JPH1064470A - Scanning device for ion-implanting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evenly implant the dopant into a wafer in a scanning device for ion-implanting device for scanning the ion beam to be implanted in a semi-conductor wafer in parallel with each other in a constant direction and formed of two pairs of deflecting electrodes by using a U-shaped electrode for at least the second deflecting electrode. SOLUTION: This device is formed by combining a first deflecting electrode, which is provided along the ion beam and in which two parallel electrodes are provided opposite to each other so as to generate the alternating electric field, and a second deflecting electrode, which is provided in rear of the first deflecting electrode 1 along the ion beam and in which two parallel electrodes are provided opposite to each other, so as to apply the alternating electric field in the direction opposite to the electric field of the first deflecting electrode. In this device, parallel electrodes of at least second deflecting electrode are formed into a U-shaped electrode, of which end in parallel with the beam is bent inside, so as to even the distribution of the electric field in the vertical direction of the electrode. Consequently, the distribution of ion beam in a space at the time of incidence of a sample is evened, so as to form a 90-degree angle of incidence.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a scanning device of an ion implantation apparatus in a semiconductor manufacturing process. An ion implantation apparatus is an apparatus for implanting accelerated ion beams into a sample such as a semiconductor wafer. Ion source, mass separator,
Includes acceleration tube, scanning mechanism, etc.

[0002] An ion source excites a raw material gas by high frequency, microwave, DC electric field discharge or the like to produce plasma, and extracts it as a beam by the action of an electric field. The beam contains various ions as well as the desired ions. Therefore, the beam is bent by the magnet and only ions having a desired mass are selected. This is the mass separator. The accelerator tube accelerates ions to a desired energy. The scanning mechanism scans a thin ion beam one-dimensionally or two-dimensionally and implants the ion beam over the entire surface of a wide wafer. The invention relates to an improvement of this scanning device.

[0003]

2. Description of the Related Art There are two types of scanning devices, those using a magnetic field and those using an electric field. Scanning is to change the electric or magnetic field periodically to oscillate the beam path left and right. Scanning can be performed with only one bend. However, this implies that the beam incident at the edge of the sample is inclined with respect to the plane. It is strongly desired that the injection density be uniform in the plane. Accordingly, there has been an increasing number of devices that bend a beam once by the same angle but in the opposite direction so that the beam always enters the sample surface at a right angle. Then, two sets of beam deflectors are required, whether magnets or electrodes.

The present invention relates to an apparatus for scanning an ion beam using an electric field. Conventionally, parallel scanning of an ion beam has been performed using a simple parallel plate electrode. When a voltage is applied between the parallel plate electrodes, a substantially uniform electric field is formed therebetween. The electric field oscillates sinusoidally. Thereby, the beam can be uniformly oscillated between the electrodes. A periodically changing voltage is applied to the first set of parallel plate electrodes to oscillate the beam left and right. The next parallel plate electrode applies the opposite voltage synchronously and bends the beam to the opposite side. Thus, the beam is always perpendicular to the surface.

[0005]

However, a uniform electric field cannot be formed by the parallel plate electrodes. The distribution of the electric field and the lines of electric force differ between the center and the end. For this reason, the Coulomb force acting on the ions is different between the center and the end. Therefore, the amount of deflection of the ion beam is not uniform.

This will be described more specifically. When the parallel scanning of the ion beam is performed with two sets of parallel plate electrodes, the lines of electric force formed between the parallel plate electrodes are as shown in FIG. In the center, they are distributed almost in parallel. However, lines of electric force swell outward at both ends of the electrode. The lines of electric force are shaped like a drum.
This is because the lower the density of the lines of electric force at the end, the lower the Maxwell stress. Since the density of the electric flux lines cannot be reduced at the center, the density is reduced only at the ends. Therefore, the electric field becomes weak near the end. At this time, the equipotential lines are as shown in FIG. Since the equipotential surface is orthogonal to the lines of electric force, the distribution becomes like a concave lens.

[0007] The ion beam is widely incident from the center to the end. This bends in the direction of the line of electric force under the force of the electric field. However, the direction and strength of the lines of electric force differ depending on the part close to the electrode and the part far from the electrode. Therefore, the scanning speed differs between the end and the center. Since the ion beam passes between the electrodes, the bending of the beam is proportional to the sum of the Coulomb forces received during the passage time, that is, the impulse. However, since the impulse differs depending on the path that passes, the scanning speed is not proportional to the electric field. A description will be given taking a coordinate system.

The direction of the ion beam is set to the Z axis, the direction orthogonal to the electrode surface is set to the X axis, and the electrode surface is set to the YZ plane. The length of the electrode in the Z direction is W, the length in the Y direction is H, and the electrode interval is B
And The voltage applied between the electrodes can be represented by a sine wave Vsinωt. The electric field at the center is (V /
B) sinωt. At that time, the electric field becomes uniform. However, this is not the case near the electrode plate (near x = ± B). In the vicinity of the electrode, the lines of electric force are not uniform in the X-axis direction. That is, the electric field strength is not uniform. Then, the scanning amount differs.

Therefore, the deflection angle of the ion beam passing through the center portion and the ion beam passing near the electrode are different.
It would be fine if there was only one set of deflection electrodes, but a new problem arises because two sets are used. I will explain why it is necessary to use two sets of deflection electrodes.

[0010] The beam does not enter the sample at right angles if the beam is swung right and left only once. It shifts from the right angle by the angle you shake. When the uniformity of ion beam incidence is strictly required, it is required to be incident in a direction perpendicular to the plane. Then, the beam once swung by the angle Θ needs to be swung again by the same angle − 同 じ in the opposite direction. For that purpose, another electrode is provided. Now shake the same amount in the opposite direction.

Then, the beam always enters the sample surface at right angles. The first electrode is called a first deflection electrode, and the next electrode is called a second deflection electrode. FIG. 4 shows two such sets of electrodes. The first deflection electrode 1, the second deflection electrode 2, and the target 3 are arranged along the beam line. An ion beam emitted from an ion source (not shown) travels in the Z-axis direction. The beam enters the center of the first deflection electrode 1 and is scanned right and left (X direction) under the force of Vsinωt.

This enters the second deflection electrode and has the opposite force -Us
in (ωt-τ). V and U are the electric field amplitudes in the X direction of the first deflection electrode and the second deflection electrode. τ is a delay time required for the beam to reach the center of the first deflection electrode from the center of the second deflection electrode. The electrode interval B is wider in the second deflection electrode 2 than in the first deflection electrode 1. This is natural. This is because the beam already swung right and left (X direction) comes. The length W also increases. Distance B between electrodes
Although the width is large, the same impulse as that of the first electrode must be given, so that the length W (Z direction) of the electrode also increases.

Since the beam emitted from the ion source is thin and enters the center of the first deflection electrode, there is no problem. However, when entering the second deflecting electrode, it is at the end (swaying in the X direction) from the beginning.
Therefore, the influence of the non-uniform electric field formed by the parallel plate electrodes appears strongly. But be careful. In FIG. 2, since the beam passing near the electrode and the beam passing through the central portion pass through the entire length between the electrode plates in the Z direction, the time required to pass the portion where the electric flux lines are not disturbed is the longest. The time required to pass through z = ± W / 2 where there is disturbance in the lines of electric force is short.

[0014] Because of the two effects of electric field non-uniformity at the second electrode, the beam position when entering the target (sample) deviates from sinωt. In addition, the incident angle is different between the end and the center. When the beam is scanned very close to the electrode (x = ± B / 2), the deflection at the second deflection electrode tends to be excessive. That is, the beam bends inward. In this case, the ion beam cannot be uniformly implanted in the sample (target) surface. This is intuitively understood by FIG. When passing through x = 0 in the Z direction, a slightly weak electric field is felt, but x = ± B
In the vicinity of / 2, a stronger electric field is felt. That person of the electric field E ₀ of x = 0 near, the electric field E ₁ in the vicinity of x = ± B / 2
Slightly smaller than. E ₀ <E ₁ . Due to such a mismatch, the ion beam passing through the periphery is over-polarized.

The demand for the uniformity of the ion beam implantation amount is severe, and it is desired that the fluctuation in the plane be 0.5% or less. Then, the conventional scanning device in which the parallel plate electrodes are arranged in two sets of ion beam paths cannot satisfy the requirement.

[0016]

A deflection electrode for parallel scanning of an ion beam is formed in a U-shape (see FIG. 1). By doing so, the electric flux lines can be corrected as shown in FIG. However, FIG. 2 is a sectional view of the XZ plane, and FIG.
Is a sectional view of the XY plane. The cut surface is different. However, since the electrodes are parallel plate electrodes, the distribution of electric lines of force is the same on the XY plane as in FIG.

In the case of FIG. 2, the lines of electric force have a convex lens type which swells at the center, whereas a U-shaped electrode has a concave lens type which is depressed at the center. The electric field E ₀ applied to the ion beam traveling along the line of x = 0 is strengthened. Peripheral x = ± B /
Electric field E ₁ that the beam passes close to 2 feel is relatively weak. Therefore, E ₀ = E ₁ . Since the excessive deflection at the periphery is corrected, the problem of over-deflection of the peripheral beam as shown in FIG. 4 can be solved.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a U-shaped electrode as shown in FIG. 1 is used as at least a second deflection electrode. The electric fields and equipotential lines on the XY plane when the U-shaped electrode is used are as shown in FIGS. 5 and 6, respectively. The electrodes have sleeves L at both ends. As shown in FIG. 5, since the lines of electric force intersect perpendicularly with the sleeve L, the distribution has a concave lens shape narrow inside. The ion beam sways right and left (X direction) on a line drawn in the center (y = 0). The electric field E ₀ near the center is strengthened. The same can be understood from the change in the distribution of the equipotential surfaces in FIG. Since both sleeves L raise the equipotential surface on both sides, the electric field E near x = ± B / 2 on the line at y = 0 decreases. That is, the beam is scanned along the line of y = 0, and E is uniform in the line. E ₀ = E ₁ .

The beam passing through the vicinity of the electrode is prevented from being over-deflected, so that the beam can be simultaneously vertically incident on the sample. FIG.
In the U-shaped electrodes, the dimensions of both sleeves L as long 0.05 or more electrode spacing B, the effect of enhancing the electric field E ₀ of the central portion. 0.1 or more is more effective. Of course, it cannot exceed 0.5. It can be E ₀ = E ₁ at about 0.2 to 0.4.

In FIG. 4, the length of the first deflection electrode in the longitudinal direction is g, the electric field is F, the electron mass is m, the velocity of the ion beam in the X direction is u, and the velocity in the Z direction is w (constant). )
And It is assumed that the electric field E is felt only by the length g. The equation of motion at the first deflection electrode is

Mdu / dt = Fe (1) wdt = dz (2)

(2) is an equation for changing the independent variable from t to z using the fact that the velocity in the Z direction is constant. By solving this, the deviation and inclination of the beam at the end of the first deflection electrode can be determined. By extending this, the beam deviation x ₀ and the inclination dx / dz at the start end of the second deflection electrode are determined.

X ₀ = FegS / 2mw ² (3) dx / dz = Feg / mw ² (4)

## EQU1 ## A coordinate system is set in the middle of the entrance of the second deflection electrode. The electric field of the second deflection electrode is E. Assuming that the electric field holds a constant value at the length W and the electric field is sensed only during that time, the equation of motion at the second deflection electrode is

Mdu / dt = Ee (5) wdt = dz (6)

[0026] In solving this, dx / dz = (eFg / mw 2) - (eEz / mw 2) (7) x = (eFgz / mw 2) - (eEz 2 / 2mw 2) + (eFgS / 2mw 2 ) (8)

## EQU1 ## The point where the beam becomes parallel to the axial direction is where equation (7) becomes zero. Z at this time is z = Fg / E (9)

Is as follows. The electric field E of the first deflection electrode is spatially constant (although it varies with time). But second
The electric field E of the deflection electrode is not spatially uniform. This is because the beam incident point is different. The value E ₀ near the center of x = 0 is small, and the value E ₁ near the electrode where x = ± B / 2 is large. Then, the value of z at which the beam becomes parallel to the axis is large at the center and small near the electrode. If the length W of the second deflection electrode is determined so that the beam is parallel to the axis at the center,

W = Fg / E ₀ (10)

## EQU1 ## This length is too long for a beam passing near the electrodes. The beam near the electrode is already bent inward. This is the cause of over-deflection. Over-deflection does not just make the beam non-parallel. Non-uniform beam density at the sample entrance surface. If the electric field of the second deflection electrode is uniform, the value of x at z = W is W = Fg
/ E into (8),

X = (eFg / 2Mw ² ) {S + (Fg / E)} (11)

## EQU1 ## If the electric field of the second deflection electrode is spatially uniform, E → Esinωt, F → Fsinω
What replaces t is an expression that gives a time change. this is,

X = (eFg / 2Mw ² ) ｛S + (Fg / E)｝ sinωt (12)

And always a parallel beam (dx / dz = 0)
It is. It is possible to enter the sample while maintaining the same density. Ion beams having a uniform distribution are implanted on the sample surface. However, E is not spatially uniform, and becomes strongly deflected near the electrode. The relationship between the variation of the deviation of the incident angle Φ from 90 ° on the sample surface and the non-uniformity of the incident beam can be evaluated by the following equation.

TdΦ / dx (13)

T is the distance between the second deflection electrode and the sample. In the present invention, since the bent portions L are formed on both sides of the electrode plate of the second deflecting electrode, the electric lines of force are narrowed in the vicinity of y = ± H / 2 and are drawn toward x → 0. E near
Can be reduced. That is, δE / δx
= 0 (y = 0). Then, the beam on the plane of z = W is always parallel to the Z axis. Then, the change of the incident point on the sample surface is given by (12). Since the fluctuation is exactly the same as the scanning function sinωt, the incident beam density becomes uniform.

[0037]

EXAMPLE The U-shaped electrode as shown in FIG. 1 was used as the second deflection electrode in FIG. Then, the electric field intensity at the central portion increases, and the intensity at the peripheral portion relatively decreases, so that the problem of over-deflection is corrected. A more uniform deflection can be achieved. According to the present invention, in an ion beam scanning apparatus in which two sets of deflection electrodes are combined, an electric field distribution is made uniform in a direction perpendicular to the electrodes by using a U-shaped electrode as a second deflection electrode. The spatial distribution of the beam is uniform and the angle of incidence is aligned with 90 °. The dopant can be uniformly implanted into the wafer. Accurate impurity implantation can be performed. Of course, the first deflection electrode can also be a U-shaped electrode.

FIG. 7 is a graph showing the result of measuring the deviation from 90 ° of the beam injection angle on the sample surface in the wafer plane when beam scanning is performed by a conventional scanning device using parallel plate electrodes. is there. P ⁺ ions are accelerated to 50 keV and deflected by two sets of deflection electrodes. The wafer is an 8-inch wafer having a diameter of 200 mm. The horizontal axis is the point from one end along the diameter parallel to the X axis of the wafer to the other end via the center. The vertical axis represents the deviation of the incident angle of the beam from 90 °. One angle scale is 0.2 °.

There are two curves, which indicate that the beam
This is due to the different route when going back and forth between. Although a sinusoidal voltage sinωt is applied to the electrodes, it does not seem to always be at the same angle in going and returning. On the way, the beam swings from -0.2 ° to + 0.2 °. The return beam swings from -0.3 ° to + 0.1 °. The vertical swing is about 0.4 °. This is only a small angle fluctuation depending on the viewpoint. However, the required level may be more severe, and the deviation from 90 ° may be required to be 0.2 ° or 0.1 ° or less.

The conventional parallel plate electrode cannot meet such severe conditions. This is the beam parallelism (9
(A deviation from 0 °), the deviation from the parallelism has a direct relationship with the disturbance of the beam distribution, so it can be considered that this represents the fluctuation of the beam distribution. Since the beam incident density fluctuation is difficult to measure, the angle fluctuation is measured here.

FIG. 8 shows a measurement result of an in-plane distribution along a diameter parallel to the X-axis of a deviation angle from 90 ° of the incident angle on the wafer when the U-shaped electrode according to the embodiment of the present invention is used. FIG. In the dimensions of FIG. 1, L: B = 0.3:
It is one. Again, the path of the beam is slightly different for going and returning. There is a negative deviation from 90 °. This falls within the range of -0.1 ° to -0.2 ° within the wafer plane. The deflection angle is only -0.1 ° at the maximum.
Although it is shifted from 90 ° as a whole, it is not a problem. It suffices if the angle fluctuation in the plane is small.

FIG. 9 shows that the beam energy is 30 keV or more.
The result of the fluctuation measurement of the incident beam angle on the sample surface when changing in the range of 130 keV is shown. This is obtained by subtracting the minimum value from the maximum value of the deviation angle from 90 °. This is not the standard deviation σ.

The black points indicate the second deflection electrodes formed as parallel plate electrodes. This time, the maximum value-minimum value is obtained not at the measurement point of 200 mm as described above but over the full range of the horizontal axis in FIGS. The range is about 300 mm.

In the case of a parallel plate electrode, the maximum in-plane angular deviation of the beam accelerated to 130 keV is 0.36 °. In the case of the U-shaped electrode of the present invention, the angle is 0.18 °. It has been reduced by about half. It can be clearly seen that the U-shaped electrode has an excellent effect particularly as the second deflection electrode. Even when accelerating to 50 keV, the maximum and minimum angle difference between the parallel plate electrodes is 0.49.
{Circle around (2)}, in the present invention, it is sufficiently reduced to 0.26%.

This is the result of measuring the maximum value-minimum value. The standard deviation is smaller. 0 in the range of 300 mm.
It is about 1 ゜. This can sufficiently respond to the strict requirements of the current semiconductor production technology.

[0046]

According to the present invention, in an ion beam scanning apparatus in which two sets of deflection electrodes are combined, in particular, the electric field distribution is made uniform in the vertical direction by using a U-shaped electrode as the second deflection electrode. The spatial distribution of the ion beam at the time of incidence on the sample becomes uniform, and the incidence angle becomes 90 °. Wafer
Can be uniformly implanted. Accurate impurity implantation can be performed.

The fluctuation of the incident beam density is a more serious problem than the fluctuation of the angle. Here, angle fluctuation is measured instead of density fluctuation. Both are strongly correlated,
If the angle fluctuation is large, the density fluctuation also becomes large,
The latter can be evaluated by the former.

By comparing the results, it can be confirmed that the present invention can obtain a remarkable effect on the improvement of the beam parallelism.
That is, the beam incident density is also uniform. In an 8-inch wafer, the in-plane fluctuation of the beam incident angle can be made 0.1 ° or less. Density fluctuation can be reduced to 0.5% or less. This is an excellent invention.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a U-shaped electrode proposed by the present invention cut along a plane perpendicular to the axial direction.

FIG. 2 is an explanatory diagram illustrating lines of electric force by a parallel plate electrode according to a conventional example.

FIG. 3 is an explanatory diagram illustrating an equipotential surface by a parallel plate electrode according to a conventional example.

FIG. 4 is a schematic diagram of a scanning device including two deflection electrodes for horizontal scanning in an ion implantation device.

FIG. 5 is a schematic cross-sectional view showing distribution of lines of electric force formed by U-shaped electrodes.

FIG. 6 is a schematic cross-sectional view showing a distribution of equipotential surfaces formed by U-shaped electrodes.

FIG. 7 is a graph showing an in-plane distribution of an incident angle when an ion beam scanned by a parallel scanning apparatus according to a conventional example in which two parallel plate electrodes are combined is incident on the wafer.

FIG. 8 is a graph showing an in-plane distribution of an incident angle when an ion beam scanned by a parallel scanning device according to an embodiment of the present invention, which is a combination of two U-shaped electrodes, is incident on the wafer.

FIG. 9 shows a conventional example in which the second deflection electrode is a parallel plate electrode,
FIG. 7 is a graph showing a measurement result on a relationship between beam energy and a variation of a sample incident angle from 90 ° in the present invention having a parallel U-shaped electrode. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st deflection electrode 2 2nd deflection electrode 3 Target (sample)

Claims (1)

[Claims] An apparatus for scanning an ion beam implanted into a semiconductor wafer in parallel in a predetermined direction, wherein a first electrode is provided to face two parallel electrodes provided along the ion beam to generate an alternating electric field. An electrode and a second deflecting electrode provided behind the first deflecting electrode along the ion beam so as to oppose two parallel electrodes and apply an alternating electric field in a direction opposite to the electric field of the first deflecting electrode. A scanning device for an ion implantation apparatus, wherein the parallel electrodes of the two deflection electrodes are U-shaped electrodes whose ends parallel to the beam are bent inward.