JPH0723898Y2 - Ion beam scanning voltage generator - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention irradiates a sample such as a semiconductor wafer with an ion beam while electrostatically scanning the ion beam so that the sample such as a semiconductor wafer is ionized substantially uniformly. The present invention relates to an ion beam scanning voltage generator for generating a scanning voltage applied to a vertical scan electrode and a horizontal scan electrode in an electrostatic scan type ion implanter for implanting.

[Conventional technology]

In a conventional electrostatic scan type ion implanter, an ion beam extracted from an ion source is passed through an analysis magnet and further narrowed down by a Q lens, and the focused ion beam is drawn as shown in FIGS. 9 (A) and 9 (B). 1 for a pair of vertical scanning electrodes 2A, 2B
The ion beam 1 is irradiated onto the target 4 on which a sample such as a semiconductor wafer is attached through the space and the pair of horizontal scanning electrodes 3A and 3B.

In this case, the vertical scanning voltage V _V and the horizontal scanning voltage V _H between the pair of vertical scanning electrodes 2A and 2B and between the pair of horizontal scanning electrodes 3A and 3B are ion beam scanning voltages shown as an example in FIG. By applying each from the generator, the ion beam 1 is irradiated to the target 4 while reciprocally scanning in the vertical direction and the horizontal direction.

Between the pair of horizontal scanning electrodes 3A, 3B and the target 4 described above, there is disposed a mask 5 for shaping the scanning shape of the ion beam 1 into, for example, a circular shape according to the shape of the sample on the target 4, and Between the mask 5 and the target 4, a beam adjustment flag 6 having the same shape as the sample on the target 4 is arranged. The flag 6 is configured to be movable in the direction of the arrow A, and the mask 5 is set only during beam adjustment.
Between the target 5 and the target 4, and when the target 4 is irradiated with the ion beam 1, it is removed from between the mask 5 and the target 4.

The ion beam scanning voltage generator described above, as shown in FIG. 10, has a scanning frequency generator 11, a scanning oscillator 12, a scanning tracking circuit 13, a scanning amplifier 14, and a flag current detector 15 including a current amplifier. And an auto-threshold circuit 16 and a correction circuit 17.

The scanning frequency generator 11 includes a vertical direction square wave signal S _{V of} FIG. 11 (A) and a horizontal direction square wave of FIG. 11 (B) corresponding to the vertical direction scanning frequency f _V and the horizontal direction scanning frequency f _H , respectively. Generate signal S _H.

The scanning oscillator 12 has a vertical direction triangular wave signal S _{V of} FIG. 11 (C) which has the same frequency as the vertical direction square wave signal S _V and the horizontal direction square wave signal S _H generated from the scanning frequency generator 11 and is synchronized with each other. 'And the horizontal triangular wave signal of FIG. 11 (D)
Generate S _H ′.

The scanning tracking circuit 13 uses the vertical triangular wave signal S _V ′ and the horizontal triangular wave signal S _H ′ from the scanning oscillator 12 and the acceleration voltage V _A of the ion beam 1 according to the magnitude of the acceleration voltage V _A. (E) Triangle wave voltage V _VSC for vertical scan
And DC voltage V for vertical offset in FIG. 11 (F)
_VOF , horizontal scanning triangular wave voltage V _{HSC of} FIG. 11 (G) and horizontal offset DC voltage V _HOF of FIG. 11 (H) are generated.

The scan amplifier 14 includes a vertical scan triangular wave voltage V _VSC and a vertical offset DC voltage V _VOF, and a horizontal scan triangular wave voltage V _HSC and a horizontal offset DC voltage V _HOF, which are output from the scan tracking circuit 13.
Are respectively amplified and applied to the pair of vertical scanning electrodes 2A and 2B and the pair of horizontal scanning electrodes 3A and 3B. In this case, the vertical scan triangular wave voltage V _VSC ′ and the vertical offset DC voltage V _VOF ′ output from the scan amplifier 14
Is a vertical scanning voltage V _V that is added by an adder (not shown) and applied as a vertical scanning voltage V _V to the pair of vertical scanning electrodes 2A and 2B, and is output from the scanning amplifier 14.
The V _HSC ′ and the horizontal offset DC voltage V _HOF ′ are added by an adder (not shown) and applied as a horizontal scan voltage V _H to the pair of horizontal scan electrodes 3A and 3B.

By the above-mentioned four components, the vertical scanning voltage V _V and the horizontal scanning voltage V _H are basically generated, and the ion beam 1 for irradiating the target 4 can be scanned in the vertical and horizontal directions.

However, the vertical scan triangular wave voltage V _VSC , the vertical offset DC voltage V _VOF , and the horizontal direction output from the scan tracking circuit 13 to the pair of vertical scan electrodes 2A and 2B and the pair of horizontal scan electrodes 3A and 3B. The scan center and the scan width of the ion beam 1 which is reciprocally scanned in the vertical and horizontal directions are targeted only by amplifying and applying the scan triangular wave voltage V _HSC and the horizontal offset DC voltage V _{HOF as} they are in the scan amplifier 14. There is a case where the ion beam 1 does not match the position and size of the sample on the target 4, and the ion beam 1 is irradiated only on a partial region of the target on the target 4, resulting in non-uniform ion implantation.

In order to solve such a point and irradiate the entire surface of the sample with the ion beam 1, the scanning tracking circuit 13 is used so that the ion beam 1 is overscanned to the outside of the sample on the target 4 in both the vertical direction and the horizontal direction. Amplitude of vertical scan triangular wave voltage V _VSC , vertical offset DC voltage V _VOF , horizontal scan triangular wave voltage V _HSC amplitude and horizontal offset DC voltage V
_HOF needs to be adjusted.

For this adjustment, in the ion beam scanning voltage generator shown in FIG. 10, the flag current detector 15, which is a current amplifier,
An auto-threshold circuit 16 and a correction circuit 17 are provided.

Flag current detector 15 detects the flag current I _F flowing through the flag 6 which is inserted between the mask 5 and the target 4 during adjustment, flag current I flag corresponding to _F instantaneous current detection signal I _F (t) and outputs the flag average current detection signal I _F (AVE).

As shown in FIG. 12 (A), the auto-threshold circuit 16 outputs the flag instantaneous current detection signal I _F (t) output from the flag current detector 15 with a blunt rising and falling edges to the flag average current detection signal I. _The waveform is shaped into a square wave using _F (AVE) as a threshold value to form a shaping flag current detection signal I _F (t) ′ shown in FIG. 12 (B). Then, make a square wave signal F for performing this shaping flag current detection signal I _F (t) 'of the rising (or falling) rise and fall alternately (T).

The correction circuit 17 compares the lengths of the high-level period and the low-level period of the square wave signal F (T) output from the auto-threshold circuit 16, and the vertical direction output from the Tokini scanning tracking circuit 13 in which they are not equal. The scan center of the ion beam 1 is on the target 4 by potentiometer adjustment of the amplitude of the scan triangular wave voltage V _VSC , the vertical offset DC voltage V _VOF , the horizontal scan triangular wave voltage V _HSC , and the horizontal offset DC voltage V _HOF . Automatically adjust so that the sample comes to the center of the sample and the target is overscanned.

[Problems to be solved by the invention]

The ion beam scanning voltage generator described above has a flag current I _F
Is detected, and based on this flag current I _F , the triangular wave voltage V _VSC for vertical scanning and the DC voltage V for vertical offset
_VOF , horizontal scan triangular wave voltage V _HSC , and horizontal offset DC voltage V _HOF are optimally automatically adjusted, and a flag 6 must be inserted between the mask 5 and the target 4 during this adjustment. , As a result, target 4
Ion implantation into the above sample must be interrupted, which causes a problem of time loss in the implantation operation.

The scan center and the scan width of the ion beam 1 may be deviated during the ion implantation operation, and it is necessary to readjust periodically or irregularly, and the above time loss becomes a serious problem in increasing the operating rate.

An object of the present invention is to provide an ion beam scanning voltage generator capable of automatically and optimally adjusting the scan center and scan width of an ion beam without interrupting the ion implantation operation.

[Means for solving problems]

The ion beam scanning voltage generator of the present invention comprises a scanning frequency generator for generating a vertical direction square wave signal and a horizontal direction square wave signal respectively corresponding to the vertical direction scanning frequency and the horizontal direction scanning frequency, and the vertical direction square wave signal. And a scanning oscillator that generates a vertical triangular wave signal and a horizontal triangular wave signal that have the same frequency and are synchronized with the horizontal rectangular wave signal and a vertical direction based on the vertical triangular wave signal, the horizontal triangular wave signal, and the acceleration voltage of the ion beam. A scan tracking circuit for generating a scan triangular wave voltage and a vertical offset DC voltage and a horizontal scan triangular wave voltage and a horizontal offset DC voltage; and a vertical scan triangular wave voltage and a vertical offset DC voltage and a horizontal direction Triangular voltage and water for scanning A scanning amplifier that amplifies the DC voltage for direction offset and applies it to a pair of vertical scanning electrodes and a pair of horizontal scanning electrodes, a mask current detector that detects a mask current flowing through a mask, and the vertical square wave signal and Each of the vertical direction square wave signal and the horizontal direction square wave signal appearing outside the conduction time of the mask current by comparing the rising and falling timings of each of the horizontal direction square wave signals with the conduction time of the mask current. A timing comparator that generates a pulse at the rising and falling timings of, and whether the output pulse of the timing comparator is synchronized with the rising and falling edges of each of the vertical direction square wave signal and the horizontal direction square wave signal. A synchronization determiner for determining and a vertical scan according to the determination result of the synchronization determiner. And a correction circuit that selectively corrects the amplitude of the triangular wave voltage for vertical scanning, the DC voltage for vertical offset, the amplitude of the triangular wave voltage for horizontal scanning and the DC voltage for horizontal offset so as to eliminate the output pulse of the timing comparator. Is equipped with.

[Action]

According to the configuration of the present invention, the mask current flowing in the mask that shapes the scanning shape of the ion beam is detected, and the energization timing of the mask current and the rising and falling timings of the vertical square wave signal and the horizontal square wave signal are detected. With a timing comparator and generate pulses at the rising and falling timings of the vertical and horizontal square wave signals that appear outside the timing of mask current conduction from the timing comparator. The output of the output pulse is synchronized with the rising and falling edges of the vertical and horizontal square wave signals with the sync determiner, and the correction circuit scans the vertical direction according to the result of the sync determiner. Amplitude of triangular wave voltage for
Since the DC voltage for vertical offset, the amplitude of the triangular wave voltage for horizontal scan, and the DC voltage for horizontal scan are selectively corrected so as to eliminate the output pulse of the timing comparator, ion implantation to the target is performed. The scan center and scan width of the ion beam can be optimally automatically adjusted without interrupting operation,
Time loss of ion implantation for adjusting the scan center and scan width of the ion beam can be eliminated.

[Embodiment] An embodiment of the present invention will be described with reference to FIGS. 1 to 8. As shown in FIG. 1, this ion beam scanning voltage generator includes a scanning frequency generator 11, a scanning oscillator 12, a scanning tracking circuit 13, a scanning amplifier 14, a mask current detector 18 including a current amplifier, and a timing comparator 19. It is composed of a synchronism determiner 20 and a correction circuit 21.

Of these, the scanning frequency generator 11, the scanning oscillator 12, the scanning tracking circuit 13, and the scanning amplifier 14 have the same configuration as the conventional example, and detailed description thereof will be omitted. The mask current detector 18, the timing comparator 19, the synchronism determiner 20, and the correction circuit 21, which are current amplifiers, have a configuration different from that of the conventional example.

First, the mask current detector 18 consisting of a current amplifier
The mask current I _M flowing through the mask 5 is detected, and the mask current I _M is detected.
Corresponding to the mask instantaneous current detection signal I _M (t) and the mask average current detection signal I _M (AVE) are output.

The timing comparator 19 uses the mask instantaneous current detection signal I _M (t), which is output from the mask current detector 18 and has no rise or fall, as a square wave with the mask average current detection signal I _M (AVE) as a threshold value. Then, the waveform is shaped to form a shaped mask current detection signal I _M (t) ′ (the waveform shaping operation is the same as the conventional one).

Then, the timing comparator 19 is based on the vertical direction square wave signal S _V and the horizontal direction square wave signal S _H output from the scanning frequency generator 11 and the shaped mask current detection signal I _M (t) ′. , Vertical square wave signal S _V and horizontal square wave signal
'Comparing the timing of the high level period of the shaping mask current detection signal I _M (t)' S each rise and fall timing of the shaping mask current detection signal _H I _M (t) of the high-level period of Pulses are generated at the rising and falling timings of the vertical direction square wave signal S _V and the horizontal direction square wave signal S _H that appear out of timing. In addition,
The timing comparator 19 can be easily constructed by combining gate circuits.

FIG. 2 shows the waveform of each part when the scan center and scan width of the ion beam are optimally adjusted. (A) is a horizontal square wave signal S _H , (B) is a vertical square wave signal.
S _V , (C) are shaped mask current detection signals I _M (t) ′, (D)
Is the output signal F (P) of the timing comparator 19. Second
As can be seen from the figure, when the scan center of the ion beam 1 coincides with the center of the target 4 and the scan width is set to overscan the target 4, the vertical square wave signal S _V and the horizontal square wave signal When the S _H rises and falls, the ion beam 1 always hits the mask 5 and the shaped mask current detection signal I _M (t) ′ becomes high level, and the shaped mask current detection signal I _M (t) ′ becomes high level. The rising edge and the falling edge of each of the vertical direction square wave signal S _V and the horizontal direction square wave signal S _H do not appear outside the period, and the output signal F of the timing comparator 19 is output.
(P) remains low.

FIG. 3 shows the waveform of each part when the horizontal scan width is insufficient, and (A), (B), (C) and (D) are shown in FIGS. 2 (A), (B) and ( Waveforms of the same portions as C) and (D) are shown. As is clear from FIG. 3, when the horizontal scan width is insufficient, the shaping mask current detection signal I _M (t) ′ is generated at both the rising and falling timings of the horizontal square wave signal S _H. The output signal F (P) of the timing comparator 19 does not become high level, and the horizontal direction square wave signal
Pulses are generated at the rising and falling timings of S _H.

In this case, in order to adjust to the state of FIG. 2, the horizontal scanning triangular wave voltage V _HSC may be increased.

FIG. 4 shows the waveform of each part when the scan center is shifted to the right, and (A), (B), (C), and (D) are the second.
Waveforms of the same parts as in each of FIGS. As is apparent from FIG. 4, when the scan center is shifted to the right, the shaping mask current detection signal I _M (t) ′ does not become high level at the rising timing of the horizontal square wave signal S _H , Output signal F of timing comparator 19
(P) would pulse occurs on the rising edge of the horizontal square wave signal S _H.

In this case, in order to adjust to the state shown in FIG. 2, the horizontal offset DC voltage V _HOF may be reduced.

FIG. 5 shows the waveform of each part when the scan center is shifted to the left, and (A), (B), (C), and (D) are the second.
Waveforms of the same parts as in the figures (A), (B), (C), and (D) are shown. As is apparent from FIG. 5, when the scan center is shifted to the left, the shaping mask current detection signal I _M (t) ′ does not become high level at the falling timing of the horizontal square wave signal S _H. , The output signal F of the timing comparator 19
(P) would pulse occurs at the timing of falling of the horizontal square wave signal S _H.

In this case, in order to adjust to the state of FIG. 2, the horizontal offset DC voltage V _HOF may be increased.

FIG. 6 shows the waveform of each part when the scan width in the vertical direction is insufficient, and (A), (B), (C), and (D) show FIGS. 2 (A), (B), ( Waveforms of the same portions as C) and (D) are shown. As is apparent from FIG. 6, when the scan width in the vertical direction is insufficient, the shaping mask current detection signal I _M (t) ′ is generated at both the rising and falling timings of the vertical square wave signal S _V. The output signal F (P) of the timing comparator 19 does not become high level, and the vertical direction square wave signal
Pulses will be generated at the rising and falling timings of S _V.

In this case, the vertical scanning triangular wave voltage V _VSC may be increased to adjust to the state shown in FIG.

FIG. 7 shows the waveform of each part when the scan center is shifted upward, and (A), (B), (C), and (D) are the second.
Waveforms of the same parts as in the figures (A), (B), (C), and (D) are shown. As is apparent from FIG. 7, when the scan center is deviated in the upward direction, the shaping mask current detection signal I _M (t) ′ does not become high level at the rising timing of the vertical direction square wave signal S _V , Output signal F of timing comparator 19
In (P), a pulse is generated at the rising timing of the vertical direction square wave signal S _V.

In this case, in order to adjust to the state shown in FIG. 2, the vertical offset DC voltage V _HOF may be decreased.

FIG. 8 shows the waveform of each part when the scan center is shifted downward, and (A), (B), (C), and (D) are the second.
Waveforms of the same parts as in each of FIGS. As is apparent from FIG. 8, when the scan center is shifted downward, the shaping mask current detection signal I _M (t) ′ does not become high level at the falling timing of the vertical direction square wave signal S _V. , The output signal F of the timing comparator 19
In (P), a pulse is generated at the falling timing of the vertical direction square wave signal S _V.

In this case, in order to adjust to the state shown in FIG. 2, the vertical offset DC voltage V _HOF may be increased.

The synchronization determiner 20 outputs the output signal F of the timing comparator 19.
It is determined whether or not the pulse in (P) is synchronized with the rising and falling edges of the vertical direction square wave signal S _V and the horizontal direction square wave signal S _H. In this case, in the state of FIG. 2, it is determined that the vertical direction square wave signal S _V and the horizontal direction square wave signal S _V are not synchronized with the rising or falling of each. In the state shown in FIG. 3, the horizontal square wave signal S _H
Rising and in synchronization with the falling and the determination by the, in the state of FIG. 4, determines that synchronization with the rising edge of the horizontal square wave signal S _H, in the state of FIG. 5 the horizontal square wave signal Judged as being in sync with the falling edge of S _H. In the state shown in FIG. 6, it is determined that the vertical direction square wave signal S _V is synchronized with the rising and falling edges, and in the state shown in FIG. 7, it is determined that the vertical direction square wave signal S _V is synchronized with the rising edge. Judge,
In the state of FIG. 8, it is determined that the vertical square wave signal S _V is synchronized with the falling edge. The synchronization determiner 20 can also be configured by combining gate circuits.

The correction circuit 21 _adjusts the amplitude of the vertical scan triangular wave voltage V _VSC , the vertical offset DC voltage V _VOF , and the horizontal scan triangular wave voltage V according to the determination result X of the synchronization determiner 20.
The amplitude of the _HSC and the horizontal offset DC voltage V _HOF are selectively corrected so that the pulse in the output signal F (P) of the timing comparator 19 disappears. This correction is performed by potentiometer adjustment or the like. The specific voltage to be adjusted is as described in the description of FIGS. 3 to 8. This adjustment is performed by the synchronization determination unit 20 every time the potentiometer setting value is moved by a predetermined amount by a servomotor or the like.
The judgment result X is taken in, and when it is found from the judgment result X that the pulse in the output signal F (P) of the timing comparator 19 has disappeared, the servomotor etc. is stopped to stop changing the potentiometer setting value. It is completed by doing.

Adjustment of the scan center and the scan width of the ion beam 1 in this ion beam scanning voltage generator is performed before the ion implantation and also during the ion implantation.
It is held regularly, regularly or irregularly.

This ion beam scanning voltage generator uses an ion beam 1
Of the masking current I _M flowing through the mask 5 for shaping the scanning shape of, the timing of the high level period of the shaping mask current detection signal I _M (t) ′, the vertical direction square wave signal S _V and the horizontal direction square wave signal S _The timing comparator 19 compares the rising and falling timings of _H , and the timing comparator 19 causes a vertical square wave signal that appears outside the timing of the high level period of the shaped mask current detection signal I _M (t) ′. It generates pulses at the rising and falling timing of each of the S _V and horizontal square wave signal S _H, the respective output pulses and vertical square wave signal S _V and horizontal square wave signal S _H of the timing comparator rising and falling and the presence or absence of synchronization is determined by the synchronization determiner 20, the synchronization judgment unit 20 of the determination result amplitude of vertical scanning triangular wave voltage V _VSC in response to the correction circuit 21, the vertical offset Use the DC voltage V _VOF, since so as to selectively correct the amplitude and the DC voltage V _HOF for horizontal scanning of the horizontal scanning triangular wave voltage V _HSC to extinguish the output pulses of the timing comparator 19,
The scan center and scan width of the ion beam 1 can be optimally automatically adjusted without interrupting the ion implantation operation to the target 4, and the ion implantation time loss for adjusting the scan center and scan width of the ion beam 1 can be reduced. It can be eliminated, and ion implantation can be performed efficiently. This is particularly advantageous when it is necessary to readjust the scan center and the scan width of the ion beam 1 at all times during ion implantation, regularly or irregularly.

[Effect of device]

According to the ion beam scanning voltage generator of the present invention, the mask current flowing through the mask for shaping the scanning shape of the ion beam is detected, and the energization timing of the mask current and the rising edges of the vertical and horizontal square wave signals are detected. Compare the fall timing with the timing comparator,
Pulses are generated at the rising and falling timings of the vertical and horizontal square wave signals that appear outside the timing of mask current conduction from the timing comparator, and the output pulse of the timing comparator and the vertical square wave are generated. The sync determiner determines whether or not there is synchronization with the rising and falling edges of the signal and the square wave signal in the horizontal direction.
The correction circuit outputs the amplitude of the vertical scan triangular wave voltage, the vertical offset DC voltage, the horizontal scan triangular wave voltage amplitude, and the horizontal scan DC current to the output pulse of the timing comparator according to the determination result of the synchronization determiner. Since it is selectively corrected so as to disappear, the ion beam scan center and scan width can be automatically adjusted optimally without interrupting the ion implantation operation to the target. Also, it is possible to eliminate the time loss of ion implantation for adjusting the scan width.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIGS. 2 to 8 are waveform diagrams showing waveforms of respective portions when an ion beam scan center position and a scan width are optimal and improper, respectively. FIG. 9 is a schematic view of the portion from the scanning electrode to the target in the ion implantation apparatus, FIG. 10 is a block diagram showing an example of a conventional ion beam scanning voltage generator, and FIGS. 11 and 12 are respectively FIG. 3 is a waveform diagram of each part of FIG. 11 ... Scan frequency generator, 12 ... Scan oscillator, 13 ... Scan tracking circuit, 14 ... Scan amplifier, 18 ... Mask current detector, 19 ... Timing comparator, 20 ... Sync decision unit, 21 ... Correction circuit

Claims (1)

[Scope of utility model registration request] 1. A scanning frequency generator for generating a vertical direction square wave signal and a horizontal direction square wave signal respectively corresponding to the vertical direction scanning frequency and the horizontal direction scanning frequency, and the vertical direction square wave signal and the horizontal direction square wave signal. A scanning oscillator for generating a vertical triangular wave signal and a horizontal triangular wave signal which have the same frequency as each other and are synchronized with each other, and a vertical scanning triangular wave voltage and a vertical scanning voltage from the vertical triangular wave signal and the horizontal triangular wave signal and the acceleration voltage of the ion beam A scan tracking circuit for generating a directional offset DC voltage, a horizontal scan triangular wave voltage, and a horizontal offset DC voltage; and a vertical scan triangular wave voltage, a vertical offset DC voltage, a horizontal scan triangular wave voltage, and a horizontal DC voltage for direction offset A scanning amplifier that amplifies and applies to a pair of vertical scanning electrodes and a pair of horizontal scanning electrodes, a mask current detector that detects a mask current flowing in a mask, and each of the vertical square wave signal and the horizontal square wave signal. Rising and falling timing of the mask current is compared with the rising timing of the mask current, the rising and falling timing of each of the vertical square wave signal and the horizontal square wave signal appearing outside the energization timing of the mask current. A timing comparator that generates a pulse at, a synchronization determiner that determines whether or not the output pulse of the timing comparator and the rising and falling edges of each of the vertical direction square wave signal and the horizontal direction square wave signal are synchronized, Amplitude of the vertical scanning triangular wave voltage, vertical direction Ion beam scanning voltage generator provided with offset DC voltage, horizontal scanning triangular wave voltage amplitude, and horizontal offset DC voltage so as to selectively correct the output pulse of the timing comparator. .