Flash irradiation apparatus

Abstract

Provided is a flash irradiation apparatus capable of further reducing thermal history in an object to be processed.　This flash irradiation apparatus comprises: a flash discharge lamp for generating a flash by discharge; an inductor having a first terminal connected to an anode of the flash discharge lamp; a capacitor having a first terminal connected to a second terminal of the inductor and storing charge to be supplied to the flash discharge lamp; a switching element for switching energization / non-energization between a cathode of the flash discharge lamp and a second terminal of the capacitor; a first rectifier having a cathode terminal connected to the second terminal of the inductor and an anode terminal connected to the cathode of the flash discharge lamp; and a second rectifier having a cathode terminal connected to a first node between the second terminal of the inductor and the first terminal of the capacitor, and having an anode terminal connected to a second node between the first terminal of the inductor and the anode of the flash discharge lamp.

Description

flash irradiation device

[0001] The present invention relates to a flashlight irradiation device.

[0002] Conventionally, flash irradiation devices have been used for heat treatment of semiconductor substrates and heat treatment in the manufacturing process of printable electronics, etc. In particular, in recent years, with the miniaturization of semiconductor processes, instantaneous heat treatment methods using flash irradiation devices have attracted attention as a method for activating implanted impurities while suppressing their diffusion due to prolonged heating.

[0003] Therefore, the present applicant has been developing a flash irradiation device equipped with a flash discharge lamp (also called a "flash lamp") suitable for semiconductor wafer heat treatment equipment, and has developed, for example, a flash irradiation device such as that described in Patent Document 1 below.

[0004] Japanese Patent Application Laid-Open No. 2009-164201

[0005] The flash irradiation apparatus described above is an indispensable apparatus for performing short-time heat treatments on semiconductor substrates, and efforts are being made to further improve it. Recently, particularly in light of the background of studies into further miniaturization of semiconductor processes, there has been a demand for a flash irradiation apparatus that can further reduce the thermal history of the object to be treated.

[0006] In view of the above-mentioned problems, an object of the present invention is to provide a flash light irradiation apparatus that can further reduce the thermal history of an object to be processed.

[0007] A flashlight irradiation device of the present invention is characterized by comprising: a flashlight discharge lamp that generates a flashlight by discharge; an inductor having a first terminal connected to an anode of the flashlight discharge lamp; a capacitor that stores electric charge to be supplied to the flashlight discharge lamp and has a first terminal connected to a second terminal of the inductor; a switching element that switches between energization and de-energization of the cathode of the flashlight discharge lamp and the second terminal of the capacitor; a first rectifier having a cathode terminal connected to the second terminal of the inductor and an anode terminal connected to the cathode of the flashlight discharge lamp; and a second rectifier having a cathode terminal connected to a first node between the second terminal of the inductor and the first terminal of the capacitor and an anode terminal connected to a second node between the first terminal of the inductor and the anode of the flashlight discharge lamp.

[0008] When starting to light a flash discharge lamp, it is common to switch the switching element from a non-conductive state to a conductive state, or to switch the switching element from a non-conductive state to a conductive state and then apply a starting pulse voltage to the trigger electrode to start lighting. The time from when these starting operations are performed until a flash is emitted from the flash discharge lamp is extremely short, and is influenced by the parameters of the circuit elements and the shape and size of the flash discharge lamp.

[0009] In contrast, immediately after the object to be treated is irradiated with a flash of light and the switching element is switched from a conducting state to a non-conducting state, the energy stored in the inductor continues to supply power to the flash discharge lamp for a while, and as long as the power necessary for the flash discharge lamp to emit light is being supplied, the light output from the flash discharge lamp also continues.

[0010] In other words, immediately after switching the switching element from a conducting state to a non-conducting state, stopping the power supply to the flash discharge lamp using the energy stored in the inductor early contributes greatly to reducing the thermal history of the object to be treated.

[0011] One possible method for quickly stopping the power supply to the flash discharge lamp from the energy stored in the inductor is to configure a mechanism that disconnects the inductor from the flash discharge lamp immediately after or simultaneously with switching the switching element from a conducting state to a non-conducting state.

[0012] However, this method requires control of the timing for disconnecting the inductor from the flash discharge lamp, a discharge path for releasing energy, and a design that can withstand the load at the timing of disconnection, which makes the design extremely difficult and can lead to many problems, making it unrealistic.

[0013] Therefore, the inventors of the present invention have intensively studied and come up with the above-described configuration. In the flashlight irradiation device having the above-described configuration, the energy stored in the inductor is consumed mainly via the second rectifier immediately after the switching element switches from a conducting state to a non-conducting state, without requiring complex timing control or complex circuit design.

[0014] After the switching element is switched to the non-conductive state, almost no current is supplied to the flash discharge lamp due to the current flowing through the second rectifier, and therefore the time during which light output from the flash discharge lamp continues is significantly reduced. Therefore, with the above configuration, the thermal history of the object to be treated can be further reduced.

[0015] In the flashlight irradiation device, the second rectifier may have a configuration including a plurality of diode elements connected in series.

[0016] According to the above configuration, even if, for example, one of the multiple diode elements of the second rectifier is damaged and a short circuit occurs between both terminals, a short circuit between the first terminal of the capacitor and the anode of the flash discharge lamp is avoided.

[0017] In the flashlight irradiation device, during a discharge operation, a peak value of a forward current flowing through the second rectifier is set to I fp and the forward voltage of the second rectifier is V fand the resistance between the cathode terminal of the second rectifier and the first node is R p1 and the resistance between the anode terminal of the second rectifier and the second node is R p2 When the voltage V is 100 V, the following formula (1) may be satisfied: f + (R p1 + R p2 ) I fp (1)

[0018] When a current flows through the second rectifier, it can be assumed that the voltage calculated by the left side of the equation (1) is applied between the first node and the second node. Note that this voltage is a positive voltage when the voltage of the second node is taken as the voltage of the first node relative to the first node.

[0019] In this case, a voltage approximately equal to this voltage is applied between the anode and cathode of the flash discharge lamp. If this voltage exceeds the lower limit of the voltage required to keep the flash discharge lamp lit, a current will flow through the flash discharge lamp, and in some cases, there is a risk that the flash discharge lamp will emit light to the extent that it heats the object to be treated.

[0020] Here, the inventors investigated the lower limit of the voltage required to maintain lighting of flash discharge lamps used in semiconductor manufacturing processes, more specifically, flash discharge lamps used as heating light sources for heat-treating semiconductor wafers. They confirmed that, for flash discharge lamps used in semiconductor manufacturing processes (for example, flash discharge lamps used for heat-treating 12-inch silicon wafers), the voltage required to maintain lighting immediately after switching the switching element from a conducting state to a non-conducting state, i.e., the voltage between the electrodes of the flash discharge lamp immediately after it is turned off, is generally within the range of 100 V to 200 V.

[0021] Therefore, with the above configuration, the current generated by the energy stored in the inductor can be more reliably passed to the second rectifier.

[0022] According to the present invention, a flash light irradiation apparatus capable of further reducing the thermal history of an object to be processed is realized.

[0023] 1 is a side view showing a schematic diagram of an embodiment of a flashlight irradiation device, a circuit diagram showing an example of a circuit for lighting a flashlight discharge lamp, and a schematic graph showing temporal changes in current flowing from a second node to an anode of the flashlight discharge lamp and a current flowing from the second node to a second rectifier.

[0024] The flashlight irradiation device of the present invention will be described below with reference to the drawings. Note that the drawings are all schematic illustrations, and the dimensional ratios and numbers in the drawings do not necessarily match the actual dimensional ratios and numbers.

[0025] First, we will explain the configuration of the flash irradiation device 1. Fig. 1 is a side view that schematically shows one embodiment of the flash irradiation device 1. As shown in Fig. 1, the flash irradiation device 1 includes a flash discharge lamp 10 and a reflecting member 20, and is configured to irradiate a flash of light L1 onto a main surface W1a of a workpiece W1 supported by a support 30.

[0026] 1, flash discharge lamp 10 in this embodiment includes arc tube 11, anode 12p and cathode 12n arranged spaced apart within arc tube 11, and trigger tube 13 consisting of a tubular body 13a and conductor 13b. When a voltage required for light emission is applied between anode 12p and cathode 12n via power supply lines (15, 15) and a trigger pulse voltage is applied to conductor 13b of trigger tube 13, a discharge occurs within arc tube 11 and a flash of light L1 is emitted.

[0027] The reflecting member 20 is arranged on the opposite side of the workpiece W1 from the flash discharge lamp 10, and has a reflecting surface 21 that reflects the flash L1 emitted from the flash discharge lamp 10 and traveling toward the opposite side of the workpiece W1 so that the flash L1 travels toward the workpiece W1.

[0028] Next, the configuration of a circuit for lighting the flash discharge lamp 10 will be described. Fig. 2 is a circuit diagram showing an example of a circuit for lighting the flash discharge lamp 10. The circuit for lighting the flash discharge lamp 10 is composed of a power supply circuit C1 connected to the anode 12p and cathode 12n of the flash discharge lamp 10, and a trigger circuit C2 connected to the conductor 13b of the trigger tube 13 (not shown for convenience of illustration). Furthermore, this embodiment includes a control unit 9 for controlling the energized / de-energized state of the switching elements (4, 8) described below, but it is optional whether or not to include the control unit 9, and the switching elements (4, 8) may also be configured to be controlled by human operation.

[0029] As shown in FIG. 2 , the power supply circuit C1 includes an inductor 2 having a first terminal connected to the anode 12 p of the flash discharge lamp 10, a capacitor 3 having a first terminal connected to the second terminal of the inductor 2, and a switching element 4 that switches between energization and de-energization between the cathode 12 n of the flash discharge lamp 10 and the second terminal of the capacitor 3.

[0030] The power supply circuit C1 further includes a first rectifier 5a having a cathode terminal connected to the second terminal of the inductor 2 and an anode terminal connected to the cathode 12n of the flash discharge lamp 10, and a second rectifier 5b having a cathode terminal connected to a first node n1 between the second terminal of the inductor 2 and the first terminal of the capacitor 3 and an anode terminal connected to a second node n2 between the first terminal of the inductor 2 and the anode 12p of the flash discharge lamp 10. The first node n1 is at an arbitrary position between the second terminal of the inductor 2 and the first terminal of the capacitor 3, and the second node n2 is at an arbitrary position between the first terminal of the inductor 2 and the anode 12p of the flash discharge lamp 10.

[0031] A power supply circuit (for example, a DC-DC converter or the like) for charging capacitor 3 is connected in the preceding stage of capacitor 3, but explanation of the power supply circuit will be omitted in order to focus on the explanation of the configuration of power supply circuit C1 that contributes to the lighting operation of flash discharge lamp 10. Furthermore, the following explanation of the operation of power supply circuit C1 will be based on the state in which charging of capacitor 3 is complete. The same applies to trigger capacitor 7 in trigger circuit C2, which will be described later.

[0032] The inductor 2 adjusts the time constant of the current supplied to the flash discharge lamp 10. That is, the inductor 2 adjusts the rise and fall speeds of the current supplied from the capacitor 3 to the flash discharge lamp 10.

[0033] The capacitor 3 stores electric charge supplied from a power source or the like for causing the flash discharge lamp 10 to emit light, and discharges the electric charge to the flash discharge lamp 10 .

[0034] The switching element 4 is an element that switches between a conducting state and a non-conducting state between the cathode 12 n of the flash discharge lamp 10 and the second terminal of the capacitor 3. In this embodiment, the switching element 4 switches between a conducting state and a non-conducting state by controlling the voltage that the control unit 9 applies to the control terminal. Any element can be selected as the switching element 4 taking into consideration the current capacity, withstand voltage, switching speed, ON resistance, etc., but the switching element 4 in this embodiment is an IGBT (Insulated Gate Bipolar Transistor).

[0035] As shown in FIG. 2 , the first rectifier 5 a of this embodiment is composed of two diode elements (5 a1, 5 a2) connected in series, and after the switching element 4 is switched from a conducting state to a non-conducting state, the first rectifier 5 a regenerates the current that flows from the anode 12 p to the cathode 12 n of the flash discharge lamp 10 to the first terminal of the capacitor 3.

[0036] In this way, first rectifier 5a regenerates current, thereby protecting switching element 4 from a high-voltage load. If first rectifier 5a were not provided, the voltage across both terminals of switching element 4 would exceed 6,500 V, which is the withstand voltage of a typical high-voltage / high-current switching element. Protection from such a voltage that is significantly higher than that of a typical light-emitting device is particularly important in flash irradiation device 1, which requires high light output to heat-treat workpiece W1.

[0037] Although the first rectifier 5a in this embodiment is composed of two diode elements (5a1, 5a2) connected in series, the number of diode elements constituting the first rectifier 5a may be one or three or more. However, there is a risk that a diode element will lose its rectifying function due to deterioration or wear, causing a short circuit between its anode terminal and cathode terminal. For this reason, from the perspective of fail-safe, it is preferable that the first rectifier 5a be configured with a plurality of diode elements connected in series so that a short circuit between the first terminal of the capacitor 3 and the cathode 12n of the flash discharge lamp 10 is avoided even if one diode element shorts out.

[0038] Furthermore, the diode elements constituting the first rectifier 5a may be, for example, parasitic diode elements formed in semiconductor devices, as long as they have a rectifying function and have acceptable withstand voltage and current capacity.

[0039] 2, second rectifier 5b of this embodiment is made up of two diode elements (5b1, 5b2) connected in series, and after switching element 4 is switched from a conducting state to a non-conducting state, causes the current that flows to second node n2 due to the energy stored in inductor 2 to flow to the first terminal of capacitor 3. As a result, in flash irradiation device 1, the current that flows to anode 12p of flash discharge lamp 10 drops more sharply after switching element 4 is switched from a conducting state to a non-conducting state, compared to the conventional configuration.

[0040] Although the second rectifier 5b in this embodiment is configured with two diode elements (5b1, 5b2) connected in series, the number of diode elements constituting the second rectifier 5b may be one or three or more. However, for the same reasons as for the first rectifier 5a, it is preferable that the second rectifier 5b be configured with a plurality of diode elements connected in series.

[0041] Furthermore, the diode elements constituting the second rectifier 5b have a rectifying function similar to the first rectifier 5a, and may be, for example, parasitic diode elements formed in a semiconductor device, as long as they have acceptable voltage resistance and current capacity.

[0042] 2, the trigger circuit C2 includes a transformer 6, a trigger capacitor 7 connected in series to the primary side of the transformer 6, and a switching element 8. One terminal of the secondary side of the transformer 6 is connected to the conductor 13b of the flash discharge lamp 10, and the other terminal is connected to the second terminal of the capacitor 3.

[0043] When the switching element 8 is switched from a non-conductive state to a conductive state under the control of the control unit 9 while the trigger capacitor 7 is charged, the charge stored in the trigger capacitor 7 of the trigger circuit C2 is discharged, generating a current on the primary side of the transformer 6. This generation of current generates an electromotive force on the secondary side of the transformer 6, and a pulse voltage is applied to the conductor 13b of the flash discharge lamp 10. At this time, if the capacitor 3 of the power supply circuit C1 is charged and the switching element 4 is controlled to be in a conductive state, the pulse voltage applied to the conductor 13b will trigger a discharge to occur between the anode 12p and cathode 12n of the flash discharge lamp 10, causing a flash L1 to be emitted.

[0044] The switching element 8 can be selected from any element taking into consideration current capacity, withstand voltage, switching speed, ON resistance, etc., but the switching element 8 in this embodiment is a thyristor.

[0045] As described above, the control unit 9 is an element that controls the energized / de-energized state of the switching elements (4, 8), and is, for example, a processing unit such as a CPU or an MPU.

[0046] Here, the operation from the state in which the capacitor 3 and the trigger capacitor 7 are charged to the end of lighting of the flash discharge lamp 10 will be described with reference to the graph shown in the drawing.

[0047] 3 is a schematic graph showing the time variation of current I1 flowing from second node n2 to anode 12p of flash discharge lamp 10, and current I2 flowing from second node n2 to second rectifier 5b. In the graph of current I1 shown in FIG. 3, the waveform in a conventional configuration not including second rectifier 5b is shown by a dashed line.

[0048] First, charging of capacitor 3 and trigger capacitor 7 is completed, and control unit 9 controls switching element 4 of power supply circuit C1 from a non-conductive state to a conductive state, and then switching element 8 of trigger circuit C2 from a non-conductive state to a conductive state is time t1. Then, in order to stop lighting of flash discharge lamp 10, control unit 9 switches switching element 4 of power supply circuit C1 from a conductive state to a non-conductive state is time t2.

[0049] At time t1, a pulse voltage is applied to conductor 13b of flash discharge lamp 10, starting discharge, and gradually increasing current I1 flows from capacitor 3 to anode 12p of flash discharge lamp 10 via second node n2. At this time, because the potential of first node n1 is higher than that of second node n2, no current I2 flows through second rectifier 5b.

[0050] Then, a certain amount of current I1 flows through flash discharge lamp 10, and when irradiation of flash L1 necessary for heat treatment of object W1 is completed (time t2), control unit 9 switches switching element 4 from the conducting state to the non-conducting state. Immediately after this, a current flows from first node n1 to second node n2 due to the energy stored in inductor 2. Then, when the potential of second node n2 becomes higher than first node n1 and this potential difference becomes larger than the voltage at which forward current can be passed through second rectifier 5b (hereinafter referred to as the "forward voltage"), current I2 flowing through second rectifier 5b gradually increases.

[0051] Note that second node n2 is connected to second rectifier 5b and anode 12p of flash discharge lamp 10, but the impedance of second rectifier 5b, through which current I2 flows, is extremely small compared to the impedance between anode 12p and cathode 12n of flash discharge lamp 10. For this reason, most of the current generated by the energy stored in inductor 2 flows from second node n2 to first node n1 by second rectifier 5b, and the time variations of current I1 and current I2 have waveforms as shown in FIG.

[0052] In the case of a conventional configuration that does not include second rectifier 5b, current I2 is not generated, and the current generated by the energy stored in inductor 2 has nowhere to go other than flash discharge lamp 10. For this reason, as shown by the dashed line in Figure 3, after time t2 has passed, current I1 flows through flash discharge lamp 10 for a while, and the output of flash L1 is maintained at a relatively high intensity.

[0053] As described above, after the switching element 4 is switched from the conducting state to the non-conducting state, the current I2 flows through the second rectifier 5b when the voltage of the second node n2 relative to the first node n1 is greater than the forward voltage of the second rectifier 5b. Therefore, when the current I2 flows through the second rectifier 5b, the sum of the forward voltages of the diode elements (5b1, 5b2) constituting the second rectifier 5b (forward voltage V f ), and the peak value of the current I2 (peak current I of the forward current of the second rectifier 5b fp) and the resistance value (R p1 , R p2 ) is applied between the first node n1 and the second node n2. If this total exceeds the lower limit of the voltage required to light the flash discharge lamp 10, there is a risk that discharge will occur from the anode 12p to the cathode 12n of the flash discharge lamp 10.

[0054] As mentioned above, the lower limit of the voltage required to light the flash discharge lamp 10 depends on the shape and size of the lamp, but when the inventors investigated various flash discharge lamps used to heat semiconductor wafers, they found that the lower limit was generally within the range of 100V to 200V. For this reason, it is preferable that the above parameters satisfy the relationship of the above formula (1). Just to be sure, the above formula (1) is presented again. 100[V] ≧ V f + (R p1 + R p2 ) I fp (1)

[0055] As a specific example, the peak current I fp 2 kA, and the forward voltage V of the second rectifier 5b f Assuming that the voltage is 5V, each resistance value (R p1 , R p2 ) is 47.5 mΩ or less, the flashlight irradiation device 1 that satisfies the above formula (1) is realized. These values ​​are obtained by setting the peak current I fp This value is based on the forward voltage of commercially available diode elements. This level of resistance can be easily achieved by selecting a commercially available cable made of a material with a relatively low resistance and adjusting the cable length.

[0056] The condition of the above formula (1) is a preferable condition for further suppressing the maintenance of lighting of the flash discharge lamp 10, but the peak current I fpIf the time during which the gas flows is extremely short and is not considered to have a significant effect on the thermal history of the workpiece W1, this condition does not need to be satisfied.

[0057] 3, in flash light irradiation device 1 having the above configuration, after switching element 4 is switched from a conducting state to a non-conducting state, the current flowing through flash light discharge lamp 10 drops sharply. This prevents flash light discharge lamp 10 from being kept lit for an unnecessarily long time, further reducing the thermal history of object to be treated W1.

[0058] The configuration of the flashlight irradiation device 1 described above is merely an example, and the present invention is not limited to the configurations shown in the drawings. For example, any circuit element (e.g., a high-resistance element or a smoothing element) may be connected to each of the power supply circuit C1 and trigger circuit C2 shown in Figure 2, as long as it does not interfere with the main circuit operation.

[0059] REFERENCE SIGNS LIST 1: flash light irradiation device 2: inductor 3: capacitor 4: switching element 5a: first rectifier 5a1: diode element 5a2: diode element 5b: second rectifier 5b1: diode element 5b2: diode element 6: transformer 7: trigger capacitor 8: switching element 9: control unit 10: flash light discharge lamp 11: arc tube 12n: cathode 12p: anode 13: trigger tube 13a: tube body 13b: conductor 20: reflecting member 21: reflecting surface 30: support C1: power supply circuit C2: trigger circuit L1: flash light W1: object to be treated W1a: main surface

Claims

1. A flashlight irradiation device comprising: a flashlight discharge lamp that generates a flashlight by discharge; an inductor having a first terminal connected to an anode of the flashlight discharge lamp; a capacitor having a first terminal connected to a second terminal of the inductor and storing electric charge to be supplied to the flashlight discharge lamp; a switching element that switches between energization and de-energization of the cathode of the flashlight discharge lamp and the second terminal of the capacitor; a first rectifier having a cathode terminal connected to the second terminal of the inductor and an anode terminal connected to the cathode of the flashlight discharge lamp; and a second rectifier having a cathode terminal connected to a first node between the second terminal of the inductor and the first terminal of the capacitor and an anode terminal connected to a second node between the first terminal of the inductor and the anode of the flashlight discharge lamp.

2. The flash irradiation device according to claim 1, wherein the second rectifier has a plurality of diode elements connected in series.

3. In the discharging operation, the peak value of the forward current flowing through the second rectifier is I fp and the forward voltage of the second rectifier is V f The resistance between the cathode terminal of the second rectifier and the first node is R p1 and the resistance between the anode terminal of the second rectifier and the second node is R p2 3. The flashlight irradiation device according to claim 1, wherein the following formula (1) is satisfied: 100 [V] ≧ V f + (R p1 + R p2 ) I fp (1)

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