Patent Application
20070229087
The present invention relates to an ion balance sensor used for balancing the amount of positive and negative ions in a manufacturing process of semiconductor devices or the like, when the positive and negative ions are sprayed to the devices by an ionizer to discharge the devices, in order to prevent electrification of the devices.
As a conventional art of the ion balance sensor used for this type of ionizer (discharger), for example, one disclosed in Japanese Patent Application Laid-Open No. 2003-217892 (paragraphs [0012] to [0021] and FIGS. 1 to 3) is known.
In the conventional art, two electrostatic potential sensors are provided in an ion balance measuring apparatus, with an electrostatic potential sensor for measuring electrostatic potential of an object to be discharged being directed to the object, an electrostatic potential sensor for measuring electrostatic potential around the own ion balance measuring apparatus being arranged so as not to be directed to the object, a difference between the measurement values of the two electrostatic potential sensors is calculated, and an error included in the measurement values of the electrostatic potential of the object due to an influence of ions around the own apparatus is reduced, thereby measuring the electrostatic potential of the object.
As another conventional art, as described in Japanese Patent Application Laid-Open No. 2001-43992 (for example, paragraphs [0021] to and FIG. 5), positive/negative ion output-balancing method and apparatus are known, in which a mesh-like ion balance sensor is arranged at a supply opening of an ionizer, and a voltage measured by the ion balance sensor is compared with a reference value, to control on/off of positive and negative high-voltage power sources based on the comparison result, thereby appropriately maintaining the ion balance.
In the invention described in Patent document 1, since two electrostatic potential sensors and a calculator are required, a circuit configuration of the ion balance measuring apparatus becomes complicated, and as a result, the ion balance measuring apparatus becomes large and the manufacturing cost increases.
In the invention described in Patent document 2, only the ion balance near the supply opening of the ionizer is controlled, and the ion balance on the surface of an actual object to be discharged cannot be controlled accurately.
Therefore, it is an object of the present invention to provide an ion balance sensor that can detect the ion balance accurately with a simple configuration, enabling small size and reduction of the manufacturing cost, and can detect the ion balance near the surface of the object to be discharged.
To achieve the above object, the invention according to claim 1 is an ion balance sensor comprising: an antenna charged with positive ions or negative ions; and a normally-on type MOSFET in which the antenna is connected to a gate electrode, an ion balance-detecting resistance is connected between a grounded source electrode and the gate electrode, and a DC power source and a load resistance are serially connected between the source electrode and a drain electrode, wherein a voltage of the gate electrode is changed due to a voltage drop by a current flowing between the charged antenna and an earth via the ion balance-detecting resistance, and a change of drain current due to the voltage of the gate electrode is detected, thereby detecting positive and negative balance of ions used for charging the antenna.
The invention according to claim 2 is an ion balance sensor comprising: an antenna charged with positive ions or negative ions; and a normally-off type n-channel MOSFET and a normally-off type p-channel MOSFET, in each of which the antenna is connected to a gate electrode, an ion balance-detecting resistance is connected between a grounded source electrode and the gate electrode, and a DC power source and a light-emitting diode (LED) are serially connected between the source electrode and a drain electrode, wherein a voltage of the gate electrode is changed due to a voltage drop by a current flowing between the charged antenna and an earth via the ion balance-detecting resistance, and a drain current of either one of the MOSFETs is increased by the voltage of the gate electrode, so that the LED on this MOSFET side is allowed to emit light, thereby detecting positive and negative balance of ions used for charging the antenna.
The invention according to claim 3 is the ion balance sensor according to claim 1 or 2, wherein the ion balance-detecting resistance is formed of a plurality of resistances having a different value of resistance, and one of the resistances is selected and connected between the source electrode and the gate electrode.
The invention according to claim 4 is the ion balance sensor according to any one of claims 1 to 3, wherein a hollow space is formed by a probe constituting the antenna, and the MOSFET including the gate electrode and the ion balance-detecting resistance are built in the space.
The invention according to claim 5 is the ion balance sensor according to any one of claims 1 to 4, wherein a resistance of the ion balance-detecting resistance is set to be smaller than a resistance in the opposite direction of a protective diode connected between the source electrode and the gate electrode of the MOSFET for preventing electrostatic breakdown.
According to the present invention, electric current flows between the antenna charged with positive ions or negative ions and the earth via the ion-balance-detecting resistance, and a voltage is applied to the gate electrode of the MOSFET due to a voltage drop in the resistance. Since the channel of the MOSFET is controlled according to the voltage and the drain current changes, by extracting the change of the drain current as a voltage change, it can be detected with which ions the antenna has been charged. In other words, ion balance of the positive and negative ions can be detected.
In the present invention, since the circuit configuration is very simple, the circuit can be made small and the manufacturing cost can be reduced. Further, since the antenna can be used near the object to be discharged, the ion balance at a position where the positive and negative ions reach can be accurately detected, and hence, it is remarkably useful when it is applied to a manufacturing process of semiconductor devices or the like.
Best modes for carrying out the invention will be explained below with reference to the drawings.
In
A load resistance RL and a DC power source VDS are serially connected between a source electrode S and a drain electrode D of an MOSFET 11. The source electrode S is grounded (connected to a bulk electrode). Reference sign Out denotes an output terminal derived from between the load resistance RL and the DC power source VDS.
Reference sign DGS denotes a protective diode built in beforehand in a manufacturing process in order to prevent electrostatic breakdown of the MOSFET 11, which is connected between the gate electrode G and the source electrode S with the illustrated polarity.
In the first embodiment, an ion balance-detecting resistance R is connected between the gate electrode G and the source electrode S. It is assumed here that a resistance of the resistance R is a known value sufficiently lower than a resistance in the opposite direction of the protective diode DGS.
An operation in the first embodiment is explained next.
Since the MOSFET 11 is the normally-on type, it has a known characteristic as shown in
It is assumed that a voltage VOUT of the output terminal Out is V1 (negative value) as shown in
When the positive ions increases than the negative ions on and after time t1 in
When the negative ions increases than the positive ions on and after time t1, electric current flows from the earth side toward the antenna 20 via the ion balance-detecting resistance R due to the excessive negative ions of the antenna 20, and hence, the voltage VGS making the gate electrode G side negative is generated at the opposite ends of the resistance R. Since the voltage VGS acts so as to narrow the n-channel, the drain current ID decreases as compared to on and before time t1, and as a result, the voltage VOUT increases on the positive side and changes as shown by V1n in
By setting the resistance of the ion balance-detecting resistance R to a value sufficiently lower than the resistance in the opposite direction of the protective diode DGS connected parallel therewith, the combined resistance of these becomes predominant by the resistance R. Accordingly, a voltage drop due to the current flowing from the antenna 20 charged to either positive or negative through the resistance R can be reliably detected as the voltage VGS between the gate and the source.
Particularly, it is difficult to obtain a desired value as the resistance in the opposite direction of the protective diode DGS, which is likely to be affected by a temperature change and has a difference according to individual MOSFET. Therefore, use of the resistance R whose value is known contributes to a reliable operation of the MOSFET 11 corresponding to the ion balance.
According to the first embodiment, the output voltage VOUT in the state of VGS=0, which means that the ions are well balanced, is measured beforehand, and the polarity of the excessive ions used for charging the antenna 20, in other words, an unbalanced state of the positive and negative ions sprayed to the antenna 20 can be detected according to which side of positive and negative sides the voltage VOUT changes.
Therefore, the positive and negative ion balance can be appropriately controlled by adjusting the positive or negative voltage to be applied to an emitter of the ionizer according to feed-back control corresponding to the detected unbalanced state.
Also in the second embodiment, the unbalanced state of the positive and negative ions can be detected based on to which polarity the output voltage VOUT changes from the state of VGS=0 in which ions are well balanced.
In the first and the second embodiments, if unbalance between the positive and negative ions is large, the voltage VGS applied to the gate electrode G increases due to a voltage drop of the ion balance-detecting resistance R, and the drain current ID saturates, thereby making it impossible to detect the state of change of the output voltage VOUT due to the drain current ID.
In the third embodiment, therefore, a plurality of resistances having a different resistance (each resistance has a value sufficiently lower than a resistance in the opposite direction of the protective diode DGS) is provided in parallel as the ion balance-detecting resistance, and an ion balance-detecting resistance having an optimum resistance can be selected for a target discharging system.
In other words, in
The operation thereof is the same as in the first embodiment shown in
In the first to the third embodiments, when noise is mixed in a lead wire between the antenna 20 and the gate electrode G from the circumference, regardless of the charging polarity of the antenna 20, there is a possibility that the MOSFET is turned on due to the noise, thereby increasing the drain current ID. The fourth embodiment is for solving this problem.
That is, a probe 21 including a hollow spherical portion 21a and a tubular portion 21b is formed as a conductive member corresponding to the antenna 20 in the first to the third embodiments, and the MOSFET 11 itself including the gate electrode G is built in the spherical portion 21a, and one point of the spherical portion 21a is connected to the gate electrode G.
A lead wire 31 is connected to the source electrode S and the drain electrode, and these lead wires 31 are enclosed by a shield cover 32, pass through the tubular portion 21b, and are guided to the outside. A DC power source and a load resistance (not shown) are connected to the lead wire 31. In
When the configuration is as shown in
In the spherical portion 21a, a component including the MOSFET 11 and a plurality of ion balance-detecting resistances R1, R2, R3, . . . can be built in, as shown in
In the present embodiment, not only the spherical portion 21a and the tubular portion 21b are integrated and formed of a conductive member as shown in
In
A light-emitting diode LED1 and a DC power source VDS1 are serially connected between the source electrode S and the drain electrode D of the MOSFET 11′, and a light-emitting diode LED2 and a DC power source VDS2 are serially connected between the source electrode S and the drain electrode D of the MOSFET 12′. The luminescent color of the light-emitting diodes LED1 and LED2 are different, for example, one is red and the other is green.
According to the above configuration, depending on unbalance of the positive and negative ions used for charging the antenna, for example, when there are positive ions more than negative ions, the light-emitting diode LED1 can be allowed to emit light, and when there are negative ions more than positive ions, the light-emitting diode LED2 can be allowed to emit light. Thus, the positive and negative ion balance can be visually displayed by separating the color.
Although not shown, also in this embodiment, a plurality of ion balance-detecting resistances can be provided so as to be changed over, or the antenna 20 can be formed in the shape of the probe 21 shown in
According to respective embodiments of the present invention, a practical and inexpensive ion balance sensor can be provided only by adding some parts to the MOSFET.
In the respective embodiments, an instance in which a stand-alone MOSFET is used has been explained; however, the present invention is also applicable to an MOSFET formed in an input stage of an operation amplifier, which is a so-called FET input operation amplifier.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-198346 | Jul 2004 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP05/10444 | 6/1/2005 | WO | 11/17/2006 |
