JPS6219685B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an object surface unevenness measuring device that measures minute unevenness on an object surface in a non-contact manner.

Conventional methods for measuring minute irregularities on the surface of an object include a contact type surface roughness meter using a stylus with a sharp tip, and a first method that measures the gap between the nozzle end and the uneven surface from the flow resistance of air ejected from a thin nozzle. There was a device or a second device that determined the gap from capacitance. These conventional devices have the following drawbacks. The method of measuring surface roughness using a contact-type surface roughness meter using a stylus cannot be used on objects with soft surfaces because it scratches them. 1st above
The method of measuring surface roughness using the device and the second device is to
measurement was difficult. In addition, the method for measuring surface roughness using the second device cannot select an insulating material as the measurement target, and the method for measuring surface roughness using the first device uses air pressure, for example, to measure the surface roughness of the surface. It was not possible to select a plastic object or a viscous object as the object of measurement because it causes deformation of the shape.

The purpose of the present invention is to eliminate the above-mentioned conventional problems and to provide a method for measuring irregularities on the surface of an object, which can measure the surface of any object with high precision without affecting the object in any way. The goal is to provide equipment.

In order to achieve the above object, in the present invention, a projection object such as a fine periodic pattern such as a grating is illuminated with a light source, and the transmitted light or reflected light is imaged onto the object to be measured using a projection optical system. do. By doing this, even for objects with smooth and glossy surfaces, a fine periodic pattern with contrast can be imaged on the surface of the object. If there is no object at the desired position, a blurred fine pattern with poor contrast is projected. Therefore, in the present invention, a projection object having a fine periodic pattern of transmission or reflection, a first light source that illuminates the projection object, and a periodicity of the projection object illuminated by the first light source are provided. an optical system that projects an image of the pattern onto an object to be measured and forms an image of the periodic pattern projected onto the object; an imaging device that captures an image; a focusing fine movement mechanism that slightly moves either the optical system or the object to be measured; and a focusing point fine movement mechanism that causes a video signal detected by the imaging device to correspond to the periodic pattern. a focused point detection circuit that takes the differential or difference and integrates it to detect the frequency component of the periodic pattern; and a signal of the frequency component of the periodic pattern detected by the focused point detection circuit so that it becomes a predetermined value. a control means for activating the focusing point fine movement mechanism to position the surface of the object to be measured in a focused state; and a control means for positioning the surface of the object to be measured in a focused state; It is possible to measure the position of the surface of the object to be measured. In a device using the above principle, if the projection optical system that projects the above-mentioned projection object onto the object to be measured and the imaging optical system that images the object to be measured on the imaging surface of the imaging device are used together, the optical system is simplified. Furthermore, when a fine pattern of several micrometers is projected onto the object plane and the pattern projected onto the object to be measured is imaged onto the imaging surface using, for example, a 40x objective lens, the depth of focus becomes several micrometers, and the focal point position If the surface to be measured is shifted to a position deviated by 10 μm, the in-focus signal becomes small and in-focus control becomes impossible. Therefore, if a pattern with a component with a larger period than the above-mentioned fine pattern is simultaneously projected, the period of brightness and darkness of the above-mentioned large component will be generated on the imaging surface even if the pattern is 10 μm or more away from the focused point. Based on this signal, the focused point will be It becomes possible to make rough adjustments. Even if such a pattern with a large period is used, if the surface to be measured is located at a distance of, for example, 50 μm or more from the focused point, it will be difficult to obtain a focused point signal even from the pattern with this large period. So for example
By irradiating light onto the object to be measured from a slightly oblique direction using a He-Ne laser, etc., receiving the reflected light with a well-known position sensor, and reading the detection signal, the object can be measured by 50 μm or more from the focal point position. Even if there is a deviation, it is possible to detect the approximate amount of deviation from the in-focus position. By doing this, the relative positional relationship between the optical system and the measured object can be adjusted so that even if the measured object is significantly out of focus at the initial stage when it is installed in the measuring device, the deviation will be less than 50 μm. It becomes possible to make rough adjustments. Thereafter, by finely adjusting the focal point using the method described above, it becomes possible to measure surface irregularities.

The present invention will be described in detail below using examples.
FIG. 1a is a diagram showing an embodiment of the surface roughness measuring device of the present invention. Projected object 2 by first light source 1
to illuminate. As shown in FIG. 1b, this projection object 2 has a portion 2a having a width a that transmits light and a portion 2b that blocks light, which are arranged at a constant period P. The light transmitted through the portion 2a of the projection object 2 forms an image of the projection object on the object to be measured 4 by the projection optical system 3. In this embodiment, since the projection direction of the projection object is oblique to the surface of the object to be measured, the projection object 2 is arranged at an angle with respect to the optical axis 1a of the projection optical system 3, just as the surface to be measured is a horizontal plane. At a certain time, a uniform image is formed on the surface to be measured. The image of the projection object formed on the surface to be measured is formed on the imaging surface 61 of the imaging device 6 by the imaging optical system 5. The projection optical system 3 and the imaging optical system 5 are arranged as described below. That is, when the projection object 2 is focused on the object to be measured 4 by the projection optical system, an image of the surface of the object to be measured 4 is focused by the imaging optical system 5 onto the imaging plane 61. It is imaged. Therefore, when the surface of the object to be measured 4 is not located at the imaging plane position of the projection object 2, the image of the projection object on the surface of the object to be measured will be out of focus, and the image on the imaging surface 61 will also be out of focus. The imaging signal thus captured and converted into an electrical signal is input to the focused point detection circuit 7. This focused point detection circuit 7 will be explained in detail later. The focused point detection circuit 7 determines from the image pickup signal whether the object to be measured 4 is above or below the focused point position. After making such a determination, the focusing point drive circuit 8 drives the focusing point fine movement mechanism 94 based on this judgment signal, and moves the object 4 to be measured in the vertical direction toward the in-focus state. A new imaging signal is generated due to the upper and lower positions of the object to be measured 4, and the above-described operations occur continuously in a closed loop until a focused state is reached. Next, the focused point detection circuit 7 will be explained using FIG. 4. If, for example, a television camera is used as the imaging device in FIG. 1, the imaging signal will be the signal obtained by taking the x and y coordinates on the television image in FIG. 3a, as shown in FIG. signal strength I
changes. The time axis t also corresponds to the x-axis of the television screen, and the area y ₀ in the figure corresponds to one raster signal of y=y ₀ . Signals between adjacent rasters are unnecessary and are not used for signal processing. The image signal I is differentiated or differentiated as shown in the embodiment of FIG. 4, and the integral or sum of the absolute value of the value or the maximum value is first determined by an arithmetic circuit. Fourth
Figure a shows this circuit. The image signal I is differentiated by a circuit 72, and further its absolute value is determined.

That is, if the difference in brightness and darkness is obtained by differentiating or subtracting the imaging signal I with respect to the imaging scanning direction (the direction in which the pattern of the projection object 2 is arranged) x, and then taking the absolute value Id, then The degree of change in the imaging signal is determined. The pattern projected onto the object to be measured is a pattern that changes in the x direction like white, black, white, black, etc., so as it approaches the focal point position, the contrast difference between white and black, that is, the contrast signal Id. becomes larger. In this way, the contrast difference Id between white and black increases greatly, and the degree of in-focus increases as it approaches the in-focus position, and reaches its maximum at the in-focus position.

The above Id is obtained for each pixel, but in order to eliminate the effects of noise in the detection imaging system and unevenness in a minute area of the object to be measured, the Id is calculated over a somewhat wide range, that is, the desired image area S, by the circuit 73. This contrast signal Id is then integrated to obtain an in-focus signal _O1 . The image area S is one raster or a portion thereof. Figure 4b
FIG. 7 is a diagram showing another embodiment of the focused point detection circuit.
72 and 73 are the same as the same numbers in FIG. 4a. An A/D converter 74 converts the integrated value for one raster into digital information, and a two-dimensional signal sum circuit 75 consisting of a digital adder calculates the sum of multiple rasters to obtain a focused signal within a two-dimensional area.
Get O ₁ . In FIG. 4c, a differential signal is obtained from the image pickup signal, its absolute value is further obtained in a circuit 76, and the result is summed in a circuit 77. This summation is performed for one raster or multiple rasters. In the embodiment shown in FIG. 4d, the maximum value within a region S of the differential or difference signal is determined by a circuit 78. In each of the focused point detection circuits 7 shown in FIGS. 4A to 4D, the output result _O1 is the maximum in the focused state. The focused point detection signal O ₁ obtained in this manner is input to a memory circuit 791 and a comparison circuit 79 as shown in FIG. 4e. The comparison circuit 79 outputs the in-focus point detection signal O ₁ (t) at time t.
The in-focus point detection signal O ₁ (t-Δ
t) is input and comparison (O ₁ (t)−O ₁ (t−Δ
t)) is performed, and the change value O ₂ (t) of the in-focus signal that occurs between time t-Δt and time t is output. This change value O ₂ (t) is determined by the focusing point drive circuit 8
The focusing point drive circuit 8 generates a signal that drives a motor that moves the stage 10 holding the object to be measured 4 up and down in accordance with this change value.
Bring the surface of the object to be measured into focus.
The above-mentioned focused point feedback is performed at intervals of Δt, and when the focused point state is reached, the vertical movement of the stage 10 stops. In this example, a pulse motor is used as the motor to drive the stage.
The amount of vertical movement of the stage is measured by counting the number of pulses within the focusing point drive circuit 8. Furthermore, since the stage 10 is being fed at a low speed in the horizontal direction, changes in the unevenness of the surface of the object to be measured can be measured from changes in this count value.

FIG. 2a is a diagram showing another embodiment of the surface roughness measuring device of the present invention. Components having the same part numbers in this figure and those in FIG. 1 are the same. Illumination light emitted from a light source 1 illuminates a projection object 2' through a uniform illumination lens 11. As shown in FIG. 2b, the projection object 2' consists of a grating with a period P and a grating with a period P' ten times this period. For example, the period P is 200 μm and the period P' is 2 mm. The light transmitted through the projection object is transmitted through a projection optical system consisting of a half mirror 36 and a projection imaging lens 35.
The image of the projection object 2' is projected onto the surface of the object 4 to be measured. A projected image of the surface of the object to be measured is obtained by an imaging optical system consisting of a projection imaging lens 35.
An image is formed on the imaging surface 61. The imaging signal obtained by the imaging device 6 is input to the focused point detection circuit 71, and the sum or integral value of the absolute values of the above-mentioned differentials or differences is obtained. The focused point detection signal O ₁ obtained in this embodiment changes as the object to be measured deviates from the focused point position Z ₀ as shown in FIG. 5b. This signal changes as shown in FIG. 5a with respect to the period P and P' components of the projection object 2'.
That is, for a projected object with a pattern consisting only of frequency components of P, the in-focus point detection signal changes as shown in O ₁ , and for a projected object with a pattern consisting only of large frequency components P', it changes to O ₁ '. A focused point detection signal shown in FIG. In a pattern with only the P component, the focused point detection signal can hardly be detected when the distance from the focused point position _Z0 is ΔZ ₀ , but if the P' component is present, detection up to ΔZ ₁ becomes possible. For example, if the aforementioned pattern period (P = 0.2 mm, P' = 2 mm) is used and a 40x objective lens is used as the projection imaging lens 35, the pitch of the pattern projected onto the projection object will be 5 μm on the fine side and 5 μm on the coarse side. According to experiments, ΔZ ₀ is about 6 μm, ΔZ ₁ is about 30 μm, based on the relationship between the depth of focus of the objective lens and the brightness.
The focused point tracking operation can now handle sudden changes of ±30 μm. In addition, in this embodiment, as a method of controlling the surface of the object to be measured to come to a focused position, a projection imaging lens 3 consisting of an objective lens is used.
5 is driven up and down. Further, the driving distance of this lens is read by a linear scale head 102 which is well known in itself and which is directly connected to this lens, and the linear scale circuit 1
03 is used to obtain the displacement detection output 104 through electrical processing. In the above embodiment, two types of periodic patterns are used, but if a third periodic pattern, which is larger, is used, coarse adjustment can be made over a wider range. It is also possible to use other implementation methods as the in-focus point detection means of this embodiment as shown below.
It is also highly effective. This will be explained using FIG. Figure 6a shows the imaging signal I at intervals Δx _p and Δ where the difference signal value is large in patterns with periods P and P'.
A circuit ₇₆ calculates the sum of the signals from circuits 76 and 76', which calculates the difference at , focused signal
Let it be O ₁ . Further, in the embodiment shown in FIG. 6b, the output signals of the frequency filter circuit 701 that passes the image signal I with a period P and the frequency filter circuit 701' that passes the signal with the period P' are used as the new image signal _I0. , I ₀ ', and from this signal, a differential absolute value converting circuit 72 and an integrating circuit 73 obtain in-focus point signals, respectively. At this time, one signal is multiplied by α so that the next comparison can be performed optimally. Thereafter, the larger value is set as the in-focus signal. By doing so, it becomes possible to give an optimal focusing point signal pattern (see FIG. 5a) to each periodic pattern, and highly accurate focusing point control becomes possible.

FIG. 7 is a diagram showing another embodiment of the surface roughness measuring device of the present invention. Components having the same part number in the same figure and the same part number in FIG. 2 are the same parts. In this embodiment, a plurality of projection objects 21,
22, 23, and 24 are arranged at different positions near the optical axis LL' of the projection optical system, and the respective projection objects are projected onto the object to be measured and imaged. At this time, each projection object is imaged at a different position (on a horizontal plane) on the object to be measured, and imaging signals corresponding to each projection object are obtained separately. In-focus point detection signals obtained separately from each imaging signal in the same manner as described above are shown in FIG. Focus point signals O ₂₁ to _{O 24} are obtained corresponding to 24. O ₂₁ and O ₂₂ use a pattern with period p,
Since O ₂₃ and O ₂₄ use a large period p′ pattern,
O ₂₃ and O ₂₄ have a more widespread pattern than O ₂₁ and O ₂₂ . From this focused signal, O ₂₂ -
A differential signal shown in FIG. 8b is obtained by using a focused point detection circuit 71' equipped with a differential focused point circuit that forms O ₂₁ , O ₂₄ -O ₂₃ signals. By using the sum signal of each differential signal in Fig. 8c,
Control is applied from a distance away from the focused state, allowing highly accurate measurements.

Next, another embodiment of the surface roughness measuring device of the present invention will be described using FIG. 9. In this embodiment, the parts whose numbers are the same as those in FIG. 2 are the same. The second light source 10 is, for example, a laser or the like.
Use a light source with excellent directionality. This light is irradiated obliquely onto the object by the projection imaging lens 35. The reflected light is directed onto a displacement detector 62, which is known per se. At this time, the projection imaging lens is arranged so that the object to be measured 4 is imaged on the detection surface and the imaging surface 61 of the displacement detector 62.The light from the second light source detects the displacement when the object to be measured is at the focused position. It is reflected to the center of the instrument, but if it deviates up or down from the focal point position, the position of the reflected light shifts to the left or right on the displacement detection surface as shown in Figure 9, so if you extract this as an electrical signal, you will see a vertical fluctuation of ±1 mm or more. However, since it is possible to extract a signal corresponding to this variation, it is possible to perform rough adjustment. In addition, in this embodiment, if the first light source and the second light source are selected to have different wavelengths, and a wavelength selection means is used in which the filters 63 and 64 select and extract only the light of the necessary wavelength, the light source can be used accurately with less mutual interference. measurements can be achieved.

Next, another embodiment of the surface roughness measuring device of the present invention will be described using FIG. 10.

Part numbers in FIG. 10 and those in FIG. 9 that are the same represent the same item. In FIG. 10, 111 is a variable filter. This filter 1
11 has a disk-shaped outer shape and has the same transmittance on a line going in one direction from the center, and the transmittance gradually changes depending on the angle. 113 is a motor for rotating this filter. A signal obtained by the imaging device is input to a light amount adjustment circuit, and the average brightness of one screen is determined. This average brightness is compared with a preset value, and the motor is rotated in a rotational direction corresponding to the sign of the difference, thereby controlling to the above set value. 111, 112, 113 like this
By using the light amount adjusting means consisting of the following, an image having a constant average level of brightness is received on the imaging surface.
Therefore, for example, even if the object to be measured consists of a black part and a white part, substantially the same signals can be obtained, and it is possible to measure the surface roughness with high accuracy independent of the reflectance of the object to be measured. In the above embodiment, the light amount is adjusted by using a variable filter as the light amount adjusting means, but the present invention can also be achieved by using a light amount adjusting means that changes the voltage applied to the light source and adjusts the amount of light irradiated by the light source. It goes without saying that the purpose of the invention can be achieved. Further, in the embodiment shown in FIG. 10, a third filter (color filter) 63' is attached to the light source 1 so that the transmission wavelength range of this color filter does not overlap with the wavelength (or wavelength range) of the second light source. Furthermore, a second filter is installed in front of the displacement detector to block the light having the wavelength of the first light source and to transmit the wavelength of the second light source.
Wavelength selection means each having a filter identical to the third filter is provided on the front surface of the wavelength selection means. By doing so, only desired light is incident on the displacement detector 62 and the imaging surface 61, respectively, and signals with less noise can be obtained.

As described in detail above, according to the present invention, it is possible to measure the surface irregularities of an object in any state with high accuracy without affecting the object, which has an epoch-making effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing one embodiment of the surface roughness measuring device of the present invention, FIG. 2 is a schematic diagram showing another embodiment of the surface roughness measuring device of the present invention, and FIG. 4 is a block diagram showing the focused point detection circuit used in FIG. 1, FIG. 5 is a diagram showing the focused point detection signal obtained from the device shown in FIG. 2, and 6. The figure is a diagram of the in-focus point detection circuit used in Figure 2, Figure 7 is a diagram showing another embodiment of the surface roughness measuring device of the present invention, and Figure 8 is a diagram showing the circuit obtained from the device shown in Figure 7. FIG. 9 is a diagram showing another embodiment of the surface roughness measuring device of the present invention, and FIG. 10 is a diagram showing another embodiment of the surface roughness measuring device of the present invention. FIG. Explanation of symbols: 1... First light source, 2... Projection object, 3... Projection optical system, 4... Measured object, 5...
... Imaging optical system, 6... Imaging device, 9, 70... Focused point detection circuit, 8... Focused point drive circuit, 94...
... Focusing point fine movement mechanism, 72... Differential absolute value conversion circuit,
76, 76'...Difference absolute value conversion circuit.

Claims (1)

[Claims] 1. A projection object having a fine periodic pattern of transmission or reflection, and a first projection object that illuminates the projection object.
and projecting an image of the periodic pattern of the projection object illuminated by the first light source onto the object to be measured, and forming an image of the periodic pattern projected onto the object to be measured. an imaging device that captures an image of a periodic pattern formed by the optical system; and a focusing fine movement mechanism that slightly moves either the optical system or the object to be measured;
a focused point detection circuit that takes differentiation or difference and integration of the video signal detected by the imaging device in correspondence with the periodic pattern and detects a frequency component of the periodic pattern; a control means for positioning the surface of the object to be measured in a focused state by activating the focusing point fine movement mechanism so that the signal of the frequency component of the detected periodic pattern becomes a predetermined value; and the surface of the object to be measured. and measuring means for measuring the unevenness of the surface of the object to be measured by varying the measurement position at and detecting the amount of displacement of the focusing point fine movement mechanism positioned in the focused state by the control means. A device for measuring unevenness on the surface of an object. 2 The projection object has a fine periodic pattern formed by a composite pattern having a pattern having a first period and a pattern having a period larger than the first period, and further includes the focused point detection circuit. A circuit detects a signal of a first frequency component corresponding to the first periodic pattern and a signal of a second frequency component corresponding to the second periodic pattern, and compares the signals of these frequency components, An apparatus for measuring irregularities on an object surface according to claim 1, further comprising a circuit for selecting a signal of one of the frequency components. 3. At least two or more projection objects having the periodic pattern are disposed on different planes near the optical axis of the projection optical system, and are displaced in the optical axis direction, and the focused point detection circuit is configured to detect the object to be measured, respectively. Each periodic pattern projected above is imaged by an optical system, and a difference signal between the frequency component signals of each periodic pattern detected based on each video signal obtained from the imaging device is detected. 2. An apparatus for measuring irregularities on an object surface according to claim 1, further comprising a differential focusing circuit which uses a difference signal as a signal of frequency components of a periodic pattern. 4 A projection object having a fine periodic pattern of transmission or reflection, and a first projection object that illuminates the projection object.
and a second light source with excellent directivity for the object to be measured.
irradiation means for obliquely irradiating a light beam emitted from a light source onto a position to be measured or in the vicinity of the position to be measured of an object to be measured; The periodic pattern is projected onto an object, and an image of the periodic pattern projected onto the object to be measured is formed, and the light irradiated by the irradiation means and reflected from the object to be measured is directed to a predetermined area. an optical system that forms an image at the position; an imaging device that captures an image of the periodic pattern formed by the optical system; and an imaging device that is installed at the predetermined position and is capable of detecting displacement in a direction perpendicular to the optical axis. a displacement detector; a focusing point fine movement mechanism for finely moving either the optical system or the object to be measured; In order to form an image in a substantially focused state on the imaging surface of the imaging device by the system,
A first control means for coarsely moving the focusing point fine movement mechanism; and a first control means for coarsely moving the focusing point fine movement mechanism, and taking differentiation or difference and integration of the video signal detected by the imaging device in correspondence with the periodic pattern, and A focused point detection circuit detects a frequency component, and the focused point fine movement mechanism is precisely operated so that the signal of the frequency component of the periodic pattern detected by the focused point detection circuit becomes a predetermined value. a second control means that positions the surface of the object in a focused state; and a focused point that is positioned in a focused state by the second control means for differentiating the measurement position on the surface of the object to be measured; 1. An apparatus for measuring unevenness on the surface of an object, characterized in that it is equipped with a measuring means for measuring the unevenness on the surface of an object to be measured by detecting the amount of displacement of a fine movement mechanism. 5. The apparatus for measuring irregularities on the surface of an object according to claim 4, wherein the light irradiated onto the object to be measured from the first and second light sources has different spectral characteristics. 6 A projection object having a fine periodic pattern of transmission or reflection, and a first projection object that illuminates the projection object.
a light source, a light amount adjusting means for varying the intensity of reflected light of the projection object projected onto the object to be measured by the first light source, and a periodic pattern of the projection object illuminated by the first light source. an optical system that projects an image of the periodic pattern onto an object to be measured and forms an image of the periodic pattern projected onto the object; and an image of the periodic pattern formed by the optical system. an imaging device configured to take an image of the image; a focusing fine movement mechanism that slightly moves either the optical system or the object to be measured; Alternatively, a focused point detection circuit detects the frequency component of the periodic pattern by taking the difference and integration, and the focused point detection circuit detects the frequency component of the periodic pattern so that the signal of the frequency component of the periodic pattern detected by the focused point detection circuit becomes a predetermined value. A control means for activating a focusing fine movement mechanism to position the surface of the object to be measured in a focused state, and a control means for positioning the surface of the object to be measured in a focused state at different positions on the surface of the measured object, at which time the control means positions the surface in a focused state. 1. A measuring device for measuring unevenness on the surface of an object, comprising: measuring means for measuring unevenness on the surface of an object to be measured by detecting the amount of displacement of the focusing fine movement mechanism.