JPH1030989A - Surface inspecting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rid a wafer of an area where inspection is impossible due to scattered light from edges of the wafer, and surely inspect the whole surface of the wafer by carrying out reciprocating scanning with two luminous fluxes by a scanning optical system and carrying out signal processing based on the scanning signals of the two scanning luminous fluxes in the direction from an object to be measured toward outside of the object to be measured. SOLUTION: A light source part 21 is provided with a first and a second laser light source and being divided into approximately two ranges, the surface of a wafer 1 is scanned by luminous fluxes 11, 12. The first light source is turned on to carry out forward-scanning from the right to the left and the second light source is turned on to carry out backward-scanning from the left to the right. Though light beam comes into collision with an edge near the terminal of the outward scanning or in the middle of the outward scanning and intense scattered light is caused, no inconvenience to the inspection is caused for the forward part from the point is the outside of the wafer 1 and is not necessary to be inspected. That is, during the time when intense scattered light is emitted near the terminal part or in the middle of the forward scanning with the beam and normal operation of a photoelectric transformer of a light receiving part 30 is not carried out, the spot P1 is moved in the outside of the wafer 1 or a part of the backward scanning route and no trouble is caused.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface inspection apparatus for inspecting the surface condition of an object, and more particularly, to a surface inspection apparatus which is most suitable as a wafer surface inspection apparatus for inspecting foreign matter and scratches on the surface of a semiconductor wafer. About.

[0002]

2. Description of the Related Art Generally, a semiconductor integrated circuit is manufactured by forming a circuit on a semiconductor substrate (wafer) by a photolithography process. At this time, a large number of identical integrated circuits are formed on one wafer, and finally, they are separated into a single integrated circuit chip. At this time, if a foreign substance is present on the wafer, a defect occurs in a circuit pattern formed in that part, and the integrated circuit becomes unusable. As a result, the number of integrated circuits that can be obtained from one substrate is reduced, and the yield is reduced.

[0003] It is considered that such foreign matter is attached in a CVD process for forming a metal film on the wafer surface. That is, the foreign matter generated in the process device adheres to the wafer coming out of the device and becomes a defect in a subsequent lithography process.

Therefore, at a semiconductor integrated circuit manufacturing site, the generation of foreign substances is monitored using a wafer for inspection called a monitor wafer. The inspection wafer is passed through the process equipment in the same manner as the material wafer, and the monitor wafer is inspected before and after the inspection wafer. If the generation of foreign matter is found, measures such as cleaning of the equipment are taken.

As a general inspection method, a method is generally used in which a laser beam is focused on the wafer surface, scattered light from the focused point is received, and a foreign substance or the like is detected from the signal. FIG.
1 shows an example of a conventional wafer surface inspection apparatus.

[0006] A laser is used as a light source, and light emitted from the laser is focused on the wafer surface by an optical system. The collected laser light is scanned in one direction using an optical deflector or the like, and at the same time, the wafer is moved in a direction orthogonal to the above direction. As a result, the entire surface of the wafer is scanned.

[0007] The scattered light from the focal point on the wafer is received by a photoelectric converter via a lens. The photoelectric converter that has received the scattered light outputs a pulse-like signal corresponding to the intensity of the scattered light when the focal point crosses a foreign substance or the like. The size of the scattering object is determined based on the magnitude of the signal output.

[0008]

When inspecting the entire surface of a wafer with a laser beam, it is necessary to scan a slightly larger area than the wafer. This is because there is a moment when the light beam returns to a stationary state when the light beam is turned back. In general, at this point, a pulse signal cannot be obtained and inspection cannot be performed.

However, if the scanning range is set slightly wider than the wafer, the following problems occur when light strikes the edge of the wafer.

That is, in the wafer surface inspection apparatus, a high-sensitivity photoelectric converter is used to detect weak scattered light due to foreign matter on the wafer. On the other hand, since the scattered light generated at the edge of the wafer is much larger than the scattered light of the foreign matter, the photoelectric converter does not operate normally for a while after receiving the scattered light. During this time, the focal point continues to move, so that a certain range from the edge of the wafer cannot be measured.

For example, if the beam is raster-scanned and measurement is performed during scanning in one direction, an untestable area shown by hatching in FIG. 12 is formed. The size of this area is
The larger the beam scanning speed is, the larger the beam scanning speed becomes. Therefore, when a wafer having a larger diameter is to be inspected in a short time, a non-inspection area becomes large, and accurate inspection cannot be performed.

The present invention has been made in view of such circumstances, and an object of the present invention is to eliminate a range that cannot be inspected due to scattered light from an edge of a wafer and to reliably inspect the entire surface of the wafer. An object of the present invention is to provide a surface inspection device.

[0013]

SUMMARY OF THE INVENTION The present invention provides a light source, a scanning optical system including a scanning means for scanning a light beam from the light source, and a scanning optical system for converging light on a surface to be inspected, and a scanning means for scanning the surface of an inspection object by the scanning means. Moving means for moving in a direction different from the direction,
In a surface inspection apparatus having a light receiving unit including a photoelectric converter that receives scattered light from the light condensing point and a signal processing unit that processes a signal from the light receiving unit, the scanning optical system includes:
The signal processing unit is configured to perform reciprocal scanning with two light beams, and to perform signal processing based on a signal in a scan in which the two scanning light beams travel from the target to the outside of the target. The gist is a surface inspection apparatus characterized by the above.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A surface inspection apparatus according to the present invention includes a light source, a scanning optical system including a scanning unit for scanning a light beam from the light source, and a scanning optical system for converging light on a surface to be inspected. A moving unit for moving in a direction different from the scanning direction of the unit, a light receiving unit provided with a photoelectric converter for receiving scattered light from the focal point, and a signal processing unit for processing a signal from the light receiving unit It has.

The scanning optical system is configured to reciprocally scan with two light beams, and the signal processing unit includes:
The two scanning light beams are configured to perform signal processing based on signals in scanning in a direction from the target to the outside of the target.

The entire target area is scanned at least once by one of the two light beams. With one light beam, a substantial surface inspection is performed intermittently in time.

In a preferred embodiment of the present invention, the scanning unit is provided with a synchronizing means for controlling so that one of the two reciprocating light converging points is effective on the outward path and the other on the return path. .

Further, the light source unit includes one light source,
The synchronizing unit can be configured so that a light beam from the light source can be switched to two scanning optical systems.

Further, the light source unit may include at least two light sources having the same wavelength, and the synchronization unit may be configured to provide a shutter in an optical path of a scanning light beam from the two light sources.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an optical diagram conceptually showing a surface inspection apparatus, and FIG. 2 is a block diagram.

The surface inspection apparatus includes a moving unit 10 and an optical system 2.
0, a light receiving unit 30, and a signal processing unit 40.

The moving section 10 includes the stage 2 which can reciprocate at least in one direction. This stage 2 moves an object such as a wafer 1 at a constant slow speed in FIG.
In the direction of arrow A. In FIG. 1, the stage 2 is hidden below the wafer 1.

The optical system 20 includes a light source 21 and a scanning mirror 2.
3, a focusing lens 25 and a condenser lens 27 are provided.

The light source section 21 includes first and second laser light sources having a high intensity such as a semiconductor laser,
And the luminous flux 12 are approximately 2 on the wafer 1 to be inspected.
Are divided into two ranges, and are arranged so as to be incident in directions that can be scanned.

Based on the signals V1 and V2 shown in FIG.
The light source and the second light source are alternately turned on, and the forward scan (t0-t) is performed.
In 5), the light beam 11 emitted from the light source 21 scans, and in the backward scanning (t5-t10), the light beam 12 emitted from the light source 2 scans.

As shown in FIG. 9, the first and second shutters 7
It is also possible to obtain the beams from the first and second light sources 21a and 21b alternately by providing a and 7b and opening and closing them in synchronization with the synchronization circuit 6.

The scanning mirror 23 is rotated by an optical deflector 26 corresponding to a scanning unit according to a signal from the arithmetic control unit 41, and reciprocates the light beam 11 and the light beam 12 emitted from the light source unit 21.

The converging lens 25 is provided on the wafer 1 as an object, the first light beam 11 and the second light beam 12 emitted from the light source 21.
To form spots P1 and P2. The spots P1 and P2 are linearly scanned on the wafer 1 by the rotational movement of the scanning mirror 23 to form a scanning line SL.

The condensing lens 27 condenses the scattered light scattered by the foreign matter on the wafer 1 on the light receiving surface of the photoelectric converter.
The condensing lens 27 is arranged in a direction and at a position where the regular reflection light, which is the result of the regular reflection of the scanning light from the light source on the wafer surface, does not enter.

Next, a scanning method using an optical system will be described.

In this embodiment, scanning from right to left is defined as forward scanning, and scanning from left to right is defined as backward scanning. In FIG. 4, the left side is the first beam side, and the right side is the second beam side.

In this embodiment, the first light source is turned on in the forward scan to scan the first light beam, and the second light source is turned on in the backward scan to scan the second light beam. In FIG. 4, the scanning lines are shown sparsely for easy understanding.
The beam scans the entire surface of the wafer 1 densely.

Taking the first light beam side as an example, strong scattered light hits the edge near the end of the forward scan of the beam or in the middle of the forward scan, but this position corresponds to the outside of the wafer and needs to be inspected. There is no problem in inspection because there is no. In other words, the spot P1 moves outside the wafer and a part of the return path (transition area) while strong scattered light is generated near or in the middle of the forward scan of the beam and a later-described photoelectric converter 31 does not operate normally. There is no problem. In addition, even if there is an object that is scattered by a light beam just outside the wafer to be inspected, the inspection is not hindered for the same reason, which reduces restrictions on manufacturing the apparatus. Help.

The light receiving section 30 has a photoelectric converter 31. The photoelectric converter 31 receives scattered light scattered by the foreign matter irradiated with the scanning light, and outputs an electric signal corresponding to the scattered light. For example, a photomultiplier can be used as the photoelectric converter. In the forward scan, light scattered by the first light beam is received. In the backward scan, light scattered by the second light beam is received.

The signal processing section 40 includes a control operation processing section 41, a storage section 41, a reference signal generator 43, and a display section 44.

As described above, since only the data of the forward scan on the first light beam side and the data of the backward scan on the second light beam side are fetched, no signal appears in the same order as scanned by one scanning line. Therefore, in order to handle the data as time-series data indicating one end to the other end of the wafer, a device such as rearrangement of data is required.

That is, the scattered light data does not appear during the period from t0 to t5, and the scattered light data from the position L5 to the position L10 appears in order during the period from t5 to t10.

Then, the scattered light data does not appear during the period from t10 to t15, and the scattered light data from the position L15 to the position L20 appears in order during the period from t15 to t20.

Since the actual interval between scanning lines is narrow, the order of data in the period from t5 to t10 is connected to the data from t20 to t15 by reversing the data order in the latter half of the return path, as if by one scanning line. It can be handled as if a wafer were scanned and a scattered light signal (whole scan data) was obtained.

As a process for this, "a method of specifying memory addresses in a predetermined order when reading data".
Are shown in FIG. 5 and FIG.

FIG. 5 is a scanning and storing flowchart.
FIG. 6 is a reading flowchart. In FIG. 5, data is stored in memory in the order of scanning.

Sl: The number of scans n is set to n = 1.

S2: The number i is set to i = 1.

S3: The data of the signal from the light receiving section is sequentially stored in AD (i).

S4: It is determined whether one scan is completed. If not completed, the process proceeds to S5, and if completed, the process proceeds to S6.

S5: Set i = i + 1 and increment i by one. It is determined whether i is 5 or less. As long as the value is 5 or less, the process returns to S3, and the data is read in the direction in which the forward scan data address decreases. If i exceeds 5, the process proceeds to S6.

S6: It is determined whether all readings have been completed. If all scanning has not been completed, the process proceeds to S7, and if completed, the process ends.

S7: n = n + 1, n is increased by 1, and S2
Return to

In FIG. 6, data is read from the memory in a predetermined order, and a scattered light signal (whole scan data) is obtained as if a wafer were scanned by one scanning line.

When storing data in the memory, the signals from the photoelectric converters are stored as they are in time series. At this time, the data in the first half of the forward scan and the first half of the backward scan, in which the scanning is not valid, are excluded from the storage targets. Then, the storage capacity of the memory can be used efficiently.

However, these data may be stored.

Sl: The number of scans n is set to n = 1.

S2: The scanning position i is set to i = 1.

S3: Data read for forward scan. AD
The data of (10n-4-i) is read.

S4: The scanning position is set to i = i + 1, and i is incremented by one.

S5: It is determined whether i is 5 or less. If the value is 5 or less, the process returns to S3, and the outward scan data is read in the direction in which the address decreases. If i exceeds 5, the process proceeds to S6.

S6: The backward scan data is read in the order of increasing address AD (10 (n-1) + i).

S7: It is determined whether i = 10. That is, it is determined whether one scan is completed. If one scan is not completed, the process returns to S3.

S8: It is determined whether all readings have been completed.

S9: If all scanning is not completed, n = n +
It is set to 1, n is incremented by 1, and the process returns to S2.

A specific example will be described.

The data is stored sequentially in time series.

On the other hand, at the time of data reading, the address at which the data of the forward scan (first half) is stored is read in the order of the address AD (10n-5-i) which is the reverse of the storage order.

The memory address corresponding to the backward scan data is in the order of increasing address AD (10 (n-1) +
Read out in i).

That is, the data of AD1 to AD5, which are the memory addresses corresponding to the data of the forward scan, are
5 is sequentially read up to AD1 in the direction in which the address decreases.

Data from AD6 to AD10, which are memory addresses corresponding to the backward scan data, are sequentially read from AD6 to AD10 in the direction in which the address increases.

Thereafter, similar processing is repeated.

Thus, the data stored up to the memory address can be treated as a scattered light signal (whole scan data) obtained by scanning the wafer with one scanning line.

As described in the prior art, when the light source unit is turned on during the entire scanning period, the light beam hits the edge of the wafer, and when the scattered light enters the light receiver, the light receiving unit is saturated. Then, a range that cannot be measured for a while (shaded area in FIG. 13) is formed. Therefore, as a result of intensive research, the present inventor has taken data after passing the time of uninspection due to scattered light at the edge of the wafer, and if this is also performed in the opposite direction scanning, a small part of the upper and lower parts of the wafer It was found that almost the entire data could be obtained except for, and the present invention was completed.

In the first embodiment, the inspection is started from the time when the light beam reaches the center line of the wafer in order to minimize the area where data is acquired twice.

Next, a second embodiment will be described.

The second embodiment is a modification of the signal processing section.

That is, in order to treat the data as time-series data indicating one end to the other end of the wafer, the data rearrangement is performed in a different manner from the first embodiment. Method ".

[Method of Specifying Memory Address in Predetermined Order in Data Storage] When storing data in a memory, the entire scanning data can be formed by devising the order of specifying memory addresses. It is a method.

This will be described with reference to the flowchart of FIG.

Sl: The number of scans n is set to n = 1.

S2: The scanning position i is set to i = 1.

S3: It is determined whether the scan is the forward scan.

S4: In forward scan, data is transferred to address A
D (10n-4-i).

S5: At the time of backward scanning, data is transferred to address A
D (10 (n-1) + i).

S6: It is determined whether the scanning is completed.

S7: If one scan is not completed, i =
i is incremented by 1 as i + 1.

S8: It is determined whether or not all scanning is completed.

S9: If all scans have not been completed, n = n +
Set to 1 and increase n by 1.

FIG. 8 shows the relationship between stored data and addresses on an object.

As a specific example, the scanning is started, and during the first half of the forward scan (t0 ≦ t <t5), the data is stored in the direction of decreasing the address in the order of the address AD (10n−5−i). .

The data in the backward scanning period (such as t5 ≦ t <10) is sequentially stored in memory addresses AD6 to AD10.

That is, the forward scanning period (t0 ≦ t <t
In 5), the output data of the light receiving section is sequentially stored in memory addresses AD5 to AD0. In this case, the data is stored in the direction in which the memory address decreases.

During the backward scanning period (t5 ≦ t <t10), the output data of the light receiving section is stored in the memory address AD5
To AD0 sequentially. In this case, the data is stored in the direction in which the memory address decreases. Thereafter, similar processing is repeated.

As a result, the memory addresses AD1 to A1
The data stored up to D10 can be treated as a scattered light signal (whole scan data) obtained by scanning the wafer with one scanning line.

In this case, by sequentially reading out the memory addresses, the entire scanning data can be obtained.

Next, a third embodiment will be described with reference to FIG.

The third embodiment has a configuration in which there is one light source 21 and this is switched by the movable reflecting mirror 9. The movable reflecting mirror 9 is driven by a driving circuit 8.

The switching signal given to the drive circuit 8 is shown in FIG.
In the forward scan in which a signal similar to the signal shown in (1) can be used, the movable reflecting mirror enters the optical path and reflects the light from the light source upward to form the first light flux. In the backward scanning, the light beam is retracted from the optical path, and the light beam proceeds as it is to become the second light beam.

Further, a modified example will be described.

In the first embodiment, the front scan data is formed by joining the data in the second half of the forward scan and the second half of the backward scan. However, it is possible to provide an overlapping area to receive the data. Can also.

In this case, the data connection can be ensured by comparing the data in the overlapping areas.

Further, as shown in FIG. 10, the moving section may be configured to rotate the stage. At this time, if the diameter address (180 °) is used, the data is appropriately rearranged in the same manner as described above. When the radius address (360 °) is used, the address increases from the center to the outside.

[0099]

According to the surface inspection apparatus of the present invention, a portion near the edge of a wafer which could not be inspected conventionally can be inspected, and the possibility of overlooking the generation of foreign matter can be reduced.

[Brief description of the drawings]

FIG. 1 is an optical layout diagram of a first embodiment.

FIG. 2 is a block diagram of the first embodiment.

FIG. 3 is a signal waveform diagram for driving a light source.

FIG. 4 is a diagram showing data stored as data by the signal processing unit of the first embodiment on an object.

FIG. 5 is a flowchart of data storage according to the first embodiment.

FIG. 6 is a flowchart of data reading of the first embodiment.

FIG. 7 is a flowchart of data storage according to the second embodiment.

FIG. 8 is a diagram illustrating data stored as data by a signal processing unit according to the second embodiment on an object.

FIG. 9 is a diagram illustrating an example of a light beam switching unit.

FIG. 10 is a diagram showing another example of the light beam switching means.

FIG. 11 is a diagram showing a modification of a method of rotating and moving a moving unit.

FIG. 12 is a schematic configuration diagram of a conventional wafer surface inspection device.

FIG. 13 is a diagram showing an untestable area when a wafer is raster-scanned.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Wafer 2 Stage 3, 4 Light beam switching means 10 Moving part 11 1st light beam 12 2nd light beam 20 Optical system 21 Light source part 23 Scanning mirror 25 Condensing lens 26 Optical deflector 27 Condensing lens 30 Light receiving part 31 Photoelectric converter 40 signal processing section P ₁ , P ₂ spot SL scanning line

Claims (4)

[Claims] 1. A scanning optical system comprising a light source, a scanning unit for scanning a light beam from the light source, and converging on a surface to be inspected, and a moving unit for moving the surface of the inspection object in a direction different from the scanning direction of the scanning unit. Moving means, a light receiving unit provided with a photoelectric converter for receiving scattered light from the focal point, and a signal processing unit for processing a signal from the light receiving unit, wherein the scanning optical system Is configured to perform reciprocal scanning with two light beams, and the signal processing unit performs signal processing based on a signal in a scanning direction in which the two scanning light beams travel from the object to the outside of the object. A surface inspection apparatus characterized by comprising. 2. The scanning unit according to claim 1, wherein the scanning unit is provided with a synchronizing means for controlling so that one of the two converging points reciprocating is effective in the outward path and the other is effective in the backward path. Surface inspection equipment. 3. The light source unit includes one light source, and the synchronization unit is configured to switch a light beam from the light source to two scanning optical systems. Surface inspection device as described. 4. The light source unit includes at least two light sources having the same wavelength.
The light source includes two light sources, and the synchronization unit includes: a light source that scans light beams from the two light sources;
The surface inspection apparatus according to claim 2, further comprising a shutter.