JPH0660813B2 - Surface roughness measuring device and surface roughness measuring method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface roughness measuring device and a surface roughness measuring method, and more particularly to a laser beam using a measured object such as a metal plate as a light beam. It relates to a surface roughness measuring device and a surface roughness measuring method for calculating the surface roughness of the object to be measured from the output obtained by irradiating the reflected spot light with a linear light receiving element. is there.

[Conventional technology]

The roughness of the surface of an object is usually measured by a so-called stylus method in which a stylus is brought into sliding contact with the surface of the object to be measured.

However, the stylus type has a drawback that a soft surface material such as aluminum damages the surface by the stylus and takes a lot of time for measurement.

As a method that can avoid the drawbacks of the stylus method, there is an optical method that optically measures the surface roughness. This optical roughness measuring method is to irradiate the surface of the measured object with light, and calculate the half width and standard deviation indicating the spread of the reflected light intensity distribution curve of the reflected light from the surface of the measured object using a phototransistor. And CdS
It is obtained by moving a single optical sensor such as a light receiving element.

[Problems to be Solved by the Invention]

In the case of the optical type, since it can be measured in a non-contact manner with respect to the surface of the object to be measured, it has an advantage of not damaging the surface of the object to be measured, on the other hand, the half width or standard deviation of the reflected light intensity distribution curve. For the measurement of, it is necessary to measure not only the background of this distribution curve, but also the entire distribution curve, and therefore the optical sensor must be moved, resulting in a complicated configuration. However, there was a problem that the measurement speed took a considerable amount of time.

The present invention has been made in view of the above circumstances, and an object thereof is to measure the reflected light intensity only near the peak of the reflected light intensity distribution curve with a small light receiving element array that does not have a movable portion. This makes it possible to provide a surface roughness measuring device and a surface roughness measuring method that can easily measure the surface roughness of a measured object without contact, while simplifying the data processing process and therefore the configuration. To provide.

[Means for Solving the Problems]

The surface roughness measuring device according to the present invention, in order to achieve the above object, a light beam generator that irradiates a light beam substantially perpendicularly to the surface of the object to be measured, and a reflected spot light from the surface of the object to be measured. A line-shaped light-receiving element array having a length that covers at least the vicinity of the peak of the reflected spot light and is arranged at a position where light can be received, and an analog / analog for converting an analog signal output from the light-receiving element array into a digital signal. The digital converter, the memory for storing the output of the analog / digital converter, and the n pieces of output data corresponding to the reflected spot light near the peak among the data stored in the memory are used for the measurement. A Gaussian function is approximated to the vicinity of the peak of the distribution curve of the intensity of reflected light from the body surface, and a Gaussian curve parameter GCP representing the standard deviation of this Gaussian function is However, In is a natural logarithm, _{y i} is the reflected light _{intensity, t i = i- (n +} 1) / 2 (i = 1,2, ..., n) T i = 12t i 2 + n 2 +1 (C is an interval on the surface of the light receiving element array of each of n points).
Calculated from the measurement points of the reflected light intensity y _i equal to or more than the points,
The present invention is characterized by comprising arithmetic means for calculating the surface roughness of the object to be measured from the comparison between the Gaussian curve parameter GCP and the center line average roughness data associated in advance.

Further, the surface roughness measuring method according to the present invention, in order to achieve the above-mentioned object, irradiates a light beam substantially perpendicularly to the surface of the object to be measured, and the reflected spot light from the surface of the object to be measured,
Light is received by a line-shaped light-receiving element array having a length capable of covering at least the vicinity of the peak of the reflected spot light, and among the outputs of the light-receiving element array, n outputs corresponding to the reflected spot light near the peak. Using the data, the vicinity of the peak of the reflected light intensity distribution curve from the surface of the measured object is approximated by a Gaussian function, and a Gaussian curve parameter GCP representing the standard deviation of this Gaussian function is However, In is a natural logarithm, _{y i} is the reflected light _{intensity, t i = i- (n +} 1) / 2 (i = 1,2, ..., n) T i = 12t i 2 -n 2 +1 (C is an interval on the surface of the light receiving element array of each of n points).
The surface roughness of the measured object is calculated by calculating from the measurement points of the reflected light intensity y _i equal to or more than the points, and further comparing the Gaussian curve parameter GCP with the center line average roughness data associated in advance. It is characterized by.

[Work]

In the surface roughness measuring device and the measuring method configured as described above, the light beam output from the light beam generator is irradiated substantially perpendicularly to the surface of the object to be measured, and the reflected light is reflected on the surface of the object to be measured. Light is received by a line of light-receiving elements arranged almost parallel to the
After being converted into a digital signal by the digital converter, it is stored in the memory. Using the data stored in this memory, the vicinity of the peak of the intensity distribution of the reflected light from the surface of the object to be measured is approximated by a Gaussian function, and the Gaussian curve parameter representing the spread of this Gaussian function is calculated by a predetermined arithmetic expression. The Gaussian curve parameter corresponds to the surface roughness of the object to be measured, so that the surface roughness of the object to be measured can be obtained.

〔Example〕

Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the overall configuration of an embodiment of a surface roughness measuring device according to the present invention.

In FIG. 1, reference numeral 1 denotes a laser oscillator as a light beam generator made of, for example, an argon gas laser, and a laser beam 2 as a light beam output from the laser oscillator 1 is reflected by a mirror 3 on the object 4 to be measured. It is designed to irradiate the surface.

The beam spot 5 of the laser beam 2 with which the surface of the object to be measured 4 is irradiated has a diameter of about 2 mm in this embodiment, and the beam spot 5 irradiates the surface of the object to be measured 4 in a substantially vertical direction. It is supposed to do. This DUT 4
In this embodiment, a mirror 3 is used to irradiate the laser beam 2 onto the laser beam 2. However, depending on the installation location of the laser oscillator 1 and the DUT 4, the mirror 3 may be used.
May be omitted, and the point is that the laser beam 2 is incident on the surface of the DUT 4 in a direction substantially perpendicular thereto.

Further, a line-shaped light receiving element array 6 is arranged substantially parallel to the surface of the object to be measured 4 and separated by a predetermined distance (60 mm in this embodiment). The light receiving element array 6 is, for example, a plasma coupled device (Plasma Coupled Devi).
Hereinafter, "PCD" is used for short.

The light receiving element array 6 has a length that covers the vicinity of the peak of the reflected spot light from the surface of the DUT 4. In this embodiment, a PCD of 512 elements is used as the light receiving element array 6, and the width between each element is 50 μm. Therefore, the length of the PCD is 50 μm × 512 elements = 25.6 mm. is there.

The analog signal output from the light-receiving element array 6 is converted into a serial signal by the parallel-series exchange circuit 7, and then input to an analog / digital (hereinafter, referred to as “A / D”) converter 8 where it is digitally converted. After converting to signal, memory 9
It is transferred to and stored there.

Further, the data stored in the memory 9 is read by a read command from the control device 10 and sent to the arithmetic device 11.

Based on the command from the controller 10, the arithmetic unit 11 approximates the peak of the reflected light intensity distribution from the data stored in the memory 9, in other words, the reflected light intensity y _i data, by using a Gaussian function. Gaussian curve parameter GCP representing the spread of Where In is the natural logarithm, y _i is the reflected light intensity, t _i = i− (n + 1) / 2 (i = 1, 2, ..., N) T _i = 12t _i ² −n ² +1 (C is the distance between each of the n points on the light receiving element array surface), and the surface roughness of the DUT 4 is calculated from this GCP and the data corresponding to the surface roughness in advance. It has become. The calculation result of the arithmetic unit 11 is
Based on an instruction from the control device 10, it is displayed on the display device 12 or printed out by the printer 13.

The operation of this embodiment thus configured will be described. Eight types of aluminum test pieces having different surface roughness are used as the measured object 4. First, the laser beam 2 output from the laser oscillator 1 is reflected by the mirror 3 and
Is irradiated as a beam spot 5 almost perpendicularly to the surface of the. The reflected spot light from the surface of the object to be measured 4 is received by the light receiving element array 6 arranged in a fixed state substantially parallel to the object to be measured 4, and the reflected light intensity distribution corresponding to the roughness of the surface of the object to be measured 4 is received. Are photoelectrically converted by the light receiving element array 6 and the electric signals thereof are output from the light receiving element array 6, respectively.

The above-mentioned reflected light intensity distribution is generally specular reflected light (reflected light whose incident light and light intensity distribution do not change so that incident light is reflected as it is, such as reflection of light by a mirror surface) and diffuse reflected light (incident light is (Reflections that are scattered on the surface of the object and have no regular reflection light component)
Made of.

When the center line average roughness Ra of the surface of the DUT 4 is about the wavelength of the laser beam 2, the reflected light is specularly reflected light.

The output signal of the light-receiving element array 6 is used as a parallel-serial conversion circuit 7
Is input to, and after converting the parallel signal to the serial signal there,
It is sent to the A / D converter 8 and converted into a digital signal. This digital signal is stored in a predetermined area of the memory 9 based on a command from the control device 10.

The n pieces of data as the reflected light intensities y _i stored in the memory 9 are read by a command from the control device 10 and sent to the arithmetic device 11. In this arithmetic unit 11, n
Based on the individual reflected light intensity y _i data, the GCP of the above equation (1)
Is calculated to evaluate the spread of the reflected light intensity.

In this case, the laser beam 2 irradiated on the surface of the DUT 4
The reflected light of 1 spreads as the surface roughness of the DUT 4 increases.

Therefore, a case will be described in which the spread of the light intensity distribution curve is evaluated using the standard deviation δ of the Gaussian function that approximates the vicinity of the peak of the light intensity distribution curve reflected from the surface of the DUT 4.

Here, a Gaussian function that approximates the vicinity of the peak of the headquarters light intensity distribution curve is represented by the following equation (2).

g (x) = A * exp [-a (x-p) ² ] ... (2) However, A and a are positive constants, p represents the position of the main axis of a Gaussian function.

The variance δ ² representing the spread of this Gaussian function is defined by the following equation (3).

The variance δ ² representing the spread of the Gaussian function of equation (3) is
Even if the position is moved to the position p of the main axis of the Gaussian function at the origin of the x-coordinate, its value does not change, so it can be rewritten as the following equation (4).

However, f (x) is a function obtained by moving the position of the main axis of g (x) in the above equation (2) to the origin, and f (x) = A · exp (−ax ² ) ... (5) is there.

Substituting this equation (5) into the above equation (4) and calculating the integral, Therefore, the standard deviation δ of the Gaussian function is Becomes

The standard deviation δ of this Gaussian function is the above GCP (Gaussia
n curve parameter), therefore, if the constant a of the above equation (2), which is a Gaussian function that approximates the reflected light intensity distribution curve, is obtained, then GCP representing the spread of the Gaussian function can be obtained from equation (7). I want it.

FIG. 2 is a schematic diagram of a reflected light intensity distribution curve when measured at a constant interval c on the surface of the light receiving element array 6.
In the figure, x is the position on the light receiving surface of the light receiving element array 6 for measuring the reflected light intensity, and y on the vertical axis is the reflected light intensity.

As shown in FIG. 2, n points (x ₁ , y ₁ ), ..., (x _i , y _i ), near the peak of the reflected light intensity distribution curve,
..., (x _n , y _n ) was fitted by the method of least squares (2)
By substituting the constant a of the Gaussian function of the equation into the equation (7), GC
P is obtained by the above equation (1).

In addition, when the Gaussian function is applied to the intensity z ₁ = y _i = y _bi obtained by subtracting the background intensity (hereinafter referred to as “BG”) y _bi from the actually measured value y _i of the light receiving element array 6, Instead of the actually measured value y _i of the light intensity in the equation (1), z _i may be substituted.

However, when the BG intensity is subtracted, not only it takes much time, but also when the reflected light spreads, the BG intensity cannot be accurately determined. Therefore, in this embodiment, the BG intensity is not subtracted and I asked for GCP.

In the above formula (1), Therefore, even if the light intensity is multiplied by a constant, the GCP value does not change.

Next, the experimental results will be described. Using the above-mentioned Gaussian curve method, the measured object 4 has different surface roughnesses.
The surface roughness of each type of aluminum test piece was measured as described above with reference to FIG. 1, the GCP was calculated from the reflected light intensity distribution by the arithmetic unit 11, and the stylus roughness measuring device (Taly was used in advance). -surf 5M) was used to measure the centerline average roughness Ra of the test piece and compared with GCP.

The wavelength of the argon gas laser used in this experiment is 51
It is 4.5 nm. The PCD as the light receiving element array 6 used for the measurement of the reflected light intensity distribution has the number of elements of 51 as described above.
2 (the width of one element is 50 μm), the acquisition time of reflected light intensity data was 20 ms, and GCP was measured at three points for each test piece.

Further, using a stylus type surface roughness measuring device, a roughness of a measurement length of 1.75 mm, which is almost the same as the diameter of the beam spot 5 of the laser beam 2 on the test piece, is measured three times within one laser beam irradiation surface. It measured and took the average value.

FIGS. 3 (a), (b) and (c) show roughness waveforms of three test pieces out of eight kinds of test pieces (measurements) measured by a stylus type roughness measuring device, respectively. The center line average roughness Ra is 0.1 μm, 0.3 μm, and 0.5 μm, respectively, and the horizontal axis represents the distance (mm) and the vertical axis represents the roughness height (μm). .

Further, FIGS. 4 (a), (b) and (c) are graphs showing the results of PCD measurement of the reflected light intensity distribution of the laser beam of these test pieces, respectively, and FIGS. FIG. 4 (a) for b) and (c),
4 (b) and 4 (c) correspond to each other. In FIGS. 4 (a) to 4 (c), the horizontal axis represents the position x on the light receiving surface of the PCD, and the vertical axis represents the reflected light. The intensity y _i is shown.

FIG. 4 (a) is a graph showing the intensity distribution of the reflected light from the smoothest test piece surface, showing the intensity distribution of the specularly reflected light that is the incident light reflected as it is, similar to the intensity distribution of the incident laser beam. Can be approximated by a Gaussian function.

Further, FIG. 4 (c) is a reflected light intensity distribution from the rough surface of the test piece and shows a diffuse reflected light intensity distribution in which the specular reflected light component has completely disappeared. This intensity distribution curve also has a Gaussian function. It turns out that it can be approximated well.

On the other hand, FIG. 4 (b) is the result of a test piece having a roughness intermediate between those of the test pieces used in FIG. 4 (a) and FIG. 4 (c). Shows the distribution where the diffused light intensities from the rough surface of the test piece overlap.

FIG. 5 shows the GCP obtained by using the above equation (1) after smoothing the data of the light intensity measured by the PCD as the light receiving element array 6 by taking the average of seven adjacent points.
The two are almost the same except for one point having the largest GCP obtained by substituting all the measurement points into the equation (1) without smoothing.

Therefore, it is considered unnecessary to smooth the light intensity data when obtaining the spread of the light intensity distribution curve by GCP.

Further, FIG. 6 shows the relationship between the GCP measured at three points for each of eight types of test pieces having different roughnesses and the centerline average roughness Ra obtained by the stylus type roughness measuring device. The straight line B in the figure is an empirical formula obtained by the least square method, and the center line average roughness Ra (μm) in the range of 0.1 μm <Ra <0.5 μm is obtained by the above calculation. From GCP (mm), Ra = 8.8 × 10 ^-2 GCP + 3.2 × 10 ^-2 ......
(8) is required. The measurement time for one GCP is about 2 seconds.

Next, the surface roughness obtained as described above is determined by the control device 1
Based on the command of 0, it is displayed on the display device 12 or printed out by the printer 13.

As described above, according to this embodiment, the surface of the DUT 4 is irradiated with the laser beam 2 substantially at a right angle, and the reflected light is received by the line-shaped light receiving element array 6, and the surface of the DUT 4 is exposed. The reflected light intensity distribution corresponding to the roughness is measured, and GCP which is the standard deviation of the Gaussian function approximating the vicinity of the peak of the reflected light intensity distribution curve is calculated using a predetermined arithmetic expression.
By comparing with the value of the surface roughness that is corresponded in advance to the value of,
For example, since the arithmetic device 11 is configured to perform the arithmetic operation of the equation (8), there is an advantage that the surface roughness of the measured object 4 can be quickly measured without contact.

Further, as is clear from the above experimental results, the GCP obtained by smoothing the reflected light intensity data that can be approximated by a Gaussian function in the vicinity of the peak of the reflected light intensity distribution curve is not smoothed. Since it substantially matches the GCP calculated directly from the measured value of the light intensity, it is not necessary to smooth the light intensity data when obtaining the spread of the light intensity distribution curve by GCP. Therefore, the calculation process is simplified accordingly.

Further, as the center line average roughness Ra increases, GCP
In the range of 0.1 μm <Ra <0.54 μm, there is an advantage that the center line average roughness of the object to be measured can be measured from the equation (8).

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

For example, instead of PCD as the light receiving element array 6, CCD
(Charge Coupled Device, charge imaging device), BB
D (Bucket Brigade Device, Bucket Relay Device), CTD (Charge Transfer Device, Charge Transfer Device), CID (Chrge Injection Device, Charge Injection Device), CPD (Charge Priming Device)
1 or a plurality of such devices may be used, and when the centerline average roughness Ra is calculated from the equation (8), the centerline average roughness Ra of 0. Although it is set within the range of 1 μm <Ra <0.5 μm, it is not limited to this.

Further, the functional parts of the memory 9, the control device 10, the arithmetic device 11 and the like can use the corresponding functions of the microcomputer or the personal computer.

〔The invention's effect〕

As described above in detail, since the half width and the standard deviation representing the spread of the conventionally used reflected light intensity distribution curve need to measure the entire reflected light intensity distribution curve, the reflected spot light is received. A large array of light-receiving elements must be used or moved, which complicates the arithmetic processing process, which complicates the arithmetic processing circuit, slows the arithmetic processing, and is more likely to mix noise with accurate surface roughness. However, according to the present invention, the position where the surface of the object to be measured is irradiated with the light beam substantially perpendicularly and the reflected spot light from the surface of the object to be measured can be received. Is received by a line-shaped light receiving element array having a length that is arranged in and has a length that covers at least the vicinity of the peak of the reflected light spot light,
GCP representing the spread of the Gaussian function that approximates the peak of the reflected light intensity distribution curve is However, In is a natural logarithm, _{y i} is the reflected light _{intensity, t i = i- (n +} 1) / 2 (i = 1,2, ..., n) T i = 12t i 2 -n 2 +1 (C is an interval on the surface of the light receiving element array of each of n points).
Calculated from the reflected light intensity y _i above the point and the measurement point, and
Since the surface roughness of the measured object is calculated from the comparison between the Gaussian curve parameter GCP and the center line average roughness data associated in advance, the reflected light only near the peak of the reflected light intensity distribution curve is calculated. It is possible to measure at the same time with one small light receiving element array without moving it, and the surface roughness of the object to be measured can be measured accurately and quickly with almost no noise mixing and with GCP. When obtaining the spread of the light intensity distribution curve, GCP can be calculated from the data only near the peak of the light intensity distribution curve, and since it is not necessary to smooth the light intensity data, the calculation process can be performed in a short time. It is possible to provide a surface roughness measuring device and a surface roughness measuring method that can be performed and can simplify an arithmetic circuit.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of an embodiment of a surface roughness measuring device according to the present invention, and FIG. 2 is a reflected light from a surface of a measured object measured by a light receiving element array in the embodiment. The schematic diagrams of the intensity distribution curves, FIGS. 3 (a) to 3 (c), show the surface roughness of three types of test pieces when the roughness is different, respectively, measured by a stylus type roughness measuring device. Waveforms in the case, FIGS. 4 (a) to 4 (c), respectively, are reflected lights by the laser beam of the test piece corresponding to the waveforms shown in FIGS. 3 (a) to 3 (c). P is the intensity distribution
FIG. 5 is a characteristic diagram of the position versus reflected light intensity on the received light of PCD when measured by CD respectively, and FIG. 5 shows GCP after smoothing data of the light intensity measured by PCD by the average of seven adjacent points and smoothing. 6 is an explanatory view showing a comparison result with GCP which is not used, and FIG. 6 is a center line average roughness obtained by a GCP and a stylus type roughness measuring device which are measured at three points for eight kinds of test pieces having different roughness. It is explanatory drawing which shows the relationship with Ra. 1 ... Laser oscillator, 2 ... Laser beam, 3 ... Mirror, 4 ... Object to be measured, 6 ... Light receiving element array, 7 ... Parallel-serial conversion circuit, 8 ... A / D converter, 9 ...... Memory, 10 ...... Control device, 11 …… Computing device, 12 …… Display device, 13 …… Printer.

Claims (2)

[Claims] 1. A light beam generator for irradiating a surface of a measured object with a light beam substantially perpendicularly to the surface of the measured object, and a light beam generator arranged at a position capable of receiving reflected spot light from the surface of the measured object and at least a peak of the reflected spot light. A line-shaped light receiving element array having a length that covers the vicinity, an analog / digital converter for converting an analog signal output from this light receiving element array into a digital signal, and the output of this analog / digital converter is stored. Memory and the n pieces of output data corresponding to the reflected spot light near the peak among the data stored in the memory, the vicinity of the peak of the reflected light intensity distribution curve from the surface of the object to be measured is Gaussian. The Gaussian curve parameter GCP that represents the standard deviation of this Gaussian function is approximated by However, In is a natural logarithm, _{y i} is the reflected light _{intensity, t i = i- (n +} 1) / 2 (i = 1,2, ..., n) T i = 12t i 2 -n 2 +1 (C is an interval on the surface of the light receiving element array of each of n points).
Calculated from the measurement points of the reflected light intensity y _i equal to or more than the points,
A surface roughness measuring device comprising: a calculation unit that calculates the surface roughness of the object to be measured from the comparison between the Gaussian curve parameter GCP and the centerline average roughness data associated in advance. 2. A linear shape having a length capable of irradiating a surface of the object to be measured with a light beam substantially perpendicularly and covering the reflected spot light from the surface of the object to be measured at least near the peak of the reflected spot light. Of the light receiving element array, and using the n output data corresponding to the reflected spot light near the peak among the outputs of the light receiving element array, the peak of the reflected light intensity distribution curve from the surface of the measured object is obtained. A Gaussian function is used to approximate the neighborhood, and a Gaussian curve parameter GCP representing the standard deviation of this Gaussian function is However, In is a natural logarithm, _{y i} is the reflected light _{intensity, t i = i- (n +} 1) / 2 (i = 1,2, ..., n) T i = 12t i 2 -n 2 +1 (C is an interval on the surface of the light receiving element array of each of n points).
The surface roughness of the measured object is calculated by calculating from the measurement points of the reflected light intensity y _i equal to or more than the points, and further comparing the Gaussian curve parameter GCP with the center line average roughness data associated in advance. A method for measuring surface roughness.