JPH054026B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is for irradiating the surface of an object to be inspected with laser beams from multiple directions and detecting foreign matter attached to the surface of the object to be inspected based on the scattered light. The present invention relates to a surface inspection device.

More specifically, the present invention relates to drive control of a laser oscillator for irradiating a laser beam onto the surface of an object to be inspected in such a surface inspection apparatus.

[Prior Art] As an apparatus for inspecting the surface of semiconductor wafers, etc., the surface of the object to be inspected is irradiated with polarized or non-polarized laser beams from multiple directions, and the scattered foreign particles are detected on the surface of the object to be inspected based on the scattered light. There is a surface inspection device configured to detect this.

Generally, in such surface inspection equipment, in order to stabilize the intensity of the irradiated laser beam, each laser oscillator for laser beam irradiation is controlled by a feedback control circuit so that its monitor light has a predetermined intensity. Driving conditions are now controlled.

[Problems to be Solved] In such a surface inspection apparatus, a laser beam emitted from one laser oscillator may be reflected by the surface of the object to be inspected and enter another laser oscillator.

Now, the amount of monitor light from the laser oscillator should be proportional to the output level of the laser oscillator.
However, as described above, when a laser beam from another laser oscillator is incident, it works to increase the amount of monitored light, so the feedback control circuit of that laser oscillator works to lower the output level of that laser oscillator.

As a result, the specified irradiation laser beam intensity (output level) may not be obtained, leading to a decrease in the detection sensitivity of minute foreign objects, and furthermore, the detection accuracy may become unstable due to fluctuations in the irradiation laser beam intensity due to fluctuations in the reflected laser beam intensity. Problems such as this are occurring.

[Object of the Invention] Therefore, the object of the present invention is to provide a surface that prevents a decrease in the detection sensitivity of minute foreign objects and stabilizes the detection accuracy by eliminating the adverse effects caused by such reflected laser beams. The purpose is to provide inspection equipment.

[Means for Solving the Problems] In order to achieve this object, the present invention irradiates the surface of an object to be inspected with laser beams from a plurality of directions using a plurality of laser oscillators, and uses the scattered light of the object to irradiate the surface of the object to be inspected. In a surface inspection device that detects foreign matter adhering to the surface of an object to be inspected, the driving conditions of each laser oscillator are controlled by a feedback control circuit so that the monitor light has a predetermined intensity. , given the hold instruction,
The device is characterized by providing drive condition fixing means associated with the feedback control circuit for fixing the drive conditions of each laser oscillator to the drive conditions at the time the hold instruction is given until the hold instruction is released. It is.

[Function] With this configuration, if a hold instruction is given to the drive condition fixing means at a point in time when no reflected beam of a laser beam from another laser oscillator is incident on the laser oscillator, the output level of each laser oscillator can be adjusted to reflect the reflected laser oscillator. Unaffected by laser beam incidence,
It can be fixed at a predetermined level.

Therefore, for example, when the object to be inspected is not set at the inspection position and the irradiated laser beam is reflected and does not enter the laser oscillator, a hold instruction is given to the driving condition fixing means, and the inspection of the object to be inspected is completed. If the hold instruction is not released until then, the surface of the object to be inspected can be inspected while stably maintaining the intensity of the irradiated laser beam at a sufficient specified intensity.

As described above, according to the present invention, it is possible to eliminate the adverse effects caused by the incidence of a reflected laser beam on a conventional laser oscillator, and to solve problems such as a decrease in the detection sensitivity of minute foreign objects and fluctuations in detection accuracy.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram of a surface inspection apparatus according to the present invention.

This surface inspection device irradiates the surface of the object to be inspected with S-polarized laser beams from multiple directions, so that foreign matter adhering to the surface of a patterned wafer can be detected by distinguishing it from the pattern. The polarized light component is photoelectrically converted, and the presence or absence of foreign matter adhering to the surface of the object to be inspected is determined from the level of the converted signal.

10 and 12 are S-polarized laser oscillators;
For example, a semiconductor laser diode is used. An object to be inspected 14 (for example, a semiconductor wafer) is set at an inspection position on an XYZ stage 16, and the same point on its surface is irradiated with an S-polarized laser beam by S-polarized laser oscillators 10 and 12. The object to be inspected is moved in the X and Y directions by the XYZ stage 16, and the irradiation point of the S-polarized laser beam is
Move according to that movement. That is, the surface of the object to be inspected is scanned in the X direction and the Y direction by the S-polarized laser beam.

18 is an objective lens, 20 is an S polarization cut filter, and 22 is a photomultiplier. Laser light scattered in a substantially perpendicular direction from the surface of the object to be inspected enters the S-polarization cut filter 20 via the objective lens 18, where only the P-polarization component is extracted and enters the photomultiplier 22, where it is electrically The signal is converted into a signal and input to the control processing section 24.

In the control processing unit 24, the photomultiplier 22
By comparing the output signal with a predetermined threshold, it is determined whether or not there is an attached foreign object, and the size and position information of the detected attached foreign object are stored in an internal memory. Note that the movement of the XYZ table 16 is controlled by the control processing section 24.

The S-polarized laser oscillator 10 is driven by a feedback control circuit so that its output level is maintained at a specified value. This feedback control circuit includes a photodiode 30 that photoelectrically converts the monitor light of the S-polarized laser oscillator 10, a deviation detection circuit 32 that detects a deviation voltage (current) between the output voltage (current) of this photodiode 30 and a reference value Rf, and this It consists of a drive circuit 34 that drives the S-polarized laser oscillator 10 under drive conditions (drive current value, etc.) depending on the deviation voltage (current).

Note that the monitoring photodiode 30 may be housed in the same container as the laser oscillator 10, or may be provided outside.

The other S-polarized laser oscillator 12 is similarly driven by a feedback control circuit consisting of a monitoring photodiode 36, a deviation detection circuit 38, and a drive circuit 40.

Note that the reference value Rf is given from the control processing section 24.

Now, when the object to be inspected 14 is set at the inspection position as shown in the figure, the irradiated S-polarized laser beam is reflected on its surface, and the S-polarized laser oscillators 10 and 12
In the past, the above-mentioned adverse effects occurred.

In this embodiment, hold circuits 42, 44 are inserted between the deviation detection circuits 32, 38 and the drive circuits 34, 40 in each feedback control circuit as drive condition fixing means to eliminate the adverse effects. There is.

Each hold circuit 42, 44 includes a control processing section 2.
A hold signal HLD is supplied from 4. This hold signal HLD is set to the L level when the surface inspection of the object to be inspected 14 is completed, and is set to the H level immediately before the next object to be inspected 14 is set at the inspection position as shown in the figure. H until the end of the inspection
held at the level.

Each hold circuit 42, 44 includes a control processing unit 24
During a period in which the hold signal HLD supplied from the control circuit 12 is at L level (a period in which a hold instruction is not given), the input deviation voltage (current) is input as is to the subsequent drive circuits 34 and 40. However, when the hold signal HLD changes to H level (when a hold instruction is given), the deviation voltage (current) at that point is held until the hold signal HLD changes to L level (until the hold instruction is released). ,
The held deviation voltage (current) is transferred to the drive circuit 34,
Continue to enter 40.

Therefore, the driving conditions for the S-polarized laser oscillators 10 and 12 during the inspection period are such that the object to be inspected 14 is not set at the inspection position, the irradiated laser beam is reflected from the surface of the object to be inspected, and the S-polarized laser oscillator 10 , 12, the output level of the S-polarized laser oscillators 10, 12 can be maintained at a sufficiently specified level.

In this way, in this surface inspection device, the intensity of the irradiated S-polarized laser beam is stably maintained at the specified sufficiently high intensity during surface inspection, so the detection sensitivity and detection accuracy of minute foreign objects are more stable than before. can be improved.

Although one embodiment has been described above, the present invention is not limited thereto.

For example, although the embodiment described above irradiates a laser beam from two directions, the present invention is equally applicable to an apparatus that irradiates from three or more directions.

Furthermore, although the embodiments described above utilize polarized laser beams, the present invention is equally applicable to devices that use non-polarized laser beams.

In the embodiment described above, a hold circuit as a drive condition fixing means is inserted between the drive circuit and the deviation detection circuit, but it may also be inserted between the monitoring photodiode and the deviation detection circuit. Further, the driving condition fixing means is not limited to such a hold circuit, but may be realized as other circuit means that can achieve a similar driving condition fixing effect.

In addition to this, the present invention can be implemented with appropriate modifications within the scope without departing from the gist thereof.

[Effects of the Invention] As explained in detail above, the present invention irradiates the surface of an object to be inspected with laser beams from a plurality of directions using a plurality of laser oscillators, and detects the surface of the object to be inspected based on the scattered light. The device is used to detect attached foreign matter, and each laser oscillator gives a hold instruction in a surface inspection device whose drive conditions are controlled by a feedback control circuit so that the monitor light has a predetermined intensity. When you are
According to the present invention, a driving condition fixing means associated with the feedback control circuit is provided for fixing the driving condition of each laser oscillator to the driving condition at the time when the hold instruction is given until the laser oscillator is released. For example, it is possible to realize a surface inspection device that eliminates the adverse effects of the conventional laser beam incident on a laser oscillator and improves the stability of detection sensitivity and detection accuracy of minute foreign objects.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a simplified configuration of an embodiment of a surface inspection apparatus according to the present invention. 10, 12...S polarization laser oscillator, 14...
Object to be inspected, 18...Objective lens, 20...S polarization cut filter, 22...Photomultiplier,
30, 36...Monitoring photodiode, 32,
38... Deviation detection circuit, 34, 40... Drive circuit, 42, 44... Hold circuit.

Claims (1)

[Claims] 1. A device that irradiates the surface of an object to be inspected with laser beams from multiple directions using a plurality of laser oscillators, and detects foreign matter attached to the surface of the object based on the scattered light. In the surface inspection apparatus, the driving conditions of each laser oscillator are controlled by a feedback control circuit so that the monitor light has a predetermined intensity, and when a hold instruction is given, the hold instruction is A surface inspection characterized by comprising drive condition fixing means associated with the feedback control circuit for fixing the drive conditions of each of the laser oscillators to the drive conditions at the time when the hold instruction was given until the hold instruction is given. Device. 2. The hold instruction as set forth in claim 1 is characterized in that the hold instruction is given before the object to be inspected is set at the inspection position and is released after the inspection of the surface of the object to be inspected is completed. Surface inspection equipment.