayer object tilt or height detecting device comprising: a detecting means for detecting the tilt of the object to be measured; and a processing circuit for deriving the tilt or height of the object from the signal obtained by the detecting means. 9. A reference light generating means for generating a fixed reference light coherent with the specularly reflected light is provided, and the specularly reflected light and the reference light are detected by the detecting means in the form of interference fringes. 7. The optical multilayer object tilt or height detection device according to claim 6, further comprising a processing circuit for deriving the tilt or height from the pitch and phase of the interference signal. 10. The reference light generated by the reference light generating means is configured to pass through almost the same optical path as the irradiation light and specularly reflected light that are caused to interfere with the reference light, except that the reference light is not reflected at the surface of the object to be measured. An optical multilayer object tilt or height detection device according to claim 9. 11. A mask serving as an original image, an illumination optical system that irradiates the mask with exposure illumination light, a projection optical system that forms an image of the mask on the object to be exposed using the light that has passed through the mask, and the object to be exposed. irradiation means for causing the light emitted from the second light source to enter the mask at or near the image formation position of the mask with an incident angle of the principal ray of 85° or more; and information on the light specularly reflected by the object to be exposed. 1. A projection exposure apparatus comprising: a detection means for detecting; and a processing circuit for deriving the inclination or height of an object to be measured from a signal obtained by the detection means.