JPH02176411A - Surface-waviness checking apparatus and optical quantity correcting method thereof - Google Patents

Abstract

PURPOSE:To remove the effect of fluctuation in reflectivity and to make it possible to perform highly accurate checking by controlling the quantity of light emitted from a light-emission driving means through a feedback means from the quantity of received light from a received light detecting means. CONSTITUTION:A feedback means 16 is provided between a received light detecting means 13 and a light-emission driving means 12. A driving signal ID (quantity of emitted light) which is outputted from the light-emission driving means 12 is controlled a received light signal S11 (quantity of received light) which is outputted from the received light detecting means 13. Therefore, the fluctuation of reflectivity rho of the surface of a material to be measured 17 is automatically incorporated in the received light signal S11 which is proportional to the quantity of the received light. Thus, the driving current ID which is proportional to the quantity of the emitted laser light L11 can be controlled by the received light signal incorporating the reflectivity rho all the time. The effect of the reflectivity can be corrected automatically.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a surface waviness inspection device, particularly a device that measures the state of surface waviness by irradiating a semiconductor laser beam onto an object to be measured such as a magnetic disk or a semiconductor wafer. Regarding the control of the amount of emitted light, it is possible to achieve high accuracy by omitting the normalization process of the amount of light received by the light receiving detection system and removing the influence of changes in the reflectance, without making changes in the reflectance of the surface of the object to be measured irrelevant. The apparatus is equipped with a light emitting means, a light emission driving means, a light receiving detection means, and a control means, and the laser beam from the light emitting means is emitted to the object to be measured, and the laser beam is emitted from the object to be measured. In the surface waviness inspection device for inspecting the surface waviness of the object to be measured by receiving and detecting the reflected light of The structure includes controlling the amount of light emitted from the light emitting driving means based on the amount of received light, and an output limiting means is provided between the light emitting means and the light emitting driving means, and the output from the light emitting driving means is controlled. The amount of light emitted is
The configuration includes shutting off when an arbitrary set value is exceeded and outputting shut-off information to the control means.

[Industrial application field]

The present invention relates to a surface waviness inspection device and a method for correcting the amount of light therefor. More specifically, the present invention relates to a device for measuring the state of surface waviness of an object to be measured such as a magnetic disk or a semiconductor wafer, and a method for correcting the light amount of its light emitting/receiving system. It's about how to do it.

BACKGROUND ART In recent years, surface waviness inspection devices have been used that non-contact and non-destructively measure the surface waviness shape of a high-precision polished surface of a semiconductor wafer or the like by irradiating a laser beam onto an object to be inspected. At this time, the reflectance of the surface of the object to be inspected is not always constant, and variations in this reflectance are included in the amount of received light and induce measurement errors.

Therefore, variations in the amount of received light due to unevenness in reflectance are corrected by normalizing by the total amount of received light, or by introducing another monitoring system and normalizing by surface reflectance.

However, introducing a separate monitoring system will increase inspection costs, and calculating the total amount of light received every time the reflectance changes and standardizing the amount of light received will require a long time for the inspection process. However, this poses a problem in that it is not possible to speed up the inspection.

Therefore, there is a need for a device and a light amount correction method that control the amount of emitted light so that the total amount of received light is always constant regardless of changes in the reflectance of the object to be measured.

[Conventional technology]

FIG. 6.7 is an explanatory diagram of a conventional example.

FIG. 6 is a configuration diagram of a conventional surface waviness inspection device.

In the figure, 1 is a semiconductor laser projection system, 2 is a semiconductor laser drive power supply, 3 is a 4-split detector, 4 is a current-voltage conversion circuit, 5 is a control circuit, Sl is a light reception signal, S2 is a differential output, and S3 is light reception Each shows the light quantity sum output.

The surface waviness inspection device irradiates the object to be measured 6, such as a semiconductor wafer, with a laser beam L1, and photoelectrically converts the reflected light L2 by a 4-split photodetector 3, a current-voltage conversion circuit 4, and a control circuit 5. The state of surface waviness of the measurement object 6 is output as detection result data DOT.

FIGS. 7(a) and 7(b) are explanatory diagrams relating to a conventional light amount correction method, and FIG. 7(a) is an explanatory diagram relating to drive control of a semiconductor laser projection system. In a),
The semiconductor laser projection system 1 includes a light emitting element 1a, a light receiving element 1b, and a substrate 1c formed in the same package. The amount of light emitted by the laser beam Ll is kept constant by controlling the drive current ID flowing into the light emitting element 1a. This control is performed by inputting the light receiving element output current iPD output from the light receiving element lb and controlling the output of the driving current ID by the semiconductor laser driving power supply 2.

FIG. 2B is a schematic diagram of a light receiving area of a four-part photodetector.

In the figure, A, B, C, and D are the amount of light received in each divided region, and the reflected light L2 is detected in the four divided light receiving regions.The incident position of the reflected light L2 is the 7 varies with variations in the inclination angle ρ of the surface. Further, a variation in the reflectance ρ results in a variation in the amount of received light. At this time, the variation in the reflectance ρ is different from the amount of change in the position of the incident light representing the surface waviness shape of the object 6 to be measured. Therefore, the variation in reflectance ρ is
This adversely affects the true measurement of the surface waviness shape of the object 7 to be measured. In order to eliminate the influence of this variation in reflectance ρ, the following method has been used.

The first method is to calibrate the differential amount of received light including the fluctuation of the reflectance ρ using correction factors xi and x2. this is,
The differential received light amount (A+B)-(C+D) or (A+D)-(B+C) is normalized using the total light amount X=A+B+C+D. Here, the total amount of received light A+B+C
+D is calculated by the control n circuit 5 every time the reflectance ρ of the surface of the object to be measured 6 changes.

In addition, the second method introduces another sensor system for measuring reflectance, detects the surface reflectance, and calculates the difference in the amount of received light (A+B).
-(C+D), (A+D)-(B+H are normalized and their influence is removed.

[Problem to be solved by the invention]

By the way, according to the conventional example, the semiconductor laser projection system 1 is as follows.
Feedback control is performed by the semiconductor laser drive power supply 2, and the laser light L1 is kept constant. Furthermore, in the light receiving and detecting system, the influence of fluctuations in reflectance on the surface of the object to be measured 6 is removed by the first method as shown in FIG. 7(b) and the second method described above.

This causes the following problems.

(2) The semiconductor laser projection system 1 controls the drive current ID regardless of the fluctuation of the reflectance ρ of the object to be measured 7 regarding the light emission scene.

■First. According to the method, calculation processing such as addition processing of the total amount of received light X-A+B+C+D is required every time the reflectance ρ changes. This makes it impossible to speed up the inspection process as a whole.

(2) According to the second method, it is necessary to introduce a sensor system for measuring reflectance. This causes an increase in inspection costs.

The present invention was created in view of the problems of the conventional example, and it is possible to detect light reception without making the fluctuation of the reflectance of the surface of the object to be measured irrelevant for controlling the amount of light emitted by a semiconductor laser projection system. It is an object of the present invention to provide a surface waviness inspection device and a light amount correction method thereof, which can omit the standardization process of the amount of light received by the system, remove the influence of fluctuations in the reflectance, and perform inspection with high accuracy.

[Means to solve the problem] 1. FIG. 2 each shows a principle diagram of the surface waviness inspection device and the light amount correction method of the present invention.

The device includes a light emitting means 11, a light emission driving means 12, a light reception detecting means 13, and a control means 14, and emits a laser beam L11 from the light emitting means 11 to an object to be measured 17, and In the surface waviness inspection device for detecting the reflected light L22 from the object 17 to inspect the surface waviness of the object to be measured 17, a feedback means 16 is provided between the light reception detecting means 13 and the light emission driving means 12, The drive signal rD (light emission amount) output from the light emission driving means 12 is controlled based on the light reception signal 311 (light reception light amount) output from the light reception detection means 13, and the light emission means 11 and the light emission An output limiting means 15 is provided between the driving means 12 and is cut off when the driving signal ID (emitted light M) outputted from the light emitting driving means 12 exceeds an arbitrary set value SR. Blocking information S on 14
The method is to irradiate a laser beam L11 to a measured object 17 having an arbitrary reflectance ρ, receive and detect reflected light L21 from the measured object 17, and detect the reflected light L21 from the measured object 17. The light emission amount of the laser beam L11 is controlled so that the total light amount including the influence of the detected reflectance ρ is always constant,
Achieve the above objectives.

[Effect]

According to the device of the present invention, the light reception signal S11 outputted from the light reception detection means 13 is transmitted to the light emission driver rL by the feedback means 16.
He returned to the 12th.

Therefore, fluctuations in the reflectance ρ of the surface of the object to be measured are automatically included in the light reception signal S11 that is proportional to the amount of light received. Therefore, the driving current I is proportional to the amount of light emitted by the laser beam L11.
D can always be controlled using a light reception signal that includes the reflectance ρ.

This makes it possible to always keep the amount of light heard and received constant regardless of changes in the reflectance of the object to be measured.

Furthermore, according to the device of the present invention, when the drive current ID output from the light emitting drive means 12 exceeds an arbitrary set value [R, the output limiting means 15 cuts off the cutoff information, and the cutoff information is output to the control means 14. be done.

For this reason, the reflectance ρ of the surface of the object to be measured fluctuates sharply.
Control port 4 for the listening/receiving sight of the light emitting/receiving system! (If it deviates significantly from a, it is possible to interrupt the measurement of the surface waviness state and recognize the occurrence of the abnormality.

At this time, the output limiting means 15 can prevent excessive current from being applied to the light emitting means 11.
It becomes possible to protect the

Further, according to the method of the present invention, the amount of light emitted by the laser beam L11 is controlled so that the amount of light that is heard and received, including the influence of the reflectance ρ, is always constant.

For this reason, the total received light 11X-A+B
There is no need to introduce +C+D or another sensor system and normalize it by surface reflectance.

Therefore, it is possible to reduce the inspection processing time with respect to the addition processing time and page division processing time related to standardization.

This reduces the burden on the control circuit 14 and makes it possible to speed up the surface waviness inspection process as a whole.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

3 to 5 are diagrams for explaining a surface waviness inspection device and its light amount correction method according to an embodiment of the present invention, and FIG. 3 shows a configuration diagram of the surface inspection device according to an embodiment of the present invention. There is.

In the figure, numeral 21 is a semiconductor laser projection system which is an embodiment of the light emitting means 11, and is used to irradiate an object to be measured such as a semiconductor wafer 27 with laser light L21. 22 is
This is a semiconductor laser driving power source which is an example of the light emitting driving means 12, and a driving power source ID is provided to the semiconductor laser projection system 21.
It is intended to supply

23a is a four-division light detection circuit, and 23b is a current/voltage conversion circuit, which is an embodiment of the light reception detection means 13. The four-division light detection circuit 23a receives and detects reflected light L22 from the semiconductor wafer 27 and the like. The current-voltage conversion circuit 23b photoelectrically converts the amount of light received by the four-division photodetection circuit 23a, further converts the photovoltaic current into voltage, and outputs the light reception signal S11 and the light reception detection signal 312. The light reception signal S11 is a signal obtained by converting the amount of light received and heard into the four-division light detection circuit 23a into a current/voltage. In addition, the light reception detection signal S12 is the vertical and horizontal difference output of the 4-division light detection circuit 23 (■A+VB) - (VC+VD)
and (VA+VD)-(VB-VC).

Kono differential output (vA+VB) - (VC+VD) and (VA
+VD)-(VB+VC) is an amount proportional to the amount of positional displacement of the reflected light L22.

A CPU (Central Processing Unit) 24 is an embodiment of the control means 14, and holds in advance a conversion table for recognizing the surface waviness shape such as angle data from the position data of the reflected light L22.

The CPU 24 receives the light reception detection signal S12 and the abnormality detection signal S1.
3 is input, and the surface waviness state of the semiconductor sea urchin 27 is output as detection result data DO'T based on the angle data held in the conversion table.

Reference numeral 25 denotes a current limiter circuit which is an embodiment of the output limiting means 15, and a configuration diagram thereof is shown in FIG. 4(a). This has a function of automatically cutting off the drive current ID that exceeds a certain set value IR. In addition, the current limiter circuit 25 has a drive current! When D is shut off, the information is converted into an abnormality detection signal S13 and has a function of notifying the CPU 24. R is the setting signal S1 of the CPU 24
4.

The abnormality detection signal S13 is a notification signal of the occurrence of an abnormal situation indicating adhesion of dust or the like on the surface of the semiconductor wafer 27 or the like. This is because the reflectance is significantly reduced due to dust adhesion or scratches on the surface of semiconductor wafers, etc., and in order to increase the amount of light generated by the semiconductor laser projection system to compensate for this, the drive current TD is set to a value! This occurred after exceeding R.

A gain control circuit 26 is an embodiment of the feedback means 16, and is used to adjust the received light signal S11 when it is not at a desired control value. Note that Swl is a selection switch, and the gain control circuit 26 is omitted. This means that when the light reception signal 311 satisfies the desired control value,
Point b is selected and the gain control circuit 26 is passed.

These constitute a surface waviness inspection device according to an embodiment of the present invention.

FIGS. 4(a) and 4(b) are explanatory diagrams of a surface waviness device according to an embodiment of the present invention, and FIG. 4(a) is a configuration diagram of a current limiter circuit.

In the same figure (a), the current limiter circuit 25 includes an operational amplifier 51, a comparator 52, and a resistor R.

It consists of relay switch SW2 etc.

The drive current r output from the semiconductor laser drive current 22
When D exceeds a certain set value rR, relay switch S is activated.
W2 operates, and the inflow to the semiconductor laser projection system 21 is blocked. The set value IR is determined in anticipation of damage to the light emitting element of the semiconductor laser projection system 21, etc.

FIG. 5B is a diagram showing the relationship between the amount of light received by the rudder and the drive current using the reflectance ρ as a parameter.

In the figure, the vertical axis represents the drive current ID, and the horizontal axis represents the amount of light received by the rudder X. ■D□8 indicates the maximum drive current that can flow into the semiconductor laser projection system 21. AX is
This is the operating range of the current limiter circuit, and is the range in which drive current TD exceeding ID and □ is cut off.

BX is a control target value, which is arbitrarily set to the amount of light received by the rudder X. ρ1. ρ2. ρ3 is the reflectance, ρ
The relationship is 3>ρ2>ρl. This represents a variation in the reflectance ρ of the surface of the semiconductor wafer 27 or the like. Further, the variation in the reflectance ρ reflected in the total received light 1x is controlled by changing the drive current ID so as to keep the control target value B constant. Further, it is thought that the variation in the reflectance ρ is caused by the laser beam L21 being scattered by scratches, dust, etc. on the surface of the semiconductor wafer 27.

At this time, the amount of received light decreases significantly.

In this way, the light reception signal S11 outputted from the current/voltage conversion circuit 23b is fed back to the semiconductor laser drive voltage [22] by the gain control circuit 26 and the like.

Therefore, fluctuations in the reflectance ρ of the surface of the semiconductor wafer 27 are automatically included in the light reception signal 311 which is proportional to the amount of light received. Therefore, for the drive current ID which is proportional to the amount of light emitted by the laser beam L11, the light reception signal S always includes the reflectance ρ.
11.

This makes it possible to always keep the total received light 1x constant regardless of variations in the reflectance ρ of the semiconductor wafer 27 and the like.

Further, according to the embodiment of the present invention, the driving type ? When AID exceeds an arbitrary set value IR, it is cut off by the current limit circuit 25, and the abnormality detection signal S L, 3 is output to the CPU 24.

Therefore, if the reflectance ρ of the surface of the semiconductor wafer 27 etc. fluctuates drastically and the total received light of the 4-split photodetector 23a or the current/voltage conversion circuit 23b greatly deviates from the control target value, the surface It becomes possible to interrupt the measurement of the undulation state and recognize the occurrence of an abnormality.

FIG. 5 is a flowchart relating to a light amount correction method according to an embodiment of the present invention.

In the figure, first, in step P1, a semiconductor wafer 27 having an arbitrary reflectance ρ is irradiated with a laser beam L21. Next, in step P2, the reflected light L2 from the semiconductor wafer 27
2 is detected by light reception. At this time, the influence of the variation in the reflectance ρ of the surface of the semiconductor wafer 27 is included in the total received light 1x.

Next, in step P3, it is determined whether the amount of light to be heard or received is large or small.

This judgment may be made via the CPU 24, or may be made by the measurer if the reflectance is approximately constant with the reflectance of the surface of the semiconductor wafer 27 or the like.

At this time, if the received light signal S11 satisfies the amount of feedback (YES), the process moves to step P5. If the feedback amount is not satisfied (No), step P
Move to 4.

In step P4, gain is adjusted. The gain adjustment is
This may be carried out via the CPU 24 or may be carried out by the measuring person. At this time, if the received light signal S11 has a small amplitude, for example, it is amplified, and if the received light signal S11 is large, it is amplified. Reduce that gain.

Next, the total received light received in step P5! The signal 1X is converted into a light reception signal 311 and fed back to the semiconductor laser drive power source 22.

Further, in step P6, the amount of light emitted by the laser beam L21 is controlled to make the control target value B=the total amount of received light X.

Next, in step P7, the magnitude of the drive current ID is determined. This judgment is made by the comparator 52 of the current limiter circuit 25.
will be carried out. At this time, if the drive current [D exceeds the set value IR (YES), the process moves to step P8.

In step P8, the drive current ID is cut off.

Thereafter, in step P9, the CPU 24 is notified of the occurrence of an abnormal situation. After the notification ends, the process moves to step PI2.

If the drive current ID is not cut off in step P7 (NO), the process moves to step PIO.

After step PIO, similarly to the conventional example, the light reception detection signal 312 is output to the CPU 24, and the light reception detection signal S12 is compared with the data held by the CPU 24 at step pH to inspect the surface waviness of the semiconductor wafer 27. .

Thereafter, in step P12, it is determined whether or not all inspections have been completed. If it does not end (No), return to step P1 again and perform steps P1 to P7. PiO-P12 or step PL-P9. The process contents of P12 are repeated, and if all are completed (YES), the surface waviness inspection process is ended.

In this way, the amount of light emitted by the laser beam L11 is controlled so that the amount of light that is heard and received, including the influence of the reflectance ρ, is always constant.

For this reason, unlike the conventional method, variations in the amount of received light due to fluctuations in the reflectance p of the semiconductor wafer 27 can be reduced by the total received light 1i.
X-A+B+C+D and the process of introducing another sensor system and standardizing it by surface reflectance become unnecessary. Therefore, it is possible to reduce the addition processing time and division processing time related to standardization.

This reduces the burden on the CPU 24 and makes it possible to speed up the surface waviness inspection process as a whole.

〔Effect of the invention〕

As described above, according to the present invention, the influence of fluctuations in reflectance on the surface of the object to be measured can be automatically corrected by controlling the amount of light received and heard to be constant.

Therefore, it is possible to perform surface waviness inspection processing with high precision in the automatically corrected light emitting/receiving system.

Further, it is necessary to standardize the amount of received light as in the conventional method. Therefore, the inspection processing time can be shortened.

This makes it possible to improve the processing efficiency of the surface waviness inspection device.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram of the surface waviness inspection device of the present invention, FIG. 2 is a principle diagram of the light intensity correction method of the surface waviness inspection device of the present invention, and FIG. 3 is a surface diagram of an embodiment of the present invention. 4(a) and 4(b) are explanatory diagrams of a surface waviness inspection device according to an embodiment of the present invention; FIG. 5 is a diagram of a light amount correction method according to an embodiment of the present invention. Flowchart, FIG. 6 is a block diagram of a conventional surface waviness inspection device, and 1u (a) and (b) are explanatory diagrams of a conventional sight correction method. (Explanation of symbols) 1.11.21. ... Light emitting means (semiconductor laser projection system), 2.12.22 ... Light emission driving means (semiconductor laser driving power supply), 13 ... Light reception detection means, 5.14.24 ... Control means ( CPU or control circuit), 15.25... Output control means (current limiter circuit), 16.26... Feedback means (gain control circuit), 6.17
．． 27...Object to be measured (semiconductor wafer, etc.), 3.23a
...4-split photodetector, 4.23b...Current/1it pressure conversion circuit, 51...
Operational amplifier, 52... Comparator, 1a... Light emitting element, lb... Light receiving element, lc... Substrate, Ll, L11, L21... Laser light, L2. L12
．． L22...Reflected light, ρ, ρ1. ρ2. ρ3...Reflectance, IR...Set value, ! D... Drive type fi (light emission amount), 31, S11... Light reception signal (light reception amount), S2. S1
2... Light reception detection signal (difference output), S3... Light reception light amount sum output, S13... Shutdown information (abnormality detection signal), 314...
Setting signal, DOT...detection result data, SWI, SW2...switch or relay switch,
R...Resistor, iPD, IF...Feedback current (light receiving element output current), A
, B, C, D... amount of received light, xi, x2... correction factor, AX... operating range of the current limiter circuit, BX... control target value, X... total amount of received light.

Claims (1)

[Claims] (1) A light emitting means (11), a light emitting driving means (12),
It includes a light reception detection means (13) and a control means (14), and emits the laser beam (L11) from the light emitting means (11) to the object to be measured (17), and emits the laser beam (L11) from the object to be measured (17). The reflected light (L22) of the object to be measured (1) is received and detected.
7) In the surface waviness inspection device for inspecting surface waviness, a feedback means (16) is provided between the light reception detection means (13) and the light emission driving means (12), and the feedback means (16) is provided between the light reception detection means (13) and the light emission driving means (12). A surface waviness inspection apparatus characterized in that the amount of light emitted from the light emission driving means (12) is controlled based on the amount of light received by the light emitting device. (2) Output limiting means (15) is provided between the light emitting means (11) according to claim 1 and the light emitting driving means (12), and the amount of light emitted from the light emitting driving means (12) is controlled. A surface waviness inspection device characterized in that it is shut off when an arbitrary set value (IR) is exceeded, and outputs shutoff information (S13) to the control means (14). (3) Irradiate a laser beam (L11) to an object to be measured (17) having an arbitrary reflectance (ρ), and
receiving and detecting the reflected light (L21) from the laser beam, and controlling the amount of emitted light of the laser beam (L11) so that the total amount of received light including the influence of the detected reflectance (ρ) is always constant. A light amount correction method for a surface waviness inspection device characterized by: