JPH11283931A - Ion implantation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To repair the defects produced by ion implantation in an early stage, and at the same time, to limit the position of an impurity to a shallow depth from the surface. SOLUTION: In the ion implantation method, the probability of an impurity being moved nearer to the surface of a substrate and defects being repaired is improved, by locally raising the temperature of the substrate by reflecting shock waves generated in the substrate by means of an acoustic wave reflecting plate 3006 in such a way that the position of ions is measured by means of a detector 3009, when ion implantation is performed by using cluster ions and the information is transmitted to an acoustic wave reflecting mobile device 3010, and then a mobile plate 3005 and the reflection plate 3006 are moved to the prescribed positions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shallow junction process using ion implantation of a semiconductor.

[0002]

2. Description of the Related Art As element formation techniques for high integration and high speed of MOSFETs, there are problems in thinning the gate insulating film and making the source / drain diffusion phases shallow. in this case,
An impurity layer is formed by ion implantation. However, at the time of ion implantation, defects at a deep portion of the surface are induced, and the diffusion of impurities is promoted by the defects, so that it is difficult to form an impurity layer at a shallow portion of the surface, which is a factor preventing a shallow junction.

In order to reduce the induction of defects at the time of ion implantation, it is generally considered to reduce the energy of implanted ions to 1 keV or less. For this reason, it is necessary to reduce the applied voltage of ions, but there is a limit to the reduction in voltage of the ion implanter, and it has been considered to use atom clusters instead of single atoms for charged ions. By using cluster ions, the effective ion implantation energy per single atom can be easily reduced to 1 keV or less at the same applied voltage.

As a conventional device forming technique, B ⁺ to BF ₂ ⁺
Low energy ion implantation technology using ions is being studied. International Device Conference (Technical Digest of In)
ternational Electron Device Meeting, 1996, San Die
go, CA (IEEE1996) .pp.435. ) Reports that the use of decaborane B ₁₀ F ₁₄ ⁺ ions is experimentally studied for the purpose of increasing the boron density of the implanted ion beam and further increasing the cluster atoms. However, conventionally, other than the use of the cluster, no method has been studied for reducing defects at a deep portion of the surface which occur at the time of ion implantation.

[0005]

SUMMARY OF THE INVENTION In the present invention, when implanting ions using a cluster, a defect deep in the surface can be effectively repaired as early as possible, and the MOSFET can be repaired.
Shallow junctions for high integration and high speed.

[0006]

Most of the defects induced deep in the surface during ion implantation are caused by the escape of atoms from the crystal lattice. Therefore, in the present invention, the temperature of the crystal lattice is locally increased so that the atoms can easily move to the position where the original crystal lattice is formed. A shock wave generated at the time of ion implantation is used so that the temperature rise occurs locally and near a defect generated at the time of ion implantation. For this purpose, there is provided a means for measuring the collision position of the cluster ions and transmitting the position information to a moving device for positioning a movable reflector directly behind the collision position. As a result, the spherically symmetric shock wave generated almost simultaneously with the defect at the time of ion implantation is reflected on the back of the crystal substrate, so that atoms can easily form the original crystal lattice for the defect generated at a deep position on the surface. The temperature of the crystal lattice can be locally increased.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below, taking as an example the case where silicon used as a semiconductor is used as a substrate and, for example, boron is implanted as an impurity. Further, a case will be described in which the acceleration voltage of the ion implanter for ion implantation is set to about 5 keV, which is the most frequently used in the current accelerated ion implanter.

FIG. 1 schematically shows an ion implantation apparatus according to one embodiment of the present invention. In the figure, 3001 is a vacuum device, 300
7 is a chamber. The ion cluster 3003 applied from the ion source 3002 and jumping out is
04 to form an impurity layer. At this time, a defect (not shown) deep in the surface is induced. This defect promotes the diffusion of impurities and makes it difficult to form an impurity layer at a shallow surface, which hinders a shallow junction. Therefore, it is necessary to immediately erase the defect.

First, means for detecting the collision position of the incident ion cluster will be described.

An ion cluster 30 is formed by a detector DX3008 in the x-axis direction and a detector DY3009 in the y-axis direction.
03 is measured at which coordinates on the substrate 3004. The position of the z-axis can be determined by the height position of the detectors DX3008 and DY3009 from the substrate surface.
As an example of the detector, the position of the ion cluster 3003 can be determined by a photoelectric effect using a laser beam. Since the reflection of the shock wave need not be highly accurate, the number of laser beams used in the detector may be small. Furthermore, the larger the ion cluster 3003, the larger the object to be detected. Therefore, the number of laser beams used in the detector can be reduced.

Here, the state of ion collision will be described a little. In order to investigate how the ion clusters collide with the substrate, a simulation was performed by the molecular dynamics method. When the acceleration voltage of the ion implanter is simulated for the cluster ion implantation of about 5 keV and low energy which is most used in the current acceleration ion implanter, the many energy of the atoms or ions interacting with each other due to the low energy is simulated. Multiple collisions must be handled.
In such a case, molecular dynamics is extremely effective.
In molecular dynamics, the force acting on each atom is calculated from the atomic arrangement and the time evolution of the atom is calculated, so that multiple collisions of atoms or ions interacting with each other can be handled in a natural way. is there.

In the simulation of the present inventor, the silicon crystal is accurately reproduced, and the most frequently used stilling is used.
The er-Weber potential was adopted. With this potential, a two-body potential, which depends only on the distance between two atoms, cannot correctly reproduce the atomic arrangement of the diamond crystal. Therefore, the angle dependence between three adjacent atoms is also taken into account.

In the process of implanting ion clusters, the effect of the collision is extremely large on the surface, which is significantly different from the collision process that proceeds inside a solid as observed in the case of ion implantation of a single atom. The macro behavior that the whole substrate surface is greatly dented by collision and returns to its original state. The incident ions are decomposed and distributed to a shallow portion of the substrate because of high collision energy.

In the case of ion implantation of a single atom, the impurity ions and the atoms in the substrate collide one after another, and the collided atoms collide with the atoms in another substrate in the same manner. Cascade scattering, in which atoms or ions form pairs and collide, becomes dominant. However,
At the time of cluster ion collision, most of the atoms in the cluster collide with the atoms of the substrate almost at the same time, and perform more complex multibody motion or cooperative motion than cascade scattering.

Further, the result of a simulation of the change when the number of cluster atoms is changed will be described.

In a collision when the number Nc of atoms constituting the cluster atoms is changed to 1, 8, 20, and 90, a macro behavior in which the whole substrate is greatly dented and returned to its original position as Nc increases. Becomes larger. Since the impact of the ion collision occurs at a shallow part of the surface, the generation of defects is extremely large near the surface.

When Nc = 1, 8, 20, and 90,
As the number of atoms in the ion cluster increases, the position of the defect becomes shallower. Therefore, when the number of atoms in the ion cluster is increased, the defects are more likely to exist at a shallower position than at a deeper position on the surface. However, the fact that many defects are generated near the surface at a shallow level does not pose a problem in the process because, at present, near the surface is often subjected to surface treatment and shaving. Conversely, when the number of atoms in the ion cluster is increased, the number of defects generated at a shallow portion of the surface increases, and the macroscopic behavior increases, thereby suppressing the generation of defects at a deep portion of the surface.

This result is favorable in device fabrication because the increase in diffusion during annealing is often caused by defects deeper than the surface and affects the device characteristics. As described above, defect formation on a deep surface, which is not preferable in device design, is suppressed by ion implantation of cluster ions.

The shock wave generated by cluster ion collision and its reflection will be described. 2 and 3
Then, in order to visualize the physical phenomena in the region that cannot be observed in the experiment below the point where the ions collided, the crystalline solid was displayed at the cut section virtually cut. In FIG. 2, reference numeral 614 denotes an incident ion decomposed due to high collision energy. As shown in FIG. 2, as a result of visualizing the local temperature distribution, a shock wave 615 having a z-axis downward velocity with a thickness of several atoms, which was not observed by ion implantation of a single atom ion, was formed. And was found to be propagated inside. The formation of a shock wave is not clear when Nc = 8, but becomes more pronounced in the order of Nc = 20 and Nc = 90. Even when Nc = 90, no defect was formed after the shock wave passed. This indicates that the shockwave is sufficient to move the atoms at the defect location, but does not have enough energy to place the atoms forming the stable lattice at the defect location.

The speed of the atoms of the substrate is set so that the temperature of the substrate is originally 300 K at normal temperature.
When c = 20, an atomic layer having a lower temperature was provided below the substrate, and a reflector was set. As shown in FIG.
The shock wave 615 is reflected by the reflection plate 617, and changes into a shock wave having an upward velocity in the z-axis as indicated by 616 in FIG. This makes it possible to cause a local temperature rise near the surface.

As shown in FIG. 4, from the detailed analysis result of the time change of the position of the atom using the z-axis coordinate of the atom immediately below the collision point, the shock wave is about 9 k
It has a speed of m / s and is almost equal to the experimental value of 8.43 km / s. In FIG. 4, the traveling direction of the shock wave reflected at the boundary between the low temperature region and the high temperature region is indicated by an arrow along a wavy line.

The following effects can be expected by the reflection of the shock wave. The defect created during the collision loses kinetic energy and the value of the activation energy for movement (1e
V), it can no longer diffuse,
Occurs by vibrating around a stable or metastable position. The distribution of defects generated at the time of the collision is shown by 613 in FIGS. However, the defects created during the collision,
That is, the atom located at the defect position which is a metastable position
Kinetic energy is obtained by a local temperature rise near the surface due to the shock wave. As a result, the atom located at the defect position has an activation energy value (1 eV) for movement.
Degree), diffusion becomes possible, and it is possible to move to a more stable position. That is, the number of crystal defects is reduced. This means that defects or defects at a deep position of ions or defects caused by channeling are repaired and the impurities are turned upward, which is convenient.
By the shock wave with the upward speed of the z axis,
This is because the impurity ions also move closer to the surface. This is advantageous for shallow junctions.

As is apparent from the results of the above simulation, the shock wave can be reflected by the reflector, and the probability of moving impurities closer to the surface and repairing the defect can be increased. As the reflector, a material having the characteristic of piezo or the same material as that of the substrate having a lower temperature than the substrate is used. Increasing the local temperature near the surface by reflection makes it possible to repair local defects near the surface without increasing defects as a whole system, rather than raising the temperature of the entire substrate by energy dissipation.

In order to enhance the effect, as shown in FIG. 1, a movable plate 300 having the same material and the same crystal structure as the substrate is used.
5 is applied to the substrate. If the substrate is thin, give it a thickness to gain time for control, or increase the radius of curvature so that the sound wave reflected near the surface focuses near the surface as shown in FIG. 5 instead of a simple flat plate. Adjusted reflector 61
By incorporating 7, sound waves transmitted in the form of shock waves are effectively reflected. FIG. 5 shows a case where the shock wave is reflected by the reflector 700 and concentrated at one point deep in the crystal.

The shock wave generated by the collision of the ion cluster has a shape considerably deviated from the spherical wave. The energy is easy to diverge if left untouched. Therefore, as shown in FIG. 6, a material whose shock wave propagates at a speed lower than that of the substrate and the movable plate is inserted into the movable plate 3005 of FIG. 1 (or FIG. 8) in the form of a lens 900. In this wave lens, the outer surface and the inner surface have different curvatures, and the sound wave 700 as a shock wave (the wave 800 at the advanced time) is transmitted by the thickness of the lens. It can be designed so that the shape of the shock wave, which is sound waves, can be changed. Thereby,
Waves can be propagated in the form of 1000 in FIG.

At this time, a mechanism (850 in FIG. 7) for changing the upper and lower shapes of the lens is provided, and by controlling the direction of the lens, the shock waves reflected in a certain area of the crystal are aggregated near the surface, and locally. The temperature can be raised. Considering that the longitudinal wave from the ion cluster is 9 km / s in silicon and the spread of the wave is determined by the size of the ion cluster, the lens size is 300.
It may be on the order of nm to microns. A simple lens is formed of, for example, a void surrounding a vacuum state with silicon. Alternatively, it is composed of a void filled with a rare gas.

The physical process of inserting a lens will be described in detail. Since the speed of wave propagation is slow with a lens,
The shock wave (800 in FIG. 6) takes the form of an inward spherical wave (1000 in FIG. 6) when reaching the reflector. When this wave is reflected by the reflector 617, 1050 in FIG.
As shown in FIG. Before this wave hits the lens, if it is turned upside down over the lens part, which is a part of the movable plate, after passing through the lens, the wave will be more like a spherical wave (710 in FIG. 7) on the surface. Heading. As a result, the sound wave can be focused at a certain point of the crystal near the surface, and the temperature can be efficiently increased locally. To change the vertical position of the lens, the timing at which the shock wave arrives at the lens can be determined from the sound speed, the thickness of the substrate and lens, and the structure and material data of the movable plate. It can be realized by rotating well.

In the embodiment shown in FIG. 1, the collision coordinate data of the ions is sent to the controller 3011 and transmitted to the moving device 3010 of the sound wave reflecting plate. Sound wave reflector moving device 3010
Are shown in FIG. FIG. 1 is a bird's-eye view as viewed from the position where the positive direction of the z-axis is upward, while FIG. 8 is a bird's-eye view as viewed from the position where the positive direction of the z-axis is lower, that is, the substrate from below.

In the moving device of the sound wave reflecting plate shown in FIG. 8, the pulse generating circuit, the clock circuit and the judging circuit synchronize with each other, and the ion collision coordinate data, the predetermined substrate thickness data and the movable plate data are also stored. At the same time, find the optimal position for placing the reflector. Furthermore, in the acoustic wave reflector moving device, the optimal position for placing the reflector is transmitted to servo and drive circuits in the X, Y, and Z axes, and the shock wave, which is a sound wave, is moved to the back of the crystal substrate before reaching the substrate. The movable plate or reflector is moved to be reflected. At this time, as shown at 8000 and 8001 in FIG. 8, by providing a buffer mechanism and a metal probe, by measuring the tunnel current on the surface, the control of the reflector can be further enhanced. Alternatively, using a metal probe more aggressively, an energy pulse having the necessary energy is generated from the atomic displacement in the z-axis direction from the optimal position, and the local temperature is increased to cause impurities to be deposited on the surface. It can be moved closer and the probability of repairing the defect can be increased.

In the above invention, in the ion cluster implantation method, an apparatus for detecting a collision position of the ion cluster with the substrate and a means for transmitting the collision position to the control unit;
Although there was a single movable device for moving and positioning the sound wave reflecting plate on the back side of the substrate, these were made into a plurality of devices, and the plurality of sound wave reflecting plates were moved to the back side of the substrate to form a substrate for the ion cluster. Shock waves, which are a plurality of longitudinal waves generated when ion clusters collide with each other, are reflected below the substrate one after another, and the ion clusters collide more efficiently above the substrate. For defects generated at a deep position from the surface that sometimes occurs, the temperature of the crystal lattice is locally increased so that atoms can easily form the original crystal lattice, and impurities are arranged near the surface. Can be moved.

[0031]

According to the present invention, it is possible to effectively repair a defect at a deep portion of the surface as early as possible and to suppress the diffusion of impurities promoted by the defect.
It is possible to further reduce the junction for higher integration and higher speed of the FET.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram of a defect distribution and a shock wave on a cut surface of a substrate.

FIG. 3 is a diagram showing a defect distribution on a cut surface of a substrate and a reflection of a shock wave.

FIG. 4 is a diagram showing displacement of atoms in a (−) z-axis direction in a substrate after collision.

FIG. 5 is a diagram of a cut surface of a movable plate, a reflection plate, and a reflection of a shock wave.

FIG. 6 is a schematic diagram showing the state of the wave shape of the shock wave before conversion and reflection.

FIG. 7 is a schematic diagram of a state after shock wave conversion and reflection of a shock wave.

FIG. 8 is a schematic diagram of an apparatus and a sound wave reflecting plate moving device according to an embodiment of the present invention.

[Explanation of symbols]

3002 ... Ion source, 3003 ... Cluster ion,
3004: silicon substrate, 3005: movable plate, 3006
... Sound wave reflecting plate, 3008, 3009 ... Detector, 30
10 ... Sound wave reflecting plate movable device.

Claims (6)

[Claims] An ion cluster has means for detecting a collision position between an ion cluster and a substrate and transmitting the collision position to a control unit, and a movable device for moving and positioning a sound wave reflecting plate behind the substrate. The shock wave, which is a longitudinal wave of sound generated when the ion beam strikes, is reflected below the substrate. An ion implantation method characterized by locally increasing the temperature of a crystal lattice so as to easily form a lattice and moving the crystal lattice so that impurities are arranged near the surface. 2. A method according to claim 1, wherein a movable plate having the same material, material, and crystal axis as the substrate is prepared, and when the substrate is thin, the thickness is given to adjust the time for device control and operation. An ion implantation method characterized in that: 3. A shock wave according to claim 1, further comprising a reflector having a radius of curvature adjusted so that a sound wave reflected by a surface other than a simple flat plate is focused near the surface. An ion implantation method characterized in that a sound wave transmitted in the form of is reflected so as to be concentrated at a certain point deep in the crystal, and the local temperature is raised only in a part of the ion. 4. A method according to claim 1, wherein a lens having a curvature different between an outer surface and an inner surface formed of a material slower than a speed at which the shock wave of the substrate and the movable plate is transmitted is inserted into the movable plate below the substrate. A mechanism that changes the shape of the upper and lower lenses is used to convert the wave shape so that the sound wave transmitted in the form of a shock wave is concentrated at one point deep in the crystal by using the speed at which the wave is transmitted depending on the thickness of the lens An ion implantation method characterized in that a local temperature is raised only in a very small part by propagating a wave. 5. The method according to claim 1, wherein a plurality of devices for detecting a collision position of the ion cluster with the substrate, means for transmitting the collision position to the control unit,
It has a plurality of movable devices that move and position the sound wave reflecting plate on the back side of the substrate, and a plurality of longitudinal waves generated when the ion clusters collide are generated when the ion clusters collide with the substrate one after another. Shock waves, which are sound waves, are reflected one after another below the substrate, so that atoms can easily form the original crystal lattice for defects generated deep from the surface that occur when ion clusters collide above. An ion implantation method characterized by locally increasing the temperature of a crystal lattice and moving impurities so as to dispose impurities near a surface. 6. The method according to claim 1, wherein a shock wave, which is a longitudinal sound wave generated when the ion cluster collides, is reflected below the substrate, and simultaneously an energy pulse is generated. For defects generated at a deep position from the surface generated when the ion cluster collides above, the temperature of the crystal lattice is locally increased so that atoms can easily form the original crystal lattice, and impurities are further removed. An ion implantation method characterized in that the ion implantation method is moved so as to be arranged near the surface.