Inspection apparatus and inspection method

A defect inspection apparatus enable to efficiently perform a temperature control without involving an enlarged size can be achieved.The parts constituting the defect inspection apparatus are classified into parts need temperature control and parts not to need temperature control; all the parts need temperature control are accommodated together into a temperature-controlled part accommodating section 604, and the parts not to need temperature control are arranged in a heat radiating unit 605. The temperature in the temperature-controlled part accommodating section 604 is measured by a temperature measuring instrument 603 and a control CPU 602 in a temperature control unit 601 carries out control according to the measured temperature so that the interior of the temperature-controlled part accommodating section 604 is kept at a fixed temperature. Therefore, it becomes easy to keep the fixed temperature, when compared with a case in which individual parts are temperature-controlled separately by being heated or cooled, yielding an energy saving effect.

RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/JP2007/063126, filed on Jun. 29, 2007, which in turn claims the benefit of Japanese Application No. 2006-180638, filed on Jun. 30, 2006, and Japanese Application No. 2007-092779, filed on Mar. 30, 2007, and the disclosures of which Applications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to an inspection apparatus and an inspection method. The present invention is suitable, for example, to a defect inspecting apparatus for checking for the presence of minute foreign matter and other types of defects by using an optical system, such as a semiconductor inspecting apparatus, as well as a defect inspection method.

BACKGROUND ART

As semiconductor circuits are becoming increasingly fine, minute foreign matter on semiconductor substrates becomes to affect the quality of semiconductor products.

As a technology for detecting this type of foreign matter on the semiconductor substrates, Patent Document 1 discloses an inspection apparatus and inspection method that improve detection sensitivity and a throughput by achieving high-efficiency linear illumination from a direction in which diffracted light is not delivered so as to reduce light diffracted from a pattern and by enabling thresholds to be set according to pattern-depending signal variations.

Patent Document 2 discloses an inspection apparatus that comprises a unit for storing the relation between temperatures measured in advance or calculated through simulation and focused point offsets, a unit for predicting a focused point offset from this relation between temperatures and focused point offsets according to a temperature detection result obtained by a temperature detecting unit, and a unit for correcting a focused point offset according to the prediction provided by that unit.

DISCLOSURE OF THE INVENTION

In the prior art, however, there is no consideration for a case in which the relation between actual variations due to temperatures and focused point offsets is not constant.

For example, it is apparent that different members used in a defect inspection apparatus respond to a change in temperature at different speeds and causes different amounts of variations. Accordingly, the amount of variations, that are its comprehensive result, varies as the temperature changes with time.

The time elapsed after the temperature changes may be minute or sufficient, however, the difference between the amount of variations, which are a comprehensive result, and an amount of prediction is within the depth of focus of an optical inspection system, the sensitivity of the inspection apparatus drops only a little.

If the amount of variations, which are a comprehensive result, is greater than the depth of focus of the inspection optical system with the amount of prediction considered or if the amount of variations is small at present but the depth of focus, which is given by “z=±λ/2NA2” may become small due to technological innovation in the future, the drop of the inspection sensitivity of the apparatus for temperature changes can be no longer neglected.

To prevent this drop of the inspection sensitivity, it is necessary to suppress the amount of variations, which is a comprehensive result.

The use of a low thermal expansion material can be considered as a unit for suppressing the amount of variations caused by temperature changes, and temperature control can be considered as a unit for suppressing temperature changes.

However, the former unit is problematic in that the weight of the inspection apparatus is significantly increased, increasing burdens on the apparatus manufacturing line and a semiconductor line.

As an example of the latter unit, temperature control technology has been developed to maintain high precision in wafer overlaying positioning and the ease of imaging.

Specifically, an entire exposing apparatus is covered with a temperature control chamber, and temperatures of a measuring optical path space, a stage, structural supporting bodies, a lens, and a structural supporting body of the lens are controlled by individual chambers.

However, differences in positional precision demanded for targets, differences in optical structures, and different thermal sources make it difficult to apply the above temperature control technology to a defect inspection apparatus without alternation.

For example, the use of a temperature control chamber that covers an entire inspection apparatus enlarges the apparatus, resulting in large footprints. Therefore, burdens on the apparatus manufacturing line and semiconductor line are increased.

Technology that can efficiently control temperature while preventing the inspection apparatus from being enlarged is necessary.

An object of the present invention is to provide a defect inspection apparatus and a defect inspection method that can efficiently control temperature without involving an enlarged size.

In a defect inspection apparatus and a defect inspection method according to the present invention that emit light to a test object and detect reflected or scattered light to check for a defect in the test object, a plurality of parts that need temperature control are selected from a plurality of parts in the defect inspection apparatus and placed in a temperature-controlled part accommodating section, the temperature in the temperature-controlled part accommodating section is measured, and a temperature control unit performs temperature control so that the interior of the temperature-controlled part accommodating section is kept at a prescribed temperature.

According to the present invention, a defect inspection apparatus and a defect inspection method that can efficiently perform temperature control without involving an enlarged size can be achieved.

LEGEND

1: substrate under inspection (wafer),2: chip,3: slit beam,4: area detected by an image sensor such as a TDI sensor,100: illumination optical system,101: laser light source,102: concave lens,103: convex lens,104: optical filter group,105: mirror,106: optical branching element (direction11),107: illumination lens,108: incident mirror,109: angle-of-elevation switching mirror,110: direction-11lighting fixture,114: optical branching element (direction12),115: optical branching element (direction12),120: direction-12lighting fixture,130: direction-13lighting fixture,200: inspection optical system,201: objective lens,202: Fourier transform face,203: imaging lens,204: varifocal lens group,205: detector,206: sensor Z driving mechanism,207: spatial filter control unit,208: lens driving control unit,209: detected field,210: auto focus unit,300: stage unit,301: X stage,302: Y stage,303: Z stage,304: angle stage,305: stage controller,400: control system,401: driving processing system,402: image processing system,403: display system,404: input system,500: base,501: stone surface plate,502: optical surface plate,503: second optical surface plate,600: temperature control system,601: temperature control unit,602: control CPU in the temperature control unit,603: temperature measuring instrument,604: temperature-controlled part accommodating section,605: heat radiating unit,611: outward pipe of the temperature control medium,612: inward pipe of the temperature control medium,613: flow path in the main body of the temperature control unit,614: clean filter,615: fan filter unit (FFU),616: airflow (of clean air),617a,617b: heat insulating valve,1500: focus detection optical system,1501: focus detection light source,1502: focus detection phototransmitting optical system,503: photoreceiving optical system,1504: focus detection sensor,1505: focus signal processing unit,1600: atmospheric pressure and temperature sensor system,1601: atmospheric pressure sensor,1602: atmospheric pressure data logger,1603: temperature sensor,1604: temperature data logger

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

A defect inspection apparatus in a first embodiment of the present invention will be described with reference toFIGS. 1 to 7.

In the embodiment described below, a surface foreign matter inspection apparatus will be used as an example of the defect inspection apparatus.

The first embodiment of the present invention suppresses variations in focused positions through temperature control to ensure stable inspection sensitivity, reduces the number of times an apparatus has needed to stop on an apparatus manufacturing line or semiconductor line to calibrate inspection sensitivity due to variations in focused positions, achieves efficient heat exchange while reducing the price of the apparatus and footprints by devising an arrangement of the apparatus, and eliminates the use of a fan filter unit (FFU) by using temperature-controlled air as clean air.

FIG. 1shows the entire structure of a defect inspection apparatus to which the present invention is applied. The defect inspection apparatus in the first embodiment, shown inFIG. 1, comprises a stage unit300, an illumination optical system100, at least one inspection optical system200, a control system400, and a temperature control system600(shown inFIG. 2).

The stage unit300has an X stage301, a Y stage302, a Z stage303, an angle stage304, and a stage controller305. When a wafer1is placed on the stage unit300, the angle stage304performs alignment in an angular direction and the Z stage303performs alignment in the Z direction.

When the wafer1is scanned, the X stage301performs scanning in the X direction, the Y stage302feeds the wafer1in the Y direction, and then the X stage301performs scanning in the reverse direction. This cycle is repeated.

The illumination optical system100has a common optical path and a plurality of illuminating unit, which are a lighting fixture110(first illuminating unit) in a direction11(shown inFIG. 5), a lighting fixture120(second illuminating unit) in a direction12(shown inFIG. 5), a lighting fixture130(third illuminating unit) in a direction13(shown inFIG. 5).

Parts in the common optical path include a laser light source101, a concave lens102and convex lens103that fulfill the role of a beam expander, an optical filter group104including an ND filter and a wavelength plate, and a mirror105for routing an optical path.

The illumination optical system100has an optical branching element (or mirror)106that can be switched to a transparent glass plate as a part of a lighting fixture in each direction, an illumination lens107, an incident mirror108for directing the optical path in the vertical direction, and angle-of-elevation switching mirrors109.

The beam that has passed through the illumination lens107is directed as slit beams3from three directions11,12, and13on the wafer1so that its short-side direction matches the array direction of chips2, as shown inFIG. 5.

To perform defect inspection at high speed, the slit beams3are directed so that the scanning direction X on the X stage301matches the short-side direction and the scanning direction Y on the Y stage302matches the long-side direction.

That is, when the amount of feed in the Y direction is increased, the total amount of scanning on the stages can be reduced.

The illumination intensity (power) of a beam light flux emitted from the laser light source101can be controlled by using the ND filter of the optical filter group104or the like.

The inspection optical system200comprises an objective lens201, a Fourier transform face202, which is controlled by a spatial filter control unit207, an imaging lens203, a varifocal lens group204, which is controlled by a lens driving control unit208, and a detector205, such as a TDI sensor. The inspection optical system200first directs the slit illumination3to the wafer1and gathers generated light and scattered light with the objective lens201.

An interfered part of diffracted light, which appears on the Fourier transform face202dominated by repeated patterns on the wafer1, is then shielded by a spatial filter (not shown).

Light that has transmitted through the spatial filter undergoes magnification ratio adjustment by the varifocal lens group204.

Finally, the imaging lens203forms an image on the detector205. An area that concurrently satisfies a detected field209(shown inFIG. 4) on the wafer1and a detected area4(shown inFIG. 4) is focused on the sensor of the detector205.

When the slit beams3are directed to the wafer1on which various forms of circuit patterns are formed, reflected and scattered lights are ejected from the circuit patterns and defects such as foreign matter on the wafer1. Reflected and scattered lights generated from the circuit patterns are shielded by the spatial filter. Lights that have transmitted through the spatial filter are focused on the detector205and undergo photoelectric conversion.

The control system400comprises a driving control system401for controlling a driving mechanism and the sensor, an image processing system402, a display system403, and an input system404.

The image processing system402comprises an A/D converter for data resulting from photoelectric conversion by the detector205, a data memory, a difference processing circuit for obtaining a difference in signals between chips2, a memory for tentatively storing a differential signal between chips2, a threshold calculating part for setting a pattern threshold, a comparison circuit, and an inspection result storing system for storing and outputting defect detection results such as for foreign matter.

Furthermore, as shown inFIG. 6, units in the first embodiment of the present invention include an auto focus system210having optical paths provided separately from the objective lens201and inspection optical system200, an optical surface plate502on which to mount the inspection optical system200, auto focus system210, and illumination optical system100, and a stone surface plate501on which to mount the optical surface plate502and stage unit300, and a temperature control system600(shown inFIG. 2).

FIG. 2illustrates the principle of the first embodiment of the present invention. As shown inFIG. 2, the temperature control system600comprises a temperature control unit601, a temperature measuring instrument603(first temperature measuring unit), an outward pipe611and an inward pipe612for supplying temperature-controlled airflow to the main body of the apparatus, and a temperature-controlled part accommodating section604.

The temperature-controlled part accommodating section604occupies space between the lower end of the stone surface plate501and the lower end of a sensor Z driving mechanism206; the inspection optical system200and auto focus system210are accommodated in the space.

Out of a plurality of parts in the defect inspection apparatus, the temperature-controlled part accommodating section604accommodates a plurality of parts that need temperature control. Parts that do not need temperature control are accommodated in a heat radiating unit605.

That is, the parts constituting the defect inspection apparatus are classified into parts that need temperature control and parts that do not need temperature control; the parts that need temperature control are kept at a fixed temperature in a collective manner.

The heat radiating unit605inFIG. 2accommodates at least the detector205and other parts that become heat sources, and may accommodate a driving part (not shown) of the stage unit300, the laser light source101, and the control system400and other parts that become heat sources.

Causes why the imaging position is shifted due to temperature changes are a first focal length change caused by a change in index of refraction on an optical path, a second focal length change caused by deformation of the cylinder of the objective lens201, and a third focal length change caused by deformation of the optical surface plate502or stone surface plate501and a positional change of the auto focus unit210or objective lens201mounted on the optical surface plate502and stone surface plate501.

In particular, the third focal length change varies at a start point and end point of the temperature change and during the duration of the change, because the causative parts comprise a plurality of members having different thermal time constants.

Accordingly, if the present invention is not applied, it is difficult to predict the amount of change and make compensation, so periodic calibration is needed to avoid unstable inspection sensitivity and the apparatus is forced to stop on the apparatus manufacturing line or semiconductor line each time calibration is performed.

In the first embodiment of the present invention, since the temperatures of the parts related to imaging position displacement (objective lens201, auto focus unit210, stone surface plate501, and optical surface plate502) are fixed, that is, these parts (objective lens201, auto focus unit210, stone surface plate501, and optical surface plate502) are accommodated in the temperature-controlled part accommodating section604and controlled so that their temperatures are fixed, focal length changes (imaging position displacement) that are difficult to predict can be eliminated and thereby inspection sensitivity can be made more stable.

If the apparatus temperature is controlled in the range around 23° C., for example, as shown inFIG. 7, the inspection sensitivity is stabilized, so the number of times the apparatus has to stop on the apparatus manufacturing line or semiconductor line due to inspection sensitivity calibration can be reduced.

In the first embodiment of the present invention, temperature-controlled clean air is supplied into the temperature-controlled part accommodating section604(in which a heat insulating material is used to prevent heat inflow from and heat outflow to the ambient space), as shown inFIGS. 2 and 6, so the interior of the defect inspection apparatus can be kept clean without a fan filter unit (FFU) being installed.

Dust generated in the apparatus flows along an airflow613of the clean air and is efficiently removed by a clean filter614(shown inFIG. 6).

To keep the interior of the defect inspection apparatus clean, the clean air preferably circulates in the temperature-controlled part accommodating section604and temperature control unit601in such a way that the clean air is supplied downwardly.

The clean filter614is preferably disposed at an intermediate point in the outward pipe611and immediately before the temperature-controlled part accommodating section604.

This is because the degree of cleanness can be made highest as compared when the clean filter614is disposed in other places.

Incidentally, the clean air must flow in one direction, so the airflow cannot be circulated within the temperature-controlled part accommodating section604.

A slight temperature gradient is generated along the airflow613in the temperature-controlled part accommodating section604.

Here, a key point is that stable temperature around each target that needs temperature control rather than a uniform temperature distribution in the temperature-controlled part accommodating section604.

When the temperature state including the temperature gradient in each target that needs temperature control is stabilized, the stability of the inspection sensitivity can be improved.

FIG. 3is an operation flowchart for temperature control in the first embodiment of the present invention.

When power is turned on in step1000inFIG. 3, the temperature control system600sets a temperature control medium to initial temperature t0in step1001and flows the temperature control medium into the temperature-controlled part accommodating section604.

In step1002, temperature t in the temperature-controlled part accommodating section604is always monitored by the temperature measuring instruments603, and obtained temperature data is loaded into a control CPU602in the temperature control unit through a communication cable.

To keep the temperature in the temperature-controlled part accommodating section604at a fixed level, the control CPU602in the temperature control unit601controls the temperature of the air so that a deviation from a temperature range, which is set in advance by detecting temperature changes, is eliminated.

Upon the startup of the temperature control unit601, the control CPU in the temperature control unit begins to flow air at the initial temperature that is set in advance, and adjusts the temperature of the air while checking feedback from the temperature measuring instruments603.

That is, in step1003, the control CPU602determines whether the measured temperature t is within a prescribed temperature range (more than t0×Δt0but less than t0+Δt0). If the temperature t falls within the prescribed temperature, the sequence proceeds to step1004, in which the temperature of the temperature control medium is set to t0+Δt1and the sequence returns to step1002.

If the measured temperature t is not within the prescribed range in step1003, the sequence proceeds to step1005, in which it is determined whether t0+(t0−t) is within the range of temperatures controllable by the temperature control unit601.

If t0+(t0−t) is within the range of temperatures controllable by the temperature control unit601, the sequence proceeds to step1006, in which the temperature of the temperature control medium is set to t0+(t0−t) and the sequence returns to step1002.

If t0+(t0−t) is not within the range of temperatures controllable by the temperature control unit601in step1005, the sequence proceeds to step1007, in which the temperature of the temperature control medium is set to a control temperature limit lower than t0+(t0−t) and the sequence returns to step1002.

Ideally, the temperature gradient is t0+Δt1in the outward pipe611, t0in the temperature measuring instruments603, and t0+t2in the inward pipe612.

As described above, the air has a temperature gradient along the airflow613. Accordingly, the longer a physical distance from the temperature measuring instruments603along the airflow613is, the lower the temperature stability is.

The temperature measuring instruments603are thus preferably disposed near its target that needs temperature control; for example, it is preferably grounded.

Furthermore, temperature characteristics, such as the amount of response displacement and response speed, should be considered for temperature variations of each target that needs temperature control.

In the first embodiment, temperature variations of the stone surface plate501are largest, followed by the optical surface plate502and other parts (the auto focus unit210and objective lens201) in that order, and the response speed is reduced in that order.

As the response speed is increased, more unstable temperatures are followed. As the response speed is decreased, a result of a more averaged unstable temperature appears as variations, so the effect is small.

Accordingly, in the first embodiment, a position at which to dispose the temperature measuring instruments603was set to a mountable position at which the sum of the distance from the objective lens201and the distance from the auto focus unit210is minimized.

As described above, in the first embodiment of the present invention, the parts constituting the defect inspection apparatus are classified into parts that need temperature control and parts that do not need temperature control; all the parts that need temperature control are accommodated together into the temperature-controlled part accommodating section604so that a fixed temperature is kept.

Therefore, it becomes easy to keep a fixed temperature, when compared with a case in which individual parts are temperature-controlled separately by being heated or cooled, yielding an energy saving effect.

When compared with the case in which individual parts are temperature-controlled separately by being heated or cooled, it suffices to perform temperature control in a collective manner, reducing required temperature detecting devices and simplifying temperature control.

In addition, there is no need to cover the entire defect inspection apparatus, so it is not enlarged.

When the parts that need temperature control undergo temperature control in a collective manner as in the first embodiment of the present invention, it become possible to reduce footprints by about 10% to 20%, when compared with a case in which the entire apparatus is covered with a temperature control chamber.

A heat insulating material may be used to thermally isolate all the parts together that need temperature control from the ambient environment.

Second Embodiment

In the second embodiment of the present invention, a liquid is used as the temperature control medium, the height of the apparatus is reduced so that the FFU can be mounted, and inspection sensitivity is improved by eliminating optical path fluctuations by the use of airflows in the illumination optical system100and inspection optical system200.

The basic structure is the same as in the first embodiment; that is, the parts constituting the defect inspection apparatus are classified into parts that need temperature control and parts that do not need temperature control, and the parts that need temperature control are kept at a fixed temperature in a collective manner.

Identical parts are therefore indicated by identical reference numerals, and only descriptions that differ between the first and second embodiments will be given below.

On the optical surface plate502inFIG. 8, the illumination optical system100, at least one set of the inspection optical system200, the auto focus unit210, and a second optical surface plate503are mounted.

The stone surface plate501and the like are supported by bases500. To simplify the drawing, columns for supporting the optical surface plate502from the stone surface plate501are omitted.

The sensor Z driving mechanism206and detector205are mounted on the second optical surface plate503.

The range accommodated by the temperature-controlled part accommodating section604is from the lower end of the optical surface plate502to the upper end of the second optical surface plate503.

In a broad sense, the stone surface plate501can also be included in the temperature-controlled part accommodating section604. Other members are included in the heat radiating unit605.

The interior of the temperature-controlled part accommodating section604is monitored by the temperature measuring instruments603. Obtained temperature data is loaded in a control CPU602in the temperature control unit601through a communication cable.

To keep the temperature in the apparatus at a fixed level, the control CPU602in the temperature control unit601controls the temperature of the temperature control liquid so that a deviation from a temperature range, which is set in advance by detecting temperature changes, is eliminated.

This liquid circulates along the flow path613; the liquid passes through the temperature control unit601, outward pipe611, temperature-controlled part accommodating section604, and inward pipe612, and returns to the temperature control unit601.

The liquid used for this temperature control is preferably, for example, pure water, fluorine-based inert liquid, hydro fluoro ether (HFE), ethylene glycol, or another substance that does not corrode the members included along the flow path613.

The temperature control liquid directly performs temperature control on the stone surface plate501, optical surface plate502, and the second optical surface plate503. The surface plates, the temperatures of which are directly controlled, function as indirect temperature control units and control the temperature in the temperature-controlled part accommodating section604.

In the example shown inFIG. 8, a set of the temperature measuring instrument603and temperature control unit601performs temperature control.

In this case, a device is preferably made for a place at which to mount the temperature measuring instrument603, as described later.

A plurality of sets of temperature control units601, control CPUs602in temperature control units, and temperature measuring instruments603may be used to perform temperature control separately for the stone surface plate501, optical surface plate502, and second optical surface plate503.

In this case, the temperature measuring instruments603are preferably disposed near the center of the flow path613of each surface plate.

The temperature control liquid in the second embodiment of the present invention lacks an air cleaning function as used in the first embodiment.

Accordingly, the FFU615is preferably disposed in such a way that clean air along an airflow616between the stone surface plate501and optical surface plate502blows dust near the surface of the wafer1off the apparatus.

If the clean air is directed in the direction of the airflow616(from left to right inFIG. 8), rather than downwardly, the FFU615may be disposed next to the apparatus, enabling the height of the apparatus to be reduced.

In the second embodiment of the present invention, it becomes easy to keep a fixed temperature, when compared with a case in which individual parts are temperature-controlled separately by being heated or cooled, yielding an energy saving effect, as in the first embodiment.

In the second embodiment of the present invention, there is no airflow in the temperature-controlled part accommodating section604, so optical path fluctuations in the illumination optical system100and inspection optical system200can be significantly reduced, improving the sensitivity stability.

A position at which to dispose the temperature measuring instruments603in the second embodiment of the present invention is preferably set to a position within the optical surface plate502at which the sum of the distance from the objective lens201and the distance from the auto focus unit210is minimized.

This is because if the temperature measuring instruments603are disposed at the same position as in the first embodiment, an ambient temperature is measured.

InFIG. 8, part of the objective lens201and auto focus unit210touches the airflow616, but only their ends are brought into contact and most parts are temperature-controlled by internal thermal conduction.

In the second embodiment of the present invention, temperature is indirectly controlled, so the temperature controlled in the temperature-controlled part accommodating section604is more stable than in the first embodiment. However, the temperature in the temperature-controlled part accommodating section604responds slowly to temperature control by the temperature control unit601.

Consequently, variations in ambient temperature are highly likely to affect the temperature-controlled part accommodating section604through side walls.

For these reasons, a heat insulating material is preferably used for the side walls of the temperature-controlled part accommodating section604.

The flow path613is preferably arranged near its upper surface of the second optical surface plate503.

The reason for this arrangement is to prevent a temperature gradient from occurring in the second optical surface plate503due to the effect of the outside air and temperature variations of the detector205.

For a similar reason, in the first optical surface plate502, the flow path613is disposed near its lower surface; in the stone surface plate501, the flow path613is disposed near its upper and lower surfaces as much as possible.

In this embodiment, each surface plate is holed so as to form the airflow. A temperature-controlled sheet may be attached to each surface plate instead of making holes so as to perform temperature control.

It is also possible to use both a holed surface plate and a surface plate to which a sheet is attached.

Third Embodiment

In the third embodiment of the present invention, in addition to the temperature control unit601, heat sources in the apparatus are used for temperature control, reducing burdens on the apparatus manufacturing line and semiconductor line caused by energy.

The basic structure is the same as in the first embodiment; that is, the parts constituting the defect inspection apparatus are classified into parts that need temperature control and parts that do not need temperature control, and the parts that need temperature control are kept at a fixed temperature in a collective manner.

Only descriptions that differ between the first and third embodiments will be given below.

InFIG. 9, the temperature control unit601is connected to the heat radiating unit605(first heat radiating unit) via a pipe that is provided with a heat insulating valve617a. The temperature control unit601is also connected to an apparatus618(second heat radiating unit) in the outside environment via another pipe that is provided with a heat insulating valve617b.

The temperature control unit601does not control the temperature of a medium by using only electric power; the control CPU602in the temperature control unit601adjusts the heat insulating valves617aand617band heat from the heat radiating unit605and apparatus in the outside environment are used to control the temperature of the medium.

That is, a second temperature measuring unit measures the temperature of the heat radiating unit605, and a third temperature measuring unit measures the temperature of the apparatus618in the outside environment; when the temperature in the temperature-controlled part accommodating section604controlled to be at a constant temperature, either the heat radiating unit605or the apparatus618in the outside environment is determined to be suitable for heat exchange, and the operation of opening and closing the insulating valves617aand617bis controlled so that the heat exchanging medium can be circulated.

This arrangement can not only reduce electric power consumed by the temperature control unit601but also can reduce heat radiated from the temperature control unit601and heat radiating unit605, improving the energy efficiency of the apparatus manufacturing line and semiconductor line.

In a variation of the third embodiment, a plurality of parts and regions in the heat radiating unit605in the inspection apparatus are classified into parts and regions with high generated heat temperatures and parts and regions with low generated heat temperatures and accommodated in a high-temperature part accommodating section and a low-temperature part accommodating section, each of which is equipped with a temperature measuring unit and also provided with pipes and valves to connect with the temperature control unit601, and determines which section to be exchanged a heat according to the measured temperature.

In this arrangement, parts and regions that do not need temperature control can be used to fix the temperatures of parts that need temperature control, enabling the temperatures to be controlled more efficiently, that is, with less energy consumption.

In this variation, the apparatus618in the outside environment may be used for heat exchange, and an arrangement in which the apparatus618in the outside environment is not used for heat exchange may be formed.

Although the above embodiments have been described by using a defect inspection apparatus that uses laser light to detect wafer defects, such as foreign matter, dirt, cracks, crystal defects, COPs, and pattern defects, as an example, the present invention can be applied to not only apparatuses that use laser light to inspect foreign matter on the wafer but also defect inspection apparatuses that use other types of light.

Specifically, some optical systems use not only laser light but also halogen lamps, mercury vapor lamps, Xe lamps, etc., and other optical systems are electronic optical systems that use electronic beams. The present invention can also be applied to defect inspection apparatuses using these optical systems.

Test objects are applied not only to wafers used as semiconductor substrates but also to glass substrates used in flat panel display units, ALTIC substrates, sapphire substrates used in sensors and LEDs, disk substrates, etc.

The present invention can be applied to a wide range of inspection apparatuses intended for surface inspection, mask inspection, bevel inspection, etc.

The temperature control according to the present invention can be performed by using heating due to a heater as well as electronic refrigeration and heating utilizing the Peltier effect or Seebeck effect.

Fourth Embodiment

In this embodiment described below, the focus position changes according to, for example, the weather conditions including atmospheric pressure and temperature.

This embodiment relates to an inspection apparatus that checks for foreign matte, defects, and the like on a semiconductor wafer etc. in, for example, a semiconductor manufacturing process.

To increase a yield in a semiconductor manufacturing process by minimizing failures, it is usually important to detect foreign matter and defects on wafers in the process with high sensitivity, classify detected results, determine causes, and take action accordingly.

An inspection apparatus (referred to below as the foreign matter inspection apparatus) is used to detect and classify these foreign matters and defects. High sensitivity, high throughput, and high classification performance are demanded for the foreign matter inspection apparatus.

The following documents relates to this type of foreign matter inspection apparatus.

The foreign matter inspection apparatuses disclosed in these documents perform focus adjustment in order to obtain high sensitivity.

The focus position changes according to the weather conditions including atmospheric pressure and temperature.

Specifically, changes in atmospheric pressure and temperature each cause a change in air density, changing the index of refraction of air and then changing the focus position.

Noting that changes in atmospheric pressure and temperature cause a change in focal position in an optical system, this embodiment was devised in the course of taking action against sensitivity variations involved in the weather conditions.

As described above, an apparatus including an optical system usually needs focus adjustment to obtain an optimum image.

With an exposing apparatus such as a stepper or scanner, the quality of an image can be directly monitored through a through-the-lens (TTL); even if a focus change occurs in the exposure optical system due to an atmospheric pressure and temperature, the focus can be adjusted by monitoring the image quality and thereby the focus changed by the atmospheric pressure and temperature can also be adjusted.

This arrangement is applied not only to an exposing apparatus but also to general apparatuses that can directly monitor image quality through an optical system, such as for example a camera.

However, the foreign matter inspection apparatus cannot adjust the focus by a method in which image quality is directly monitored through a microscopic optical system.

To solve this problem, a focus control optical system is provided in addition to the microscopic optical system intended for foreign matter inspection.

To achieve focus adjustment by a detection optical system in the foreign matter inspection apparatus, a Z coordinate at which signal intensity is maximized, which is a performance index of the apparatus, is found by the microscopic optical system in advance; a focus control optical system then performs control so that the Z coordinate is maintained.

An operation for searching for the Z coordinate at which the signal intensity is maximized is a calibration operation rather than an operation specific to the foreign matter inspection apparatus. Although it is necessary that the Z coordinate is frequently searched for so as to suppress the effect by focus variations to a minor level, this operation is complicated and drops the availability of the apparatus.

As described above, the focus adjustment in the foreign matter inspection apparatus involves problems described below.

A functional problem in the focus adjustment is that the optimum Z coordinate at which the signal intensity is maximized varies with changes in weather conditions including atmospheric pressure and temperature, reducing the sensitivity.

A problem with a focus adjustment task is that the task is complicated and takes much time (three to eight minutes).

To suppress the effect by focus variations to a minor level, the focus adjustment task needs to be performed frequently at time intervals shorter than time intervals at which the atmospheric pressure and temperature change.

According to measurements, the atmospheric pressure and temperature may change at time intervals of about two hours. To avoid an effect by this change, the focus adjustment operation must be performed about once per hour.

This embodiment addresses this problem with an object of always maintaining a maximum sensitivity and eliminating the focus adjustment task that would otherwise need to be performed to maintain high sensitivity.

Another object of this embodiment is to improve the availability of the apparatus by eliminating the focus adjustment task that would otherwise reduce the availability.

A first feature of this embodiment to achieve the above objects is that attention has been focused on that a Z coordinate is changed by changes in atmospheric pressure and temperature, as described below.

First, according to the equation of state of a gas, “PV=nRT” holds.

Let n be w/M (w: mass, M: molecular weight) and V be w/d (d: density [g/L]), then the equation of state of a gas can be rewritten as “d=PM/TR” and further as “Δd=ΔPM/ΔTR”.

This unit that a change in air density is proportional to a change in atmospheric pressure and inversely proportional to a change in temperature.

According to the Gladstone-Dale equation, “N=1+d·r” then holds.

This unit that a change in air density is proportional to a change in index of refraction in an optical system.

According to the Snell's law, a change in index of refraction finally becomes a change in focal length (Z coordinate).

A second feature of this embodiment is that since an atmospheric pressure sensor and a temperature sensor are provided, a change in focus due to a weather condition change can be comprehensively compensated for.

If, for example, only an atmospheric sensor or temperature sensor is used for compensation, it cannot be said that a change in focus due to weather condition changes is comprehensively compensated for.

However, it would be understood that, in an environment in which either the atmospheric pressure or temperature is controlled, it suffices to provide for compensation for a non-controlled parameter.

A third feature of this embodiment is that, in addition to stabilizing a Z coordinate by compensating for changes in atmospheric pressure and temperature, the Z coordinate continue to be compensated so that the maximum sensitivity is always obtained.

The method for this is achieved by the following simple control. An optimum Z coordinate at which the signal intensity is maximized is searched for in advance, and the atmospheric pressure, temperature, and optimum Z coordinate at that time (respectively referred to as the reference atmospheric pressure, reference temperature, and reference Z value) are used as three reference values; an atmospheric pressure and temperature are measured at an arbitrary point of time at which to detect foreign matter; differences from the reference values are taken and converted to a Z coordinate, and the converted Z coordinate is added to the reference Z value.

This embodiment is not limited to the foreign matter inspection apparatus, but efficiently effected to maintain the maximum signal intensity without performing the complicated focus adjustment operation in comprehensive apparatuses in which a focus adjustment operation cannot be performed by a method of directly monitoring image quality and a microscopic optical system and a focus control optical system are provided.

According to this embodiment described above, it suffices to search for an optimum Z coordinate once, after which the Z coordinate can be controlled while variations in atmospheric pressure and temperature are being monitored. Even apparatuses that cannot directly monitor image quality, such as the foreign matter inspection apparatus, can perform inspection with the signal intensity always kept at the maximum level.

According to this embodiment, the complicated focus adjustment task that would otherwise need to be performed about once per hour in three to eight minutes is eliminated, improving the availability of the apparatus.

This embodiment relates to focus adjustment in a foreign matter inspection apparatus that has the features described above and inspects foreign matter on a wafer.

FIG. 1is a drawing to show the schematic structure of the foreign matter inspection apparatus of this embodiment.

FIG. 10is a drawing to show the schematic structure of the foreign matter detection optical system and the structure of the focus detection optical system of the foreign matter inspection apparatus.

FIG. 11is a block diagram of an embodiment for compensating for an atmospheric pressure and temperature.

The embodiment of the foreign matter inspection apparatus comprises a stage unit300having an X stage301, Y stage302, Z stage303, and θ stage304on which a wafer1to be inspected is mounted as well as a stage controller305, a illumination optical system100having a laser light source101etc., illumination beam spot imaging units110,120, and130, an foreign matter inspection optical system200having a objective lens201, spatial filter202, imaging lens203, varifocal lens group204, and a one-dimensional detector (image sensor)205such as a TDI sensor, and a control system400having a signal processing system402, an output unit for storing defect detection results such as for foreign matter and delivering the defect detection results, a calculation processing system401for controlling the driving of a motor etc., coordinates, and sensors, a display system403, and an input system404.

Other reference numerals are indicating as followings.1500: focus detection optical system,1501: focus detection light source,1502: focus detection phototransmitting optical system,1503: photoreceiving optical system,1504: focus detection sensor,1505: focus signal processing unit,1600: atmospheric pressure and temperature sensor system,1601: atmospheric pressure sensor,1602: atmospheric pressure data logger,1603: temperature sensor,1604: temperature data logger.

The three illumination beam spot imaging units110,120, and130are structured so that lights emitted from the laser light source101illuminate the wafer1to be inspected from three directions.

The inspection optical system200is structured so that light produced from the wafer1is detected by a detection lens (objective lens)201, the spatial filter202that shields a Fourier transformed image due to reflected and diffracted light from a repetition pattern, the imaging lens203, and the one-dimensional detector205such as a TDI sensor.

For a stage operation during inspection, the X stage301and Y stage302are driven to perform illumination scanning on illumination beam spots over the entire surface of the wafer1under inspection.

For focus control during inspection, the focus detection optical system1500detects a position on the surface of the wafer1that is undergoing illumination scanning, and transfers a detected position signal to the focus signal processing unit1505. The focus signal processing unit1505converts the position signal to the amount of movement of the Z driving apparatus303aand transfers the converted signal to the Z stage control unit305a.

The Z stage control unit305athen drives the Z driving apparatus303a, and the Z stage303moves up and down so that a fixed distance is maintained between the objective lens201and the surface of the wafer1.

The distance between the objective lens201and the surface of the wafer1can be arbitrarily controlled by setting an offset in the Z stage control unit305a.

In this embodiment, focus variations caused by changes in atmospheric pressure and temperature are controlled as offsets given to the Z stage control unit305a.

Next, a procedure for compensating for focus variations in this embodiment will be explained.

At first, an example of temperature compensation will be used to explain a flow of compensation.

FIG. 12is a graph to indicate temperature variations and changes in the focus Z coordinate when temperature is not compensated.

The focus Z coordinate is the Z coordinate at which the signal intensity is maximized, which is obtained by the focus adjustment task.

The temperature was changed step by step by a temperature controlled bath. The atmospheric pressure is constant.

Accordingly,FIG. 12was obtained by performing the focus adjustment task repeatedly at different temperatures.

FIG. 13a graph to indicate the relation between the temperature and the focus Z coordinate.

The temperature and focus Z coordinate can be represented as a linear function. It can be seen that the focus Z coordinate changes by −1.80 μm each time the temperature changes by 1° C. This value is saved as a temperature coefficient.

The temperature coefficient takes various values for different optical system structures.

FIG. 14is a graph to indicate temperature variations and Z compensated values for temperatures.

A Z compensated value for a temperature is obtained from the equation below.
Zcompensated value for temperature=Zreference value+(temperature coefficient×(temperature reference value−temperature at arbitrary point of time))

That is, in the characteristics inFIG. 12, the Z reference value and temperature reference value were obtained at time T1; values after T1were calculated as Z compensated values. That is, the focus Z coordinate value is obtained by calculation without having to performing the complicated focus adjustment task.

FIG. 15a graph obtained by subtracting the characteristics inFIG. 12from the characteristics inFIG. 14. That is,FIG. 15indicates focus error in Z compensation for temperatures.

Remaining compensation error is caused due to deviation from the linear function between the temperature and the focus Z coordinate.

Focus error due to the Z compensation for temperatures is 0.1 μm or less, which is sufficiently small and is not problematic in practical use.

Next, an example of atmospheric pressure compensation will be used to explain a flow of compensation. A procedure for this compensation is the same as the procedure for temperature compensation.

FIG. 16a graph to indicate atmospheric pressure variations and changes in the focus Z coordinate when atmospheric pressure is not compensated.

Changes in atmospheric pressure were obtained as changes in weather. Temperature was kept constant in a temperature controlled bath.

FIG. 17is a graph to indicate the relation between the atmospheric pressure and the focus Z coordinate.

The atmospheric pressure and focus Z coordinate can be represented as a linear function. It can be seen that the focus Z coordinate changes by +0.12 μm each time the atmospheric pressure changes by 1 hPa. This value is saved as an atmospheric pressure coefficient.

The atmospheric pressure coefficient also takes various values for different optical system structures.

FIG. 18is a graph to indicate atmospheric pressure variations and Z compensated values for atmospheric pressures.

A Z compensated value for an atmospheric pressure is obtained from the equation below.
Zcompensated value for atmospheric pressure=Zreference value+(atmospheric pressure coefficient×(atmospheric pressure reference value−atmospheric pressure at arbitrary point of time))

That is, in the characteristics inFIG. 16, the Z reference value and atmospheric pressure reference values were obtained at time T2; values after T2were calculated as Z compensated values.

FIG. 19is a graph obtained by subtracting the characteristics inFIG. 16from the characteristics in FIG.18. That is,FIG. 19indicates focus error in Z compensation for atmospheric pressures.

Remaining compensation error is caused due to deviation from the linear function between the atmospheric pressure and the focus Z coordinate.

Focus error due to the Z compensation for atmospheric pressures is 0.1 μm or less, which is sufficiently small.

Next, an arrangement for compensation will be explained.

FIG. 11is a block diagram of an embodiment for compensating for an atmospheric pressure and temperature.

An atmospheric pressure measured by the atmospheric pressure sensor1601at an arbitrary point of time is stored in the atmospheric pressure data logger1602.

A temperature measured by the temperature sensor1603at an arbitrary point of time is stored in the temperature data logger1604.

Stored in the control CPU401are a Z coordinate (Z reference value) at which a maximum sensitivity is obtained, an atmospheric pressure (atmospheric pressure reference value) at that point of time, a temperature (temperature reference value) at that point of time, the coefficient (atmospheric pressure coefficient), which is obtained in advance so as to convert atmospheric pressures to Z coordinates, and the coefficient (temperature coefficient), which is also obtained in advance so as to convert temperatures to Z coordinates.

In compensation for atmospheric pressure variations, a difference between an atmospheric pressure measured at an arbitrary point of time and the atmospheric pressure reference value is taken, the difference is multiplied by the atmospheric pressure coefficient to obtain a Z converted value for the difference, and the Z converted value for the atmospheric pressure is added to the Z reference value, yielding a Z compensated value.

In compensation for temperature variations, a difference between a temperature measured at an arbitrary point of time and the temperature reference value is taken, the difference is multiplied by the temperature coefficient to obtain a Z converted value for the difference, and the Z converted value for the temperature is added to the Z reference value, yielding a Z compensated value.

Compensation for atmospheric pressure variations and compensation for temperature variations are performed separately.

Accordingly, when a Z compensated value for an atmospheric pressure and another Z compensated value for a temperature are added to the Z reference value to obtain a Z compensated value, the atmospheric pressure and temperature can be compensated for at the same time.

The obtained Z compensated value is sent to the Z stage control unit305a, and an offset is given to the focus following operation performed by the Z stage303.

The offset given to the focus following operation provides the effect that variations in focus caused by changes in atmospheric pressure and temperature are corrected.

As described above, when control is performed, variations in focus caused by changes in atmospheric pressure and temperature are corrected.