This application claims priority to prior application JP 2001-397817, the disclosure of which is incorporated herein by reference.
The present invention relates to an ion beam processing method and an ion beam processing apparatus.
There are various types of usage for the ion beam processing apparatus. For example, it is used as an ion implantation system. The ion implantation system is for implanting ions in semiconductor devices. For recent ion implantation system, following development and progress in a microfabrication technology of a semiconductor device, the energy of implanted ions is decreasing in order to implant the ions shallowly in the semiconductor substrate. However, in low ion energy range, in the midway of a beam line structure from an ion source to the semiconductor substrate, ion beam spreads because of charges of their own. This is because repulsion is attributed to a space charge effect. Therefore, in the low ion energy range, transport efficiency of ion beam is reduced, which causes a problem not to get sufficient ion beam current.
In ion beam, because of the electrical repulsive force: space charge effect, each positive ion bears off other positive ions. As a result, the ion beam is diffused. The space charge effect works more strongly as ion beam energy is lower, and also as ion beam current is higher.
Thus, especially in the low energy ion implantation, in order to obtain higher ion beam current, it is important to reduce the space charge effect and to prevent from diffusion of ion beam.
The space charge effect by ions having positive charges is mitigated by an amount equal to cancellation of total charges in a space if there are electrons or ions having negative charges. For example, as shown by P1 to P6 of FIG. 1, secondary electrons generated from a surface of a structure when ion beam collide with the structure in the beam line structure, electrons emitted when ion beam collide with gas remaining in the beam line structure to ionize the residual gas, or negative ions generated by electron impartation act to mitigate the space charge effect.
The space charge effect by positive ions is mitigated by amount of electrons secondarily emitted by ion impact to the beam line structure, by ion collisions with residual gas in the beam line structure or so. Negative ions, generated by capture of the secondary electrons, also mitigate the space charge effect.
Referring to FIG. 1, ions are generated by an ion source 200, and are extracted by an extraction electrode 201 as ion beam. The ion beam is transported in a vacuum chamber 202 and passes through an analysis slit 203 and are irradiated to a target semiconductor substrate 204. A mass analysis magnet unit is arranged outside the vacuum chamber 202, which is not shown here.
In FIG. 1, P1 denotes collision of ion beam with the extraction electrode 201, P2 collision of heavier ions than target ions with the inner wall of the vacuum chamber 202, P3 collision of ions with residual gas, P4 collision of lighter ions than the target ions with the inner wall of the vacuum chamber 202, P5 collision of ion beam with the analysis slit 203, and P6 collision of ion beam with the semiconductor substrate 204.
The following method is known, which actively induces the above-described operation in order to reduce the space charge effect and to increase beam current ultimately. Gas is intentionally introduced into the vacuum chamber constituting the beam line structure, and the space charge effect is reduced by electrons ejected by collision ionization of the gas with ions. This method is disclosed in, for example Japanese Patent No. 2765111. Simply put, when gas is introduced into an ion beam transport line, collision of ions of ion beam with the gas molecules is increased. As a result, the amount of electrons present in the ion beam is substantially increased to mitigate the space charge effect of the ion beam.
In addition to the above method, another method is known using the neutralization by the molecules that are easily turned to negative ions or are easily polarized, e.g., water (H2O). This method serves the same purpose as that of the above, and disclosed in Japanese Patent Application Laid-Open No. Hei 11 (1999)-96961.
The method based on the gas introduction increases the amount of generated electrons, results in loss of ion beam by collision with the gas. Generally, a beam current is maximized under a certain gas pressure and, even if more gas is introduced, ion beam current will decrease.
Thus, the amount of electrons is decided by balance of generation and disappearance of electrons. In order to completely cancel the space charge effect, this balance must be changed and the number of electrons must be increased.
From another standpoint, to substantially increase the amount of electrons, necessary for neutralization of ion beam, without any losses of ion beam themselves, a method of extending the life time of electrons or negative ions which have been present from generation to disappearance is effective.
In addition, for the conventional ion implantation system, between the both poles of the mass analysis magnet unit, a detachable/separable mass analysis magnet unit beam line vacuum chamber is arranged to transport ion beam while analyzing mass. The ion beam passed in the mass analysis magnet unit beam line vacuum chamber are diffused to reduce beam current.
Especially, in the low ion energy range, a reduction in beam current is significant. As a method of obtaining much more beam current in the low energy range, a deceleration mode is known. However, even by the deceleration mode, diffusion of ion beam cannot be suppressed.
As a method of suppressing diffusion of ion beam, application of a continuous cusp field in the ion beam is known to be effective. However, in the conventional ion implantation system, it is difficult to secure space for forming a cusp field.
Further, in the conventional ion implantation system, to use an apparatus with deceleration mode, the analysis magnetic pole surfaces of the mass analysis magnet unit, the magnets for forming the cusp field, and the beam line vacuum chamber must be set to different potentials. However, it is difficult to secure a space for arranging the magnets for forming the cusp field, and then a space for arranging its insulating material. The insulating material can be arranged by increasing a distance between the analysis magnetic pole surfaces of the mass analysis magnet unit. However, when the distance between the both pole surfaces of the mass analysis magnet unit is increased, electric power consumption necessity for analyzing mass of ion beam will increase.
At present, demand for space and energy conservation grows in the industrial field, and increases in size of the apparatus and electric power consumption run counter to such demand.
Therefore, a purpose of the present invention is to enable acquisition of higher beam current by forming a cusp field in a beam line structure of an ion beam processing apparatus in order to suppress diffusion of ion beam, and to transport much more ion beam.
Another purpose of the present invention is to increase the ion beam current easily in low energy range in an ion implantation system for implanting ions in semiconductor substrate such as silicon wafer.
Yet another purpose of the present invention is to provide an effective supporting method and an effective supporting structure of a set of magnets for forming a cusp field in a beam line structure.
An ion beam processing method of the present invention subjects ions extracted from an ion source by an extraction electrode to mass analysis by a mass analysis magnet unit and by a mass analysis slit, and are drifted or accelerated/decelerated to implant the ions in a substrate.
According to a first aspect of the present invention, a set of magnets for forming continuous cusp fields is continuously disposed in a continuous beam line structure from front part of the mass analysis magnet unit through the mass analysis magnet unit to rear part of the mass analysis magnet unit. Thus, the ion beam is continuously confined by magnetic field.
In the ion beam processing method of the first aspect, the continuous cusp fields may be formed so as to be uniform magnetic field strength, or different magnetic field strength in accordance with each section of the beam line structure.
According to a second aspect of the present invention, an ion beam processing method is applied to an ion implantation system for subjecting ions extracted from an ion source by an extraction electrode to mass analysis by a mass analysis magnet unit and a mass analysis slit, and drifting or accelerating/decelerating the ions to implant the ions in a substrate. The ion beam processing method comprise the steps of: confining the ion beam by continuous magnetic field in a beam line structure from the vicinity of the extraction electrode through the mass analysis magnet unit and the mass analysis slit to the vicinity of the substrate.
According to a third aspect of the present invention, an ion beam processing method comprises the steps of: confining the ion beam by continuous first cusp field in a continuous beam line structure from front part of the mass analysis magnet unit through the mass analysis magnet unit to rear part of the mass analysis magnet unit; forming the continuous cusp field; confining the ion beam by second cusp field different in magnetic field strength from the first cusp field in the beam line structure between the rear part of the mass analysis magnet unit and a substrate processing chamber; and in other word confining substantially the entire beam line structure by continuously disposing first and second magnetic fields.
In the ion beam processing method of the third aspect, the distance between cusp magnetic poles of the first and second cusp fields, or magnetic flux densities of the first and second cusp fields may be equal to each other or different from each other.
According to a fourth aspect of the present invention, an ion beam processing method is applied to an ion beam processing apparatus having a beam line vacuum chamber from an ion source to a processing chamber. The ion beam processing method comprises the step of: confining ion beam by forming a beam line structure for ion beam transport from the ion source through the beam line vacuum chamber into the processing chamber, arranging a mass analysis magnet unit outside a partial section of the beam line vacuum chamber, disposing an effective magnetic field area of the mass analysis magnet unit in a partial section in the beam line structure, and forming continuous cusp fields in the beam line vacuum chamber and also in the effective magnetic field area of the mass analysis magnet unit in the beam line structure.
According to a fifth aspect of the present invention, an ion beam processing method comprises the step of: confining ion beam by forming a beam line structure for ion beam transport from the ion source through the beam line vacuum chamber into the processing chamber, arranging a mass analysis magnet unit outside a partial section of the beam line vacuum chamber, disposing an effective magnetic field area of the mass analysis magnet unit in a partial section in the beam line structure, and forming continuous cusp fields in the continuous beam line vacuum chamber of the beam line structure from front part of the mass analysis magnet unit before the effective magnetic field area through the effective magnetic field area of the mass analysis magnet unit to rear part of the beam line structure outside the effective magnetic field area of the mass analysis magnet unit.
According to a sixth aspect of the present invention, an ion beam processing method comprises the step of: confining ion beam by forming a beam line structure for ion beam transport from the ion source through the beam line vacuum chamber into the processing chamber, arranging a mass analysis magnet unit from the outside in a partial section of the beam line vacuum chamber, disposing an effective magnetic field area of the mass analysis magnet unit in a partial section in the beam line structure, and arranging a set of magnets for forming continuous cusp field in the continuous beam line vacuum chamber of the beam line structure from front part of the mass analysis magnet unit before the effective magnetic field area through the effective magnetic field area of the mass analysis magnet unit to rear part of the beam line structure outside the effective magnetic field area of the mass analysis magnet unit to form continuous cusp field.
In the ion beam processing method of each of the fourth to sixth aspects, the continuous cusp field is formed by disposing a plurality of opposing cusp field units in the beam line vacuum chamber.
An ion beam processing apparatus according to a first aspect of the present invention comprises: a beam line vacuum chamber extending from an ion source to a processing chamber; a beam line structure for transporting ion beam from the ion source through the beam line vacuum chamber to the processing chamber; a mass analysis magnet unit arranged outside the beam line vacuum chamber, an effective magnetic field area of the mass analysis magnet unit being disposed in a partial section of the beam line structure; and a set of continuous cusp field forming magnets arranged in the beam line vacuum chamber part of the beam line structure to confine ion beam by forming continuous cusp field.
An ion beam processing apparatus according to a second aspect of the present invention comprises: a beam line structure for transporting ion beam from an ion source through a beam line vacuum chamber to a processing chamber; a mass analysis magnet unit arranged from the outside in a partial section of the beam line vacuum chamber, an effective magnetic field area of the mass analysis magnet unit being disposed in a partial section of the beam line structure; and a set of continuous cusp field forming magnets arranged in the continuous beam line vacuum chamber part of the beam line structure from front part of the mass analysis magnet unit before the effective magnetic field area of the mass analysis magnet unit to rear part of the beam line structure outside the effective magnetic field area of the mass analysis magnet unit to confine ion beam by forming continuous cusp field.
In the ion beam processing apparatus of each of the first and second aspects, a plurality of continuous cusp field forming magnets may be fixed and may be held at regular intervals directly on an inner wall of the beam line vacuum chamber located in a section between the inner wall of the beam line vacuum chamber and the magnetic pole surface of the mass analysis magnet unit.
In the ion beam processing apparatus of each of the first and second aspects, a plurality of continuous cusp field forming magnets may be fixed and may be held at regular intervals directly on an outer wall of the beam line vacuum chamber located in a section between the inner wall of the beam line vacuum chamber and the magnetic pole surface of the mass analysis magnet unit.
In the ion beam processing apparatus of each of the first and second aspect, a plurality of continuous cusp field forming magnets may be fixed and may be held at regular intervals inside the beam line vacuum chamber located in a section between the inner wall of the beam line vacuum chamber and the magnetic pole surface of the mass analysis magnet unit.
In the ion beam processing apparatus of each of the first and second aspects, a plurality of continuous cusp field forming magnets may be fixed and may be held at regular intervals directly on an outer wall of the magnetic pole surface located in a section between the inner wall of the beam line vacuum chamber and the magnetic pole surface of the mass analysis magnet unit.
In the ion beam processing apparatus of each of the first and second aspects, a plurality of continuous cusp field forming magnets may be fixed and may be held at regular intervals inside the magnetic pole surface located in a section between the inner wall of the beam line vacuum chamber and the magnetic pole surface of the mass analysis magnet unit.
An ion beam processing apparatus according to a third aspect o the present invention comprises: a beam line structure for transporting ion beam from an ion source through a beam line vacuum chamber to a processing chamber, a section of the beam line vacuum chamber constituting the beam line structure being tubular with polygonal or circular section perpendicular to the beam direction, an inner side wall of the tubular beam line vacuum chamber being thin in a partial section or all sections of the beam line vacuum chamber constituting the beam line structure; and reinforcing members arranged outside the inner side wall.
An ion beam processing apparatus according to a fourth aspect of the present invention comprises: a beam line structure for ion beam transport from an ion source through a beam line vacuum chamber to a processing chamber, a section of the beam line vacuum chamber constituting the beam line structure being tubular with polygonal or circular section perpendicular to the beam direction, an outer side wall of the tubular beam line vacuum chamber being thin in a partial section or all sections of the beam line vacuum chamber constituting the beam line structure; and reinforcing members and inner wall members arranged inside the outer side wall.
In the ion beam processing apparatus of each of the third and fourth aspects, a partial section of the beam line vacuum chamber constituting the beam line structure includes a section of a mass analysis magnet unit arranged in a position near the ion source of the beam line vacuum chamber constituting the beam line structure (first modified example).
In the ion beam processing apparatus according to the first modified example, the third and fourth aspects, the reinforcing members may be arranged at regular intervals.
In the ion beam processing apparatus according to the first modified example, the third and fourth aspects, a plurality of continuous cusp field forming magnets may be arranged as the reinforcing members at regular intervals.
In the ion beam processing apparatus according to the first modified example, the third and fourth aspects, the reinforcing members and a plurality of continuous cusp field forming magnets may be alternately arranged at regular intervals (second modified example).
In the ion beam processing apparatus according to the first modified example, the third and fourth aspects, in accordance with the shape of the tubular beam line vacuum chamber with polygonal or circular section, the reinforcing members and a plurality of continuous cusp field forming magnets may be alternately arranged at regular intervals in at least a group of opposing locations of the tubular beam line vacuum chamber with polygonal or circular section.
In the ion beam processing apparatus according to the first modified example, the third and fourth aspects, the reinforcing members may be arranged as reinforcing ribs at proper intervals in a direction perpendicular or obliquely to the beam line structure, or in the same direction as the beam line structure.
In the ion beam processing apparatus according to the second modified example, the reinforcing members and the continuous cusp field forming magnets may be alternately arranged closely.
In the ion beam processing apparatus according to the second modified example, the inner side or outer side wall of the beam line vacuum chamber constituted to be thin, may be thick in a part where no reinforcing member is disposed, in accordance with the shape of the tubular beam line vacuum chamber with polygonal or circular section.
In the ion beam processing apparatus according to each of the first and second aspects, a plurality of continuous cusp field forming magnets may be fixed and may be held at regular intervals directly to the beam line vacuum chamber (third modified example).
In the ion beam processing apparatus according the third modified example, concaves may be formed outside the beam line vacuum chamber to embed the plurality of cusp field forming magnets, and thus the plurality of cusp field forming magnets may be arranged so as to close to the inside of the beam line vacuum chamber, i.e., to a vacuum side (fourth modified example).
In the ion beam processing apparatus of the fourth modified example, the plurality of cusp field forming magnets may be directly fitted to be fixed in the concaves of the beam line vacuum chamber, whereby strength of the beam line vacuum chamber can be increased.
An ion beam processing apparatus according to a fifth aspect of the present invention comprises: a beam line vacuum chamber including effective magnetic field area of a mass analysis magnet at least partially, and the plurality of continuous cusp field forming magnets arranged to the continuous beam line vacuum chamber including the effective magnetic field area of the mass analysis magnet unit and also including the back and forward area of the effective magnetic field area.
In the beam line structure, the plurality of the continuous cusp field forming magnets are fixed to be held at regular intervals in the magnet pole surface side of the mass analysis magnet unit by a hold member.
In the ion beam processing apparatus of the fifth aspect, in the beam line vacuum chamber of the front and rear parts of the effective magnetic field area of the mass analysis magnet unit, a support member for fixing the hold member may be mounted on the magnetic pole surface of the mass analysis magnet unit, and the plurality of continuous cusp field forming magnets may be fixed to be held at regular intervals in the magnetic pole surface of the mass analysis magnet unit and the hold member by a support member.
In the ion beam processing apparatus of the fifth aspect, concaves may be formed in parts of the beam line vacuum chamber corresponding to the plurality of cusp field forming magnets fixed at the regular intervals to the magnetic pole surface of the mass analysis magnet unit and the hold member by the support member, and thus the cusp field forming magnets may be arranged so as to close to the inside of the beam line vacuum chamber, i.e., to the vacuum side.
In the ion beam processing apparatus of the fifth aspect, the hold member, the support member, or the fixing member for fixing and holding the cusp field forming magnets arranged between the magnetic pole surface of the mass analysis magnet unit and the beam line vacuum chamber, may be implemented by an insulating material to function as an insulator between the magnetic pole surface of the mass analysis magnet unit and the beam line vacuum chamber.
In the ion beam processing apparatus of each of the first and second aspects, a plurality of continuous cusp field forming magnets may be fixed to be held at regular intervals to the beam line vacuum chamber by a support member.
In the ion beam processing apparatus of each of the first and second aspects, concaves may be formed in the beam line vacuum chamber to arrange the cusp field forming magnets therein, whereby the cusp field magnets are arranged so as to close to the inside of the beam line vacuum chamber, i.e., to the vacuum side.
In the ion beam processing apparatus of each of the first and second aspects, concaves may be formed only in a necessary part of the beam line vacuum chamber to form a part of no reduction in thickness, whereby strength is provided to prevent destruction by a vacuum pressure.
In the ion beam processing apparatus of each of the first and second aspects, a support member for fixing and holding the cusp field forming magnets arranged between the magnetic pole surface of the mass analysis magnet and the beam line vacuum chamber may be implemented by an insulating material to function as an insulator between the magnetic pole surface of the mass analysis magnet unit and the beam line vacuum chamber.
In the ion beam processing method of each of the fourth to sixth aspects, an ion beam processing apparatus according to a sixth aspect of the present invention is provided by fixing a plurality of continuous cusp field forming magnets at regular intervals inside the beam line vacuum chamber.
In the ion beam processing apparatus of the sixth aspect, a magnet cover may be disposed to prevent exposure of the cusp field forming magnets to ion beam.
In the ion beam processing apparatus of the sixth aspect, the cusp field forming magnets may be fixed to be held in the beam line vacuum chamber directly or through a hold member.
In the ion beam processing apparatus of the sixth aspect, space parts may be formed inside the wall of the beam line chamber to embed the cusp field forming magnets.
In the ion beam processing apparatus of the sixth aspect, the cusp field forming magnets may be fixed to be held inside the beam line vacuum chamber through a cover hold member.
In the ion beam processing apparatus of the sixth aspect, concaves may be formed in the vacuum side of the beam line vacuum chamber to embed the cusp field forming magnets, whereby the cusp field forming magnets are arranged so as to close to the inside of the beam line vacuum chamber, i.e., to the vacuum side.
According to the present invention, an ion beam processing apparatus may comprise a continuous beam line structure from front part of the mass analysis magnet unit to rear part thereof, wherein the beam line structure is constituted to be partially detachable in order to widen one magnetic pole surface of the mass analysis magnet unit in spacing with respect to the other magnetic pole surface.