Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
2000-05-26
2001-12-11
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S224000, C315S324000
Reexamination Certificate
active
06329765
ABSTRACT:
FIELD OF TECHNOLOGY
This invention concerns a filament lamp lighting device for such uses as general lighting or heat: treatment equipment. In more detail, it concerns a filament lamp lighting device that connects to the filament lamp on the output side and controls the output power.
BACKGROUND OF TECHNOLOGY
Filament lamp lighting devices are widely used for heat treatment and general lighting. Light irradiation heat treatment equipment for semiconductor wafers (hereafter wafers) can be cited as one application of filament lamp lighting devices to heat treatment.
Heat treatment is used in the process of semiconductor manufacturing for rapidly heating wafers, maintaining them at a high temperature, and rapid cooling. It is carried out in a broad range of processes such as film formation, diffusion and annealing.
In all the above processes, the wafer is treated at a high temperature, and when this heat treatment is done using light irradiation heat treatment equipment, the wafer can be heated rapidly, exceeding 1000° C. in 10 to 30 seconds. And when the light irradiation is stopped, rapid cooling is possible.
However, if the temperature distribution of the wafer is uneven when the wafer is heated, the phenomenon known as slip occurs in the wafer. In other words, defects occur in the crystal dislocation, and poor quality products are liable to result.
Therefore, when using light irradiation heat treatment equipment for heat treatment of wafers, it is necessary that the heating, temperature maintenance and cooling of the wafer be done with uniform temperature distribution.
Light irradiation heat treatment equipment intended to irradiate so that the temperature distribution of the wafer will be uniform includes, for example, that presented in JPO kokai patent report H8-45863. The light source of the light irradiation heat treatment equipment described in that report had a number of ring-shaped infrared lamps of different diameters arranged in concentric circles. By arranging the lights in that way, the wafer could be divided into concentric zones, and temperature control was simplified.
To make the temperature of the wafer uniform, the temperature of each zone of the wafer was measured and the heat generated by the infrared lamp corresponding to each zone was controlled accordingly. That is, if the temperature were lower at the periphery of the wafer, the input power to the lamp covering the center of the wafer would be increased, and the amount of heat generated by the lamp would go up and apply more heat to the wafer. The variation of the heat generated by the lamp is referred to below as “light adjustment.”
Halogen lamps with filaments that radiate infrared light efficiently are generally used as the infrared lamps in light irradiation heat treatment equipment. Moreover, an alternating current power supply is generally used as the lighting power supply.
Light adjustment of filament lamps is done in the following way.
(1) For light adjustment of a filament lamp in a general lighting fixture, a circuit with a triac is normally used, and adjustment is done by controlling the continuity angle of the triac.
(2) Light adjustment of light irradiation heat treatment equipment basically applies the same circuit, and so a thyristor is used. The basic structure of lamp lighting device using thyristors is shown in FIG.
9
. Now, one lamp lighting device is used for a single lamp. Consequently, in equipment to control the lighting of multiple lamps, the number of lamp lighting devices depends on the number of lamps. The devices are housed on the equipment power supply box.
In the lighting device shown in
FIG. 9
, control of the power input to the lamp, or light adjustment, is done by varying the timing of the gate current of thyristors SCR
1
and SCR
2
.
Power control by thyristor is done by two methods, continuity angle control and zero cross control. Now, terminology is defined below. Input power from a commercial alternating current power supply to the lamp lighting device is called “input.” The power output from the lamp lighting device to the lamp is called “output.” Accordingly, “output power” is “lamp input power.”
(a) Continuity Angle Control
In
FIG. 9
, alternating current from a commercial alternating current power supply
21
is input to the lamp lighting device
100
. Within the lamp lighting device
100
is a lamp lighting control circuit
200
that comprises the first thyristor SCR
1
and the second thyristor SCR
2
. When the gate signal generated by the gate signal generation circuit of the controller
300
lets the gate current flow to the gates G
1
, G
2
of the thyristors SCR
1
, SCR
2
of the lamp lighting control circuit
200
, then current is output from the lamp lighting device
100
to the lamp
23
until the current supplied to the thyristors SCR
1
, SCR
2
of the lamp lighting control circuit
200
becomes zero.
FIG. 10
is a diagram showing the various waveforms in the event of continuity angle control of the thyristors in FIG.
9
. FIG.
10
(
a
) shows the input voltage waveform to the lamp lighting device
100
. FIG.
10
(
b
) is a diagram showing an example of the timing of the gate current flow to the gates G
1
, G
2
of the thyristors SCR
1
, SCR
2
, in which (1) is the gate current for the first thyristor SCR
1
and (2) is the gate current for the second thyristor SCR
2
. FIG.
10
(
c
) shows the waveform of the output current when the gate current flows with the timing from FIG.
10
(
b
). Now, in the case of filament lamp lighting devices, the output voltage has the same waveform as the output current.
Consequently, the output power from the lamp lighting device
100
is the product of the out current waveform and the output voltage waveform shown by the shaded area of FIG.
10
(
c
). By varying the timing of the gate current supplied to the thyristors SCR
1
, SCR
2
, it is possible to vary the output voltage waveform an output current waveform shown in FIG.
10
(
c
), and so light adjustment that varies the output power, which is the lamp input power, is possible.
(b) Zero Cross Control
FIG. 11
is a diagram showing the various waveforms in the event of zero cross control of the thyristors in FIG.
9
. The structure of the control circuit is the same as
FIG. 9
, and the timing of the gate current to the thyristors SCR
1
, SCR
2
is as shown in FIG.
11
(
b
). In the figure, (1) is the gate current for the first thyristor SCR
1
and (2) is the gate current for the second thyristor SCR
2
.
FIG.
11
(
c
) shows the output current and output voltage when the gate current has the timing shown in FIG.
11
(
b
). As shown in FIG.
11
(
c
), the lamp input voltage is varied and light adjustment is carried out by means of intermittence of output current and output voltage waveforms.
However, the two control methods described above have the following problems.
(1) Occurrence of Transient Noise (Continuity Angle Control)
In the continuity angle control method illustrated in
FIG. 10
, a high voltage is suddenly impressed on the lamp as shown in FIG.
10
(
c
). Because of that, noise known as transient noise occurs within the lamp lighting device, and that sometimes causes the device control system to malfunction. And because of a rush current flow in the lamp filament, the filament is in a state of overload, which is liable to cause filament breakage.
(2) Drop in Response Speed; Lack of Constant Control (Zero Cross Control)
In the case of zero cross control, the voltage of the power source is sent through the thyristor at the time of the zero cross, so a high voltage is not impressed suddenly on the lamp. Nevertheless, the cycles of the commercial input frequency are thinned out as shown in FIG.
11
(
b
) so the response time of the light adjustment cannot be faster than the frequency of the commercial power supply, and rapid light adjustment is not possible. Moreover, the output power cannot be varied continually, and so minute light adjustment is not possible.
(3) Occurrence of High-frequency Distortion
Taking the example of continuity angle control shown in
FI
Lee Wilson
Nixon & Peabody LLP
Safran David S.
Ushiodenki Kabushiki Kaisha
Wong Don
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