Flash illumination device

Abstract

This invention provides a flash irradiation device that can suppress the decrease in output when flash irradiation is repeated and has higher energy efficiency when the flash lamp is lit than conventional devices. [Solution] The flash irradiation device comprises a flash lamp including a first terminal and a second terminal, a capacitor including a first electrode and a second electrode, a first switching element that controls the connection state between the flash lamp and the capacitor, a second switching element arranged in parallel with the first switching element and controlling the connection state between the flash lamp and the capacitor, and a control unit that controls the first and second switching elements. The control unit performs a first control in which the second switching element is repeatedly turned on and off at high speed while the first switching element is in the off state and a voltage is applied to the flash lamp, and a second control in which the first switching element is turned on during the execution of the first control and a main discharge is generated based on the remaining voltage of the capacitor.

Description

[Technical Field]

[0001] This invention relates to a flash irradiation device. [Background technology]

[0002] Traditionally, flash irradiation using flash lamps has been used as a heat treatment method in the manufacturing processes of semiconductor wafers and printable electronics. In recent years, in particular, with the miniaturization of semiconductor processes, instantaneous heat treatment methods using flash irradiation devices have attracted attention as a way to activate injected impurities while suppressing their diffusion due to prolonged heating.

[0003] Incidentally, in flash lamps, the flashing light can cause some of the glass material constituting the discharge tube to evaporate or the oxygen component contained in the glass material to desorb, resulting in clouding on the inner wall of the discharge tube. This clouding tends to become more pronounced when the flash lamp is repeatedly irradiated, causing a decrease in the output of the flash lamp.

[0004] Therefore, the applicant has been developing a flash lamp lighting device, for example, as shown in Patent Document 1 below. Patent Document 1 discloses a lamp lighting device that can perform flash irradiation while forming a shimmer discharge near the tube axis of the discharge tube, from the viewpoint of suppressing the clouding of the inner wall of the discharge tube that occurs when flash irradiation is repeated. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2009-164080 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Figure 12 is a schematic diagram showing the circuit configuration of a lamp lighting device according to Patent Document 1. As shown in Figure 12, the lamp lighting device 100 includes a flash lamp 70, a capacitor 80, an inductor 81, a resistor 82, a switching element 83, a trigger electrode 90, and a trigger circuit 91.

[0007] Figure 13 is a schematic diagram showing the configuration of the flash lamp 70 shown in Figure 12. In Figure 13, an XYZ coordinate system is shown, where the vertically upward direction is the Z direction and the plane perpendicular to the Z direction is the XY plane. As shown in Figures 12 and 13, the flash lamp 70 has a discharge tube 71 filled with discharge gas and a pair of electrodes (72, 73) arranged inside the discharge tube 71. Terminal 70a on the electrode 72 side is electrically connected to electrode 80a of capacitor 80 via inductor 81. Terminal 70b on the electrode 73 side is electrically connected to electrode 80b of capacitor 80 via switching element 83 (see Figure 12).

[0008] The switching element 83 can be switched between an on state and an off state by a control circuit (not shown), which controls the electrical connection between terminal 70b and electrode 80b.

[0009] The resistor 82 is arranged in parallel with the switching element 83 and is electrically connected to node N10, to which the terminal 70b of the flash lamp 70 and the switching element 83 are connected, and to the electrode 80b of the capacitor 80.

[0010] The trigger circuit 91 is a circuit that applies a voltage to the trigger electrode 90 in order to cause dielectric breakdown within the discharge tube 71 of the flash lamp 70. The trigger electrode 90 is made of a metal rod, for example, made of tungsten, and a pair of electrodes (72, 73) are arranged to extend in directions opposite to each other. The trigger electrode 90 is positioned below the flash lamp 70 in the vertical direction, as shown in Figure 13.

[0011] Figure 14 is a timing chart showing the operation of the lamp lighting device 100 shown in Figure 12. In Figure 14, the charging voltage V of the capacitor 80 c The current I supplied to the flash lamp 70 F The timing of the on / off control of the switching element 83 is shown. As shown in Figure 14, the capacitor 80 is charged to a desired voltage V by a power supply (not shown). 10 The battery is in a charged state. Then, at timing t10, the trigger circuit 91 is driven.

[0012] When the trigger circuit 91 is activated and a voltage is applied to the trigger electrode 90 (timing t10), the discharge gas inside the discharge tube 71 becomes ionized, causing dielectric breakdown between the pair of electrodes (72, 73). As a result, a discharge S10 is formed on the inner wall of the discharge tube 71 on the side closer to the trigger electrode 90 (see Figure 13). At this point, the switching element 83 is in the off state, so the current I supplied from the capacitor 80 to the flash lamp 70 is reduced. F This is limited to resistance 82 (current I 10 In this way, the discharge S10 is maintained by the weak limiting current restricted by resistor 82. For example, the resistance value of resistor 82 is set to approximately 10 kΩ.

[0013] Because the discharge S10 is maintained by a weak limiting current, it moves vertically upward over time due to thermal convection within the discharge tube 71 (see Figure 13). In other words, the discharge S10 is formed near the inner wall of the discharge tube 71 and then moves towards the tube axis of the discharge tube 71.

[0014] Then, at timing t20 when the discharge S10 approaches the tube axis of the discharge tube 71, the switching element 83 is switched to the ON state. As a result, a large current is instantaneously supplied to the flash lamp 70 based on the charging voltage remaining in the capacitor 80 (current I 11 ), the main discharge of the flash lamp 70 is performed. Before the main discharge is performed, the discharge S10 formed between the pair of electrodes (72, 73) is sometimes referred to as a "simmer discharge".

[0015] With the discharge S10 approaching the tube axis of the arc tube 71, when the main discharge of the flash lamp 70 is executed, generation of the main discharge near the inner wall of the arc tube 71 is suppressed, and clouding of the inner wall of the arc tube 71 is less likely to occur. By suppressing the occurrence of clouding in the arc tube 71, it is possible to suppress a decrease in the output of the flash lamp 70 when flash irradiation is repeated, and as a result, the flash lamp 70 can have a longer life.

[0016] In the configuration according to Patent Document 1, in order to cause the discharge S10 to rise by thermal convection, it is necessary to set the current input to the flash lamp 70 to a weak limiting current. In this regard, according to the intensive studies of the present inventors, when the shimmer current is set as the weak limiting current, it has been found that it is difficult to increase the energy efficiency of the flash lamp when flash irradiation is executed after the shimmer discharge. That is, there is room for improvement in terms of suppressing the occurrence of clouding in the arc tube due to the shimmer discharge and increasing the energy efficiency at the time of lighting of the flash lamp.

[0017] In view of the above, an object of the present invention is to provide a flash irradiation device that can suppress a decrease in output when flash irradiation is repeated and has a higher energy efficiency at the time of lighting of the flash lamp than in the past.

Means for Solving the Problems

[0018] The flash irradiation device according to the present invention includes a first terminal and a second terminal, and a flash lamp that discharges when a voltage is applied between the first terminal and the second terminal, a capacitor including a first electrode electrically connectable to the first terminal and a second electrode electrically connectable to the second terminal, a first switching element that controls an electrical connection between the flash lamp and the capacitor, a second switching element that is arranged in parallel with the first switching element and controls an electrical connection between the flash lamp and the capacitor, The system includes a control unit that controls the on / off state of the first switching element and the second switching element, The control unit, A first control involves repeatedly turning the second switching element on and off at high speed while keeping the first switching element in the off state, thereby applying voltage from the charged capacitor to the flash lamp. The invention is characterized by performing a second control, which involves switching the first switching element to the ON state during the execution of the first control, and applying the remaining voltage of the capacitor remaining after the first control to the flash lamp to generate a main discharge.

[0019] The inventors have discovered that by rapidly and repeatedly switching the second switching element on and off, the discharge formed inside the flash lamp expands, allowing the discharge to be formed at a location away from the inner wall of the flash tube. In other words, by executing the first control before the second control, the occurrence of the main discharge near the inner wall of the flash tube is suppressed. This makes it possible to suppress the decrease in output of the flash lamp when flash irradiation is repeated.

[0020] Furthermore, through diligent research by the inventors, it has been found that by expanding the discharge through the first control, the energy efficiency of the flash lamp during illumination can be increased compared to conventional methods. More specifically, the execution of the first control promotes the ionization of the discharge gas inside the discharge tube, and after the execution of the first control, the execution of the second control efficiently generates the main discharge. This point will be described in detail in the section on "Modes for Carrying Out the Invention."

[0021] The above-mentioned flash irradiation device is An inductor may be provided that is arranged in parallel with the first switching element and in series with the second switching element.

[0022] From the viewpoint of minimizing the energy consumed by the capacitor in the first control, it is preferable that the off time of the second switching element in the first control is longer than the on time. The above configuration is advantageous because the current supplied to the flash lamp in the first control can be adjusted by the inductor, and the off time of the second switching element can be easily designed.

[0023] In the above-mentioned flash irradiation device, The control unit may be configured to execute the second control after executing the first control for a time of 40 msec to 100 msec.

[0024] As will be explained in more detail later, the above configuration is preferable because it makes it easy to generate the main discharge while maintaining a stable discharge within the flash lamp.

[0025] Furthermore, in the above-mentioned flash irradiation device, The control unit is configured to perform the second control after a predetermined time has elapsed from the start of the first control. The predetermined time may be the time during which the discharge diameter of the discharge formed by the first control is half or more of the diameter of the discharge tube of the flash lamp.

[0026] In the above-mentioned flash irradiation device, The control unit may, after the second control has started, turn off the second switching element and stop the first control.

[0027] Furthermore, the above-mentioned flash irradiation device is A trigger electrode is positioned along the axial direction of the light-emitting tube of the flash lamp and assists in starting the flash lamp, The system includes a support unit that supports an object to be illuminated by the flash of light emitted by the aforementioned flash lamp, The trigger electrode may be positioned outside the space between the light-emitting tube and the object to be irradiated.

[0028] In devices that irradiate objects such as semiconductor wafers with a flash of light, auxiliary heating mechanisms such as halogen heaters or LEDs are sometimes positioned vertically below the object to be irradiated, and the flash lamp is typically mounted vertically above the object to be irradiated. In this configuration, as exemplified by Patent Document 1, where a discharge formed inside the flash lamp is levitated by thermal convection and the discharge is moved away from the inner wall of the discharge tube, the trigger electrode needs to be positioned vertically below the discharge tube. In this case, since the trigger electrode is positioned in the space between the discharge tube and the object to be irradiated, a portion of the flash emitted by the flash lamp is blocked by the trigger electrode, making it difficult to uniformly irradiate the object with the flash.

[0029] In contrast, in the above configuration, the first control expands the discharge formed inside the flash lamp, allowing the discharge to be formed at a location away from the inner wall of the flash lamp's discharge tube. In other words, in a configuration in which the first control moves the discharge formation location away from the inner wall of the discharge tube, the installation position of the trigger electrode is not limited to the vertically downward direction of the discharge tube. According to the above configuration, the trigger electrode is positioned outside the space between the flash lamp's discharge tube and the object to be illuminated, so the flash is not obstructed by the trigger electrode, which is preferable. For example, the trigger electrode may be positioned vertically upward direction of the discharge tube. [Effects of the Invention]

[0030] According to the present invention, a flash irradiation device is provided that can suppress the decrease in output when flash irradiation is repeated and has higher energy efficiency when the flash lamp is lit than conventional devices. [Brief explanation of the drawing]

[0031] [Figure 1] This is a drawing showing the configuration of one embodiment of the flash irradiation device according to the present invention. [Figure 2] This is a cross-sectional view showing an example of a flash lamp configuration. [Figure 3] This is a block diagram showing an example of the configuration of the control unit. [Figure 4]This is a timing chart showing an example of the operation of a flash irradiation device. [Figure 5] This diagram schematically illustrates the discharge process inside a discharge tube. [Figure 6] This diagram shows an example of a scenario in which a flash of light is irradiated onto an object. [Figure 7] This is a diagram showing the configuration of the flash irradiation device used to verify the proportionality of 1. [Figure 8] This graph shows the output characteristics of the flash irradiation device in Example 1. [Figure 9] This graph shows the results of the evaluation of the lifespan of flash lamps. [Figure 10] This is a timing chart showing another example of the operation of a flash irradiation device. [Figure 11] This diagram shows an example configuration of a flash irradiation device, following Figure 1. [Figure 12] This is a schematic diagram showing the circuit configuration of a lamp lighting device according to Patent Document 1. [Figure 13] Figure 12 is a schematic diagram showing the configuration of the flash lamp. [Figure 14] Figure 12 is a timing chart showing the operation of the lamp lighting device. [Modes for carrying out the invention]

[0032] The configuration of the flash irradiation device according to the present invention will be described below with reference to the drawings. Note that the following drawings are schematic illustrations, and the dimensional ratios and numbers shown in the drawings do not necessarily correspond to the actual dimensional ratios and numbers.

[0033] Figure 1 is a diagram showing the configuration of one embodiment of the flash irradiation device according to the present invention. As shown in Figure 1, the flash irradiation device 1 includes a flash lamp 2, a capacitor 4, an inductor 6, a first switching element 11, a second switching element 12, and a control unit 15.

[0034] Figure 2 is a cross-sectional view showing an example of the configuration of the flash lamp 2. In Figure 2, an XYZ coordinate system is shown, where the direction parallel to the tube axis A1 of the discharge tube 20 is defined as the X direction, and the plane perpendicular to the X direction is defined as the YZ plane. This coordinate system will be referred to as appropriate in the following description. In this embodiment, the Z direction corresponds to the vertically upward direction.

[0035] Furthermore, in the following descriptions, when expressing direction, positive and negative directions are distinguished, and these are indicated with a sign, such as "+X direction" and "-X direction." When expressing direction without distinguishing between positive and negative directions, it is simply written as "X direction." In other words, in this specification, when simply written as "X direction," both "+X direction" and "-X direction" are included. The same applies to the Y direction and Z direction.

[0036] As shown in Figure 2, the flash lamp 2 has a discharge tube 20 filled with a discharge gas such as xenon, an anode 21, a cathode 22, a first terminal 2a consisting of a lead connected to the anode 21, and a second terminal 2b consisting of a lead connected to the cathode 22. The anode 21 and cathode 22 are spaced apart from each other with respect to the X direction, that is, with respect to the tube axis A1 direction of the discharge tube 20.

[0037] Furthermore, as shown in Figure 2, the flash lamp 2 has a trigger electrode 25 positioned close to the outer surface of the discharge tube 20. For example, the trigger electrode 25 is made of a tungsten metal rod and is positioned to extend in the direction of the tube axis A1 of the discharge tube 20. In this embodiment, the trigger electrode 25 is installed on the +Z side of the flash lamp 2, i.e., vertically upward. As shown in Figure 1, the trigger electrode 25 is configured to be able to have a trigger voltage applied by driving the trigger circuit 26.

[0038] The discharge tube 20 is made of a glass material such as quartz glass. For example, the length of the discharge tube 20 in the X direction is 200 mm or more and 500 mm or less, and the thickness of the discharge tube 20 is 0.8 mm or more and 3 mm or less. The outer diameter of the discharge tube 20 is 10 mm or more and 30 mm or less.

[0039] Although not shown in the diagram, the number of flash lamps 2 in the flash irradiation device 1 is not limited.

[0040] The anode 21 and cathode 22 are made of a metallic material such as tungsten and are placed inside the discharge tube 20. More specifically, the cathode 22 may be made of tungsten containing a substance (also called an "emitter") that has the effect of reducing the work function. Examples of such emitters include barium aluminate, lanthanum oxide, and thorium oxide.

[0041] As shown in Figure 1, the capacitor 4 has a first electrode 4a that can be electrically connected to the first terminal 2a of the flash lamp 2, and a second electrode 4b that can be electrically connected to the second terminal 2b of the flash lamp 2. The first electrode 4a and the second electrode 4b can be connected to a power supply (not shown), and the capacitor 4 is configured to be rechargeable by the power supply.

[0042] As shown in Figure 1, the first switching element 11 is positioned between node N1, to which the second electrode 4b of the capacitor 4 is connected, and node N2, to which the second terminal 2b of the flash lamp 2 is connected. The first switching element 11 controls the electrical connection between the second terminal 2b of the flash lamp 2 and the second electrode 4b of the capacitor 4. Also, as shown in Figure 1, a diode 30 is connected between the first switching element 11 and node N1.

[0043] As shown in Figure 1, the second switching element 12 is arranged in parallel with the first switching element 11 and connects nodes N1 and N2. The second switching element 12 controls the electrical connection between the second terminal 2b of the flash lamp 2 and the second electrode 4b of the capacitor 4. In this embodiment, an inductor 6 is connected between the second switching element 12 and node N2. Also, similar to the first switching element 11, a diode 31 is connected between the second switching element 12 and node N1.

[0044] For example, the first switching element 11 and the second switching element 12 are composed of IGBTs (Insulated Gate Bipolar Transistors), and the control unit 15 controls the voltage applied to the control terminals to switch between the on and off states. The configuration of the control unit 15 will be described later.

[0045] It is optional whether the first switching element 11 and the second switching element 12 are composed of IGBTs. The first switching element 11 and the second switching element 12 can be configured in any way as long as their electrical connection state can be changed by the control signal from the control unit 15.

[0046] Diode 30 has a first switching element 11 connected to its anode side, suppressing the flow of reverse current into the first switching element 11 due to back electromotive force. Similarly, diode 31 has a second switching element 12 connected to its anode side, suppressing the flow of reverse current into the second switching element 12. Note that the present invention is not limited to whether or not diodes (30, 31) are present.

[0047] One terminal of the inductor 6 is connected to the second switching element 12 at node N3, and the other terminal is connected to node N2. In other words, as shown in Figure 1, the inductor 6 is arranged in parallel with the first switching element 11 and in series with the second switching element 12. The inductor 6 adjusts the time constant of the current supplied to the flash lamp 2 when the second switching element 12 is turned on. That is, it adjusts the rise and fall speeds of the current supplied from the capacitor 4 to the flash lamp 2.

[0048] Furthermore, in this embodiment, the flash irradiation device 1 has a diode 32 that connects node N3 and node N4 to which the first terminal 2a of the flash lamp 2 is connected (see Figure 1). The anode of the diode 32 is located on the node N3 side, and the cathode is located on the node N4 side. As will be described later, it is preferable for the flash irradiation device 1 to have a diode 32 in order to suppress the flow of reverse current into the second switching element 12 due to the back electromotive force of the inductor 6 when the on / off control of the second switching element 12 is performed. In addition, having a diode 32 is preferable because it makes it easier to protect the circuit when a high voltage of, for example, 1000V or more is applied.

[0049] As shown in Figure 1, the control unit 15 is connected to the first switching element 11, the second switching element 12, and the trigger circuit 26. More specifically, the control unit 15 is connected to the gate terminals of the first switching element 11 and the second switching element 12, respectively. The control unit 15 is a control means capable of transmitting control signals to the first switching element 11 and the second switching element 12, and is configured to include, for example, a processor such as a CPU and a memory for storing information.

[0050] Figure 3 is a block diagram showing an example configuration of the control unit 15. As shown in Figure 3, the control unit 15 includes a first conduction control unit 15a that controls the on and off states of the first switching element 11, a second conduction control unit 15b that controls the on and off states of the second switching element 12, and a start control unit 15c that controls the drive state of the trigger circuit 26. Note that, as will be described later with reference to Figure 11, the first conduction control unit 15a and the second conduction control unit 15b may be configured separately.

[0051] Next, the operation of the flash irradiation device 1 will be described. Figure 4 is a timing chart showing an example of the operation of the flash irradiation device 1. In Figure 4, the charging voltage V of the capacitor 4 c The current I is then supplied to flash lamp 2. F The timing of the on / off control of the first switching element 11 and the second switching element 12 is shown.

[0052] First, the capacitor 4 is charged by applying a voltage from a power supply (not shown). In FIG. 4, the capacitor 4 is charged to a desired charging voltage V1.

[0053] Next, at timing t1, the trigger circuit 26 is driven by the start control unit 15c. At the same time, the second switching element 12 is turned on. As a result, a trigger voltage is applied from the trigger electrode 25 to the flash lamp 2. When the trigger voltage is applied, the gas in the arc tube 20 becomes ionized and dielectric breakdown occurs, and a discharge occurs between the anode 21 and the cathode 22. Then, due to the occurrence of the discharge, a current starts to flow through the path in which the second switching element 12 is arranged (see FIG. 1) to the flash lamp 2. In FIG. 4, the second switching element 12 is turned on simultaneously with the driving of the trigger circuit 26, but this point is arbitrary. For example, the second switching element 12 may be turned on at a timing before the driving of the trigger circuit 26.

[0054] As shown in FIG. 4, after driving the trigger circuit 26 at timing t1, the control unit 15 repeats on-off control for rapidly switching between the on state and the off state of the second switching element 12.

[0055] In FIG. 4, an on-time x1 during which the second switching element 12 is in the on state and an off-time x2 during which the second switching element 12 is in the off state are schematically shown. As an example, the control unit 15 turns off the second switching element 12 when the current I F flowing through the flash lamp 2 reaches a predetermined current value I off and turns on the second switching element 12 when the current I F reaches a predetermined current value I onThe second switching element 12 is configured to be turned ON at the point in time. For example, the control unit 15 has a memory unit (not shown), and performs ON / OFF control of the second switching element 12 based on the information stored in the memory unit. The control unit 15 may also perform ON / OFF control of the second switching element 12 based on predetermined ON time x1 and OFF time x2.

[0056] The rise and fall rates of the current flowing through the flash lamp 2 can be adjusted, for example, by the design of the inductor 6.

[0057] The inventors have found that by repeatedly controlling the on / off state of the second switching element 12 to supply current to the flash lamp 2, the discharge formed between the anode 21 and the cathode 22 expands, and the discharge can be formed at a position further away from the inner wall of the discharge tube 20 compared to when it was started, more specifically near the tube axis A1 of the discharge tube 20.

[0058] Figure 5 is a schematic diagram showing the discharge inside the discharge tube 20. As shown in Figure 5, when a trigger voltage is applied, dielectric breakdown occurs inside the discharge tube 20, and a discharge S1 is formed near the inner wall 20a on the side of the discharge tube 20 closest to the trigger electrode 25. Subsequently, the on / off control of the second switching element 12 is repeated, and current is supplied to the flash lamp 2, causing the discharge S1 to grow and expand, as shown in Figure 5, and increasing the discharge diameter r1 of the discharge S1. Furthermore, as a result of the expansion caused by the on / off control of the second switching element 12, the discharge S1 is formed at a position further away from the inner wall 20a of the discharge tube 20 compared to when it was started (discharge S2). In Figure 5, the position of discharge S1 immediately after starting is shown by a dashed line, and the position of discharge S2 after expansion is shown by a solid line.

[0059] Thus, the control by which the control unit 15 rapidly switches the second switching element 12 between the on state and the off state corresponds to the "first control".

[0060] As shown in Figure 4, the control unit 15 turns on the first switching element 11 at timing t2, after a predetermined time Tx has elapsed since starting the on / off control (first control) of the second switching element 12. As a result, a large current is instantaneously supplied to the flash lamp 2 based on the remaining charge voltage in the capacitor 4, and the main discharge of the flash lamp 2 is performed. As an example, the control unit 15 turns on the first switching element 11 based on information stored in an arbitrary memory unit (not shown).

[0061] Thus, the control unit 15 switches the first switching element 11 to the ON state after the first control, thereby generating the main discharge, which corresponds to the "second control".

[0062] As described with reference to Figure 5, the first control is performed to form a discharge S2 at a position away from the inner wall 20a. In this state, the second control is performed to suppress the occurrence of the main discharge near the inner wall 20a, making it less likely for the inner wall 20a to become cloudy. Therefore, it is possible to suppress the decrease in output of the flash lamp 2 when flash irradiation is repeated.

[0063] Furthermore, by supplying current while rapidly controlling the on / off state of the second switching element 12 and expanding the discharge S2, it is possible to improve the energy efficiency of the flash lamp 2 when it is lit. This point will be described in detail in the "Verification 2" section.

[0064] As shown in Figure 4, after the first switching element 11 is turned ON (second control), the control unit 15 holds the second switching element 12 OFF and stops the first control.

[0065] It is acceptable for the second switching element 12 to be turned off at the same time that the first switching element 11 is turned on. However, even if the control unit 15 simultaneously transmits control signals to the first switching element 11 and the second switching element 12, it is expected that there will be a delay between the timing when the first switching element 11 turns on and the timing when the second switching element 12 turns off. In this case, the discharge S2 may decrease between the time the second switching element 12 turns off and the time when the first switching element 11 turns on. In light of this, it is preferable that the first control is stopped after the second control is started.

[0066] In the second switching element 12, a smaller current flows compared to the first switching element 11 as a result of repeated on / off control. In light of this, the rated current of the second switching element 12 may be smaller than the rated current of the first switching element 11. For example, the rated current of the second switching element 12 may be in the range of 1A to 100A. Also, the rated current of the first switching element 11 may be in the range of 1000A to 5000A.

[0067] As described above, the on / off control of the second switching element 12 (first control) forms a discharge S2 near the tube axis A1 of the discharge tube 20. When the second control is executed in this state, the main discharge of the flash lamp 2 can be generated starting from discharge S2. As a result, the generation of the main discharge near the inner wall 20a of the discharge tube 20 is suppressed, making it less likely for the inner wall 20a to become cloudy, and thus extending the lifespan of the flash lamp 2.

[0068] In other words, according to this embodiment, as described with reference to Figures 12 to 14, the discharge S2 can be formed near the tube axis A1 of the discharge tube 20, similar to how the discharge between electrodes is made to float by thermal convection. In the example of Figure 12, the trigger electrode needs to be positioned vertically below (-Z side) the discharge tube 71 in order to make the discharge S10 float. In contrast, in this embodiment, the discharge S2 is expanded by on / off control of the second switching element 12, so the installation position of the trigger electrode 25 is not limited.

[0069] Figure 6 is a diagram showing an example of a scene in which a flash of light is irradiated onto an object to be irradiated. Figure 6 corresponds to a view of the flash lamp 2 in the X direction. As shown in Figure 6, the flash irradiation device 1 has a support unit 40 that supports the object to be irradiated W1 on the -Z side of the flash lamp 2, i.e., vertically downward. The object to be irradiated W1 is, for example, a semiconductor wafer such as a silicon substrate. As an example, the support unit 40 is configured to support the object to be irradiated W1 by the negative pressure formed by an intake mechanism (not shown). The configuration of the support unit 40 is arbitrary as long as it can support the object to be irradiated W1 while the main surface of the object to be irradiated W1 is parallel to the XY plane. For example, the support unit 40 may have a plurality of pin-shaped protrusions that support the object to be irradiated W1.

[0070] When irradiating an object W1 with a flash, it is typical for the flash lamp 2 to be mounted vertically above (+Z side) the object W1, as shown in Figure 6. If the trigger electrode were positioned vertically below (-Z side) the flash lamp 2, a portion of the flash emitted by the flash lamp 2 would be blocked by the trigger electrode, making it difficult to uniformly irradiate the object W1 with the flash. In contrast, in this embodiment, the trigger electrode 25 is positioned vertically above (+Z side) the discharge tube 20, so the flash is not blocked by the trigger electrode 25, which is preferable.

[0071] In view of the above, it is preferable that the trigger electrode 25 be positioned outside the space P1 (see Figure 6) sandwiched between the flash tube 20 and the object to be irradiated W1. This makes it possible to suppress the obstruction of a portion of the flash emitted by the flash lamp 2 by the trigger electrode 25. More preferably, the trigger electrode 25 is positioned on the opposite side of the object to be irradiated W1 with respect to the flash tube 20.

[0072] [Verification 1] We have confirmed that the lifespan of the flash lamp 2 can be extended by repeatedly controlling the on / off state of the second switching element 12 before the main discharge is performed, and this will be explained below.

[0073] (Example 1) The flash irradiation device described with reference to Figure 1 was prepared, and after rapidly repeating the on / off control of the second switching element 12 (first control), the second control was executed to generate the main discharge of the flash lamp 2 (see also Figure 4).

[0074] In this verification, the operation of charging capacitor 4 to a predetermined charging voltage and then generating the main discharge of flash lamp 2 was repeated approximately 100,000 times, and the changes in the output of flash lamp 2 were observed. The detailed conditions are shown below.

[0075] Capacitor capacitance: 200μF In the first control, the current value I that turns off the second switching element 12 is off 9A In the first control, the current value I that turns on the second switching element 12 is on 6A Time Tx 80 msec from the start of the first control to the execution of the second control. The inner diameter of the discharge tube 20 of flash lamp 2 is 10 mm. Discharge gas: Xenon (filling pressure: 60kPa) Distance between anode 21 and cathode 22: 400 mm

[0076] (Proportional Relations 1) Figure 7 is a diagram showing the configuration of the flash irradiation device used to verify proportionality 1. In Figure 7, elements common to Figure 1 are denoted by the same reference numerals. In the flash irradiation device 60, as shown in Figure 7, a resistor 50 is placed between node N3 and the second switching element 12. Then, in proportionality 1, the trigger circuit 26 is driven with the first switching element 11 in the off state and the second switching element 12 in the on state, and a limiting current limited by the resistor 50 is supplied to the flash lamp 2.

[0077] In proportionality 1, the trigger electrode 25 was positioned vertically below the discharge tube 20. In other words, proportionality 1 was configured to levitate the discharge formed by the application of a trigger voltage by thermal convection while maintaining it with a limiting current. Proportionality 1 differs from Embodiment 1 in that, after the trigger circuit is driven, the main discharge is performed after the limiting current is supplied for a predetermined time, without performing the first control which involves repeatedly controlling the on / off state of the second switching element 12.

[0078] The limiting current was set to approximately 0.1A, and the main discharge was executed when the discharge formed between the pair of electrodes approached the axis of the discharge tube 20. The limiting current was supplied for 80 msec.

[0079] Then, the operation from charging capacitor 4 to generating the main discharge of flash lamp 2 was repeated approximately 100,000 times, and the change in the output of flash lamp 2 was observed. For the sake of clarity, in proportionality 1, the residual voltage at the time of the main discharge of capacitor 4 was set to be equivalent to the residual voltage at the time of the main discharge (time t2) in Example 1.

[0080] [Results of Verification 1] Figure 8 is a graph showing the output characteristics of the flash irradiation device in Example 1. In Figure 8, the vertical axis shows the current value supplied to the flash lamp, and the horizontal axis shows the elapsed time from the application of the trigger voltage. Figure 8 also schematically illustrates the timing t2 at which the first switching element 11 is turned on after the execution of the simmer discharge. From Figure 8, it can be understood that after the first switching element 11 is turned on, a large current is instantaneously supplied to the flash lamp 2, and the main discharge is executed.

[0081] When irradiating an object W1 such as a semiconductor wafer with a flash, it is preferable to shorten the flash irradiation time of the flash lamp 2 from the viewpoint of suppressing impurity diffusion. Specifically, the flash irradiation time is preferably 1 sec or less, and more preferably 100 msec or less. The flash irradiation time may also be the full width at half maximum of the graph showing the current value against elapsed time. Referring to Figure 8, the flash irradiation time is approximately 0.14 msec, and it can be seen that the flash irradiation device 1 is suitably applicable to flash irradiation of semiconductor wafers and the like.

[0082] Figure 9 is a graph showing the evaluation results for the lifespan of flash lamp 2. In Figure 9, the vertical axis shows the output maintenance rate of the flash lamp, and the horizontal axis shows the number of times the flash lamp was lit. The output maintenance rate of the flash lamp is the maximum current I at the time of initial ignition. max The maximum current I for each lighting state max This was considered the proportion.

[0083] As shown in Figure 9, in proportionality 1, the output maintenance rate after 100,000 lighting cycles was approximately 90%, demonstrating good lifespan characteristics. In proportionality 1, the main discharge occurred when the discharge formed between the pair of electrodes approached the tube axis of the discharge tube 20. This suppressed the occurrence of the main discharge near the inner wall of the discharge tube 20, thereby suppressing the decrease in flash lamp output caused by clouding on the inner wall.

[0084] Furthermore, as shown in Figure 9, the output maintenance rate after 100,000 lighting cycles was approximately 90% in Example 1 as well, demonstrating good life characteristics similar to those of Proportional 1. As described with reference to Figure 5, by repeatedly controlling the on / off state of the second switching element 12 (first control), it is possible to form the discharge S2 at a position away from the inner wall 20a of the discharge tube 20. In other words, it is thought that the second control, which generates the main discharge, was performed after the first control, suppressing the occurrence of the main discharge near the inner wall 20a, and as a result, the output decrease of the flash lamp was suppressed, similar to that of Proportional 1. This verification demonstrates that by generating the main discharge after repeatedly controlling the on / off state of the second switching element 12, the output decrease of the flash lamp when the main discharge is repeated can be suppressed.

[0085] [Verification 2] Next, we investigated the effect of the first control, which repeatedly controls the on / off state of the second switching element 12, on the energy efficiency of the flash lamp. This will be described below with reference to the examples.

[0086] (Example 2) In Example 1 of Verification 1 described above, the time Tx from the start of the first control to the execution of the second control was changed to 5 msec. In this verification, the charging voltage of the capacitor at the time of execution of the second control was set to approximately 3600V. The output of the flash lamp during main discharge was O p The energy efficiency of the flash lamp was measured using a calorimeter (OPHIR L30A-SH-V1), and the energy efficiency was calculated from the following equation (1). E The following equation (1) is obtained. In equation (1) below, U corresponds to the charge energy of the capacitor at time t2. Note that the output O p The measurement was performed five times, and the average value was used. O E = O p / U ···(1)

[0087] (Example 3) The procedure was performed under the same conditions as in Example 2, except that the time Tx was changed to 45 msec.

[0088] (Example 4) The procedure was executed under the same conditions as in Example 2, except that the time Tx was changed to 80 msec.

[0089] (Proportional Relations 2) Under the same conditions as in Verification 1 above, the discharge formed between the pair of electrodes was maintained with a limiting current and floated by thermal convection, after which the main discharge of the flash lamp was performed. The charging voltage of the capacitor at the time of the main discharge was adjusted to 3600V, and the energy efficiency of the flash lamp was O E The measurement method is the same as in Example 2.

[0090] [Results of Verification 2] Table 1 below shows the energy efficiency O for each example. E The results of the comparison are shown. Table 1 shows the energy efficiency of proportionality 2. E Relative values ​​based on this standard are shown for each example. [Table 1]

[0091] Table 1 shows that the energy efficiency of Example 2 is greater than that of proportionality 2. The same applies to Examples 3 and 4. Despite the capacitor charging voltage being the same at the time of main discharge, expanding the discharge by controlling the on / off state of the second switching element 12 improved the energy efficiency of the flash lamp compared to lifting the discharge by thermal convection. The inventors speculate on this point as follows: Rather than using a weak limiting current supplied to the flash lamp during discharge to lift the discharge by thermal convection, repeatedly supplying a current of several amperes allows the ionization of the discharge gas to progress within the discharge tube 20. As a result, the energy required for ionization in the main discharge during flash irradiation is reduced, and the luminous efficiency of the main discharge is improved. In other words, it is difficult to increase the energy efficiency of the flash lamp when forming a shimmer discharge with a weak limiting current.

[0092] This verification demonstrated that by expanding the discharge S2 through the first control, which rapidly repeats the on / off control of the second switching element 12, the energy efficiency during flash lamp operation can be improved compared to lifting the discharge between electrodes by thermal convection.

[0093] [Verification 3] For further consideration, a comparative verification of Example 4 and the proportional relationship 3 described below was performed. In this verification, in each case, the voltage drop from the charging voltage of capacitor 4 to the voltage at the time of main discharge, and the energy efficiency O E They were compared.

[0094] (Proportional Relations 3) The procedure was carried out under the same conditions as in Example 4, except that the trigger circuit 26 was driven with the first switching element 11 in the off state and the second switching element 12 in the on state, and then current was supplied to the flash lamp 2 while keeping the second switching element 12 in the on state until the main discharge was performed.

[0095] [Results of Verification 3] In Example 4, the voltage drop from the charging voltage of capacitor 4 to the voltage at the time of main discharge (3600V) was approximately 300V. In contrast, the voltage drop for proportionality 3 was approximately 450V. Based on equation (1) above, the energy efficiency O E When we calculated the energy efficiency of both, E The values ​​were similar. In other words, in Example 4, the energy efficiency was equivalent. E While achieving the desired result, the consumption of the charging voltage of capacitor 4 was reduced compared to proportionality 3.

[0096] In other words, according to this verification, when supplying current to the flash lamp 2 to expand the discharge inside the discharge tube 20 before the main discharge is performed, it was found that rapidly switching the second switching element 12 on and off, rather than keeping the second switching element 12 in the ON state, reduces the consumption of the charging voltage of the capacitor 4.

[0097] [Consideration] The results of Verification 1 show that, according to Example 4, good lifespan characteristics similar to those of Proportional Representation 1 can be obtained. Example 4 achieved good lifespan characteristics while improving the energy efficiency of the flash lamp, resulting in favorable results.

[0098] Furthermore, when the inventors observed the discharge formed in the flash lamp 2 using a high-speed camera, they found that at 0.5 msec after the start of the first control, the discharge between the electrodes was located near the inner wall 20a of the discharge tube 20 (discharge S1 in Figure 5), and at 10 msec, the discharge began to expand and the formation area changed. Then, after about 40 msec, it was confirmed that the discharge was stably formed at a position centered on the tube axis A1 of the discharge tube 20.

[0099] In light of this, it can be said that even in Example 3, where the time Tx from the start of the first control to the execution of the second control is 45 msec, good lifetime characteristics can be obtained, similar to Example 1. Furthermore, considering that the discharge formation region between the electrodes changes after approximately 10 msec, it can be expected that the effect of moving the discharge away from the inner wall 20a can be achieved by executing the first control for a few msec. In that case, it can be inferred that the lifetime characteristics will also be improved in Example 2, where the time Tx is 5 msec.

[0100] Furthermore, at 40 msec after the start of the first control, the discharge diameter r1 of the discharge between the electrodes (see Figure 5) was approximately half the inner diameter of the discharge tube 20 (10 mm). Therefore, it is thought that when the time Tx was 45 msec or longer, the discharge diameter r1 became larger, further increasing the energy efficiency (see Table 1).

[0101] As described above, the results of Verification 1 and Verification 2 showed that by repeatedly controlling the on / off state of the second switching element 12 before generating the main discharge, the energy efficiency of the flash lamp can be increased while achieving good life characteristics for the flash lamp. Furthermore, the results of Verification 3 showed that by adopting a configuration in which the on / off state of the second switching element 12 is repeatedly controlled, it is possible to suppress the decrease in the charging voltage of the capacitor 4 during simmer discharge.

[0102] In other words, according to the above embodiment, the decrease in output when flashing is repeated can be suppressed, and the energy efficiency when the flash lamp is lit can be improved compared to conventional methods.

[0103] Furthermore, as described above, setting the time Tx from the start of the first control to the execution of the second control to 40 msec or more makes it easier to stably form the discharge S2. In view of this, it is preferable that the time Tx be 40 msec or more. Also, setting the time Tx to 40 msec or more makes it easier to achieve energy efficiency O E This can be greatly improved and is more preferable (see Table 1). However, if the time Tx becomes too long, the charging voltage of capacitor 4 tends to decrease. In light of this, it is preferable that the time Tx be 100 msec or less.

[0104] Furthermore, considering the need to facilitate the expansion of the discharge inside the discharge tube 20 before the main discharge is executed, the current value I that switches the second switching element 12 to the ON state in the first control is on The current is preferably 3A or more, and more preferably 5A or more. Also, from a similar viewpoint, the current value I that switches the second switching element 12 to the off state in the first control is off The current value I is preferably 7A or higher, and more preferably 9A or higher. off If the current value I is too large, it is expected that the charging voltage of capacitor 4 will decrease more rapidly. In light of this, the current value I off The current is preferably 10A or less, and more preferably 8A or less.

[0105] In addition, in the first control, from the viewpoint of making it easier to suppress the consumption of the charging voltage of the capacitor 4, it is preferable that the off time x2 of the second switching element 12 is longer than the on time x1 (see also Figure 4). As an example, the ratio of on time x1 to off time x2 is 10% or less. As a detailed specific example, the on time x1 is 5 μsec or more and 30 μsec or less. Also, the off time x2 is 50 μsec or more and 1000 μsec or less. Note that if the off time x2 is too long, it is expected that the simmer discharge will disappear. In light of this, it is preferable that the off time x2 is at least 500 μsec or less.

[0106] In view of the above, it is preferable that the on / off control of the second switching element 12 be performed at high speed on the order of 1 msec or less.

[0107] <Variations> The following describes a modified version of the flash irradiation device 1.

[0108] <1> As described above, in the first control, it is preferable that the off time x2 of the second switching element 12 is longer than the on time x1. From the viewpoint of facilitating the adjustment of the off time x2, it is preferable that the flash irradiation device 1 has an inductor 6 arranged in parallel with the first switching element 11 and in series with the second switching element 12, as shown in Figure 1. However, in the present invention, it is optional whether or not the flash irradiation device 1 has an inductor 6.

[0109] <2> In the above description, the first electrode 4a of the capacitor 4 and the first terminal 2a of the flash lamp 2 were described as being connected without the use of a circuit element (see Figure 1). However, from the viewpoint of adjusting the flash irradiation time of the flash lamp 2, the flash irradiation device 1 may also be equipped with an inductor connected in series with the flash lamp 2 between the first electrode 4a and the first terminal 2a.

[0110] <3> Figure 10 is a timing chart showing another example of the operation of the flash irradiation device 1, following Figure 4. In the above explanation, it was described that the first control is stopped when the first switching element 11 is turned ON and the second switching element 12 is held OFF (see Figure 4). However, as shown in Figure 10, the first switching element 11 may be turned ON after the second switching element 12 is turned OFF.

[0111] In Figure 10, even after the second switching element 12 is turned off, the discharge S2 continues until at least the off-time x2 has elapsed. In other words, the period from when the second switching element 12 is turned off until the off-time x2 has elapsed may be considered as the execution period of the first control.

[0112] <4> As described with reference to Figure 5, by performing the main discharge with the discharge S2 formed at a position away from the inner wall 20a of the discharge tube 20, it is possible to suppress the occurrence of clouding on the inner wall 20a. In addition, as the discharge diameter r1 increases before the main discharge is performed, the ionization of the discharge gas progresses within the discharge tube 20, and the energy efficiency when the flash lamp is lit is increased. Specifically, it is preferable that the main discharge is performed after the discharge S2 has expanded and the discharge diameter r1 of the discharge S2 (see Figure 5) has become more than half of the inner diameter of the discharge tube 20. Here, considering that the thickness of the discharge tube 20 is typically small, 3 mm or less, the diameter of the discharge tube 20 when comparing it with the discharge diameter r1 may be the outer diameter of the discharge tube 20.

[0113] The time required for the discharge diameter r1 of discharge S2 to become more than half the diameter of the discharge tube 20 can be measured in advance, for example, by observing discharge S2 with a high-speed camera. Therefore, the control unit 15 may have a storage means such as a memory, and the time required for the discharge diameter r1 to become more than half the diameter of the discharge tube 20 may be stored in the memory, and the control unit 15 may determine the time Tx from the start of the first control to the execution of the second control based on that time.

[0114] <5> Figure 11 is a diagram showing an example configuration of the flash irradiation device 1, following Figure 1. In the above description, the control unit 15 was described as including the first continuity control unit 15a and the second continuity control unit 15b. However, as shown in Figure 11, the first continuity control unit 15a and the second continuity control unit 15b may be configured separately in the flash irradiation device 1. The same applies to the start control unit 15c.

[0115] <6> In the above description, the first switching element 11 and the second switching element 12 were described as being located between node N1 and node N2. However, the arrangement of the first switching element 11 and the second switching element 12 is not limited to the above, as long as the electrical connection between the flash lamp 2 and the capacitor 4 can be controlled. For example, the first switching element 11 and the second switching element 12 may be located between the first terminal 2a of the flash lamp 2 and the first electrode 4a of the capacitor 4. Furthermore, from the viewpoint of simplifying the design of the reference potential in the switching element, it is preferable that the first switching element 11 and the second switching element 12 control the electrical connection between the second terminal 2b and the second electrode 4b, which are located on the ground side (see Figure 1, etc.).

[0116] <7> The configuration of the flash irradiation device 1 according to the present invention is not limited to the embodiments described above. [Explanation of Symbols]

[0117] 1 : Flash irradiation device 2: Flash lamp 2a: First terminal 2b: Second terminal 4: Capacitor 4a: First electrode 4b: Second electrode 6: Inductor 11: First switching element 12: Second switching element 15: Control Unit 15a: First conduction control unit 15b: Second conduction control unit 15c: Startup control unit 20: Discharge tube 21,22 : Electrode 25: Trigger electrode 26: Trigger Circuit 30, 31, 32: Diodes 40: Support unit

Claims

1. A flash lamp including a first terminal and a second terminal, which discharges when a voltage is applied between the first terminal and the second terminal, A capacitor including a first electrode electrically connectable to the first terminal and a second electrode electrically connectable to the second terminal, A first switching element that controls the electrical connection between the flash lamp and the capacitor, A second switching element is arranged in parallel with the first switching element and controls the electrical connection between the flash lamp and the capacitor, The system includes a control unit that controls the on / off state of the first switching element and the second switching element, The control unit, A first control involves repeatedly turning the second switching element on and off at high speed while keeping the first switching element in the off state, thereby applying voltage from the charged capacitor to the flash lamp. A flash irradiation device characterized by performing a second control, which involves switching the first switching element to the ON state during the execution of the first control, and applying the remaining voltage of the capacitor remaining after the first control to the flash lamp to generate a main discharge.

2. The flash irradiation device according to claim 1, characterized by comprising an inductor arranged in parallel with the first switching element and arranged in series with the second switching element.

3. The flash irradiation device according to claim 1 or 2, characterized in that the control unit is configured to execute the second control after executing the first control for a time of 40 msec to 100 msec.

4. The flash irradiation device according to claim 2, characterized in that, in the first control, the off time of the second switching element is longer than the on time.

5. The flash irradiation device according to claim 1 or 2, characterized in that the control unit stops the first control by turning off the second switching element after the second control has started.

6. The control unit is configured to perform the second control after a predetermined time has elapsed from the start of the first control. The flash irradiation device according to claim 1 or 2, characterized in that the predetermined time is the time during which the discharge diameter of the discharge formed by the first control is half or more of the diameter of the light-emitting tube of the flash lamp.

7. A trigger electrode is positioned along the axial direction of the light-emitting tube of the flash lamp and assists in starting the flash lamp, The system includes a support unit that supports an object to be illuminated by the flash of light emitted by the aforementioned flash lamp, The flash irradiation device according to claim 1 or 2, characterized in that the trigger electrode is positioned outside the space sandwiched between the light-emitting tube and the object to be irradiated.

Images