JP3358235B2 - Scanning voltage waveform shaping method of ion beam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an ion implantation apparatus of a type in which an ion beam is electrically parallel scanned (parallel scan) to implant an ion into a target. The present invention relates to an ion beam scanning voltage waveform shaping method capable of improving the implantation uniformity by correcting the scanning speed of an ion beam.

[0002]

2. Description of the Related Art A scanning voltage waveform shaping method for an ion beam, which is capable of improving the uniformity of implantation by making the scanning speed of the ion beam on a target constant, has been previously proposed by the same applicant. (Japanese Unexamined Patent Application Publication No.
No. -22900). The main points are described below.

FIG. 8 is a schematic diagram showing an example in which a configuration for implementing a conventional scanning voltage waveform shaping method is added to a parallel scan type ion implantation apparatus.

[0004] Two sets of scanning electrodes 4 and 6 for electrostatically scanning the spot-like ion beam 2 are provided on the upstream side of a target (eg, a wafer) 10 to be subjected to ion implantation. Are applied from the common scanning power supply 8 so that the scanning voltages V ₁ and V ₂ are 180 degrees out of phase with each other.

The target 10 is a target driving device 1
6 mechanically scans the ion beam 2 in a direction substantially perpendicular to the direction in which the ion beam 2 is scanned (in this example, the front and back sides of the paper).

A scanning power supply 8 generates an arbitrary waveform generator that generates a scanning signal having a waveform corresponding to the scanning voltage waveform data based on scanning voltage waveform data externally supplied (in this example, from an arithmetic processing unit 20 described later). 81 and a high-voltage amplifier 82 that boosts a scanning signal therefrom and outputs scanning voltages V ₁ and V ₂ having phases different from each other by 180 degrees.
And 83 are provided.

Further, first and second multipoint beam monitors 12 and 14 are arranged on the upstream side and the downstream side in the beam traveling direction (Z direction) of the injection position with respect to the target 10, respectively. Each multi-point beam monitor 12, 14
Consists of a plurality of beam current measurement arrays whose positions are known in advance in this example.

The change over time of the beam current I measured by each of the multipoint beam monitors 12 and 14 is recorded by a data logger 18 and used as data for waveform shaping by an arithmetic processing unit 20.

The ion beam 2 incident on the scanning electrode 4 from the left in the figure is bent by an angle corresponding to the voltage applied to the scanning electrode 4, and is bent back by the same angle at the scanning electrode 6 on the downstream side. The light exits the scanning electrode 6 at substantially the same angle as when the light enters the scanning electrode 4. As a result, the target 10
And the angle of incidence on each of the multipoint beam monitors 12 and 14 is substantially constant, and the ion beam 2 displaced in the X direction according to the voltage applied to the scanning electrodes 4 and 6 can be obtained. Therefore, the scanning electrode 4,
The scanning voltages V ₁ and V ₂ applied to the target 6 are changed continuously (specifically, in a triangular wave shape), so that the target 10
In addition, the ion beam 2 can be scanned in parallel on each of the multipoint beam monitors 12 and 14.

The arithmetic processing unit 20 generates scanning voltage waveform data V (t) such that the ion implantation amount on the target 10 becomes uniform with the following logic.

First, the multi-point beam monitor 12 on the upstream side
Thus, the sampling of the ion beam 2 being scanned is
Do. An example of the waveform of the beam current I obtained by this
Is shown in FIG. The horizontal axis is the time axis, and T is one reciprocating scan.
You. The solid line in the figure indicates the channel where the multipoint beam monitor 12 is located.
(For example, X = X_f1Beam current measurement array) signal,
The dashed line indicates the inner channel (for example, X = X_f2of
Beam current measurement array), and the peak time is
At that time, the correctness of the channel on which the
This indicates that the ion beam 2 is incident on the surface.
In this manner, the position ｛X_f1, X_f2, ...,
X_fnEach channel of the multipoint beam monitor 12 for which｝ is known
When the ion beam 2 is incident on the position
Time T_f1, T _f2, ..., T_fn｝ Is obtained.

Similarly, the multipoint beam monitor 1 on the downstream side
4, the position {X _b1 , X _b2 ,..., X _bn }
The incident time of the ion beam 2 with respect to ｛T _b1 , T _b2 ,.
, T _bn } data is obtained.

Arbitrary waveform generator 81 from arithmetic processing unit 20
Is a function V (t) indicating a scanning voltage with respect to the time t. Therefore, the function V (t) and the data {T _f1 ,..., T _fn } and {T _b1,.・ ・ 、 T
from _bn}, two multipoint beam monitor 12 and 14 in (i.e. Z = Z _f and Z = Z _b position), data point sequence showing the relationship between the scanning position X of the input and the ion beam 2 of the scanning voltage V ｛(V _f1 , X _f1 ), (V _f2 , X _f2 ), ...
·, (V _fn , X _fn )} and {(V _b1 , X _b1 ),
(V _b2 , X _b2 ),..., (V _bn , X _bn )} are obtained. In short, if the time t is known, the scanning voltage V at that time is known, and if the time t is known, the scanning position at that time is known. If V is known, the scanning position X can be known.

A multi-point beam monitor 12 (Z = Z _f ) and a multi-point beam monitor 14 (Z = Z _b ) by approximating a higher-order function by, for example, the least square method using the data point sequence.
The functions X _f (V) and X _b (V) representing the relationship between the scanning voltage V and the scanning position X of the ion beam 2 are obtained. These two functions and multipoint beam monitor 12 (Z = Z _f), multipoint beam monitor 14 (Z = Z _b) and target 10 (Z
= Z _t ), a function X _t (V) representing the relationship between the scanning voltage V and the scanning position X of the ion beam 2 on the target 10 is expressed as follows.

[0015]

[Number 1] _{X t (V) = {(} Z b -Z t) X f (V) + (Z t -
_{Z f) X b (V)} } / (Z b -Z f)

The arithmetic processing unit 20 uses this equation 1 to calculate
Scanning speed dX _t of the ion beam 2 on the target 10
(V) / dt is generated such that scan voltage waveform data becomes constant. More specifically,

## EQU2 ## dX _t (V) / dt = {dX _t (V) / dV}.
Since {dV (t) / dt}, the scan voltage waveform data is generated such that the scan voltage waveform data becomes constant regardless of the scan position of the ion beam 2.

Here, when the scanning voltage V is a triangular wave,
The function X _t (V) representing the scanning position of the ion beam is usually not linear but slightly S-shaped as shown in FIG. 10, for example. This is because, when the trajectory of the ion beam 2 has a large amplitude as shown in FIG. 8, the ion beam 2 passes near the electrode having a high potential (positive potential) while passing through the scanning electrode 6 on the downstream side. The ion beam 2 is decelerated and the effect of the bending back is increased, and the ion beam 2 tends to be slightly focused toward the center, and thus dV / d
This is because, in scanning with a triangular wave having a constant t =, the scanning speed increases in the small amplitude portion and decreases in the large amplitude portion.

The derivative dX _t (V) / of this function X _t (V)
dV is shown in FIG. This represents the scanning speed with the scanning voltage V as a variable. Therefore, in this state, the amount of ions implanted into the target 10 increases toward the periphery.

In order to correct such unevenness of the scanning speed, the derivative dV (t) / dt of the scanning voltage V (t) is used.
Is, as shown in FIG. 12, the derivative dX _t (V) of FIG.
By changing the scan voltage waveform in the opposite relationship to / dV, the scan voltage waveform may be shaped so that the derivative of Equation 2, that is, the scan speed dX _t (V) / dt is kept constant.

The scanning voltage V (t) thus shaped
Is shown by a solid line F in FIG. The broken line E in the figure is the original triangular wave, whereas the solid line F has a sharper peak near its peak. Such waveform is in this example made in the processing unit 20, which is given to the arbitrary waveform generator 81, the scanning voltage V _1, V ₂ is made. As described above, both scan voltages V ₁ and V ₂ are obtained by amplifying the same scan voltage waveform data so that the phases are different by 180 degrees. If the scanning of the ion beam 2 is performed with such scanning voltages V ₁ and V ₂ , the ion beam 2
Of the target 10 even if there is non-uniformity of the
Since the scanning speed of the ion beam 2 above becomes constant, the uniformity of the implantation amount in the plane of the target 10 can be improved.

[0021]

However, the above-mentioned scanning voltage waveform shaping method focuses on the target 10.
The above is only the scanning speed of the ion beam, and it is assumed that the spot size of the ion beam 2 does not change with respect to the scanning position. However, actually, the spot size (that is, beam current density) of the ion beam 2 may change depending on the scanning position.

The main cause is that which can be called neutral point action by electrostatic scanning.
In the Q lens for shaping the ion beam 2 on the upstream side of the scanning electrode 4, the beam focusing state may slightly change depending on the beam position. This neutral point effect will be described with reference to FIGS.

In FIG. 3, the scanning voltages V ₁ and V ₂ are both shown as triangular waves for easy understanding, but the scanning electrodes 4 and 6 to which such scanning voltages V ₁ and V ₂ are applied are shown.
When the ion beam 2 is electrostatically scanned by, for example, as shown in FIG. 4, when the ion beam 2 is at the end A or C between the scanning electrodes, the spot size is large and the ion beam 2 is at the center B between the scanning electrodes. There is a problem that the spot size sometimes becomes small.

This is because, due to the difference between the moving speeds of the ions and the electrons contained in the ion beam 2 (the ions are several thousand times heavier than the electrons and therefore hard to move), the portion (time) where the electric field is applied This is because the ions and the electrons are separated, the number of electrons contained in the ion beam 2 decreases, and the ion beam 2 diverges due to its own electric charge, thereby increasing the beam size. That is, when the ion beam 2 passes other than near the center B between the scanning electrodes 4 (or 6), some electric field is applied, so that the divergence of the ion beam 2 is large and its spot size is large. On the other hand, when the ion beam 2 passes near the center B between the scanning electrodes 4 (or 6), the pair of scanning electrodes are both at zero potential (FIG. 3).
), Electrons and ions do not separate in the ion beam 2,
Therefore, since the ion beam 2 does not easily diverge, its spot size becomes the smallest.

When the spot size of the ion beam 2 changes as described above, since the beam current of the entire ion beam 2 is constant, the beam current density is reduced when the ion beam 2 passes through the center B between the scanning electrodes. Since the injection amount increases and the injection amount increases, the beam current density decreases when passing through the ends A and C, and the injection amount decreases. If this is ignored, there is a problem that the injection uniformity to the target 10 is deteriorated.

Accordingly, the present invention provides an ion beam in which the uniformity of implantation in the target surface can be further improved by considering the beam current density distribution in the scanning direction of the ion beam as described above. The main object of the present invention is to provide a scanning voltage waveform shaping method.

[0027]

In order to achieve the above object, a scanning voltage waveform shaping method according to the present invention is directed to a movable third beam monitor which can be moved into and out of an implantation position with respect to the target, and is provided in a scanning direction of an ion beam. Which is capable of measuring the beam current density distribution of the target, thereby obtaining a fourth function representing the beam current density distribution in the beam scanning direction at the injection position with respect to the target. Instead of shaping the scanning voltage waveform of the ion beam so that the product of the derivative of the voltage and the product of the voltage becomes constant regardless of the scanning position of the ion beam, the reciprocal of the fourth function representing the beam current density distribution and the third Or the product of the derivative of the function of
It is characterized in that the scanning voltage waveform of the ion beam is shaped so that a mathematically equivalent function is constant regardless of the scanning position of the ion beam.

[0028]

FIG. 1 is a schematic diagram showing an example in which a configuration for implementing a scanning voltage waveform shaping method according to the present invention is added to a parallel scan type ion implantation apparatus. Parts that are the same as or correspond to those in the conventional example of FIG. 8 are denoted by the same reference numerals, and differences from the conventional example will be mainly described below.

In this embodiment, a movable third beam monitor 22 which can be moved in and out as shown by an arrow D by a beam monitor driving device 26 is provided at the above-described injection position (that is, Z = Z _t ) with respect to the target 10. ing. However, the direction in which the beam monitor 22 is moved in and out is not essential as long as it does not interfere with the mechanical scanning of the target 10 by the target driving device 16 and is not limited to the example shown in the drawing.

The beam monitor 22 can measure the beam current density distribution in the beam scanning direction of the ion beam 2 (ie, the X direction in this example). In order to perform the measurement accurately, it is preferable that the beam current density distribution can be measured as finely as possible.

An example of such a beam monitor 22 is shown in FIG.
Shown in The beam monitor 22 has a slit in front of a single strip-shaped Faraday cup 23 long in the scanning direction of the ion beam 2 and having a width W smaller than the minimum spot size of the ion beam 2 and long in the scanning direction of the ion beam 2. 24 are provided. With such a structure, the ion beam 2 having a constant area is always provided on the Faraday cup 23.
Is incident, a beam current corresponding to the beam current density of the ion beam 2 flows through the Faraday cup 23. Since the scanning position X of the ion beam 2 is known from the above-described equation 1, the beam current density distribution in the scanning direction of the ion beam 2 is changed by the beam monitor 22 based on the scanning position and the beam current flowing through the Faraday cup 23. In this case, it can be measured continuously.

Alternatively, in addition to the beam monitor 22 shown in FIG.
Similarly to 2 and 14, a structure in which a number of small Faraday cups are arranged in parallel in the scanning direction of the ion beam 2 may be used. In this case, if the distance between the centers of the two Faraday cups is smaller than the diameter of the minimum spot size of the ion beam 2, the beam current density distribution in the scanning direction of the ion beam 2 can be measured almost continuously. it can.

The measurement of the beam current density distribution of the ion beam 2 by the beam monitor 22 is performed, for example, at the same time as the measurement by the multipoint beam monitors 12 and 14.
More specifically, the measurement may be performed following the measurement by the multipoint beam monitors 12 and 14.

When the spot size of the ion beam 2 changes as shown in FIG. 4, the beam current density J (X) of the ion beam 2 becomes as shown in FIG.
The distribution has a peak P in the vicinity. Here, J (X) is used as a fourth function representing the beam current density distribution.
/ A J ₀ is adopted. J ₀ is a reference value (for example, an average value) of the beam current density.

In this embodiment, instead of making dX _t (V) / dt shown in Expression 2 constant at each point on the injection position with respect to the target 10 as in the prior art, the following Expression 3 is used. The scanning voltage waveform data is generated so that the function represented is constant regardless of the scanning position of the ion beam 2.

[0036]

{J ₀ / J (X)} · {dX _t (V) / dV} ·
{DV (t) / dt}

Equation 3 is obtained by multiplying Equation 2 described above by the reciprocal J ₀ / J (X) of the fourth function. In order to make the function of Equation 2 constant regardless of the scanning position of the ion beam 2, as described above, the derivative dV (t) / dt of the scanning voltage V (t) is calculated as shown in FIG. Since the scanning voltage V (t) may be corrected as shown by a solid line F in FIG. 13, this equation 2 is replaced by the reciprocal J of the fourth function.
₀ / J (X) is multiplied by the function of equation (3).
Is constant regardless of the scanning position, the scanning voltage V
The derivative dV (t) / dt of (t) may be corrected from that shown in FIG. 12 to have a peak Q at a position corresponding to the peak P in FIG. 5, as shown in FIG.

The scanning voltage V (t) thus shaped
Is shown by a solid line G in FIG. A broken line E in the figure shows a triangular wave for reference. This solid line G corresponds to FIG.
The inclination of the portion R corresponding to the peaks P and Q is larger than that of the solid line F in FIG. In this example, such a waveform is generated in the arithmetic processing unit 20 described above, and this is supplied to the arbitrary waveform generator 81, and the scanning voltages V ₁ , V ₂
Is made.

When the scanning of the ion beam 2 is performed with such scanning voltages V ₁ and V ₂ , at the scanning position where the spot size of the ion beam 2 is reduced and the beam current density is increased (ie, near X = 0), Since the scanning speed of the ion beam 2 is increased, not only the implantation uniformity is reduced due to the unevenness of the bending back action of the ion beam 2, but also the ion beam 2
Therefore, it is possible to suppress the decrease in the injection uniformity due to the non-uniformity of the beam current density distribution in the scanning direction, so that the injection uniformity in the plane of the target 10 can be further improved.

[0040] Note that the number 3 and substantially equivalent functions, for example Toka it multiplied by constants, such as those in which the J ₀ and 1,
Of course, the scanning voltage waveform may be shaped so that the constant becomes constant.

The beam current density distribution of the ion beam 2 as shown in FIG. 5 is a typical example, and other distributions can of course be corrected by the above method.

[0042]

As described above, according to the present invention, in addition to the decrease in the injection uniformity due to the unevenness of the ion beam bending-back action, the uniformity of the implantation due to the unevenness of the beam current density distribution in the scanning direction of the ion beam. Therefore, it is possible to further improve the uniformity of implantation in the plane of the target.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an example in which a configuration for implementing a scanning voltage waveform shaping method according to the present invention is added to a parallel scan type ion implantation apparatus.

FIG. 2 is a front view showing an example of a beam monitor in FIG.

FIG. 3 is a diagram showing a triangular scanning voltage waveform.

FIG. 4 is a diagram schematically showing a change in spot size of an ion beam.

FIG. 5 is a diagram showing an example of a beam current density distribution of an ion beam.

FIG. 6 is a diagram showing an example of a derivative of a function representing a scanning voltage.

FIG. 7 is a diagram showing an example of a scanning voltage waveform according to the method of the present invention.

FIG. 8 is a schematic diagram showing an example in which a configuration for implementing a conventional scanning voltage waveform shaping method is added to a parallel scan type ion implantation apparatus.

FIG. 9 is a schematic diagram partially showing an example of a signal from a multipoint beam monitor.

FIG. 10 is a diagram illustrating an example of a function representing a scanning position of an ion beam.

FIG. 11 is a diagram showing an example of a derivative of a function representing a scanning position of an ion beam.

FIG. 12 is a diagram illustrating an example of a derivative of a function representing a scanning voltage.

FIG. 13 is a diagram showing an example of a scanning voltage waveform according to a conventional method.

[Explanation of symbols]

 Reference Signs List 2 ion beam 4, 6 scanning electrode 8 scanning power supply 10 target 12 first multipoint beam monitor 14 second multipoint beam monitor 18 data logger 20 arithmetic processing unit 22 third beam monitor 26 beam monitor driving device

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-301346 (JP, A) JP-A-5-89819 (JP, A) JP-A-5-89811 (JP, A) JP-A-7- 201975 (JP, A) JP-A-7-169432 (JP, A) JP-A-7-169431 (JP, A) JP-A-4-163845 (JP, A) JP-A-6-215724 (JP, A) JP-A-4-22900 (JP, A) JP-A-2-5346 (JP, A) JP-A-63-45744 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01J 37/147 C23C 14/48 H01J 37/04 H01J 37/317

Claims (1)

(57) [Claims] 1. A first and second multipoint beam monitor for measuring a beam current of an ion beam electrically parallel scanned by a scanning voltage at a plurality of points whose positions are known in advance in the scanning direction. The scan voltage and the first and second scan currents are sampled by each of the multi-point beam monitors while scanning the ion beam while being arranged on the upstream and downstream sides of the implantation position in the beam traveling direction. First and second functions representing the relationship between the scanning position of the ion beam and the scanning position of the ion beam on the multi-point beam monitor are determined, and based on the first and second functions, the scanning voltage and the implantation A third function representing the relationship with the scanning position of the ion beam is obtained, and the product of the derivative of the third function and the derivative of the function representing the scanning voltage is obtained. A movable third beam monitor which can be moved into and out of an implantation position with respect to the target in a method of shaping the scanning voltage waveform of the ion beam so that the scanning voltage waveform is constant regardless of the scanning position of the ion beam. That can measure the beam current density distribution in the target direction, thereby obtaining a fourth function representing the beam current density distribution in the beam scanning direction at the injection position with respect to the target, and calculating the derivative of the third function and Instead of shaping the scan voltage waveform of the ion beam so that the product of the scan voltage and the derivative with the derivative is constant regardless of the scan position of the ion beam, a fourth current representing the beam current density distribution is used.
The product of the reciprocal of the above function and the derivative of the third function and the derivative of the function representing the scanning voltage, or a mathematically equivalent function thereof, is constant regardless of the scanning position of the ion beam. A method of shaping a scanning voltage waveform of an ion beam.