JP4207488B2 - Light heating device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light heating device, and more particularly to a light heating device that rapidly heats a substrate such as a silicon wafer by light irradiation.
[0002]
[Prior art]
2. Description of the Related Art A light irradiation type heating apparatus that heats a substrate such as a silicon wafer by light irradiation is known.
In this semiconductor manufacturing process, the wafer is rapidly heated, kept at a high temperature, and rapidly cooled. A wide range such as film formation (forming an oxide film on the wafer surface) and diffusion (diffusing pre-doped impurities inside the wafer). Is done. Speaking of diffusion, an impurity is introduced into the silicon crystal in the surface layer portion of the silicon wafer by ion implantation, and the silicon wafer in this state is subjected to a heat treatment of, for example, 1000 ° C. to diffuse the impurity to cause a surface layer of the silicon wafer. An impurity diffusion layer is formed in the portion.
[0003]
In order to perform a heat treatment of a silicon wafer, a lamp is used as a heating source, and the wafer is irradiated with light emitted from the heating source so that the wafer can be heated rapidly, and then cooled rapidly. A Rapid Thermal Process device is known. A halogen lamp has been known as a heating source for such an apparatus.
[0004]
However, in recent years, there has been an increasing demand for higher integration and miniaturization of semiconductor integrated circuits. For this reason, it is necessary to form impurity diffusion at a shallower level, for example, 20 nm or less. However, it is difficult to sufficiently respond to such a request.
[0005]
Also, as a method for achieving impurity diffusion in a very shallow region, there is known an apparatus and a method for performing heat treatment by scanning a silicon wafer with an irradiation width of several millimeters by this laser beam using laser irradiation (XeCL). Yes.
However, an apparatus using laser light is very expensive, and there is a problem in terms of throughput when performing heat treatment while scanning the surface of a silicon wafer with a laser beam having a small spot diameter.
[0006]
Therefore, a method of heating a silicon wafer in a very short time using a flash lamp as a light source has been proposed. This heat treatment method using a flash lamp has a great merit because the irradiation time is extremely short, so that the temperature received by the silicon wafer as a bulk can be lowered. However, the life of the flash lamp used in this application is shown to be 100,000 to 1,000,000 times, but 30% of the lamps are deteriorated in illuminance, destroyed, or not lit without completing it. There is a problem that it exists at a rate of.
This is probably because the flash lamp used for the heat treatment of the silicon wafer is forced to be used under severe conditions in terms of heat and energy, unlike a light source used in a high-speed printer or camera.
[0007]
[Problems to be solved by the invention]
The problem to be solved by the present invention is to provide a light heating apparatus that uses a flash lamp used in a light heating process such as a silicon wafer as a heat source and that can emit flash light with a long lifetime.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems, a light heating apparatus according to the present invention includes a flash lamp that encloses a rare gas, a casing that surrounds the flash lamp, and a stage on which a silicon wafer irradiated with radiation from the flash lamp is placed. And a power supply device for controlling the light emission of the flash lamp, wherein the maximum current density in the light emission of one pulse of the flash lamp is 2.5 KA / cm ² or more and 10 μm from the start of current injection into the lamp. The current value after elapse of seconds is 200 A or more and 24 × (maximum current density (KA / cm ² ) ) ^3.5 A or less.
[0009]
As a result of intensive studies, the inventor has found that the use time has elapsed in the photo-heating process of a silicon wafer that is forced to be used under harsh and severe conditions in terms of energy, with a maximum current density of 2500 A (ampere) / cm ^2. It was discovered that the wear of the electrode is the cause of illuminance deterioration, lamp destruction, and non-lighting. In particular, a gray thin film that seems to be sputtered on the electrode, mainly on the inner wall of the arc tube around the cathode side, is formed from the beginning of light emission of the flash lamp.
And since this gray thin film shields light, the emitted light from the said part cannot fully reach | attain a silicon wafer, As a result, illumination intensity falls. Furthermore, this gray thin film absorbs light and the temperature rises compared to other parts. This is considered to cause residual stress in the arc tube and cause destruction of the arc tube. It is done. And it is thought that lamp non-lighting is also led with these arc tube discoloration and temperature rise. Actually, the present inventor has observed the electrode, particularly the cathode, and it has been confirmed that the surface is greatly roughened and the shape is changed.
[0010]
After finding out such a cause, it was found that the damage to the electrode can be reduced by considering the way of supplying the current to the lamp, specifically, the relationship between time and supply amount.
Here, the “maximum current density” means the maximum value of the current value flowing through the flash lamp, which is a value divided by the cross-sectional area of the discharge vessel. The cross-sectional area of the discharge vessel is a part between the electrodes and the inner area of the discharge vessel. The flash lamp of the present invention is a straight tube, and the cross-sectional area between the electrodes of the discharge vessel It is assumed that the processing error is constant if it is ignored.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a schematic configuration of a light heating apparatus of the present invention.
The light heating apparatus 10 uses a silicon wafer W as an object to be processed, and includes a quartz glass chamber 11 having an atmosphere gas inlet 11A and an outlet 11B, and silicon disposed in the chamber 11. And a stage 12 for supporting the wafer. A quartz flat plate 13 is provided as an airtight translucent member on the ceiling surface (upper surface in FIG. 1) of the chamber 11.
[0012]
A flash lamp 20 is provided as a heating source above the translucent member 13, and a halogen heater lamp 30 as a preheating means is provided below the chamber 11. The heater lamp 30 is embedded in the stage 12 and the temperature is controlled by a chamber control circuit 31. In the chamber control circuit 31, the raising / lowering function of the stage 12 and the opening / closing control of the gas inlet 11A and the gas outlet 11B are also performed.
[0013]
According to the light heating device 10, when the silicon wafer W into which impurities are introduced is carried into the chamber 11, the silicon wafer W is preheated to a predetermined temperature by the heater lamp 30 so that thermal diffusion of impurities does not become a problem. When the flash lamp 20 is caused to emit light, the silicon wafer W is heat-treated by flash radiation. By such a heat treatment, the silicon wafer W is heated so that the surface layer portion thereof is rapidly heated to high temperature, and then rapidly cooled and carried out of the chamber 11. The preheating is preferably performed for the purpose of reducing the temperature gradient in the thickness direction of the wafer and minimizing the energy injected into the lamp necessary to raise the temperature of the irradiated surface to a necessary level. The temperature is selected from the range of 300 to 500 ° C, and is, for example, 350 ° C.
Further, the surface temperature of the wafer during the heat treatment by the heater lamp 30 and the flash lamp 20 becomes 1000 ° C. or more, and specifically, the heat treatment is performed in the range of 1000 ° C. to 1300 ° C. Thus, by heating the maximum temperature of the wafer to 1000 ° C. or higher, the impurity diffusion layer can be reliably formed on the surface layer portion of the wafer.
[0014]
The flash lamps 20 are arranged in parallel at equal intervals along the translucent member 13. A common reflecting mirror 32 covers the flash lamps 20, and the reflecting mirror 32 is accommodated in the casing 34. The lighting operation of each flash lamp 20 is controlled by the power supply device 34.
In this embodiment, the casing 33 containing the flash lamp 20 has an opening on the radiant light side, but a translucent member may be provided so as to cover the opening.
[0015]
FIG. 2 shows a schematic configuration of the flash lamp 20.
The straight tube type quartz glass discharge vessel 21 is filled with, for example, xenon gas and sealed at both ends to define a discharge space inside. An anode 22 and a cathode 23 are disposed opposite to each other in the discharge space, and a trigger electrode 24 is held by a trigger band 25 in the longitudinal direction on the outer surface of the discharge vessel 21.
[0016]
Taking a numerical example of the flash lamp, the inner diameter of the discharge vessel is selected from a range of φ8 to 15 mm, for example, 10 mm, and the length of the discharge vessel is selected from a range of 200 to 550 mm, for example, 300 mm.
The amount of sealed xenon gas is selected from the range of 200 to 1500 torr, for example, 500 torr. The main light emitting component is not limited to xenon gas, and argon or krypton gas can be used instead. In addition to xenon gas, other substances such as mercury can be added.
The electrode is a sintered electrode mainly composed of tungsten, and the size is selected from the range of 4 to 10 mm in outer diameter, for example, 5 mm, and the length is selected from the range of 5 to 9 mm, for example, 7 mm. is there. The distance between the electrodes is selected from a range of 160 to 500 mm, for example, 280 mm. In addition, barium oxide (BaO), calcium oxide (CaO), strontium oxide (SrO), alumina (Al2O3), and the like are mixed in the cathode as an emitter.
Furthermore, the trigger electrode is in the form of a wire formed of nickel or tungsten and is in contact with the discharge vessel.
[0017]
FIG. 3 shows a power supply device 34 shown in FIG. 1 and shows a lighting circuit of the flash lamp 20, and in particular, a common charging circuit S for the plurality of flash lamps 20 and a light emitting circuit corresponding to each flash lamp. H.
The charging circuit S is connected to an AC power supply AC and includes a switching inverter circuit, a transformer T, a rectifier circuit, and an inverter circuit control circuit.
A light emitting circuit H (H1, H2,... Hn) provided for each flash lamp is connected to the subsequent stage of the rectifier circuit. Each light emitting circuit H includes a backflow prevention diode D, a voltage detection resistor circuit R, a main capacitor C, a choke coil L, and the like, and a flash lamp 20 is connected to the light emitting circuit H.
Each flash lamp 20 is provided with a trigger electrode 24, and this trigger electrode 24 is connected to a trigger circuit 26. Note that 20 to 30 flash lamps 20 and light emitting devices H are actually connected.
[0018]
In such a power supply device, energy is charged in the main capacitor C of each light emitting circuit H through the inverter circuit. When the main capacitor C is charged with sufficient energy, application of the trigger electrode 24 induces an electric field using a discharge vessel made of quartz glass as a dielectric, and the energy of the main capacitor C is discharged and flashed along with it. Emits light (flash). Here, in each light-emitting circuit H, the charging voltage of the main capacitor C is detected, and when the main capacitors C of all the light-emitting circuits have been charged, the voltage is applied to all the trigger electrodes at the same time, so that the flash lamps are simultaneously operated In order to emit light all at once.
[0019]
With regard to the light emission of the flash lamp by such a power feeding device, as a numerical example, charging / discharging of the main capacitor C is repeated, for example, 0.5 to 2 times per minute, specifically at a rate of 1 time. The capacitor C is selected from, for example, a range of 2000 to 5000 V, for example, 4500 V, and is selected from a range of 1200 to 7500 J when expressed in energy. For example, energy of 6000 J is charged and discharged and supplied to each flash lamp.
The number of flash lamps is selected from 5 to 30 as described above, and is 10 for example. Then, the light intensity on the irradiated surface, when the total number of flash lamps in the range of 5 to 30, selected from 10~50J / cm ² range, for example, a 20 J / cm ^2.
FIG. 4 shows the spectrum of the emitted light on the wafer mounting surface of the stage. The vertical axis indicates the relative radiation intensity with respect to the intensity at a wavelength of 500 nm, and the horizontal axis indicates the wavelength (nm).
[0020]
FIG. 5 shows a schematic diagram of a current waveform when the flash lamp is caused to emit light in accordance with voltage application by the trigger electrode by the light heating device shown in FIG. 1 and the power supply device shown in FIG. Among these, (1) represents the current waveform when the discharge current flows rapidly, and (2) represents the current waveform when the discharge current flows relatively slowly.
[0021]
Here, a certain amount of energy supplied from the flash lamp is necessary for the reason of the process of light heat treatment, and it is not necessary to reduce the integrated radiation amount (the area formed by the current waveform in FIG. 5) more than necessary. Can not. For this reason, in order to supply energy from the power feeding device to the lamp so as not to damage the electrodes, the temporal and current amount position of the peak value of the current waveform is an important point. The peak values are indicated by P1 and P2 in FIG.
Then, the inventor considers the position of the peak values P1 and P2 in consideration of the current value at the time when 10 μs has elapsed after the start of current injection from the power feeding device to the lamp. The reason for considering the current value when 10 μs has elapsed is that, in the light heating of the silicon wafer targeted by the present invention, the time during which the current flows through the lamp in one flash emission is approximately 1000 μs, and is formed in this 1000 μs. The initial value and the peak value have a large influence on the current waveform, and the initial current amount is specifically selected when 10 μm has elapsed from the start of flash emission (current starts to be injected into the lamp).
[0022]
Next, an experiment for verifying the causal relationship between the position of the peak value of the current waveform and the discoloration of the discharge vessel will be described.
The configuration is roughly the same as that of the apparatus shown in FIG. 1, and a simple apparatus in which one flash lamp is arranged for convenience is formed, and the current waveform (the waveform shown in FIG. 4) in the light emission of the flash lamp is changed. Was done.
In the experiment, a silicon wafer having a diameter of 4 inches and a thickness of 725 μm was set on a heater built-in stage, and the silicon wafer was preheated to about 350 ° C. The flash lamp employed a distance between electrodes of 160 mm, an inner diameter of 10 mm, a cross-sectional area of 78.5 mm ² , and encapsulating xenon gas as a main light emitting component.
The conditions relating to the flash lamp itself were the same, and the current waveform supplied to the flash lamp, specifically the position of the peak value, was changed by changing the conditions of the power feeding device. Specifically, the condition of the power feeding device is the value of the capacitance and inductance L of the main capacitor C shown in FIG.
[0023]
FIG. 6 shows the ratio of the current value 10 μsec after the current is injected into the lamp, the maximum current density in one pulse, and the illuminance on the stage surface after 100,000 times of the light emission to the initial illuminance. It is represented by
Regarding the illuminance ratio, if the illuminance after lighting 100,000 times is larger than 70% of the initial illuminance, it is recognized as a pass value for practical use. Anything less than that was evaluated as rejected. That is, Experiment 1, Experiment 3, Experiment 4, and Experiment 6 are acceptable, and Experiment 2 and Experiment 5 are unacceptable.
[0024]
FIG. 7 is a plot of the results shown in FIG. 6. The vertical axis represents the current value (A) after 10 μs has elapsed since the current was injected into the lamp, and the horizontal axis represents the maximum current density in one pulse. (KA / cm ² ).
From this figure, when the pass region is calculated, the current value (A) after the elapse of 10 μs after the current is injected into the lamp is related to the maximum current density B (KA / cm ³ ) in one pulse. It can be seen that 24 × B ^3.5 or less is good.
It should be noted that when the current value (A) after 10 μs has elapsed since the start of current injection into the lamp is 200 (A) or less, the light emission time becomes too long, which is not preferable in terms of blackening the lamp.
[0025]
As described above, in the photo-heating process of a silicon wafer that is forced to be used under severe conditions where the maximum current density is 2500 A (ampere) / cm ² , the problems of illuminance deterioration, lamp destruction, and non-lighting are due to the passage of usage time. Therefore, the problem can be solved well by ascertaining the cause of electrode wear due to the above and considering the method of supplying current to the lamp, specifically, the relationship between time and supply amount.
Specifically, the maximum current density in the light emission of one pulse of the flash lamp is 2.5 KA / cm ² or more, and the current value after elapse of 10 μs from the start of current injection into the lamp is 200 A or more, and The problem can be solved by setting the current density to 24 × (maximum current density (KA / cm ² ) ) ^3.5 A or less.
[Brief description of the drawings]
FIG. 1 shows an overall schematic configuration of a light heating apparatus according to the present invention.
FIG. 2 shows a flash lamp which is a heating source of the light heating apparatus according to the present invention.
FIG. 3 shows a circuit example of a power feeding device of a light heating device according to the present invention.
FIG. 4 shows the spectrum of the emission wavelength at the stage.
FIG. 5 shows a current waveform when a flash lamp is caused to emit light.
FIG. 6 shows the experimental results of the present invention.
FIG. 7 shows the experimental results of the present invention.
[Brief description of symbols]
DESCRIPTION OF SYMBOLS 10 Light heating apparatus 11 Chamber 13 Light transmission window 20 Flash lamp 33 Power supply apparatus

Claims (1)

Light composed of a flash lamp enclosing a rare gas, a casing surrounding the flash lamp, a stage on which a silicon wafer irradiated with light emitted from the flash lamp is placed, and a power supply device that controls light emission of the flash lamp In the heating device,
The flash lamp has a maximum current density in one pulse of emission of 2.5 KA / cm ² or more, and a current value after 10 μsec from the start of current injection into the lamp is 200 A or more, and 24 × (maximum Current density (KA / cm ² ) ) ^3.5 A or less, a light heating apparatus characterized by

Images