JP2006041366A - Equipment and method for judging deterioration of photoelectric conversion element, exposure device and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect deterioration of a photovoltaic conversion element precisely. <P>SOLUTION: In order to judge deterioration of a quantity of pulse light detector 8 for converting light energy into electric energy, a capacity measuring device 51 measures the capacitance between the terminals of the quantity of pulse light detector 8. A controller 100 judges deterioration of the quantity of pulse light detector 8 based on the measurement of the capacity measuring device 51. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photoelectric conversion device that converts light energy into electrical energy, and more particularly to a technique for detecting deterioration of a light receiving element (photoelectric conversion element).

  A photoelectric conversion device that converts light energy into electrical energy is used for measuring the amount of light in an industrial device or the like that performs various processes using light. The result of the light quantity measurement is important for properly operating such an industrial apparatus, and the deterioration of measurement accuracy by the photoelectric conversion apparatus makes the operation of such an industrial apparatus unstable. In particular, in the photoelectric conversion device for short wavelength light, the light receiving element is significantly deteriorated.

For example, there is a semiconductor exposure apparatus as an apparatus that converts light energy having a short wavelength into electric energy. In a semiconductor exposure apparatus, means for detecting light from a light source is necessary to control each calibration or exposure amount. At present, a KrF excimer laser (248 nm) and an ArF excimer laser (193 nm) are mainly used as light sources used by the semiconductor exposure apparatus. As a light source for the next-generation exposure apparatus, an F ₂ laser (157 nm), an EUV light source, etc. are considered promising. Such light having a short wavelength has a large photon energy and is likely to cause radiation damage to the light receiving element. In a photoelectric conversion device used in a semiconductor exposure apparatus using such a light source, a decrease in light receiving sensitivity may be a problem.

  As an element that receives light having a short wavelength, a Schottky type semiconductor light receiving element is generally used because light absorption in the element surface layer can be effectively utilized. The main cause of deterioration of the Schottky type semiconductor light-receiving element due to irradiation with short wavelength light is due to deterioration of the interface junction between the electrode and the semiconductor due to irradiation with ultraviolet light having strong photon energy. Therefore, it is necessary to periodically perform maintenance such as replacement of the light receiving element. In the conventional apparatus, the total number of irradiation pulses and the total amount of irradiation light of the light receiving element are estimated in advance and used as replacement conditions.

For example, Patent Document 1 proposes estimating a time-dependent change in conversion efficiency characteristics over a long period of time by measuring a reverse bias saturation current at the time of light irradiation to a photoelectric conversion element. It would be possible to use the value to determine the execution conditions for the exchange as described above.
JP-A-01-118281 Japanese Patent Laid-Open No. 01-146375 JP 09-288313 A

  However, the deterioration rate of the light receiving element is not necessarily uniform due to a difference in use environment of the light receiving element or individual differences. Accordingly, in the conventional method in which the total number of irradiation pulses and the total amount of irradiation light of the light receiving element are estimated in advance and used as replacement conditions, the light receiving element deteriorates before reaching the previously estimated total number of irradiation pulses and total amount of irradiation light. There was a problem. Further, even if the light receiving element can still be used sufficiently, it is replaced when the total number of irradiation pulses and the total amount of irradiation light are reached, so that the light receiving element cannot be used efficiently. Further, even if the time-dependent change in the conversion efficiency characteristic of each light receiving element is estimated by the method shown in Patent Document 1 and the replacement execution condition is determined based on this, the change in the characteristic depends on the operating environment of the light receiving element. Since it fluctuates, the above problem is still not solved.

  Patent Document 2 describes that the linearity is determined to be good by measuring the capacitance of the light receiving element, but no reference is made to the determination of deterioration of the light receiving element. Patent Document 3 describes that a camera using an electrostatic information storage medium measures the deterioration of the electrostatic information storage medium using dark current. However, it is applied to a special material such as an electrostatic information storage medium, and cannot be applied as it is to a light receiving element that receives light having a short wavelength as described above.

The present invention has been made in view of the above problems, and an object of the present invention is to make it possible to accurately detect deterioration of a photoelectric conversion element.
Another object of the present invention is to appropriately determine deterioration of a light receiving element that detects the amount of illumination light, and to replace the light receiving element at an appropriate time, particularly in an exposure apparatus.

In order to achieve the above object, the photoelectric conversion element deterioration determination apparatus according to the present invention is
A degradation determination device for a photoelectric conversion element that converts light energy into electrical energy,
Measuring means for measuring the capacitance between the terminals of the photoelectric conversion element;
Determination means for determining a deterioration state of the photoelectric conversion element based on a measurement value obtained by the measurement means.

An exposure apparatus according to another aspect of the present invention for achieving the above object comprises the following arrangement. That is,
An exposure apparatus for transferring a pattern formed on a reticle to an exposure area of a photosensitive substrate using illumination light from an exposure light source,
Control means for detecting a partial light quantity of the illumination light using a photoelectric conversion element and controlling the intensity of the illumination light based on the detected light quantity;
Measuring means for measuring the capacitance between the terminals of the photoelectric conversion element;
Determination means for determining a deterioration state of the photoelectric conversion element based on a measurement value by the measurement means;
And a notification means for notifying that when the determination means detects deterioration.

According to the present invention, it is possible to accurately detect deterioration of a photoelectric conversion element.
Further, particularly in the exposure apparatus, it is possible to appropriately determine the deterioration of the light receiving element that detects the amount of illumination light, and the light receiving element can be replaced at an appropriate time.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  In the present embodiment, parameters related to the deterioration of the light receiving element are directly monitored. For example, the main cause of deterioration of a Schottky type semiconductor light-receiving element due to irradiation with short wavelength light is due to deterioration of the interface junction between the electrode and the semiconductor due to irradiation with ultraviolet light having strong photon energy. A depletion layer for absorbing light and generating a photocurrent is interposed at the interface junction between the electrode and the semiconductor, and it can be considered that a kind of capacitor (junction capacitance) is formed. When the interface junction is irradiated with light having a short wavelength, the crystal structure is damaged, so that the junction capacitance of the semiconductor light receiving element decreases. As described above, the present inventor has found that the degradation state of the light receiving element can be determined by the junction capacitance because the junction capacitance depends on the degradation of the interface junction, which is regarded as a degradation factor.

  Therefore, according to the present embodiment, by constantly monitoring the inter-terminal capacitance including the junction capacitance and the stray capacitance of the package, it is possible to determine the degree of deterioration of the light receiving element and to realize efficient maintenance of the light receiving element.

[Deterioration judgment in photoelectric conversion device]
FIG. 2 is a diagram schematically illustrating the photoelectric conversion apparatus according to the present embodiment. In FIG. 2, a pulse light amount detector 8 converts light energy into electrical energy. The amplifier 50 amplifies the output obtained by converting light energy into electrical energy in the pulse light amount detector 8 and outputs the amplified output to the controller 100. The capacity measuring device 51 measures the inter-terminal capacity of the pulse light amount detector 8 and outputs the measurement result to the controller 100. The changeover switch 49 switches the connection destination of the output terminal of the pulse light amount detector 8 between the amplifier 50 and the capacitance measuring device 51.

  The actual operation will be described. For example, when measuring the amount of detection light (a part of illumination light) in the exposure apparatus, the pulse light amount detector 8 and the amplifier 50 are connected by the changeover switch 49. The changeover switch 49 is controlled by the controller 100. The signal intensity output from the pulse light quantity detector 8 is amplified by the amplifier 50. The controller 100 performs desired data processing on the output of the amplifier 50.

  On the other hand, when measuring the inter-terminal capacitance (ie, junction capacitance) of the pulse light amount detector 8, the controller 100 controls the changeover switch 49 to connect the pulse light amount detector 8 and the capacitance measuring device 51.

  As a method for measuring the junction capacitance of the pulse light quantity detector 8, for example, there is a measurement method by a capacitance bridge method. The principle of measuring the junction capacitance by the capacitance bridge method will be described with reference to FIG. FIG. 3 is a diagram illustrating a principle circuit for measuring a junction capacitance by the capacitance bridge method and explaining an internal configuration of the capacitance measuring device 51. As shown in FIG. 3, the capacitance measuring device 51 is connected to the pulse light amount detector 8, and includes an AC signal source 52, variable resistors 53 and 54, a standard capacitor 55, an AC ammeter 56, a bias supply choke coil. 57 and 58 and a bias power source 59 are provided.

The junction capacitance Cj of the pulse light quantity detector 8 can be obtained as follows using the bridge circuit shown in FIG. That is, when the pulse light amount detector 8 is connected and a predetermined bias voltage is applied by the bias power source 59, the resistance values of the two variable resistors 53 and 54 are set so that the measurement value of the AC ammeter 56 becomes zero. Adjust to. Then, from the resistance values P and Q of the variable resistors 53 and 54 and the value Cs of the standard capacitor 55 at that time, the junction capacitance Cj of the pulse light quantity detector 8 is expressed by the following equation:
Cj = P · Cs / Q
Ask for.

  The adjustment of the resistance values of the variable resistors 53 and 54 can be realized as follows, for example. There is a method in which the current value measured by the AC ammeter 56 is A / D converted and read into the CPU, and the resistance value is controlled by a potentiometer or the like.

  Thus, the junction capacitance Cj (inter-terminal capacitance) of the pulse light amount detector 8 measured by the capacitance measuring device 51 is sent to the controller 100. The controller 100 determines pass / fail of the pulse light amount detector 8 based on the measured junction capacitance Cj.

  Next, the quality determination of the pulse light amount detector 8 will be described. The graph shown in FIG. 4 shows the characteristics of the inter-terminal capacitance of the pulse light quantity detector 8 with respect to the irradiation light quantity (number of irradiation pulses). The horizontal axis indicates the irradiation light amount or the number of irradiation pulses irradiated to the pulse light amount detector 8, and the vertical axis indicates the inter-terminal capacitance. As shown in FIG. 4, the inter-terminal capacitance of the pulse light amount detector 8 shows a characteristic that decreases due to the irradiated light energy. As described above, this is because the crystal structure is damaged when short-wavelength light is irradiated to the interface junction. In the present embodiment, whether the pulse light amount detector 8 is good or bad is determined based on how much the capacitance has decreased with respect to the inter-terminal capacitance X [pF] before light irradiation (initial state before use). For example, the value measured by the capacitance measuring device 51 is compared with a determination threshold (0.4 times the inter-terminal capacitance before light irradiation in FIG. 4) obtained by a previously performed experiment or the like. If it is smaller than the above, control is performed on the pulse light amount detector 8 as a maintenance target.

  As another pass / fail judgment method, the pass / fail judgment threshold may be set as an absolute value instead of determining a relative pass / fail judgment threshold for the inter-terminal capacitance before irradiation.

[Application to exposure equipment]
Next, an embodiment in which the above-described photoelectric conversion apparatus is applied to an exposure apparatus will be described. Although the scanning exposure apparatus is used as the exposure apparatus, it is obvious that the exposure apparatus can be applied to other types of exposure apparatuses.

  FIG. 1 is a schematic view of a scanning exposure apparatus using a photoelectric conversion apparatus according to the present invention. In FIG. 1, a light beam emitted from a light source (laser) 1 passes through a predetermined ND filter 3 of an ND turret 2 that adjusts a pulse light amount. A plurality of ND filters numbered (pulse light quantity number) are embedded in the ND turret 2, and when adjusting the average pulse light quantity, the optimum ND filter is selected and inserted into the laser beam path. The beam shaping optical system 4 shapes the light beam that has passed through the ND filter 3 into a predetermined shape and makes it incident on the light incident surface of the optical integrator 5. The optical integrator 5 is composed of a plurality of minute lenses, and a large number of secondary light sources are formed in the vicinity of the light exit surface.

  The diaphragm turret 6 limits the size of the secondary light source surface described above by a predetermined diaphragm 7. For example, the aperture turret 6 is numbered (illumination mode number) such as an aperture stop with different circular aperture areas, a ring-shaped aperture for annular illumination, a quadrupole aperture, etc. for setting a plurality of coherence factor σ values. ) Multiple apertures are buried. A diaphragm necessary for changing the shape of the incident light source of the illumination light is selected from the diaphragm turret 6 and inserted into the optical path. A part of the pulse light reflected by the half mirror 9 is guided to the pulse light amount detector 8. By connecting the pulse light amount detector 8 and the amplifier 50 by the changeover switch 49, a detection signal corresponding to the light amount per pulse can be obtained. The detection signal is an analog signal and is output to the exposure amount calculation unit 42.

  The condenser lens 10 Koehler-illuminates the blind 11 with a light beam from a secondary light source in the vicinity of the exit surface of the optical integrator 5. A slit 12 is disposed in the vicinity of the blind 11, and the profile of the slit light that illuminates the blind 11 is formed in a rectangular or arc shape. The slit light is a conjugate surface of the blind 11 via the condenser lenses 13 and 15 and the mirror 14, and forms an image on the reticle 16 on which the element pattern is formed in a state where the illuminance and the incident angle are made uniform. The opening area of the blind 11 is similar to the desired pattern exposure area of the reticle 16 in terms of the optical magnification ratio. During exposure, the blind 11 performs synchronous scanning with respect to the reticle stage 17 at an optical magnification ratio while shielding the outside of the exposure area of the reticle 16.

  The ND turret 2, the beam shaping optical system 4, the optical integrator 5, the half mirror 9, the condenser lenses 10 and 15, the slit 12, and the mirror 14 are optical units constituting an illumination optical system. The inside of the housing of the illumination optical system is purged with an organic substance that causes a photochemical reaction by the introduced nitrogen, thereby suppressing optical performance deterioration of the optical unit.

  The reticle 16 is held by a reticle stage 17. The slit light that has passed through the reticle 16 passes through the projection optical system 18 and is imaged again as slit light on the exposure field angle region on the pattern surface of the reticle 16 and the optical conjugate surface. The focus detection system 19 detects the height and inclination of the exposure surface on the wafer 21 held by the wafer stage 20. During scanning exposure, the reticle stage 17 and the wafer stage 20 are moved to the projection optical system 18 while controlling the wafer stage 20 so that the exposure surface of the wafer 21 coincides with the exposure field surface based on the information of the focus detection system 19. Run synchronously. As a result, the wafer 21 is exposed to slit light, and the pattern is transferred to the photoresist layer on the wafer 21.

  On the wafer stage 20, a pulse light amount detector 22 is installed, and the slit light pulse light amount on the exposure field angle can be measured. The pulse light amount detector 22 is a one-dimensional sensor array whose longitudinal direction coincides with the scanning direction.

  Next, the configuration of the control system in the scanning exposure apparatus of this embodiment will be described. The stage drive control unit 41 performs synchronous running control of the reticle stage 17 and the wafer stage 20 during scanning exposure, including exposure surface position control. The exposure amount calculation unit 42 converts the electrical signal photoelectrically converted by the pulse light amount detector 8 and the pulse light amount detector 22 into a logical value and outputs the logical value to the main control unit 43. Note that the pulse light amount detector 8 is configured to allow measurement even during exposure. On the other hand, the pulse light quantity detector 22 detects the light quantity of the slit light that irradiates the wafer 21 before the exposure process. Simultaneously with the measurement by the pulse light amount detector 22, the light amount measurement by the pulse light amount detector 8 is performed, and the correlation between the light amounts detected by both detectors is obtained. Using this correlation, an output value from the pulse light amount detector 8 is converted into a light amount on the wafer 21 and used as a monitor light amount for exposure amount control. Hereinafter, the monitor light amount will be described as being the same as the pulse light amount on the wafer. Further, the logical value (unit bit) converted by the exposure light amount calculation unit 42 output from the pulse light amount detectors 8 and 22 represents the pulse light amount itself. On the other hand, the pulse light amount detector 22 performs measurement while scanning the exposure slit light by the wafer stage 20, and can simultaneously measure the deviation from the integrated exposure amount and the set exposure amount at each point in the exposure region.

  The laser controller 44 (controls the laser output and the oscillation frequency) controls the oscillation frequency and output energy of the light source 1 by outputting a trigger signal 31 and an applied voltage signal 32 in accordance with the desired pulse light quantity. When the laser control unit 44 generates the trigger signal 31 and the applied voltage signal 32, the pulse light amount signal 34 from the exposure amount calculation unit 42 and the exposure parameters 35 and 36 from the main control unit 43 are used.

  Desired exposure parameters (particularly integrated exposure amount, required integrated exposure amount accuracy, or aperture shape) are input to the main control unit 43 from the input device 45 as a man-machine interface or media interface, and stored in the storage unit 46. The results obtained from the pulse light quantity detectors 8 and 22 and the correlation between the results of the detectors are displayed on the display unit 47. The main control unit 43 calculates a parameter group necessary for the scanning exposure from the data given from the input device 45, the parameters unique to the exposure apparatus, and the data measured by the measuring means such as the pulse light quantity detectors 8 and 22. This is transmitted to the laser controller 44 and the stage drive controller 41. The photoelectric conversion device 48 is a device that measures the amount of incident light or the capacitance between terminals of the pulse light amount detector 8 based on a command from the main control unit 43. That is, the main control unit 43 includes the controller 100 shown in FIG.

  Next, a sequence for measuring the inter-terminal capacitance of the pulse light amount detector 8 will be described. FIG. 5 shows a sequence between a general exposure apparatus and a laser system. In step S101, a reset sequence between the exposure apparatus and the laser that occurs when the exposure apparatus is reset is executed. That is, a signal line between the exposure apparatus and the laser is checked, and optical adjustment inside the exposure apparatus is performed. When the reset sequence in step S101 is completed, the exposure apparatus is ready for actual exposure on the wafer. First, in step S102, the exposure apparatus checks whether or not there is a gas exchange request for the laser. If there is no request, the exposure apparatus proceeds to step S103 and executes an exposure sequence. In the exposure sequence, control for setting the wavelength of the laser to a target wavelength, exposure amount control for controlling the exposure amount on the wafer, and the like are executed.

  On the other hand, if a gas replacement request has occurred in step S102, the process proceeds to step S104, and laser gas replacement is executed. Generally, about 10 minutes is spent as the gas exchange time. Meanwhile, since the laser cannot oscillate, the exposure apparatus waits for the end of the gas exchange of the laser before proceeding to the exposure sequence (step S103). When the exposure sequence ends, the process moves to sequence 102 again, and the above operation is repeated.

  On the other hand, in the scanning exposure apparatus of the present embodiment, attention is paid to the fact that the exposure apparatus is not irradiated with the exposure light during the gas exchange, and the pulse light quantity detector 8 is used during the gas exchange of the laser. The measurement of the inter-terminal capacitance / determining whether or not is acceptable. FIG. 6 shows a quality determination sequence of the semiconductor light receiving element in the scanning exposure apparatus of the present embodiment. Note that the same step numbers are assigned to the same processing steps as in FIG.

  If a gas replacement request is generated in step S102, the exposure apparatus sends a gas replacement command to the laser and executes laser gas replacement (step S104). On the other hand, in the exposure apparatus, steps S105 to S107 are executed simultaneously with the gas exchange process in step S104. In step S <b> 105, the output terminal of the pulse light amount detector 8 is connected to the capacitance measuring device 51 by the changeover switch 49. And the capacity | capacitance measuring device 51 measures the capacity | capacitance between terminals of a photoelectric conversion element (pulse light quantity detector 8). Next, in step S106, the quality of the photoelectric conversion element is determined by the method described with reference to FIG. As a result of the pass / fail determination, if maintenance is not required, the process proceeds from step S106 to step S108. On the other hand, if maintenance is required, the process proceeds from step S106 to step S107, and the operator is notified. As a configuration for notification, an error / warning is generated, and notification to an operator is executed by a user interface. In step S108, it is confirmed that the laser gas replacement and the photoelectric conversion element pass / fail determination have been completed, and the process proceeds to the exposure sequence (step S103).

  Note that immediately after the photoelectric conversion element (pulse light amount detector 8) is replaced, the initial value of the capacitance of the photoelectric conversion element is measured before the illumination light for exposure is irradiated. This measured value is held in a memory (not shown) and used for calculation of the determination threshold described with reference to FIG.

  In the above-described embodiment, a specific example is described for the pulse light amount detector 8, but the present invention is not limited to such application, and for example, is applied to the pulse light amount detector 22 installed on the wafer stage. It is also possible to do.

  In addition, as a photoelectric conversion element, a semiconductor light receiving element having a Schottky junction type as a basic structure has been described as an example. The present invention can also be applied to a semiconductor light receiving element.

  In this embodiment, a scanning exposure apparatus using an excimer laser as a light source has been described as a specific example. However, the present invention can also be applied to an exposure apparatus using EUV light as a light source.

  As described above, according to the above-described embodiment, it is possible to efficiently use and replace the semiconductor light receiving element by periodically measuring the capacitance between the terminals of the semiconductor light receiving element and performing the pass / fail judgment of the semiconductor light receiving element. Is possible. Further, it is possible to avoid a risk that the sensitivity of the semiconductor light receiving element suddenly disappears during use of the apparatus and the apparatus cannot be used.

It is a figure which shows the structure of the scanning exposure apparatus by embodiment. It is a block diagram which shows the structure of the photoelectric conversion apparatus by embodiment. It is a figure explaining the principle of the junction capacity measurement by the capacity | capacitance bridge method which the capacity | capacitance measuring apparatus by embodiment uses. It is a characteristic view which shows the relationship between the capacity | capacitance between terminals with respect to the irradiation light quantity of a semiconductor light receiving element, and the total irradiation light quantity. It is a flowchart explaining the sequence by a general exposure apparatus. It is a flowchart explaining the sequence by the scanning exposure apparatus of embodiment.

Claims (8)

A degradation determination device for a photoelectric conversion element that converts light energy into electrical energy,
Measuring means for measuring the capacitance between the terminals of the photoelectric conversion element;
A deterioration determination apparatus comprising: determination means for determining a deterioration state of the photoelectric conversion element based on a measurement value obtained by the measurement means.   The said determination means determines deterioration of the said photoelectric conversion element based on the variation | change_quantity of the initial inter-terminal capacity | capacitance obtained by the said measurement means, and the present inter-terminal capacity | capacitance. Degradation judgment device.   2. The deterioration determination according to claim 1, wherein the determination unit determines deterioration of the photoelectric conversion element based on a comparison between a measurement value obtained by the measurement unit and a predetermined determination threshold value. apparatus. An exposure apparatus for transferring a pattern formed on a reticle to an exposure area of a photosensitive substrate using illumination light from an exposure light source,
Control means for detecting a partial light quantity of the illumination light using a photoelectric conversion element and controlling the intensity of the illumination light based on the detected light quantity;
Measuring means for measuring the capacitance between the terminals of the photoelectric conversion element;
Determination means for determining a deterioration state of the photoelectric conversion element based on a measurement value by the measurement means;
An exposure apparatus comprising: notifying means for notifying that the deterioration is detected by the determining means.   The exposure apparatus according to claim 4, wherein the measurement unit is caused to function while irradiation of the illumination light is stopped. The illumination light source device is an excimer laser or EUV light source;
6. The exposure apparatus according to claim 5, wherein the measuring unit functions while gas exchange is performed in the light source device. A method for determining deterioration of a photoelectric conversion element that converts light energy into electrical energy,
A measuring step of measuring the inter-terminal capacitance of the photoelectric conversion element;
A deterioration determination method comprising: a determination step of determining a deterioration state of the photoelectric conversion element based on a measurement value obtained by the measurement step. An exposure apparatus control method for transferring a pattern formed on a reticle to an exposure area of a photosensitive substrate using illumination light from an exposure light source,
A control step of detecting a partial light amount of the illumination light using a photoelectric conversion element and controlling the intensity of the illumination light based on the detected light amount;
A measuring step of measuring the inter-terminal capacitance of the photoelectric conversion element;
A determination step of determining a deterioration state of the photoelectric conversion element based on a measurement value obtained by the measurement step;
An exposure apparatus control method, comprising: a notification step of notifying that a deterioration is detected in the determination step.

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