JPH114374A - Imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely reduce a noise component of an image signal by scanning a signal charge generated by an image pickup means to generate an image signal and discharging a generated signal charge before a lighting means starts lighting. SOLUTION: An image pickup means 10 picks up an optical image of an object A lighted by a lighting means 12 that is intermittently lighted to generate signal charges. Just after the lighting means 12 finishes lighting, an image scanning means 14 scans the signal charge generated by the image pickup means 10 to generate an image signal. A discharge means 16 discharges the signal charge generated by the image pickup means 10 just before the lighting means 12 starts lighting. That is, the signal charge generated for a period when the lighting means 12 is lighted among signal charges generated by the image pickup means 10 is scanned by the image scanning means 14. Furthermore, till the lighting is started after the lighting of the lighting means 12 is finished, the signal charge generated due to noise by a dark current or the like is discharged by the discharge means 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus that picks up an optical image of a subject illuminated by a light source that emits light intermittently and generates an image signal.

[0002]

2. Description of the Related Art In recent years, with the development of image processing technology, image signals generated by an imaging device are subjected to various calculations,
It is used as a control amount for automatic control in a measuring device or a manufacturing device. For example, in a reduction projection type exposure apparatus (hereinafter, referred to as “stepper”) of an IC manufacturing apparatus, it is used as a control amount for automatically controlling an XY stage during automatic alignment.

That is, in the process of performing automatic alignment in a stepper, an image pickup device takes an image of an alignment mark on a reticle and an alignment mark on a wafer to generate an image signal. Further, the control unit of the XY stage performs a symmetric pattern matching calculation or the like on the image signal generated by the imaging device to detect a deviation amount between the reticle and the wafer. The control unit of the XY stage controls the position of the XY stage based on the detected shift amount.

Incidentally, a general stepper is provided with an alignment light source that does not expose the resist on the wafer, separately from a light source for exposure.

[0005]

However, in recent years, a stepper that performs exposure and alignment using light from the same light source has been put into practical use.

Some of such steppers use a light source that emits light intermittently (for example, excimer laser light), and the alignment mark is several ns to several tens ns.
It is illuminated in an extremely short illumination time of ec. For example,
When the light emission cycle of the light source is several milliseconds, the ratio of the light emission period (corresponding to the above-described irradiation time) to the light emission cycle is 1/1000 to 1/100.

In a stepper that suppresses the light amount of a light source in order to avoid exposure of a resist during alignment, there is a limit to the amount of signal charge generated during a light emission period. Under such circumstances, the imaging apparatus has a problem that most of the accumulation time is spent for accumulation of noise such as dark current, and the SN ratio is remarkably reduced, so that a good image signal cannot be generated.

[0008] Further, an image pickup device of an electronic camera which performs continuous photographing in synchronization with the intermittent light emission of the speedlight cannot generate a good image signal similarly to the above-described image pickup device in the stepper. There was a problem. Therefore,
It is an object of the present invention to provide an imaging apparatus capable of reliably reducing a noise component of an image signal.

[0009]

FIG. 1 is a block diagram showing a first embodiment of the present invention;
It is a principle block diagram of the invention described in 7. The image pickup apparatus according to claim 1, wherein an image pickup means for picking up an optical image of the subject A to generate signal charges;
Illuminating means 12, an illuminating means 12, an image scanning means 14 for scanning the signal charges generated by the imaging means 10 to generate an image signal immediately after the illuminating means 12 stops emitting light, and an illuminating means 12 for emitting light And discharging means 16 for discharging the signal charges generated by the image pickup means 10 immediately before the operation.

FIG. 2 is a block diagram showing the principle of the second aspect of the present invention. The image pickup apparatus according to claim 2 is an image pickup apparatus according to claim 1.
The image pickup device according to the above, further comprising a light emission control unit 18 that controls the timing of light emission of the illumination unit 12 by a control signal that defines a period during which the illumination unit 12 emits light. Based on the control signal, the timing immediately after the illuminating unit 12 stops emitting light is detected to generate an image signal, the discharging unit 16 acquires the control signal, and the illuminating unit 12 starts emitting light based on the control signal. The signal charge is discharged by detecting the immediately preceding timing.

FIG. 3 is a block diagram showing the principle of the third aspect of the present invention. An image pickup apparatus according to claim 3, which picks up an optical image of a subject A illuminated by a light source B that emits light intermittently and generates signal charges, and controls a period during which the light source B emits light. A signal is acquired, the timing immediately after the light source B stops emitting light is detected, and the imaging unit 1
The image scanning means 14 scans the signal charge generated by the signal 0 at the timing to generate an image signal, and detects the timing immediately before the light source B starts emitting light by acquiring the control signal. Discharging means 16 for discharging the generated signal charges at the timing.

FIG. 4 is a block diagram showing the principle of the present invention. The imaging device according to claim 4 captures an optical image of a subject A illuminated by a light source B that emits light intermittently, and captures light from the light source B to generate signal charges. The image scanning unit 14 detects the timing immediately after the light source B has finished emitting light, scans the signal charge generated by the imaging unit 10 at the timing to generate an image signal, and acquires light from the light source B. The timing immediately before the light source B starts emitting light is detected,
And discharging means 16 for discharging the signal charges generated by the zero at the timing.

According to a fifth aspect of the present invention, there is provided the imaging apparatus according to any one of the first to fourth aspects,
The imaging unit 10 includes a light receiving unit and a discharging unit adjacent to the light receiving unit, and the discharging unit 16 discharges signal charges via the discharging unit.

According to a sixth aspect of the present invention, in the imaging apparatus according to any one of the first to fourth aspects,
The imaging unit 10 includes a light receiving unit and a discharging unit arranged in a direction perpendicular to the light receiving unit. The discharging unit 16 discharges signal charges via the discharging unit. According to a seventh aspect of the present invention, in the imaging apparatus according to any one of the first to fourth aspects, the imaging unit includes a light receiving unit that performs photoelectric conversion of an optical image, and a light receiving unit that performs the photoelectric conversion of the optical image. A transfer path for transferring a signal charge obtained by photoelectric conversion, the image scanning unit 14 reads out the signal charge via the transfer path to generate an image signal, and the discharging unit 16 includes at least a part of the transfer path. And discharging the signal charge via the.

(Operation) In the image pickup apparatus according to the first aspect of the present invention, the image pickup means 10 picks up an optical image of the subject A illuminated by the illuminating means 12 which emits light intermittently and generates signal charges. . The image scanning unit 14 scans the signal charges generated by the imaging unit 10 immediately after the illumination unit 12 stops emitting light to generate an image signal. The discharging unit 16 discharges the signal charges generated by the imaging unit 10 immediately before the lighting unit 12 starts emitting light.

That is, of the signal charges generated by the imaging means 10, the signal charges generated during the period when the illumination means 12 emits light are scanned by the image scanning means 14.
Further, the signal charge generated by noise due to a dark current or the like after the lighting unit 12 has finished emitting light until the next start of emitting light is discharged by the discharging unit 16. Therefore, unnecessary signal charges generated during the period in which light emission is stopped are not superimposed as noise components of the image signal, so that the S / N ratio of the image signal can be reliably improved.

In the imaging device according to the second aspect of the present invention, in the imaging device according to the first aspect, the light emission control means includes a control signal for defining a period during which the illumination means emits light. The timing of light emission is controlled. The image scanning unit 14 acquires a control signal, detects a timing immediately after the lighting unit 12 has finished emitting light based on the control signal, and generates an image signal.

The discharging means 16 acquires a control signal, detects a timing immediately before the lighting means 12 starts emitting light based on the control signal, and discharges the signal charge. That is,
By transmitting a control signal defining a period during which the illuminating unit 12 emits light to the image scanning unit 14 and the discharging unit 16, it is easy to detect the timing immediately after the emission ends and the timing immediately before the emission starts. , And reliably.

In the image pickup apparatus according to the third aspect of the present invention, the image pickup means 10 picks up an optical image of the subject A illuminated by the light source B which emits light intermittently, and generates signal charges. The image scanning unit 14 acquires a control signal that defines a period during which the light source B emits light, and detects a timing immediately after the light source B stops emitting light. The image scanning means 14
Scans the signal charges generated by the imaging means 10 at the timing detected in this way to generate an image signal.

The discharging means 16 acquires the control signal, detects the timing immediately before the light source B starts to emit light, and discharges the signal charges generated by the imaging means 10 at that timing. That is, even when the light source B is provided outside, by acquiring the control signal that defines the light emission period of the light source B, the timing immediately after the light emission ends and the timing immediately before the light emission starts Since the timing can be detected, it is possible to reliably recognize the period during which light emission is suspended.

Therefore, by discharging unnecessary signal charges generated during the period in which light emission is suspended, such signal charges are not superimposed as noise components of the image signal. The ratio can be reliably improved. In the imaging apparatus according to the fourth aspect of the invention, the imaging unit 10 captures an optical image of the subject A illuminated by the light source B that emits light intermittently, and generates signal charges.

The image scanning means 14 acquires light from the light source B and detects the timing immediately after the light source B has finished emitting light. Further, the image scanning unit 14 scans the signal charges generated by the imaging unit 10 at the timing thus detected to generate an image signal. Discharging means 16
Detects light from the light source B, detects the timing immediately before the light source B starts to emit light, and discharges the signal charge generated by the imaging unit 10 at that timing. For example, when the light source B emits light intermittently at a constant cycle, the discharging unit 16 can reliably predict the next emission start timing by acquiring the light from the light source B.

Therefore, even when the light source B is provided outside, it is possible to recognize a period in which light emission is suspended, and by discharging unnecessary signal charges generated during that period, As in the third aspect, the S / N ratio of the image signal can be improved without fail. In the imaging device according to the fifth aspect of the present invention, in the imaging device according to any one of the first to fourth aspects, the discharging unit 16 is provided adjacent to a light receiving unit in the imaging unit 10. The signal charge is discharged through the discharge unit.

That is, if unnecessary signal charges are transferred from the light receiving section to the discharge section, image signals can be generated in parallel even when the discharge is not completed.

Therefore, the timing for discharging the unnecessary signal charges can be made closer to the timing for starting the light emission, so that the signal charges generated immediately before the start of the light emission can also be reliably discharged. In the imaging device according to the sixth aspect of the present invention, in the imaging device according to any one of the first to fourth aspects, the discharging unit 16 is arranged in a vertical direction of a light receiving unit in the imaging unit 10. The signal charge is discharged through the discharge unit.

That is, since the discharge can be performed without performing the transfer, unnecessary signal charges generated during the period when the light emission is stopped can be discharged at a high speed. Therefore, the timing for discharging the unnecessary signal charges can be made closer to the timing for starting the light emission, so that the signal charges generated immediately before the start of the light emission can also be reliably discharged.

According to a seventh aspect of the present invention, in the image pickup apparatus according to any one of the first to fourth aspects, the image scanning means 14 is connected to the image pickup means 10 via a transfer path. To read out the signal charges to generate an image signal. The discharging means 16 discharges the signal charges through at least a part of the transfer path. Therefore, irrespective of the presence or absence of the light-blocking region, unnecessary signal charges generated in the transfer path due to noise can be reliably discharged during the period in which light emission is suspended.

[0028]

Embodiments of the present invention will be described below in detail with reference to the drawings. (First Embodiment) FIG. 5 is a functional block diagram of an embodiment corresponding to the first to third and sixth aspects of the present invention.

In FIG. 1, the imaging device 20 includes a solid-state imaging device 22, a lens 24, a light source controller 26, a light source 28, a drive controller 30, and a half mirror 32. The solid-state imaging device 22 is disposed at a position where an optical image of an alignment mark obtained via the lens 24 is formed. The output end of the light source control unit 26 is connected to the light source 28 and the drive control unit 30. The drive control unit 30 has a plurality of output terminals, and pulses output from these output terminals are supplied to each unit in the solid-state imaging device 22 described later.

Note that such an imaging device 20 is provided in a stepper and generates an image signal by capturing an optical image of an alignment mark on a reticle or a wafer during alignment. The image signal generated in this manner is calculated by a calculation processing section in the stepper and used as a control amount for automatically controlling the XY stage.

FIG. 6 is a diagram showing a configuration of a solid-state image pickup device according to the first to third and sixth aspects of the present invention. In the figure, a plurality of light receiving sections 40 are arranged in a matrix on the imaging surface, and a transfer gate 42 is arranged adjacent to each light receiving section 40. The plurality of vertical CCDs 44 are
Are arranged via transfer gates 42 between the vertical columns. The output ends of these vertical CCDs 44 are connected to horizontal CCDs.
The output terminal of the horizontal CCD 46 is connected to an output amplifier 48.

FIG. 7 is a cross-sectional view of the solid-state imaging device shown in FIG.
It is sectional drawing on the X 'line. In the figure, a P-type well region 54 is formed on an N-type silicon substrate 52, and an N-type light receiving region 50 is provided on the P-type well region 54. The junction between the N-type light receiving region 50 and the P-type well region 54 forms a photodiode corresponding to the light receiving section 40 shown in FIG.

A buried channel region 60 is provided on the P-type well region 54, and a transfer gate electrode 56 formed on the insulating film 58 is provided between the N-type light receiving region 50 and the P-type well region 54. Is arranged. On the buried channel region 60, a vertical CCD
An electrode 62 is arranged. Note that a channel stopper 64 is provided as a diffusion region for separating each pixel.

In this embodiment, a transfer pulse, a vertical drive pulse, a horizontal drive pulse, and a reset pulse are output from the output terminal of the drive control unit 30 shown in FIG. Regarding the supply destination of these pulses, the transfer pulse is supplied to the transfer gate electrode 56 shown in FIG. 7, and the vertical drive pulse is supplied to the vertical CCD electrode 62. The horizontal drive pulse is applied to the horizontal CCD shown in FIG.
The reset pulse is supplied to the P-type well region 54 so that the N-type silicon substrate 52 and the P-type well region 54 shown in FIG.

As for the correspondence between the present invention described in the first to third and sixth aspects and the present embodiment, the imaging means 10 corresponds to the solid-state imaging device 22. In particular, the light receiving section provided in the imaging means 10 corresponds to the light receiving section 40 shown in FIG. 6, and the discharge section corresponds to the N-type silicon substrate 52 shown in FIG. The illumination unit 12 and the light source B correspond to the light source 28, the image scanning unit 14 corresponds to the “function of controlling generation of the transfer pulse, the vertical drive pulse, and the horizontal drive pulse” of the drive control unit 30, and the discharge unit 16 corresponds to “ The light emission control unit 18 corresponds to the light source control unit 26, and the subject A corresponds to the alignment mark.

FIG. 8 is a timing chart showing the light emission of the light source and the operation of the solid-state imaging device. Hereinafter, FIGS.
The operation of the embodiment according to the first to third aspects of the present invention will be described with reference to FIG. The light source control unit 26 sends a light emission timing signal instructing the start of light emission to the light source 2 every predetermined period T (here, several msec).
Give 8

The light source 28 starts to emit light when a light emission timing signal is given from the light source control unit 26, and automatically stops emitting light when a predetermined period t1 has elapsed. Note that the period t1 differs depending on the type of the light source 28, but in the present embodiment, it is assumed that the light source 28 is an excimer laser, and the period t1 is set to several nsec. That is, the light source 28 emits light during the period t1 and stops emitting light during the period t2 until the light emission timing signal is supplied again, thereby intermittently illuminating the alignment mark at a period T as shown in FIG. Hereinafter, the period t1 is referred to as a “light emission period t1”, and the period t2 is referred to as a “light emission suspension period t2”.

The light emitted from the light source 28 reaches the alignment mark via the half mirror 32, and an optical image of the alignment mark is formed on the solid-state image sensor 22 via the half mirror 32 and the lens 24. . In the solid-state imaging device 22, photoelectric conversion is performed in the light receiving unit 40, and signal charges are generated according to the optical image. The light source control unit 2
The light emission timing signal output from the driving control unit 3
It is acquired even if it is 0.

The drive control unit 30 generates a transfer pulse as shown in FIG. 8 at a time when the light emission timing signal is acquired and a delay of several nsec (a time when the light emission period t1 ends). In the solid-state imaging device 22, at the time of the rise of the transfer pulse, the signal charge is read out to the vertical CCD 44 via the transfer gate 42.

The signal charges read out to the vertical CCD 44 in this manner are transferred to the horizontal CCD 46 based on the vertical drive pulse supplied from the drive control unit 30. The signal charge transferred to the horizontal CCD 46 is transferred in the direction of the output amplifier 48 based on the horizontal drive pulse supplied from the drive control unit 30 and output as an image signal.

By the way, in the N-type light receiving region 50 corresponding to the light receiving portion 40, even during the light emission suspension period t2, unnecessary signal charges (hereinafter simply referred to as "unnecessary charges") due to noise such as dark current. Generated.

The drive control unit 30 predicts the time when the light emission timing signal is output from the light emission control unit 28 again based on the cycle T. In addition, the drive control unit 30 determines a time t required for discharging unnecessary charges from the time point thus predicted.
At a point preceding by 3 (here, several to several tens of nsec), a reset pulse is generated as shown in FIG.

In this embodiment, the pulse width of the reset pulse is set in association with the time t3 (several to several tens of nsec), and the potential difference between the P-type well region 54 and the N-type silicon substrate 52 is It is assumed that the light emission timing signal is stabilized immediately before being output. In the solid-state imaging device 22,
When a reset pulse having a higher reverse bias voltage than the normal state is supplied to the P-type well region 54, the P-type well region 54 is completely depleted, and the junction between the N-type light receiving region 50 and the N-type silicon substrate 52 is formed. Forward direction. Therefore, unnecessary charges generated in the N-type light receiving region 50 are
It is discharged to 2.

That is, in the present embodiment, since unnecessary charges can be discharged prior to the light emission of the light source 28, the amount of unnecessary charges superimposed on the signal charges in the light receiving section 40 can be reliably reduced. it can. In particular, by extending the trailing edge of the reset pulse to the start of light emission, unnecessary charges superimposed on the signal charges can be completely eliminated. Therefore, the noise component of the image signal can be reduced, and the S / N ratio of the image signal can be reliably improved.

In this embodiment, the imaging device 20 includes the light source control unit 26 and the light source 28. Since the light source control unit 26 and the light source 28 are used also at the time of exposing the resist, If the light emission timing signal can be obtained by the control unit 30, the light emission timing signal need not be included in the configuration of the imaging device 20. (Second Embodiment) FIG. 9 is a functional block diagram of an embodiment corresponding to the fourth and fifth aspects of the present invention.

In the figure, an imaging device 70 includes a sampling half mirror 72, a half mirror 74, and a lens 7.
6, the solid-state imaging device 78 and the drive control unit 80. Such an imaging device 70 is provided in a stepper including a light source 82 and a light source control unit 84, and performs imaging of an alignment mark on a reticle or a wafer during alignment.

Here, the light emitted from the light source 82 is applied to the sampling half mirror 72 and the half mirror 74.
And the light reflected from the alignment mark reaches the lens 76 via the half mirror 74. Further, the light branched via the sampling half mirror 72 reaches the drive control unit 80.

The solid-state imaging device 78 is arranged at a position where an optical image of an alignment mark obtained through the lens 76 is formed. The drive control unit 80 has a plurality of output terminals, and pulses output from these output terminals are supplied to each unit in the solid-state imaging device 78 described later. FIG. 10 is a diagram showing a configuration of a solid-state imaging device according to the fourth and fifth aspects of the present invention.

In the figure, a plurality of light receiving sections 90 are arranged in a line. Each light receiving section 90 has two output terminals, and one output terminal is connected to the CCD 9 via a transfer gate 92.
4 and the other output terminal is connected to a reset drain 98 via a reset gate 96. Also, CCD
The output terminal of 94 is connected to the output amplifier 100. In the present embodiment, a transfer pulse, a drive pulse, and a reset pulse are output from the output terminal of the drive control unit 80 shown in FIG. These pulses are supplied to a transfer gate 92, a CCD 94 and a reset gate 96 shown in FIG.

As for the correspondence between the present invention described in claims 4 and 5 and this embodiment, the image pickup means 10 corresponds to the solid-state image pickup device 78. In particular, the light receiving section provided in the imaging means 10 corresponds to the light receiving section 90 shown in FIG. 10, and the discharge section corresponds to the reset gate 96 and the reset drain 98. The illuminating unit 12 and the light source B correspond to the light source 82, the image scanning unit 14 corresponds to the “function for controlling the generation of the transfer pulse and the driving pulse” of the drive control unit 80, and the discharging unit 16 corresponds to the “function for controlling the generation of the transfer pulse and the drive pulse”. The object A corresponds to an alignment mark.

Hereinafter, referring to FIGS. 9 and 10, claim 4 will be described.
The operation of the embodiment corresponding to the inventions described in 5 and 5 will be described. The light source control unit 84, as in the above-described embodiment,
A light emission timing signal is given to the light source 82 every period T. When the light source 82 receives the light emission timing signal from the light source control unit 84, the light source 82 emits light during the light emission period t1 similarly to the above-described embodiment.
And the light emission suspension period t2 are repeated to intermittently illuminate the alignment mark at the cycle T.

The optical image of the alignment mark generated by the light from the light source 82 is formed on the solid-state imaging device 78 via the lens 76 and the half mirror 74. In the solid-state imaging device 78, photoelectric conversion is performed by the light receiving unit 90, and signal charges are generated according to the optical image. on the other hand,
The light emitted from the light source 82 is branched via the sampling half mirror 72 as described above,
Reach 0.

The drive control unit 80 generates a transfer pulse at a point of time when the light arrives and is delayed for several nsec (at the end of the light emitting period t1). In the solid-state imaging device 78, at the time of the rise of the transfer pulse, the signal charge is transferred to the C
Read to CD94.

The signal charges read to the CCD 94 in this manner are transferred to the output amplifier 100 based on the drive pulse supplied from the drive control section 80 and output as image signals. Incidentally, in the light receiving unit 90, even during the light emission suspension period t2, unnecessary charges are generated by noise such as dark current.

The drive control unit 80 predicts the point in time at which light arrives again via the sampling half mirror 72 based on the cycle T, and from that point in time t3 required for reading unnecessary charges (in this case, several nsec. ), A reset pulse is generated at a point preceding the preceding. In the solid-state imaging device 78, unnecessary charges are read from the light receiving unit 90 via the reset gate 96 at the time of the rise of the reset pulse, and are discharged by the reset drain 98 before the light emission period t 1 ends.

That is, in the present embodiment, the unnecessary charges of the light receiving section 90 are read out before the light emission of the light source 82, so that the amount of the unnecessary charges superimposed on the signal charges can be surely reduced. Therefore, the noise component of the image signal can be reduced, and the S / N ratio of the image signal can be reliably improved.

In this embodiment, since the start time of light emission can be predicted without depending on the light source control unit 84, the independence as the imaging device is maintained and only the stepper is used, as compared with the above-described embodiment. In addition, versatility to other devices is improved. In the present embodiment, the light receiving unit 90 captures an image of the alignment mark using the solid-state imaging device 78 arranged in a line. However, by providing a plurality of such solid-state imaging devices 78, the alignment mark is two-dimensionally arranged. The mark may be imaged.

(Third Embodiment) FIG. 11 is a diagram showing a configuration of a solid-state imaging device according to the fourth and seventh aspects of the present invention. In the figure, components having the same functions and configurations as those of the solid-state imaging device shown in FIG. 6 are denoted by the same reference numerals.

The difference between the solid-state imaging device of this embodiment and the solid-state imaging device shown in FIG.
Has two output terminals, and one output terminal is connected to the reset drain 104 via the reset gate 102. The features of the present embodiment reside in the control method of the drive control unit 80 and the configuration of the solid-state imaging device, and the other hardware configurations are the same as the functional block diagram of the embodiment shown in FIG. Here, illustration is omitted.

In this embodiment, a transfer pulse, a vertical drive pulse, a horizontal drive pulse, and a reset pulse are output from the output terminal of the drive control unit 80. These pulses are transmitted to the transfer gate 42, the vertical CCD 4
4. It is supplied to the horizontal CCD 46 and the reset gate 102. Further, regarding the correspondence between the inventions described in claims 4 and 7 and the present embodiment, the imaging means 10 corresponds to the solid-state imaging device 78 shown in FIG. In particular, the imaging means 10
Corresponds to the light receiving unit 40, and the transfer path corresponds to the vertical CCD 44 and the horizontal CCD 46 shown in FIG. The illumination unit 12 and the light source B correspond to the light source 82 shown in FIG. 9, and the image scanning unit 14 is a driving control unit 80 shown in FIG.
The subject A corresponds to the alignment mark shown in FIG. 9 in “Function for controlling generation of transfer pulse, vertical drive pulse, and horizontal drive pulse related to generation of image signal”. The discharging unit 16 corresponds to “the function of controlling generation of transfer pulse, vertical driving pulse, and reset pulse related to discharging of unnecessary charges” of the drive control unit 80 shown in FIG. 9 and the reset gate 102 and the reset drain 104. I do.

Hereinafter, referring to FIGS. 9 and 11, claim 4 will be described.
The operation of the embodiment corresponding to the inventions described in 7 and 7 will be described. The light source control unit 84, as in the above-described embodiment,
A light emission timing signal is given to the light source 82 every period T. When the light source 82 receives the light emission timing signal from the light source control unit 84, the light source 82 emits light during the light emission period t1 similarly to the above-described embodiment.
And the light emission suspension period t2 are repeated to intermittently illuminate the alignment mark at the cycle T.

Further, in the solid-state imaging device 78, an optical image of the alignment mark generated by the light from the light source 82 is formed as in the above-described embodiment, and a signal charge is generated in the light receiving section 40. When light arrives via the sampling half mirror 72 as in the above-described embodiment, the drive control unit 80 operates for several ns from the time when the light arrives.
When ec is delayed (when the light emission period t1 ends),
Generate a transfer pulse.

In the solid-state imaging device 78, at the time of the rise of the transfer pulse, the signal charge is read out to the vertical CCD 44 via the transfer gate 42. The signal charges read to the vertical CCD 44 in this manner are transferred to the horizontal CCD 46 based on the vertical drive pulse supplied from the drive control unit 80. In addition, horizontal CCD4
The signal charge transferred to 6 is transferred in the direction of the output amplifier 48 based on the horizontal drive pulse supplied from the drive control unit 80 and output as an image signal.

By the way, the drive control unit 80 predicts the point in time at which light arrives again via the sampling half mirror 72 as in the above-described embodiment. In addition, the drive control unit 80 instructs the transfer pulse and the charge transfer in the reverse direction at a time preceding the time t3 (in this case, several tens of nsec) required for discharging unnecessary charges from such a time. Generates a vertical drive pulse and a reset pulse.

By such a pulse, unnecessary charges generated in the light receiving section 40 are read out to the vertical CCD 44 via the transfer gate 42. In addition, vertical CCD4
Unnecessary charges read to No. 4 are transferred to the reset gate 102 by the end of the light emission period t1 and discharged by the reset drain 104 via the reset gate 102.

That is, in the present embodiment, the light emitting period t1
Unnecessary charges are completely discharged before the signal charges generated in the vertical CCD 44 are read out from the light receiving unit 40.
Unnecessary charges are not superimposed on signal charges within the circuit. Therefore, the noise component of the image signal can be reduced,
The SN ratio of the image signal can be reliably improved.

In each of the embodiments described above, claim 5
Although the operation of discharging unnecessary charges through the solid-state imaging device according to any one of claims 7 to 7 has been described, the present invention is not limited to the method of discharging unnecessary charges, and any imaging method may be used. An element may be applied. In each of the embodiments described above, the operation in the case where the imaging devices 20 and 70 are applied to a stepper has been described. However, the imaging device corresponding to the present invention is not limited to a stepper, and may be applied to, for example, an electronic camera. Thus, a good image signal can be generated.

[0068]

As described above, according to the first aspect of the present invention, unnecessary signal charges generated during a period in which light emission is stopped are not superimposed as noise components of an image signal. The SN ratio of the image signal can be reliably improved. According to the second aspect of the present invention, the detection of the timing immediately after the light emission is completed and the emission of the light are started by transmitting a control signal defining a period during which the illumination means emits light to the image scanning means and the discharge means. The immediately preceding timing can be easily and reliably detected.

Further, according to the third and fourth aspects of the present invention, even when the light source B is provided outside, it is possible to reliably recognize the period during which light emission is stopped. Unnecessary signal charges generated during such a period are not superimposed as noise components of the image signal, and the S / N ratio of the image signal can be reliably improved. According to the fifth and sixth aspects of the present invention, the timing for discharging unnecessary signal charges can be made closer to the timing for starting light emission. Can also be reliably discharged.

Further, according to the present invention, unnecessary signal charges generated on the transfer path due to noise are reliably discharged during the period when light emission is suspended, regardless of the presence or absence of the light-shielding region. be able to. Therefore, in the imaging apparatus to which these inventions are applied, noise due to dark current or the like can be surely reduced without adding a cooling device or the like. Can be generated. Further, in a stepper employing such an imaging device, it is possible to increase the speed of alignment and improve the reliability.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the principle of the present invention.

FIG. 2 is a principle block diagram of the invention according to claim 2;

FIG. 3 is a principle block diagram of the invention according to claim 3;

FIG. 4 is a principle block diagram of the invention according to claim 4;

FIG. 5 is a functional block diagram of an embodiment according to the first to third and sixth aspects of the present invention;

FIG. 6 is a diagram illustrating a configuration of a solid-state imaging device according to the first to third and sixth aspects of the present invention.

7 is a cross-sectional view of the solid-state imaging device shown in FIG. 6, taken along line XX '.

FIG. 8 is a timing chart showing light emission of a light source and operation of a solid-state imaging device.

FIG. 9 is a functional block diagram of an embodiment corresponding to the fourth and fifth aspects of the present invention.

FIG. 10 is a diagram showing a configuration of a solid-state imaging device according to the fourth and fifth aspects of the invention.

FIG. 11 is a diagram showing a configuration of a solid-state imaging device according to the fourth and seventh aspects of the invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Imaging means 12 Illumination means 14 Image scanning means 16 Ejection means 18 Light source control means 20, 70 Imaging device 22, 78 Solid-state imaging device 24, 76 Lens 26, 84 Light source control unit 28, 82, B light source 30, 80 Drive control unit 32, 74 Half mirror 40, 90 Light receiving section 42, 92 Transfer gate 44 Vertical CCD 46 Horizontal CCD 48, 100 Output amplifier 50 N-type light receiving area 52 N-type silicon substrate 54 P-type well area 56 Transfer gate electrode 58 Insulating film 60 embedded Channel region 62 Vertical CCD electrode 64 Channel stopper 72 Half mirror for sampling 94 CCD 96, 102 Reset gate 98, 104 Reset drain A Subject

Claims (7)

[Claims] An imaging unit that captures an optical image of a subject to generate a signal charge; an illumination unit that intermittently emits light to illuminate the subject; Image scanning means for scanning the signal charge generated by the means to generate an image signal; and discharging means for discharging the signal charge generated by the imaging means immediately before the lighting means starts emitting light. An imaging device characterized by the above-mentioned. 2. The imaging apparatus according to claim 1, further comprising: a light emission control unit configured to control a light emission timing of the illumination unit by a control signal defining a period during which the illumination unit emits light, wherein the image scanning unit includes: Acquiring the control signal, detecting a timing immediately after the lighting unit has finished emitting light based on the control signal, and generating the image signal, the discharging unit acquiring the control signal, and applying the control signal to the control signal. An imaging device for detecting the timing immediately before the lighting means starts emitting light and discharging the signal charge. 3. An image pickup means for picking up an optical image of a subject illuminated by a light source intermittently emitting light and generating a signal charge, and acquiring a control signal defining a period during which the light source emits light, and An image scanning unit that detects a timing immediately after the light emission ends and scans the signal charges generated by the imaging unit at the timing to generate an image signal; and acquires the control signal and starts the light source to emit light. And a discharge unit that detects a timing immediately before the operation and discharges the signal charge generated by the imaging unit at the timing. 4. An image pickup means for picking up an optical image of a subject illuminated by a light source intermittently emitting light and generating a signal charge; and acquiring light from the light source and immediately after the light source has finished emitting light. An image scanning unit that detects a timing and scans the signal charge generated by the imaging unit at the timing to generate an image signal; and a timing immediately before the light source acquires light from the light source and the light source starts emitting light. And a discharging unit for discharging the signal charges generated by the imaging unit at the timing. 5. The imaging device according to claim 1, wherein the imaging unit includes a light receiving unit, and a discharging unit adjacent to the light receiving unit, wherein the discharging unit includes: An image pickup device, wherein the signal charge is discharged through a discharge unit. 6. The image pickup apparatus according to claim 1, wherein the image pickup unit includes a light receiving unit and a discharge unit arranged in a direction perpendicular to the light receiving unit. The imaging device discharges the signal charge through the discharge unit. 7. The imaging device according to claim 1, wherein the imaging unit is obtained by a light receiving unit that performs a photoelectric conversion of an optical image and a photoelectric conversion performed by the light receiving unit. A transfer path for transferring a signal charge, wherein the image scanning unit reads out the signal charge via the transfer path to generate an image signal, and the discharge unit passes through at least a part of the transfer path. An imaging device, wherein the signal charge is discharged.