JP4396276B2 - Flash lamp light emitting device - Google Patents

Description

  The present invention relates to a flash lamp light emitting device, and more particularly, to a flash lamp light emitting device used for a heat source for heat treatment of a semiconductor manufacturing, a thin film transistor manufacturing, a liquid crystal substrate or the like.

  In the manufacture of semiconductors and thin film transistors, development of techniques for annealing using flash lamps is in progress. For example, in a state-of-the-art logic LSI, in order to activate at a high concentration without moving an ion concentration profile implanted at a depth of 10 to 15 nm on the surface layer of a silicon wafer, a predetermined time of millisec order (1 to 3 msec) In order to irradiate the flash lamp at intervals and complete the annealing process, a light emitting device using the flash lamp is used. In order to anneal the semiconductor substrate, it is necessary to raise the surface layer portion of the substrate to about 1000 ° C. Therefore, the flash lamp is turned on by inputting energy as high as 5 kJ (kilojoules), for example. There is a need.

  Recently, the flash lamp lighting pulse width has been shortened for the purpose of reducing the energy input to the lamp and reducing the power supply, etc. In addition to the above semiconductor annealing applications, ceramics are also being used. Short pulse light with a pulse width of 1 msec or less is required in fields such as modification of the surface of a thin film and adhesion and fixing of optical components by photocuring. The lighting cycle of the flash lamp in such a field is determined by the transport speed of the object (work) to be irradiated with light.

  In semiconductor annealing applications, for example, the flash lamp is turned on at intervals exceeding 15 seconds. However, if the flash lamp is turned on with a short pulse width, the current rises faster, so that the current density is high and plasma with high temperature is generated. It is formed at a position closer to the tube wall, the inner wall of the arc tube on the trigger member side is exposed to high temperature plasma, causing the problem of white turbidity and devitrification and deterioration, and the lamp life is extremely shortened It turned out to be.

  Although different from the above technical field, a flash lamp is conventionally used for pumping a laser oscillator. As described in Patent Document 1, in the laser oscillator, in order to increase the stability of the light output energy of the laser and increase the service life of the flash lamp, the flash lamp driving power source is more than the main discharge current of the flash lamp. A low level pre-discharge current has always been maintained between the flash lamp electrodes. The pulse width for pumping of the laser oscillator is 100 to 800 μs, the current value of the main discharge is about 500 A, the lighting cycle (discharge interval) is 10 to 500 Hz, and the preliminary current value is 50 to 500 mA. By always applying a pre-discharge current, physical shock from high-energy pumping pulses is reduced, glass removal from the flash lamp discharge vessel is suppressed, and electrode sputtering and evaporation are minimized. It is said that the service life can be increased.

  When the flash lamp is turned on with a short pulse width, a plasma with high current density and high temperature is formed at a position closer to the tube wall, so the inner wall of the arc tube on the trigger member side is close to the high temperature plasma. Exposure, the thermal damage of the arc tube increases. For this reason, it has been considered effective to create a discharge path away from the tube wall in advance by flowing a preliminary discharge current before the main discharge current.

However, in the technique described in Patent Document 1, a preliminary discharge current is always passed, and compared with a short light emission interval such as a frequency of 10 to 500 Hz (period 0.002 to 0.1 sec) performed by pumping of a laser oscillator. In a flash lamp light emitting device for semiconductor annealing that emits light at a predetermined long time interval, specifically, for example, at an interval of 15 seconds or more, if a preliminary discharge current is continuously supplied, heat conduction and radiation from the preliminary discharge It has been found that the tube wall temperature of the arc tube of the flash lamp is increased, and the problem that the inner surface of the arc tube becomes clouded and devitrified and deteriorates is further promoted. This is because the heating of the flash lamp tube wall in applications where the lighting cycle is short was due to the main discharge, but as the lighting cycle becomes longer, it is due to heat conduction and radiation from the preliminary discharge maintained between the electrodes. It was considered that the heating of the arc tube could not be ignored, and further, the heating from the preliminary discharge exceeded the heating by the main discharge.
Japanese Patent Publication No. 5-1986

  Accordingly, an object of the present invention is to prevent excessive heating of the arc tube and extend its life even when the flash lamp is turned on with a short pulse width of 1 msec or less and a longer time interval than conventional laser pumping applications. An object of the present invention is to provide a flash lamp light emitting device capable of performing the above.

  The present inventor flows the preliminary discharge current only before flash emission, not always, and injects into the tube wall by setting the flash lamp light-emitting device that defines the amount of charge loaded on the lamp during preliminary discharge. The present invention has been completed by finding that the heating energy decreases.

  According to the first aspect of the present invention, there is provided a flash lamp having a trigger member arranged along the tube axis direction of the arc tube, a main discharge current is supplied to the flash lamp, and a pulse width of 1 msec with a lighting period of 0.6 sec or more. The following power supply means for flash emission, preliminary discharge current supply means for supplying a predischarge current of 1 A or more for a time of 1 msec or more only before the flash emission, controlling the magnitude of the predischarge current and the flow time, And a charge amount control means for controlling the charge amount so that an amount of charge loaded on the flash lamp is 0.6 C (coulomb) or less when pre-discharge is performed by supplying a pre-discharge current. A lamp light emitting device is provided.

  The discharge starts from the trigger member side in the arc tube, and is formed at the center of the arc tube with time. However, when the flash lamp is turned on with a short pulse width of 1 ms or less, the time to reach the maximum current value is also shortened, so that high current density and high temperature plasma is formed at a position closer to the tube wall. Thus, the arc tube is locally heated. Therefore, when the lamp is lit with a short pulse width of 1 ms or less, it is effective to create a discharge path away from the tube wall in advance by preliminary discharge.

  When the preliminary discharge current is 1 A or more, arc discharge occurs between the electrodes, and when the current value is 1 A or less, glow discharge occurs between the electrodes. In the case of glow discharge, electrons are supplied when positive ions collide with the surface of the cathode, so that the wear of the electrode is increased and the life of the entire lamp is shortened. There is.

  When the preliminary discharge current duration is less than 1 msec, the discharge path cannot be formed at a position sufficiently away from the tube wall, so that a sufficient life extension effect cannot be obtained. Then, by setting the amount of charge applied to the flash lamp to 0.6 C or less during preliminary discharge, the relative heating energy injected into the tube wall is set to 1 when no preliminary discharge current is passed. The size can be 0.8 or less. If the heating energy is 0.8 or less, the time until the arc tube becomes cloudy can be significantly delayed.

  The invention according to claim 2 is used for semiconductor annealing, and has a lighting cycle of 15 seconds or more.

  The lighting cycle of the flash lamp used in the semiconductor manufacturing process is determined by the work conveyance speed, and is usually a cycle time of 15 seconds or more. In such an application, the predischarge current is allowed to flow only before flash emission, not always, and the predischarge current is intermittently supplied, so that excessive heating of the arc tube can be prevented very effectively. .

  The flash lamp light emitting device of the present invention allows the preliminary discharge current to flow only before flash emission, so that plasma with high current density and high temperature can be generated at a position away from the tube wall. Further, by defining the charge amount to be a predetermined amount, the heating energy injected into the arc tube can be suppressed, and the lamp life of the flash lamp light emitting device can be extended.

  In addition, since the pre-discharge current flows only before flash emission, unnecessary evaporation and sputtering of the cathode and anode materials can be prevented, electrode wear is kept to a minimum, and a flash lamp light emitting device with a longer lifetime is provided. Can be provided.

  FIG. 1 is a block diagram of a flash lamp light emitting device according to an embodiment of the present invention. In this figure, symbol 1 indicates a charging circuit for charging the capacitor 2 that supplies the main discharge current 8 to the flash lamp 4 via the switching element 3a. Symbol 5 indicates a preliminary discharge current circuit as a preliminary discharge current supply means connected to the flash lamp 4 via the switching element 3b and supplying a discharge current for preliminary discharge. Symbol 6 indicates a trigger circuit connected to the flash lamp 4 via a trigger transformer 7 for starting preliminary discharge.

  Symbol 21 is a signal for controlling the current value from the preliminary discharge circuit 5 and the timing and time at which the discharge current flows to the switching elements 3a and 3b via the output terminals 21a to 21d, the timing at which the trigger circuit 6 is triggered. Is a charge amount control circuit for controlling the amount of charge supplied to the flash lamp 4 during the preliminary discharge by adjusting the timing and time when the main discharge flows and the preliminary discharge current value and time flowing through the lamp. It is a charge control means in the invention.

  For example, an SCR (thyristor) is used as the switching element 3a. The SCR enters a conducting state when a current signal is input, and maintains the conducting state until the main discharge current becomes zero. When an IGBT (insulated gate bipolar transistor) is used for the switching element 3a, the main discharge current flows only for the time when the voltage signal is input. Symbol 9 indicates the direction in which the preliminary discharge current flows. The power feeding device is a portion indicated by a symbol 20 surrounded by a broken line. For example, the capacitor 2 is connected to one electrolytic capacitor having a capacity of 1000 μF. In the present invention, the number of capacitors may be one depending on the size of the capacitor, or may be in the form of a capacitor bank in which a plurality of capacitors are connected. In addition, a film capacitor may be used.

  The trigger member 17 is made of tungsten and is connected to the trigger transformer 7. The trigger member 17 may be only a metal wire, or a metal wire is sealed in a straight tubular dielectric member sealed at both ends, and a power supply line electrically connected to the metal wire is connected to the dielectric member. There may be a form derived from the body member. For example, an FET (field effect transistor) is used as the switching element 3b. The FET becomes conductive only for the time when the voltage signal is input. Then, a preliminary discharge current 9 adjusted by the charge amount control circuit 21 is supplied from the preliminary discharge current circuit 5 to the flash lamp 4 so that a predetermined charge amount flows.

  The discharge vessel of the flash lamp 4 is made of quartz glass. For example, the discharge vessel has a diameter of 13 mm and a length of 50 mm, and a pair of tungsten or tungsten-based electrodes are opposed to the inner end regions of the discharge vessel. It is arranged. A rare gas such as xenon (Xe) is sealed in the discharge vessel as a discharge gas.

  The operation of the embodiment shown in FIG. 1 will be described. First, an activation signal is sent from the output terminal 21c of the charge amount control circuit 21 to the trigger circuit 6 to generate an activation pulse voltage. When this starting pulse voltage is applied to the primary side of the trigger transformer 7, a high voltage pulse of about 15 kV that is boosted is induced on the secondary side. Then, at the same time that the high voltage pulse is applied to the trigger member 17, a synchronization signal is generated from the output terminal 21 b so that the switching element 3 b is closed, whereby the preliminary discharge current is supplied from the preliminary discharge current circuit 5 to the flash lamp 4. A preliminary discharge state is established. Then, the heating energy (described later) injected into the trigger side tube wall of the flash lamp 4 is controlled so that a constant current flows by the control signal from the output terminal 21d so as to be smaller than the case where the preliminary discharge current is not passed. The preliminary discharge current is supplied to the flash lamp 4 only during the time when the switching element 3b is closed by a signal from the output terminal 21b.

  Then, the switching element 3b is opened (turned off) by a signal from the output terminal 21b and switched by a signal from the output terminal 21a so that a current continuously flows from the preliminary discharge current 9 to the main discharge current 8 in the flash lamp. When the element 3a is closed (turned on), the charge stored in the capacitor 2 flows into the flash lamp 4 as the main discharge current 8 only for the time when the circuit 3 is closed. The decrease in the charging voltage of the capacitor 2 is charged by the charging circuit 1 and maintained at a predetermined voltage. The coil 10 is inserted for the purpose of adjusting the main discharge current waveform. Control for reducing the charge amount to 0.6 C or less is performed by the charge amount control circuit 21. For example, the control signal of the output terminal 21d of the charge amount control circuit 21 is set so that a desired current value flows, and the switching element is set for a time shorter than the value calculated by (charge amount 0.6C) / (desired current value). The signal of the output terminal 21b is set so that 3b is closed, and the charge amount is controlled. Such a control signal is generated by a digital circuit using an IC, for example.

  Next, FIG. 2 shows a block diagram of another embodiment of the present invention. The main discharge circuit is the same as in FIG. The preliminary discharge current circuit as the preliminary discharge current supply means includes a capacitor 11 (capacitance: C), a charging circuit 12 for charging the capacitor 11, and a resistor 19. The output terminals 21a to 21c of the charge amount control circuit 21 have the same function as in FIG. 1, and the output terminal 21e outputs a control signal for charging the capacitor 11 to a constant voltage.

  In the case of this embodiment, the preliminary discharge current 9 has a current waveform in which the current value decreases with time because the charge stored in the capacitor 11 flows to the flash lamp 4 as the preliminary discharge current. The power feeding device is a portion indicated by a symbol 20 surrounded by a broken line.

  The current value of the preliminary discharge current is determined by the resistance R in the circuit and the charging voltage V0 of the charging power source 12, and has a relationship of V0 / R exp (-t / CR) with respect to the change in time t. Each parameter is set, and the preliminary discharge current is supplied to the flash lamp 4 only during the time when the switching element 3b is closed by a signal from the output terminal 21b of the charge amount control circuit 21 so that the time integration becomes 0.6C or less. For example, when V0: 500 V, R: 100Ω, C: 5000 μF, the time t that is 0.6 C or less is about 140 ms, and the signal from the output terminal 21 b of the charge amount control circuit 21 is set to be shorter than this. To close the switching element 3b.

  The decrease in the charging voltage of the capacitor 11 is charged by the charging circuit 12 so as to be maintained at a predetermined voltage by a control signal from the output terminal 21e. For setting each parameter, for example, a sufficiently large CR (s) value for a desired t is selected so that the preliminary discharge current value can be considered as a substantially constant value of V0 / R. Here, the CR value represents the time during which the preliminary discharge current value V0 / R decays to 1 / e, and is called a time constant. In this case, as in FIG. 1, the desired current value is first considered as V0 / R, and then the CR value is sufficiently larger than the value calculated from (charge amount 0.6 C) / (desired current value: V0 / R). The value of C is selected so as to increase. Then, a signal from the output terminal 21b of the charge amount control circuit 21 is set so that the switching element 3b is closed for a time smaller than the calculated value, and the charge amount is controlled.

  FIG. 3 shows a block diagram of another embodiment of the present invention. In FIG. 3, a resistor 13 and a capacitor 14 are added to the main discharge circuit of FIG. The operation shown in this figure will be explained. First, when a trigger pulse is applied to the trigger member by a signal from the output terminal 21c of the charge amount control circuit 21, dielectric breakdown occurs in the lamp, and when the capacitor 2 is charged, the resistor 13 is simultaneously charged. Discharge occurs in the lamp by the capacitor 14 in which charge is stored. The preliminary discharge current flows by closing the switching element 3b on the preliminary discharge circuit side by a signal from the output terminal 21b synchronized with this. The preliminary discharge current may be the waveform of the current described in FIG. The power feeding device is a portion indicated by a symbol 20 surrounded by a broken line.

  Then, when the switching element 3b is opened by the output terminal 21b of the charge amount control circuit 21 and the switching element 3a is closed by the output terminal 21a so that the current continuously flows from the preliminary discharge current to the main discharge current in the lamp, The electric charge stored in the capacitor 2 flows into the flash lamp 4 as the main discharge current 8 only for the time when the electric charge is closed. In this way, the capacitor 14 discharges in the lamp before the preliminary discharge, so that the starting voltage of the preliminary discharge can be lowered, which is particularly effective in a preliminary discharge current circuit in which a high voltage cannot be used.

  Next, the heating energy injected into the trigger side tube wall will be described with reference to FIG. 4 drawn as a schematic diagram. When a substance receives a certain amount of heat, it rises by a temperature determined by the specific heat capacity of the substance. Since the heat capacity of the object is known, the heating energy injected into the lamp tube wall can be determined from the increased temperature.

  In FIG. 4, the horizontal axis represents the tube thickness direction, and the vertical axis represents the rising temperature of the arc tube. Initially, the inner wall of the arc tube is heated by the heat conduction and radiation by the plasma generated in the arc tube for the time when the lamp is lit. At this time, thermal energy is transmitted in the thickness direction for the time of lighting by the thermal diffusion of the arc tube, and has a temperature profile as shown in FIG. With time, the heat further propagates through the arc tube, and the temperature profile changes to the temperature profile (thermal equilibrium state) of c in the figure through the temperature profile of b in the figure. At this time, since the amount of heat is stored, the areas surrounded by the temperature profiles a to c representing the amount of heat (each hatched portion in the figure) are equal. The time during which the temperature profile shifts from a to c varies depending on the thermal diffusivity inherent to the arc tube material. For example, when the material is quartz glass and heat is transmitted through a 1 mm-thick arc tube, the thermal equilibrium of the temperature profile c It takes about 1 second to reach the state.

  After reaching thermal equilibrium as in the temperature profile c, the increased tube wall temperature decreases with heat dissipation over time, so a radiation thermometer that can measure the target temperature at a relatively fast response speed without contact. Use to measure.

The state of measurement is shown in FIGS. FIG. 5 shows the focal position of the radiation thermometer 15 from the lamp tube axis direction, and the focal position is set so as to match the position of the tube wall near the trigger member 17.
More specifically, the vicinity of the trigger member 17 is a place about 1 mm away from the trigger member. Some radiation thermometers 15 have a wide measurement field of view, but in order to measure the temperature rise of the trigger side tube wall more accurately, a small spot one is preferable.

FIG. 6 shows that the position of the focal position of the radiation thermometer in the lamp tube axis direction is substantially the center of the lamp. Between the radiation thermometer 15 and the flash lamp 18, in order to prevent a failure of the detection part of the radiation thermometer 15 due to the light of the flash lamp 18, the shutter 16 is closed while the lamp is lit and set to open at the same time when the lamp is turned off. Is provided. In the figure, the electrode notation is omitted. The heating energy injected into the tube wall was determined based on the temperature rise thus measured. The heating energy (Q) is obtained by the following equation.
Q = mcΔT
m: mass of the arc tube (kg), c: specific heat of the arc tube (J / kg · K), ΔT: rising temperature of the arc tube (K)

  FIG. 10 shows an example of the relationship between the preliminary discharge and the main discharge in this experiment, with the current value on the vertical axis and the time on the horizontal axis. The measurement results are shown in FIG. Fig. 7 shows the heating energy injected into the trigger side tube wall when the pre-discharge current is not applied when the main discharge is one shot, the pre-discharge current is 3.7 A, and the pre-discharge state is changed. Relative heating energy when 1 is shown.

  As can be seen from FIG. 7, it was found that the heating energy decreases with the preliminary discharge time, takes a minimum value, then increases and becomes larger than the case where the preliminary discharge does not flow. From this, it is possible to reduce the heating energy injected into the tube wall by generating a high temperature plasma away from the tube wall by flowing the preliminary discharge current. It is presumed that the tube wall is warmed by heat conduction and radiation. At this time, the amount of charge when the heating energy was equivalent to the case where no preliminary discharge current was passed was a value of 1.1C.

  Further, in order to investigate the relationship between the pre-discharge current value and the heating energy, the pre-discharge current value was changed to 9.8A, 18A, 23A, and 50A in addition to 3.7A, and for each of them, the pre-discharge time was increased. After the heating energy decreased, after having a minimum value, it turned to increase, and it was confirmed that it became larger than the case where no preliminary discharge was applied. The amount of charge when the heating energy is equivalent to the case where no pre-discharge current is passed is approximately 1.1 C. From this, “current × time”, which is effective in reducing the heating energy, that is, “charge” It was found that the “amount” has a predetermined range. In addition, although it experimented also when the preliminary discharge current was sent 100A or more, the effect of making heating energy small was not seen.

  When the amount of charge loaded on the flash lamp is 0.6 C or less, the relative heating energy is 0.1 when the heating energy injected into the trigger side tube wall when the preliminary discharge current is not supplied is 1. It was found to be 8 or less. When the relative heating energy was 0.8 or less, the time until the arc tube white turbidity could be significantly delayed.

  This is shown in FIG. 8 as a measurement result of relative heating energy and arc tube white turbidity at the same number of shots. The measurement conditions were a pulse width of 400 μs, a predischarge current value of 3.7 A, a lighting period of 15 sec, a main discharge input energy of 3.4 kJ, and when no predischarge current was passed before the main discharge, the predischarge current was set to 0.5, This is when the flow time is 3, 20 ms. In each case, the relative heating energy was 0.9, 0.8, and 0.7 when the time when the preliminary discharge current was not passed before the main discharge was represented as 1. If the relative heating energy is 0.8 or less, the arc tube is not clouded.

  When the lighting cycle is 15 seconds or more, the arc tube is not heated from the end of the main discharge until the start of the next preliminary discharge, and the same effect can be obtained. In addition, even when the lighting cycle is 15 sec or less, the lighting cycle exceeding the predischarge time 0.6 sec (frequency of 1.7 Hz or less) calculated from the predischarge current 1A and the charge amount 0.6C loaded on the flash lamp. In this case, since the relative heating energy of the arc tube becomes higher than 0.8 due to heat conduction and radiation from the preliminary discharge current, only the current and time within the charge amount range found by the present invention, only before the main discharge. It is effective to flow. However, since the effect is always the same as that of flowing in a short lighting cycle, there is no need to flow preliminary discharge intermittently.

FIG. 9 is an enlarged view of the change in heating energy in a short predischarge state time when the predischarge current is 3.7A and 23A. The vertical axis represents relative heating energy when the heating energy injected into the trigger side tube wall when no preliminary discharge current is applied is 1.
It is a preliminary discharge time. From FIG. 9, the heating energy rapidly decreases by 1 ms regardless of the predischarge current value, and it is effective in extending the life of the discharge lamp in particular by flowing the predischarge current for 1 ms or more. I understand.

The block diagram of one Example of the flash lamp light-emitting device in this invention is shown. The other block diagram of one Example of the flash lamp light-emitting device in this invention is shown. The other block diagram of one Example of the flash lamp light-emitting device in this invention is shown. The heat conduction state of the arc tube wall is shown. The state of measurement of heating energy is shown. The state of other measurement of heating energy is shown. The relationship between the pre-discharge time and heating energy in pre-discharge current 3.7A is shown. The relationship between heating energy and arc tube white turbidity is shown. The relationship between the preliminary discharge time and heating energy in the preliminary discharge current 23A, 3.7A is shown. The time change of the electric current value of the preliminary discharge in this invention and the main discharge is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Charging circuit 2 Main discharge current capacitor 3a Switching element 3b Switching element 4 Flash lamp 5 Predischarge current circuit 6 Trigger circuit 7 Trigger transformer 8 Direction of main discharge current flow 9 Direction of predischarge current flow 10 Coil 11 Capacitor for predischarge current DESCRIPTION OF SYMBOLS 12 Charging power supply 13 Resistance 14 Capacitor 15 Radiation thermometer 16 Shutter 17 Trigger member 18 Flash lamp 19 Resistance 20 Power supply device 21 Charge amount control circuit 21a Output terminal 21b Output terminal 21c Output terminal 21d Output terminal 21e Output terminal

Claims (2)

A flash lamp having a trigger member arranged along the tube axis direction of the arc tube;
Power supply means for supplying a main discharge current to the flash lamp and causing flash emission with a lighting period of 0.6 sec or more and a pulse width of 1 msec or less;
Preliminary discharge current supply means for supplying a preliminary discharge current of 1 A or more for a time of 1 msec or more only before the flash emission;
The amount of charge is controlled so that the amount of charge applied to the flash lamp when the preliminary discharge is performed by supplying the preliminary discharge current is 0.6 C (coulomb) or less by controlling the magnitude of the preliminary discharge current and the flow time. And a charge amount control means for controlling the flash lamp light emitting device. 2. The flash lamp light emitting device according to claim 1, wherein the flash lamp light emitting device is used for semiconductor annealing and has a lighting cycle of 15 seconds or more.

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