JP3368503B2 - Ion beam irradiation apparatus and ion beam irradiation method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion beam irradiation apparatus used when implanting impurities into a semiconductor substrate, and more particularly to an ion beam deceleration mechanism essential for implanting low mass ions.

The use of ion implantation in the manufacture of semiconductor devices is commonplace today. Along with the miniaturization of elements built into integrated circuits, shallow ion implantation has been performed to form element regions. For example CM
When forming an S / D region of a p-channel transistor of OS, it is necessary to implant low-mass ions such as boron ions (B ⁺ ) at a low energy of 10 keV or less.

On the other hand, in order not to increase the resistance of the shallow S / D region, it is necessary to increase the dose amount and to implant a large amount of ions of 10 ¹⁵ cm ^-2 or more. In order to carry out such high implantation at a practical processing speed, an implantation device capable of obtaining an ion beam current of about several mA is required.

However, when the extraction voltage for ion beam generation is lowered in order to perform low energy implantation, the current decreases in proportion to the 3/2 power of the voltage. Therefore, in the above case, the extraction voltage is 10 keV or less. It is difficult to obtain an ion current of several mA.

[0005]

2. Description of the Related Art In order to meet these contradictory requirements, a high extraction voltage is used to generate a high current ion beam, which is decelerated to irradiate a wafer with low energy, and a low mass impurity is shallowly implanted. Is being done. This technique is called post-decelera
tion).

FIG. 7 is a diagram schematically illustrating the structure of a known ion beam irradiation apparatus used for post-deceleration implantation. A conventional technique will be described below with reference to this drawing.

The housing 1 which houses the entire apparatus has a ground potential, and a potential difference corresponding to a deceleration voltage is applied between the housing 1 and the terminal 2 which is an ion beam generator. An ion source 4 and an ion source power supply 3 for operating the ion source are provided inside the terminal, and ions extracted from the ion source by applying a voltage to the extraction electrode 5 are:
The mass separation unit 7 monochromates the ions having a specific mass and electric charge. Reference numeral 6 is an insulator for insulatingly holding the ion source and the mass separation unit.

The monochromatic ion beam 10 is rotated by about 90 degrees from the initial direction and emitted, and the kinetic energy is reduced by the decelerating electric field existing inside the insulator 9 between the terminal and the housing, and then rotated. Wafer 11 mounted on disk 12
Is irradiated. The rotating disk can reciprocate in the diameter direction in addition to rotating, so that the entire surface of the wafer can be irradiated with the ion beam. The slit 8 is for removing different kinds of ions having different emission directions.

By performing deceleration implantation using such an ion beam irradiation apparatus, the ion current value when shallowly implanting low-mass ions can be increased, and the processing time can be shortened. .

[0010]

However, in the above-described prior art deceleration implantation, a problem remains in the impurity distribution in the substrate. FIG. 3 is a diagram showing the effect of the present invention. In the figure, the distribution of the implanted impurities according to the present invention and the distribution of the implanted impurities according to the prior art are shown by dotted lines. The processing condition is S for suppressing the channeling on the Si single crystal substrate.
After performing i ⁺ implantation to disturb the crystallinity of the surface layer, BF ₂ ⁺
Is injected with a drawing voltage of 35 kV and a deceleration voltage of 25 kV (final injection energy is 10 keV).

From this, it is seen that although the distribution is normal in the vicinity of the depth where the maximum concentration is reached, the impurity concentration is not normally lowered in the deeper portion, and the impurity concentration in the vicinity of 10 ¹⁷ cm ^-3 or less is observed. The distribution is clearly tail-shaped.

The reason why a portion of the same element is implanted deeper than the depth determined by the implantation energy is understood as follows. Among the ions extracted from the ion source, only specific ions are deflected in the injection axis direction in the mass separation unit. At this point, particles with different masses and charges are separated and removed, but some of the monochromatic ions lose their charge due to interaction with residual gas in the range from the mass separation part to the deceleration electrode part. It becomes sexualized.

Since the neutralized particles are not decelerated by the electric field, they are irradiated onto the substrate with high energy,
It will be deeply injected. This is the reason why the implanted impurities are distributed to a position deeper than the designed value.

Therefore, it is conceivable that the decelerated ion beam is deflected by an electric field or a magnetic field to separate high-energy neutral particles. However, providing such a deflecting portion after the decelerating electrode makes it possible to separate the distance to the wafer. Will be longer. A beam composed of charged particles of the same polarity, such as an ion beam, has a tendency to disperse, and the loss due to the dispersion increases as the range increases, which is a situation inconvenient for the ion implantation process in the wafer process. In particular, the larger the current of the ion beam is, the stronger its effect is, and it is not practical to separate neutral particles by this method.

It is an object of the present invention to provide an ion beam irradiation apparatus capable of decelerating and separating and removing neutral particles without increasing loss due to dispersion even in a high current ion beam. An ion beam irradiation apparatus that decelerates and separates neutral particles in the same region.

[0016]

In order to achieve the above object, the ion beam irradiation apparatus of the present invention has a structure in which the equipotential surface of the ion beam decelerating electric field is inclined with respect to the incident axis of the ion beam. Further, as a mode for realizing the inclination of the equipotential surface, a deceleration electrode portion is constituted by a plurality of electrode plates having different potentials, and any one of the following forms is used alone or in combination.

The center axis of the decelerating electric field is arranged in parallel with the ion beam incident axis with a space, and the fact that the curve of the equipotential surface of the decelerating electric field effectively acts as the inclination of the potential surface is utilized.

It is assumed that the center axis of the deceleration electric field is tilted with respect to the ion beam incident axis, and the equipotential surface of the deceleration electric field is tilted. The electrode plates that form the deceleration electric field are arranged radially around an imaginary axis orthogonal to the incident axis to realize a tilted equipotential surface.

[0019]

2 is a diagram for explaining the principle of ion beam deflection used in the present invention. Here, first, a situation in which the deceleration and the deflection of the ion beam are simultaneously performed by the electric field having the inclined equipotential surface will be described with reference to FIG.

It is assumed that the ion beam travels from the left side of the drawing to the right side and to the right side, and the normal line direction of the decelerating electric field equipotential surface is deviated from the normal to the upper left direction with respect to the ion beam incident axis. Since the acting direction of the force exerted on the charged particles in the electric field is the direction of the normal line of the equipotential surface, as shown in the figure, an upward component force is applied to the ion beam entering the electric field from an oblique direction. A deceleration force having a force will act, and the course will be deflected upward.

That is, if the decelerating electric field is tilted from the incident axis of the ion beam as in the present invention, the charged particles are decelerated and deflected at the same time. Since the deceleration force does not act on the neutral particles in the ion beam, they are not deflected,
It will be separated from the decelerated ion beam.

By irradiating the semiconductor substrate with the ion beam from which high-energy neutral particles have been separated and removed in this way, even when a low-mass impurity is injected into a shallow position in the substrate, the impurity reaches a deeper position. Does not occur.

Further, since the deceleration electrode also has a function of deflecting the ion beam, the range after deceleration does not need to be longer than that of the conventional device, and the substrate can be irradiated before the beam is dispersed. It will be possible.

[0024]

1 (a) and 1 (b) are diagrams schematically showing a first embodiment corresponding to the inventions of claims 3 and 4. FIG. Hereinafter, this embodiment will be described with reference to FIG.

The structure of the entire device is shown in FIG. The terminal 2 is arranged inside the housing 1, and the ion beam monochromated by the mass separation unit 7 is emitted through the slit 8 and decelerated to a predetermined energy by the deceleration unit 9. The same applies to the ion beam generator.

Details of the electrode structure of the deceleration portion are shown in FIG. The outer plate of the terminal 2 is applied with a potential of −25 kV relative to the casing 1. An electrode for forming a deceleration electric field in a desired shape is provided inside the insulator 25, the front electrode 21 has the same potential as the terminal, and the rear electrode
22 has the same potential as the case. A circular window with the central axis of the electric field as a common center is formed in these three electrodes including the intermediate electrode 23 provided between the two, and the ion beam passes through these windows.

In the present embodiment, as shown in the figure, the central axis of the electric field is parallel to the ion beam incident axis, but arranged apart from each other. The equipotential surfaces 20 of the electric field in the electrodes are substantially parallel in the central part,
As shown in the figure, in the vicinity of the electrodes on both ends, the shape of the window is swollen outward, so that the ion beam incident off the central axis is subject to a deflection force according to the swollen equipotential surface. become.

In the front of the deceleration electric field, the direction of deflection by the deceleration force R ₁ is different from the desired direction, but the amount of deflection is small because the energy of the ion beam is relatively high. The ion beam slightly deflects downward due to this deflection force, and then receives an upward deflection force due to the reverse curve of the equipotential surface at the rear portion of the deceleration electric field. At that time, since the ion beam has already been decelerated to have low energy, the amount of deflection by the deceleration force R ₂ is large, and the total deflection force is directed upward, and the decelerated ion beam is deflected upward and emitted. To do.

In FIG. 1B, the potential of the deceleration electric field changes monotonically from the front to the rear.
In some cases, an electrode is provided to generate electrons in the ion beam, as shown in FIG. In the example of this figure, the stabilizing electrode 24
Is located immediately after the front electrode 21 and is -1k from the front electrode.
A voltage of V is applied. In the deceleration electrode part having such a structure,
The incident ion beam is slightly accelerated at the beginning, but the effect on the deceleration effect or the deflection effect is small when viewed from the entire deceleration electrode section. In another embodiment described below, such an electrode for ion stabilization is provided if necessary.

Returning to FIG. 1 (a), the rotating disk 12 holding the wafer 11 has a deflected ion beam at a normal angle.
It is placed so that it is incident (normally vertical).
Neutral particles that have lost their charge after monochromatization go straight through the decelerating electric field, so a neutral particle trap 13 is provided to trap this and prevent it from reaching the wafer.

In the structure of this embodiment, the deflection force in the deceleration electric field can be increased or decreased by changing the deviation amount between the central axis of the electric field and the incident axis of the ion beam, and the mass or charge of the impurity ions to be injected. According to the above, the injection direction can be set to a predetermined direction.

FIG. 3 shows the effect of the present invention in comparison with the prior art. The solid line is an impurity concentration distribution curve when B is injected as an impurity into a Si substrate using the ion beam irradiation apparatus of the present invention. As is apparent at first glance, unlike the density distribution (displayed by a dotted line) by the conventional device, the trailing does not appear. As described above, the implantation conditions are that BF ₂ ⁺ is implanted at an energy of 10 keV after preliminarily implanting Si ⁺ to disturb the crystallinity of the substrate and prevent the occurrence of channeling.

FIG. 4 is a diagram showing a second embodiment corresponding to the inventions of claims 5 to 7. The overall configuration of the ion beam irradiation apparatus is the same as that in FIG. 1A, and FIG. 4 shows only the structure of the deceleration electrode section. Hereinafter, this embodiment will be described with reference to FIG.

As is apparent from the figure, in this embodiment, the electrode structure portion for beam deceleration is arranged such that the central axis of the electric field is inclined with respect to the ion beam incident axis. Therefore, the equipotential surface of the deceleration electric field has the effect of being curved,
On average, the ion beam is inclined with respect to the ion beam incident axis, and the deflection force as described in the "action" section is generated. Neutral particles contained in the ion beam go straight without being deflected, so that they are trapped by the neutral particle trap 13 and are not injected into the wafer 11.

In this embodiment, by changing the inclination of the central axis of the electric field, it is possible to change the deflection angle in the deceleration electrode portion, and, in the same way as in the first embodiment, with respect to the ion beam incident axis. Since the deflection angle can be changed also by changing the position of the central axis of the electric field, by using both of them together, it is possible to cope with changes in ion mass and implantation energy in a wider range.

FIG. 5 is a diagram showing a third embodiment corresponding to the inventions of claims 8 and 9. The overall configuration of the ion beam irradiation apparatus is the same as that shown in FIG. 1A, and FIG. 5 shows only the structure of the deceleration electrode section. Hereinafter, this embodiment will be described with reference to FIG.

In this embodiment, the electrode structure for beam deceleration is set as follows. First, it is assumed that the beam is incident horizontally from the left in the plane of the drawing, and an imaginary axis perpendicular to the plane of the drawing is assumed below the incident axis. The plurality of plate-shaped electrodes forming the deceleration electric field have a shape radially arranged with the virtual axis in common, and the equipotential surfaces formed thereby also exist radially. Further, the equipotential surface existing near the frontmost electrode is set to be substantially perpendicular to the incident axis of the ion beam, and the inclination of the equipotential surface increases toward the rear.

When the ion beam incident on such a decelerating electric field advances while decelerating, it gradually receives a strong deflection force as it advances. Therefore, according to this embodiment as well, it is possible to separate low-energy ions to be injected into the wafer from high-energy neutral particles.

In this embodiment, it is possible to change the deflection force for the ion beam by changing the opening angle between the radially arranged electrodes. However, the deceleration electrode structure having a fixed opening angle is used. The deflection force can also be changed more easily by rotating around the virtual central axis of the radial arrangement.

When ion implantation is performed on a semiconductor substrate using the above ion beam irradiation apparatus of the present invention, an acceleration voltage at the time of ion beam generation and a deceleration voltage for energy reduction are selected according to the ion species and implantation depth. Naturally, the deflection force in the deceleration electric field is adjusted according to these injection conditions.

[0041]

In the ion beam irradiation apparatus of the present invention, the ion beam to be irradiated receives a deflection force while passing through the deceleration electric field, and neutral particles are separated. It is possible to irradiate.

The effect of separating the neutral particles and performing the ion implantation is as shown in FIG. 3 described above. Since the deceleration and the deflection of the ion beam are performed in the same space, the beam dispersion is avoided. Therefore, it is possible to perform ion implantation efficiently.

Furthermore, with the deceleration electrode structure of the present invention, the outgoing angle of the ion beam can be changed by slightly moving or rotating it, so that it is possible to easily respond to changes in ion species and implantation conditions. can do.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an ion beam irradiation device according to a first embodiment.

FIG. 2 is a diagram for explaining the action of the deceleration electric field of the present invention.

FIG. 3 is a diagram showing an effect of the present invention in comparison with a conventional technique.

FIG. 4 is a diagram schematically showing details of the second embodiment.

FIG. 5 is a diagram schematically showing details of the third embodiment.

FIG. 6 is a diagram schematically showing a speed reducer provided with a stabilizing electrode.

FIG. 7 is a diagram schematically showing a conventional ion beam irradiation device.

[Explanation of symbols]

1 case 2 terminals 3 Ion source power supply 4 ion source 5 Extraction electrode 6 insulator 7 Mass separation section 8 slits 9 insulator 10 ion beam 11 wafer 12 rotating discs 13 Neutral particle trap 21 front electrode 22 Rear electrode 23 Intermediate electrode 24 Stabilizing electrode 25 Insulator

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 61-233955 (JP, A) JP-A 2-158042 (JP, A) JP-A 2-260358 (JP, A) JP-A 63- 131454 (JP, A) JP-A-1-305391 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01J 37/317

Claims (10)

(57) [Claims] 1. A plurality of aperture electrodes to which different electric potentials are applied between the output port of the mass separation section and the ion beam irradiation object.
In an ion beam irradiation apparatus in which an ion beam optical system for forming an ion beam decelerating electric field is arranged, the ion beam optical system is configured such that the plurality of aperture electrodes are mutually flat.
And the center of the aperture of each aperture electrode is the surface of the aperture electrode
There perpendicular collinear to the incident to the straight line and the ion beam retarding field connecting the opening centers
Parallel to the incident axis of the ion beam
Ion beam irradiation apparatus characterized by that. 2. The ion beam irradiation apparatus according to claim 1,
Te, the incident axis of the linearly with the ion beam connecting the aperture center
The ion beam irradiation device is characterized by having a structure in which the distance between can be changed . 3. An output port of a mass separation section and ion beam irradiation
Multiple aperture electrodes with different potentials applied to the projectile
Beam that forms an ion beam deceleration electric field by
In an ion beam irradiation apparatus in which an optical system is arranged, the ion beam optical system has a plurality of aperture electrodes that are mutually flat.
And the center of the aperture of each aperture electrode is the surface of the aperture electrode
On the same straight line that is perpendicular to the line and connects the center of the aperture to the ion beam deceleration electric field.
The ion beam irradiation device is characterized by having an inclination with respect to the incident axis of the ion beam. 4. The ion beam irradiation apparatus according to claim 3, wherein a straight line connecting the center of the opening and an incident axis of the ion beam are included.
Is an ion beam irradiation device characterized by having intervals . 5. The ion beam irradiation apparatus according to claim 3 or 4 , wherein the ions are straight lines connecting the centers of the openings.
Inclination of the beam with respect to the axis of incidence and / or the center of the aperture
The distance between the straight line connecting the lines and the incident axis of the ion beam can be changed
An ion beam irradiation device characterized by an effective structure . 6. An output port of a mass separation unit and ion beam irradiation
Multiple aperture electrodes with different potentials applied to the projectile
Beam that forms an ion beam deceleration electric field by
In an ion beam irradiation apparatus in which an optical system is arranged, in the ion beam optical system, the plurality of aperture electrodes are
Containing the axis of incidence of the ion beam entering the Nbimu retarding field
Are arranged radially around an axis perpendicular to the plane
The electrode located at the front of the ion beam entrance side is
Inclination from the plane perpendicular to the injection axis is located at the rearmost position in the electrode
The ion beam irradiation device is characterized in that it has a smaller inclination than the same inclination of the formed electrode . 7. The ion beam irradiation apparatus according to claim 6 , wherein the plurality of aperture electrodes are rotated around a central axis of the radial arrangement.
An ion beam irradiation device with a structure that can be rotated . 8. The ion beam irradiating device according to claim 1 , wherein the ion beam irradiation device is provided with an extension of an incident axis of the ion beam.
Note that the ion beam deceleration field traps neutral particles on the output side.
An ion beam irradiation apparatus comprising a wrap . 9. Either of claim 2, claim 4 or claim 5.
Using any of the ion beam irradiation equipment ,
The applied voltage is adjusted so that the ion particles after deceleration have the predetermined irradiation energy.
And the deflection angle of the ion beam in the ion beam deceleration electric field.
The aperture centers of the plurality of aperture electrodes are adjusted so that the degree becomes a predetermined value.
Distance between the connecting straight line and the incident axis of the ion beam, and / or
And a straight line connecting the centers of the apertures of the plurality of aperture electrodes
By adjusting the inclination of the beam with respect to the incident axis,
Ion beam characterized by performing ion beam irradiation on the
Irradiation method. 10. An ion beam irradiation apparatus according to claim 7 is used.
The plurality of aperture electrodes that form the ion beam deceleration electric field
The applied voltage is adjusted so that the ion particles after deceleration have the predetermined irradiation energy.
And the deflection angle of the ion beam in the ion beam deceleration electric field.
The plurality of aperture electrodes so that the degree becomes a predetermined value.
By adjusting the rotation angle around the central axis of the arrangement,
Ion beam characterized by performing ion beam irradiation on the
Irradiation method.