JPS58157045A - Ion implanting device - Google Patents

Abstract

PURPOSE:To implant a stable ion beam current into a specimen surface by feeding back the drift value of the ion beam current to a microwave oscillator, and correcting the drift while changing a microwave output value. CONSTITUTION:A specimen 2 is horizontally scanned with an ion beam 1 from an ion source 9 comprising a microwave oscillator 7 and an ion generating part 8, while said specimen 2 is vertically moved within a Faraday cup 10. Further, the detected current of the beam 1 is applied to an amplifier 13 which has been previously balanced by adjusting applied voltage 17, and said amplifier 13 is unbalanced to feed back a signal to an amplifier 14 when a current drift occurs in the beam 1, and thereby the oscillator 7 is controlled. At the same time, the upper limit of the oscillator 7 output is set by the input voltage 20 of a comparator 21, and a switch 22 is cut off when said output exceeds said set value. Accordingly, it is possible to stably and uniformly implant ions even with use of a large current ion source.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion implantation apparatus using a microwave ion source whose purpose is to implant an ion beam into a sample surface.

Ion implantation equipment using a microwave discharge type ion source that can extract an ion beam with a large current of 9 mA to more than 10 mA has already been put into practical use. The trend towards higher currents has progressed further, and ion implantation devices using the same type of ion source that can obtain 100 mA or more are currently in the practical stage.

The ion beam must be implanted as uniformly as possible onto the sample surface. Therefore, the ion beam is scanned two-dimensionally across the sample surface. Conventionally, the aforementioned large current ion
For two-dimensional beam scanning, a rotary scanning type in which both axes are mechanically performed as shown in FIG. 1, and a combination type of magnetic field scanning and mechanical scanning as shown in FIG. 2 have been adopted.・Both axes,
There is also a method of magnetic field scanning, but the electromagnet structure becomes large and is not very practical.

In the rotary scanning type shown in Figure 1, the ion beam 1 is rotated by 1 disk 3.
The rotating disk 3 is moved up and down so that the ion beam 1 is implanted onto the entire surface of the sample 2. In the combined magnetic field and mechanical type shown in Fig. 2, the ion beam 1 is turned into a scanning beam 5 horizontal to the surface of the sample 2 by an alternating magnetic field formed by an electromagnet 4, and the sample 2 is perpendicular to the scanning beam 5. Mechanically moved. By the way, in the above-mentioned ion implantation apparatus, the ion beam 1 is not necessarily stable (in the case of a microwave ion source, fluctuations in microwave power due to thermal fluctuations of the microwave oscillator, fluctuations in the power supply for applying high voltage or magnetic field, etc.) , PH31BH6, etc., the beam current value drifts due to pressure fluctuations in the sample gas, and the uniformity of implantation into the sample 2 is affected.
In contrast to the current drift of conventional equipment (from several mA to more than 10 mA)
In A), implantation uniformity was compensated for by changing the vertical feed rate V of the sample 2 with respect to the ion beam 1 in proportion to the implantation current l, as shown in the old method.

V=K・−・・・・・・・・・・・・・・・・・・・
...(1) Here, K: feed rate constant l: average implantation current density per unit area D: ion implantation amount per unit area However, as the current of the ion beam 1 increases,
If the value exceeds mA, the feed speed V of the sample 2 must also be increased, and mechanical followability of the feed becomes a problem, making it difficult to compensate for implantation uniformity.

FIG. 3 shows the relationship between the sample 2 and the scanning plane of the ion beam 1 in FIG. In contrast to the beam 5 which scans horizontally on the paper, the sample 2 is vertically (downward) scanned once to obtain the desired ion implantation amount.

In the figure, when the diameter of the scanning beam 5 is d and the scanning width is W, the residence time t in the scanning beam 5 for an arbitrary point on the surface of the sample 2 to obtain the desired implantation amount is t.・・・
...(2)l■ Here, e: electron charge amount 1.6 x 1O-19(C)■: total ion beam current (A). I=100mA for plywood, D=5X1015
/cm2゜d = = 5cm, w = 24cm (considering sample 2 with a diameter of 4"), then t = 1.3 sec. Here, if the current drift of ion beam 1 mentioned earlier occurs In order to obtain implantation uniformity of 196 or less, the feed response time of sample 2 must be at least 13 m5ec or less. Considering the actual mechanical configuration, it is difficult to satisfy this response speed. That's a problem.

In the conventional device (~10-odd mA), a chain or belt endless track is used to feed the sample 2, a small motor is used to downsize the drive mechanism, and the reduction ratio is set to 1150-I.
For Aoo, it was sufficient that the response speed and inertia were large, but as the current increases (~100 mA), the above-mentioned problem arises, and the disadvantage of having to consider increasing the size of the drive mechanism arises. .

On the other hand, in an ion implantation system using a high-current microwave ion source whose purpose is to implant an ion beam into a sample surface, the drift value of the single ion beam current is fed back to the microwave oscillator to reduce the drift of the ion beam current. The reason why correction has not been made in the past is that an increase in the oscillation output of the oscillator does not necessarily result in an increase in the ion beam current value. This phenomenon will be explained using FIG. 4, which schematically shows the configuration of the ion generator.

A microwave discharge plasma 28 is formed in the plasma chamber 26 to which a high voltage 27 is applied, and the inserted gas molecules are ionized and turned into an ion beam 1 toward the sample 2 at a low potential, which is extracted. In the figure, 29 is a negative high voltage 3
Secondary electron suppression electrode to which 0 is applied.

31 is a beam aperture. Further, 32 is a boundary between the plasma 28 and the ion beam 1, that is, a plasma boundary. Here, considering that the propagated microwave power gradually increases, the density of the discharge plasma 28 increases in accordance with the microwave power, and the ion beam 1 also gradually increases, but the plasma boundary 32 changes from a to b Also changes to C, and in the C state, the ion beam 1 is no longer focused, and as shown in the figure, it diverges to the electrode 29, etc., and finally the current of the ion beam 1 decreases. shows.

For the above reasons, it has conventionally been difficult to obtain excellent implantation uniformity in an ion implantation apparatus using a high-current microwave ion source.

It is therefore an object of the present invention to provide an ion implantation apparatus which makes it possible to use a high current microwave ion source and still obtain excellent implant uniformity.

In order to achieve the above object, an ion implanter of the type mentioned at the outset according to the invention provides a method for controlling the ion beam current by feeding the drift value of the ion beam current back to the microwave oscillator to change the microwave output value. Correct the drift so that a stable ion beam current is implanted into the sample surface, and interrupt the ion implantation operation if the output value of the microwave oscillator exceeds a predetermined value as a result of the above correction. The gist is that the means are in place to do so. That is, the present invention is based on the knowledge of the present inventors that the current value of the ion beam 1 can be proportionally controlled within a certain range of microwave output.

Hereinafter, a more detailed explanation will be given using examples with reference to FIG. be.

In FIG. 5, the ion source 9 consists of a microwave oscillator 7 and an ion generator 8 that generates a microwave plasma discharge. Ion beam 1 extracted from ion source 9
is formed into a horizontal scanning beam by the electromagnet 4 and is projected onto the surface of the sample 2. In addition, sample 2 is a Faraday cup 1o
within the beam and moving perpendicular to the scanning beam. Detection currents of the sample 2 and the Faraday cup 10 are received by an amplifier 11, and a current indicator 12 indicates the total current of the ion beam 1 during implantation.

The operating method of the illustrated driving device is as follows.

In the initial state, switch 22 and switch 24 are open,
It is assumed that the beam shielding plate 25 located on the sample surface is closed. In this state, the total current of the ion beam 1 is known by the detection current of the shielding plate 25. First, the current adjustment of the ion beam 1 adjusts the applied voltage I5 of the amplifier 14;
of the oscillator 7 from the control power supply 6.

This is done by adjusting the output. Next, amplifier 13
The applied voltage 17 is adjusted so that the indicator 23 becomes zero, or the value of the adjusted voltage 17 corresponds to the total current of the ion beam 1. The amount of implantation into the sample 2 is set by the applied voltage 16 of the calculator 18. Arithmetic unit 18 has voltage 1
Using the value (D) of voltage 6 and the value (I) of voltage 17, the feed speed V of the sample 2 shown in equation (1) above is calculated. To start implanting into sample 2, press switch 22. Close the switch 24 and close the shielding plate 25
It is started by opening. In the figure, reference numeral 19 denotes an electric motor for driving the sample 2, which rotates at a constant speed according to the output value of the computing unit 18 and keeps the feeding speed of the sample 2 constant. If there is a current drift in the ion beam 1 during implantation, the output balance of the amplifier 13 is lost, feedback is applied to the amplifier 14, and the current value of the ion beam 1 is quickly corrected. However, as mentioned earlier, there is a phenomenon in which the current value of the ion beam 1 increases with respect to the oscillation output of the oscillator 7 up to a certain range, but does not increase or conversely decreases beyond a certain range. be.

In this embodiment shown in FIG. 5, the output range of the oscillator 7 is limited using a comparator 21 in consideration of the plasma boundary described above.
This allows for stable hitting. In the figure,
The upper limit of the output of the oscillator 7 is set by the input voltage 20 of the comparator 21. During the implantation operation, if the current drift of the ion beam 1 is large, the feedback voltage from the amplifier 13 will also become large, and if this continues, the control power supply 6 of the oscillator 9 will run out of control, but if the output voltage of the amplifier 14 exceeds the voltage 20. When the threshold is exceeded, the comparator 21 is activated, the beam shielding plate 25 is closed, and the switch 24 or switch 22 is opened to interrupt the implantation.

The implantation is restarted by lowering the implantation current control pressure 17 (lowering the feed speed V of the sample 2), or after readjusting the ion source 9 (adjustment of extraction of the ion beam 1).

Above, nine conventional techniques and embodiments of the present invention have been described in detail regarding an ion implantation apparatus using a microwave ion source. As ion beam currents continue to increase, it is important to ensure uniform implantation into the sample. The method of feeding back the current drift of the ion beam to the output control system of the microwave oscillator, as in the present invention, is a method with high response speed that is difficult to achieve with conventional mechanical sample transfer speed control methods. This is a method that will be indispensable for similar implantation devices in the future.In addition, in the same implantation device, the method of limiting the range of microwave output values changes the plasma boundary of the ion source (explained in Fig. 4). This method prevents the ion beam current from being disturbed or the microwave oscillation source from running out of control, and is an extremely effective method for uniformly implanting the sample into the sample.

Although the present invention has been described in terms of a rotary scanning type in which beam scanning is performed mechanically on both axes and a combined type using an electromagnet (magnetic field) and a machine, it can also be effectively applied to a driving device that uses electromagnets in both axes. Of course.

[Brief explanation of the drawing]

Figures 1 and 2 are principle diagrams of the conventional ion implantation method, Figure 3 is a diagram showing the relationship between the sample and the scanning plane of the ion beam, and Figure 4 is a diagram schematically showing the configuration of the ion generator. , FIG. 5 is a circuit diagram showing the configuration of an ion implantation apparatus according to the present invention. 1... Ion beam 2... Sample 3... Rotating disk 4... Electromagnet 5... Scanning beam
6... Control power supply 7... Microwave oscillator 8.
...Ion generating section 9...Ion source 10...
・Faraday cup 11, 13.14...Amplifier
12... Current indicator 15, 16.17... Applied voltage 18... Arithmetic unit 19... Electric motor
20... Comparator input voltage 21... Comparator
22.24...Switch 23...Indicator
25... Shielding plate 26... Plasma chamber
27...High voltage 28...Plasma 29.
... Secondary electron suppression electrode 30 ... Negative high voltage 31 ... Beam aperture 32 ... Plasma boundary agent patent attorney Junnosuke Nakamura 15i] 'jr 2 Illustration 3 (2) r 4 Cause

Claims (1)

[Claims] In an ion implantation device using a microwave ion source whose primary purpose is to implant an ion beam into the sample surface, the drift value of the ion beam current is fed back to the microwave oscillator to change the microwave output value. Correcting the drift of the ion beam current so that stable ion beam current is implanted into the sample surface, and when the output value of the microwave oscillator exceeds a predetermined value due to the correction, An ion implantation device comprising means for interrupting an ion implantation operation.