JP4989111B2 - Plasma cleaning device - Google Patents

Description

  In the present invention, a chamber in which a pair of parallel upper and lower electrodes are disposed is evacuated, plasma reactive gas is supplied between both electrodes, and a high frequency voltage is applied to the lower electrode by a high frequency power source. The present invention relates to a plasma cleaning apparatus that converts the gas into plasma and etches the plasma by causing positive ions in the plasma to collide with a printed circuit board disposed above the lower electrode.

  This type of cleaning apparatus is disclosed in, for example, Patent Document 1. In general, an alumina ceramic plate that is an insulator is laid on the lower electrode, and a printed circuit board is disposed with a predetermined distance from the alumina ceramic plate to stabilize the plasma. Measures are taken to prevent abnormal discharge that is likely to occur on a printed circuit board having uneven portions.

However, if an alumina ceramic plate is laid on the lower electrode, the negative offset direct current voltage (Vdc) generated at the lower electrode, which affects the good cleaning, is reduced by about 100 V (volts), so that the abnormal discharge is eliminated, but the cleaning ability Will fall.
JP 2002-153832 A

  Accordingly, an object of the present invention is to provide a plasma cleaning apparatus that prevents abnormal discharge, suppresses a decrease in the offset DC voltage value as much as possible, achieves plasma stability, and does not decrease the cleaning ability as much as possible. .

For this reason, the first aspect of the invention provides a vacuum state in a chamber in which a pair of parallel upper and lower electrodes are disposed, and supplies a plasma reactive gas between both electrodes, and a high frequency power source is applied to the lower electrode. In a plasma cleaning apparatus that applies high frequency voltage to turn the gas into plasma, and positive ions in the plasma collide with a printed circuit board disposed above the lower electrode. The printed circuit board is stacked on the storage tray provided via the insulator, the storage tray is provided on the back surface of the door body that opens and closes the opening of the chamber, and the storage tray is opened and closed by opening and closing the door body. out capable and configured, the storage tray is located above the lower electrode, and the connection between the lower electrode and the high frequency power source An automatic matching unit including an automatic matching circuit and a measurement circuit, and a control device for controlling the high-frequency power source. The automatic matching circuit automatically matches the impedance of the high-frequency power source and the impedance of the lower electrode. The measurement circuit measures a negative offset DC voltage generated in the lower electrode to which a high-frequency voltage is applied by the high-frequency power source, and the control device is preset with the measured offset DC voltage from the measurement circuit. The high-frequency power supply is controlled such that the measured offset DC voltage is the same as the reference voltage without any deviation from the reference voltage .

  The present invention can provide a plasma cleaning apparatus that prevents abnormal discharge, suppresses a decrease in offset DC voltage value as much as possible, achieves plasma stability, and does not reduce the cleaning ability as much as possible.

  Hereinafter, the plasma cleaning apparatus according to the first embodiment of the present invention will be described first with reference to the conceptual diagram of the plasma cleaning apparatus of FIG. Reference numeral 1 denotes a rectangular parallelepiped vacuum chamber which is brought into a predetermined vacuum state by a vacuum pump (not shown), and a pair of parallel upper electrode 2 and lower electrode 3 are disposed in the vacuum chamber. That is, the upper electrode 2 is fixed to the lower surface of the upper wall of the vacuum chamber 1 through the upper electrode support member 4, and the lower electrode 3 is fixed to the upper surface of the bottom wall of the vacuum chamber 1 through the lower electrode support member 5. To do.

  Then, an alumina ceramic plate 7 as an insulator is attached to the upper surface of the storage tray 8, and an aluminum storage tray 8 on which the printed circuit board 6 is stacked via the alumina ceramic plate 7 is placed above the lower electrode 3 by a predetermined distance d. The vacuum chamber 1 is configured so that it can be taken in and out. That is, a pair of left and right rods 10 provided at the lower back of the door 9 that opens and closes the front opening of the vacuum chamber 1 penetrates and slides through a pair of left and right rod guide members 11 provided at the lower bottom of the vacuum chamber 1. A guide roller 13 that is configured to be movable and is rotatably provided on both side surfaces of the storage tray 8 that is also fixed to the rear middle portion of the door body 9 on the guide body 14 that is fixed to both sides of the lower electrode 3. The door body 9 and the storage tray 8 can be moved back and forth by holding the handle 15 of the door body 9.

  Therefore, when the operator holds the handle 15 of the door body 9 and pulls it toward the front side, the rod 10 is guided by the rod guide member 11 and the guide roller 13 rotates and slides on the guide body 14. Until the stopper 16 provided at the end is locked to the rod guide member 11, the door body 9 and the storage tray 8 are moved to the front side.

  The storage tray 8 is positioned above the lower electrode 3 via the guide roller 13 with a gap d, and the gap d is about 1 mm, for example. Further, the guide body 14 fixed to both sides of the lower electrode 3 is an insulator, and the lower electrode 3 and the storage tray 8 are not electrically connected. However, the structure that is not electrically connected is not limited to such a structure. .

  Then, an inert gas such as argon is supplied between the upper electrode 2 and the lower electrode 3 through the electrode support member 4 and the upper electrode 2.

  Reference numeral 20 denotes a high-frequency power source connected to the ground, which applies a high-frequency voltage to the lower electrode 3 via an automatic matching unit 21 to convert the plasma reactive gas into plasma. Then, the positive ions in the generated plasma collide with the printed circuit board 6 placed on the alumina ceramic plate 7 laid on the storage tray 8, thereby etching the surface of the printed circuit board 6 and causing contamination. Remove material and wash.

  The automatic matching unit 21 connected to the high frequency power source 20 is provided with an automatic matching circuit and a measurement circuit. The automatic matching circuit is a circuit that automatically matches the impedance of the high-frequency power source 20 and the impedance of the lower electrode 3 in order to supply the maximum power of the high-frequency power source 20 into the vacuum chamber 1. The measurement circuit includes an A / D circuit and a D / A circuit, and is a circuit that constantly measures a negative offset DC voltage (Vdc) generated in the lower electrode 3 to which a high-frequency voltage is applied by the high-frequency power source 20.

  Then, PID control or ON / OFF is fixed so that the control device (not shown) changes the high-frequency voltage according to the deviation between the measured offset DC voltage (Vdc) from the measurement circuit and a preset reference voltage. The high frequency power supply 20 is controlled using on / off control that repeats periodically. That is, the offset DC voltage (Vdc) is affected by the state of the dirty printed circuit board 6 (the amount of water to be contained), but is also affected by the high frequency voltage value, so that the offset DC voltage (Vdc) and the reference voltage are The high frequency power source 20 is controlled so as to change the high frequency voltage in accordance with the deviation.

  That is, if the absolute value of the offset DC voltage (Vdc) is larger than the reference voltage, the high-frequency voltage is decreased according to the deviation, and if the absolute value of the offset DC voltage (Vdc) is smaller than the reference voltage, the high-frequency voltage is increased. Is controlled to be small. As long as the control is performed in this way, feedback control using another method may be used.

  Here, the PID control refers to control that converges to a set value by combining proportional control, integral control, and differential control.

  With the above configuration, the operation will be described below. The vacuum chamber 1 is brought into a predetermined vacuum state by a vacuum pump (not shown), and a high frequency voltage from the high frequency power source 20 is applied to the lower electrode 3 via the automatic matching unit 21. Then, argon gas or the like, which is a plasma reactive gas that passes through the electrode support member 4 and the upper electrode 2 and is supplied between the upper electrode 2 and the lower electrode 3, is converted into plasma. At this time, the automatic matching circuit of the automatic matching unit 21 automatically matches the impedance of the high frequency power source 20 and the impedance of the lower electrode 3 in order to supply the maximum power of the high frequency power source 20 into the vacuum chamber 1. To do.

  As described above, the positive ions in the generated plasma collide with the printed circuit board 6 above the lower electrode 3, thereby etching the surface of the printed circuit board 6 to remove contaminants and cleaning.

  The negative offset DC voltage generated in the lower electrode 3 to which a high frequency voltage is applied by the high frequency power source 20 is always measured by a measurement circuit. Therefore, the control device to which the measured offset DC voltage value is input can perform PID control or change so as to change the high-frequency voltage according to a deviation between the offset DC voltage from the measurement circuit and a preset reference voltage. The high frequency power supply 5 is controlled using on / off control.

  That is, the control device controls the high frequency power supply 20 so as to eliminate the deviation and the measured offset DC voltage value becomes the same as the reference voltage, while increasing or decreasing the high frequency voltage value output by the high frequency power supply 20. The operation of the plasma cleaning apparatus is continued.

  Therefore, the alumina ceramic plate 7 which is an insulator is attached to the upper surface of the storage tray 8, and the aluminum storage tray 8 on which the printed circuit board 6 is stacked via the alumina ceramic plate 7 is provided above the lower electrode 3. In addition to preventing abnormal discharge, the offset DC voltage value is suppressed as much as possible to the storage tray 8 and the printed circuit board 6 having irregularities that are likely to cause abnormal discharge, and the stability of the plasma is achieved as much as possible. It is possible to provide a plasma cleaning apparatus that does not reduce the performance.

  Although the embodiments of the present invention have been described above, various alternatives, modifications, and variations can be made by those skilled in the art based on the above description, and the present invention is not limited to the various embodiments described above without departing from the spirit of the present invention. It encompasses alternatives, modifications or variations.

It is a cross-sectional top view of a plasma cleaning apparatus. It is a vertical side view of a plasma cleaning apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Upper electrode 3 Lower electrode 6 Printed circuit board 7 Alumina ceramic board 8 Storage tray 9 Door body

Claims (1)

A chamber in which a pair of parallel upper and lower electrodes are disposed is evacuated, plasma reactive gas is supplied between both electrodes, and a high-frequency voltage is applied to the lower electrode by a high-frequency power source to supply the gas. In a plasma cleaning apparatus that turns into plasma and etches when positive ions in the plasma collide with a printed circuit board disposed above the lower electrode, the printed circuit board is placed on a storage tray having a plate-like insulator provided on the upper surface. And the storage tray is provided on the rear surface of the door body that opens and closes the opening of the chamber, and the storage tray is configured to be able to be taken in and out of the chamber by opening and closing the door body. tray is located above the lower electrode, and, connected to the automatic matching circuit and the measuring times between the high frequency power source and the lower electrode And an automatic control circuit for controlling the high-frequency power source, the automatic matching circuit automatically matches the impedance of the high-frequency power source and the impedance of the lower electrode, and the measurement circuit A negative offset DC voltage generated in the lower electrode to which a high frequency voltage is applied by a high frequency power source is measured, and the control device calculates a deviation between the measured offset DC voltage from the measurement circuit and a preset reference voltage. The plasma cleaning apparatus is characterized in that the high-frequency power supply is controlled such that the measured offset DC voltage is the same as the reference voltage .

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