JPH05182623A - Ion implantation device and method of lengthening lifetime of ion source - Google Patents

Abstract

PURPOSE: To prevent the formation of a conductive coating on an electric insulation body, and extend the life of an ion source by positioning the electric insulation body for a filament on the outside of an arc chamber so as to fit onto a gas generation source main body. CONSTITUTION: An electron reflection device 118 made of fire resistant substance surrounds a filament 116 so that electrons produced in an arc chamber 110 are reflected from the filament end portion of the arc chamber 110 so as to be parted therefrom. An electric insulation body 128 is placed in the recessed portion of an insulation body fitting plate 132 on an ion source main body 122, and is positioned on the outside of the arc chamber 110 so as to electrically insulate the filament 116 in the arc chamber 110. Thereby, since the insulation body 128 is not exposed to ion seeds, no conductive coating is rapidly produced so that the life of the ion source can be extended. Preferably, the insulation body 128 is made of ceramic insulation body material, boron nitride, or aluminum oxide.

Description

Detailed Description of the Invention

This invention relates to improved systems and methods for implanting preselected ions into a target. In particular, the present invention relates to an apparatus for implanting preselected ions into a target with improved ion source lifetime and reduced ion beam contamination.

[0002]

2. Description of the Related Art In the manufacture of semiconductor devices, various kinds of hardware can be formed by diffusing or implanting positive or negative ions (impurities) such as boron, phosphorus, arsenic and antimony into a wafer. The region is modified to produce a region of varying conductivity. As the size of semiconductor devices shrinks, as in the case of LSI and VLSI manufacturing, the interconnections between them move closer together. As a result, the wafer is used efficiently and the operating speed of the device is improved, but the arrangement of the conductivity modifying means must be further increased accordingly. Improvements have also been made to the equipment used to carry out the doping.

Diffusion places conductivity modifying ions on the surface of the wafer and thermally drives them into the wafer, but the diffusion process drives the ions into the wafer both laterally and vertically. Therefore, there is a limitation in tightly controlling the shape. Therefore, the ion implantation that can anisotropically implant ions into the wafer is
It is the preferred method of adding impurities for the production of modern equipment.

Various ion implanters are known which use several types of ion sources. An ion beam of a preselected species is created by applying a current to a filament in a controlled ion source chamber that is equipped with a power source and is supplied with a gas that is an ion precursor. The ions are extracted through the opening of the ion source chamber by the voltage between the ion source chamber being positive and the extraction means. A combined acceleration system, a magnetic analysis stage that separates desired ions from unwanted ions based on mass and focuses the ion beam, and delivering the desired ions at the required beam current level to a target or substrate wafer. The system is completed with the post-acceleration stage which guarantees that. The intensity of the generated ion beam can be adjusted by system design and operating conditions. For example, the current applied to the filament can be varied to adjust the intensity of the ion beam emitted from the ion source chamber. Current state of the art ion implantation systems are described in US Pat. No. 4,754,200 to Plumbal and US Pat. No. 4,578,589 to Aitken, both of which Are incorporated herein by reference.

The most common type of ion source used commercially is known as the Freeman Source. In a Freeman source, the filament, or cathode, is a straight rod that can be made from tungsten or an alloy of tungsten, or other known ion source material such as iridium, which has an arc whose wall is the anode. -Passed through the chamber.

The arc chamber itself has an outlet opening,
Means for supplying the desired gaseous ion precursor for the desired ions, vacuum means, means for heating the cathode to about 1000 ° C. so that the cathode emits electrons, applying a magnetic field parallel to the filament A magnet to increase the electron path length and a power supply connected from the filament to the arc chamber.

When power is applied to the filament, the filament temperature rises until it emits an electron, which bombards and destroys the precursor gas molecules, resulting in a plasma containing electrons and various ions. The ions are ejected from the ion source chamber through an outlet opening and selectively passed to a target. The filament is insulated with an electrical insulator that also serves to support the filament. The insulator is made of a high temperature ceramic material such as alumina or boron nitride, which withstands high temperatures and the corrosive atmosphere created from precursor gas species such as BF ₃ and SiF ₄ and its debris. .. It can be seen that the insulator severely limits the life of the ion source. Although the exact number and type of ions produced in the ion source chamber is not known with certainty, the various ions produced in the chamber are both the graphite wall of the chamber and other ions in the chamber. Can react with to form reaction products, which adhere to the walls of the insulator and form a conductive coating. For example, when BF ₃ is supplied to the ion source chamber, from the chemical reaction of graphite with carbon and fluorine from the chamber walls, eg, C
Various carbon fluorides such as F and CF ₂ are produced which react further into fine dust which covers the insulator. Conducting compounds can also be produced from other parts of the ion source chamber. Even a very thin conductive coating shorts the arc source, impeding the stability of the ion beam emitted from the ion source chamber and eventually rendering it unusable. At this point, the chamber must be cleaned and the insulator and filament reconditioned or replaced. This is the most common and most frequent cause of ion implanters.

Some prior art researchers have proposed to prevent the formation of this conductive coating on the insulator. For example, it is known to modify the shape of the electrical insulator in the arc chamber to reduce film formation, but this does not significantly extend the life of the device. Others have proposed a shield to protect the insulator from the formation of a conductive coating, which itself adds to system instability. A cleaning discharge was also attempted to etch away the coating on the inside of the chamber, but with a degree of success as other ions can form during the etching and introduce other instabilities and unwanted ions into the chamber. Was miscellaneous.

Thus, there is a method of reducing the time that the arc chamber needs to be repaired and reducing the downtime of the ion implanter by reducing or eliminating the formation of a conductive coating on the filament insulator. Highly desired. Moreover, reducing ion beam contamination and improving ionization efficiency all contribute to the economy of the ion implanter.

[0010]

SUMMARY OF THE INVENTION The ion beam device of the present invention positions an electrical insulator for the filament outside the arc chamber to maintain the function of the ion source body to insulate the filament. Although it is mounted in a location where it can be moved, the insulator is no longer located within the arc chamber itself and is therefore not exposed to ionic species, so it is not possible for the insulator to rapidly form a conductive coating. Absent. Thus, the lifetime of the ion source is significantly extended compared to conventional ion beam devices.

To further prevent the filament insulation from forming a conductive coating from the gas in the arc chamber, further protection of the insulation from the chamber gas by at least one of a shield and an inert gas outflow. Can be done. Ion beam contamination due to contaminants from materials in the arc chamber can be reduced by making the arc chamber itself, a portion thereof, or its removable lining of tungsten.

The ionization efficiency of the arc chamber is improved by the use of a removable refractory lining,
The heat generated in the chamber when the filament is energized is transferred by radiation to the chamber wall, increasing the electron temperature during operation.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS To aid in understanding the present invention, reference is made to FIGS. Ions are generated in the arc chamber 15 of the Freeman ion source. Extraction electrode assembly 1
3 is a rectangular opening 15A in front of the arc chamber 15.
To extract a beam of ions through. The ion beam is extracted and accelerated toward the mass analysis system 20, which includes an ion beam flight tube 21 that provides a path between the magnetic poles of an analysis magnet assembly 22. The ion beam is bent as it passes through the analysis magnet assembly 22, enters the ion drift tube 32, passes through the mass analysis slit 33, is accelerated by the post-acceleration system 40, and strikes the target element 50. During part of the scanning cycle, the target element 50 is out of the beam and all of the beam current hits the beam stop 51. The suppression magnet 52 of the beam stop device 51 produces a magnetic field oriented to ensure an accurate measurement of the beam current generated by blocking the electrons arriving and leaving the beam stop. Let

The ion source assembly 11 includes a magnet assembly 12, which has a separate electromagnet within the arc chamber 15 having a cylindrical pole 12A with its axis aligned with the filament 15B. The ion source magnet is
Improving the ionization efficiency in the ion source by increasing the efficiency of ion production by spiraling the electrons emitted from the filament 15B around the filament in a path towards the wall of the arc chamber 14 acting as an anode. ..

As shown in FIG. 2, the Freeman ion source is operated from an electrical standpoint by coupling a filament power supply 60 to the filament 15B to provide a large current to the filament at a low voltage. .. The arc power supply 61 applies a voltage that is typically clamped to a maximum of about 120 volts between the filament 15B and the arc chamber 15, which acts as the anode. Filament 15B produces thermionic electrons, which are accelerated through the gas species in the arc chamber toward the arc chamber wall, creating a plasma of ionic species in arc chamber 15.
This ion implanter is more fully disclosed in U.S. Pat. No. 4,754,200, which is incorporated herein by reference in its entirety.

FIG. 3 is a side view of the Bernas type ion source according to the present invention. The Bernus ion source differs from the Freeman ion source in that the filament is in the form of a loop at one end of the arc chamber rather than a rod-shaped filament extending into the arc chamber. The present invention is applicable to both the Bernas type ion source and the Freeman type ion source.

Referring to FIG. 3, the ion arc chamber 110 is a nearly closed chamber having a gas inlet port 112. A gas such as BF ₃ or SiF ₄ can be supplied directly from the gas source 111 to the arc chamber 110. Evaporate a vaporizable metal source such as antimony, arsenic or phosphorus in a high temperature oven, then arc
It can be sent into the chamber 110. The arc chamber 110 is also provided with an outlet opening 114 through which the ion beam produced in the arc chamber 110 exits, is focused and is accelerated to the desired target. A coiled filament 116 is at one end of the arc chamber 110. Filament 1
A magnified view of 16 is shown in FIG. 2A. An electron reflector 118, suitably made of molybdenum, tungsten or other suitable refractory material, surrounds the filament 116 to reflect the electrons produced within the arc chamber 110 from the filament end of the arc chamber 110. keep away. The reflector 118 is at the same potential as the filament 116. There is a small gap between the reflector 118 and the arc chamber 110. Careful design of the reflector and arc chamber mount can maintain a gap between them to prevent reflector 118 from contacting arc chamber 110 and lining 134, but such contact causes a short circuit. Becomes A refractory electron reflector 120 is located at the other end of the arc chamber and again must not contact the arc chamber 110 for the same reason.

The filament 116 is attached to the body 122 of the driving device by a clamp 124, which will be described in detail below. Insulator 12 under clamp 124 outside arc chamber 110
8 is attached. The insulator 128 is now completely outside the arc chamber 110, and the filament /
Supporting the reflector assembly, the arc chamber 11
It is surrounded by a shield 130 that blocks gas molecules from 0 reaching the insulator 128. The insulator 128 is placed in a recess in the plate 132 on the body 122 of the ion source.

The insulator is made of a high temperature ceramic material such as boron nitride or aluminum oxide and is
The filament is electrically insulated in the chamber 110. FIG. 5 illustrates an insulator / shield assembly 128 / of the present invention.
It is an enlarged detailed view of 130, and the same numbers are used for the same parts as in FIG. One or more shields 130 that form a labyrinth around the insulator 128 prevent the insulator 12 from the gas species emitted from the arc chamber 110.
8 can be further protected. Gas species is insulator 12
Since the labyrinth wall must be struck several times before reaching 8, this labyrinth is further
Protect 8. The more surfaces around the insulator 128, the more
The gas species from the arc chamber 110 are more likely to coalesce and concentrate before reaching the insulator 128.
The shield 130 can be made of metal such as stainless steel.

Another way to protect the electrical insulator 128 is by:
Flowing an inert gas over the insulator 128 to prevent the gas ionic species from reaching the insulator 128.
The cloud of inert gas around the insulator 128 is
Acts as a further barrier to prevent the diffusion of gas species towards the. One or both, preferably both, of the shield means 130 and the inert gas barrier means (not shown) may be used to enhance the protective effect of the electrical insulator 128 located outside the arc chamber 110. I can.

To further enhance the ionization efficiency of the arc chamber 110, a removable, thermally insulating lining 134 can be placed inside the arc chamber 110. The lining 134 actually contacts the arc chamber 110 at very few locations,
Therefore, most of the lining 134 is separated from the chamber wall 136 by a gap of about 0.1 mm. Therefore, the temperature of the lining 134 becomes high and electric power is supplied to the filament 116.
And when supplied to the plasma, this heat is transferred by radiation to the wall 136 of the arc chamber 110. At this time, the wall of the arc chamber 110 becomes hotter than the conventional arc chamber. The high temperature electrons in the arc chamber 110 enhance the ionization efficiency of the ion source.

The efficiency of the ion source is the fraction of the input material (precursor gas) to the ion source that is ionized and extracted from the ion source. The more efficient this is, the less material is needed to produce a given extraction current or ion beam. Therefore, increasing the ionization efficiency has several advantages. That is, less gas ion source material needs to be supplied to the arc chamber 110, less vacuum level must be used, and less contamination of unwanted ionic species that occurs. This may also reduce the total available gas species that may coat or concentrate in or on the arc chamber itself.

The lining 134 can be made of a refractory material such as carbon, vitreous carbon, silicon carbide or molybdenum, but is preferably made of tungsten. The material of the lining is important because it may contaminate the ion-implanted target or substrate by the lining's molecules or ions. For example, Mo ²⁺ (MW9
8) cannot be decomposed from the impurity source ion BF ₂ (MW49) and therefore cannot be separated from this impurity ion during mass spectrometry, and is sent as a contaminant during ion implantation with boron. As another example, the reaction between a carbon arc chamber and plasma fluorine atoms is CF
(MW31) ions and CF ₂ (MW50) ions are generated, and the mass is similar to that of general impurities such as P (MW31) and BF ₂ (MW50). Since these fluorocarbon ions are not completely separated from the impurity ions,
Ion implantation of boron and phosphorus also becomes pollutants.

Tungsten linings are convenient to use because they do not contaminate the wafer or other substrate to be ion implanted. In fact, in our research on tungsten linings, the same advantage of less contamination of the implant with the lining material applies equally to the material of the arc chamber itself, all parts of the chamber that actually come into contact with the plasma. I found out that Generally, in the past, arc chambers have been made from carbon or molybdenum, which, as mentioned above, may be implanted with various ions of boron, phosphorus or the like, for example Mo.
There is a problem that ionic species contaminating ⁺² and CF and CF ₂ are generated. Thus, by making the arc chamber itself, or a portion of the arc chamber, for example a wall having an outlet opening, of tungsten, with or without a lining, or with a tungsten lining. Even without use, ion implantation contamination by materials in the arc chamber is reduced. Advantageously, other parts, such as the reflector for the filament, are also made of tungsten. As mentioned above in detail, the insulator is arc
The same is true when inside or outside the chamber.
Thus, it is conceivable to make all or part of the arc chamber, or parts of the arc chamber, such as the reflector, using tungsten, both conventional ion implanters and ion implanters of the present invention.

Although some material adheres to the lining 134 during operation of the arc chamber 110, it does not interfere with the operation of the filament 116. For highly toxic or corrosive input precursor gases such as SiF ₄ and BF _3, it is highly desirable to reduce the required vacuum level in the system by reducing the total amount of gas required. Problems associated with vacuum are reduced, such as collisions with natural gas species that result in unwanted ionic species in the ion beam, resulting in the implantation of unwanted species. When a source of solid ions, such as arsenic, is input to the ion source, its evaporation rate can be reduced, reducing the total amount of evaporated metal used, and thus solid metal to the outer surface of the arc chamber. The risk of condensation of is also reduced. This also reduces other sources of ion beam instability and lengthens the time between required oven refills.

Another advantage is that at higher temperatures the desired ions are produced at higher levels, so higher wall temperatures increase the yield of certain ionic species. For example, the ratio of desired B ₁₁ ion formation to undesired BF ₂ etc. ion formation improves from about 1.5: 1 to about 2: 1. This is a surprising increase in ionization efficiency. The device of the present invention is
By greatly increasing the time it takes to form the conductive coating on the electrical insulator, the life of the ion source is extended by a factor of 2 to 4 and the downtime of the ion implanter is similarly reduced. .. The lining 134 is removable so that it can be replaced as desired during maintenance of the arc chamber. Since the number of times the ion source is maintained is reduced, not only is the time between maintenance longer, but the chance of false reassembly, which is another source of ion implanter failure, is reduced.

The maintainability of the ion implanter is also improved by the use of the bifunctional filament clamp shown in FIGS. FIG. 6 is a top view of a pair of clamps 20, 201 that help to clamp the ends of a Bernas type filament with a suitable reflector.
Referring to FIG. 7, which is an expanded view of the clamp system 124, each clamp 200 and 201 includes a filament 1
Simultaneously engage both 16 and the filament reflector or guide 118 to maintain their relative alignment. Each clamp 200, 201 forms one integral assembly 4
A straight slot 2 with two jaws 202, 204, 206, 208 in the upper jaw pair 202/206
It is equipped with 09. The upper jaws 202, 206 have smaller openings 210 for clamping one end of the filament 116. Lower jaw 204, 20
8 has a keyhole slot 211 and a larger opening 212 for clamping each reflector 118.
Jaws 202 and 2 gripping one end of filament 116
06 can be opened separately to facilitate filament modification, or both pairs of jaws 2
02/206 and 204/208 Allen key 214
Can be opened together by

The Allen key 214 is inserted into a screw 216 which has two flat sides 218 and two curved sides 220 which are inserted into the clamp 200 and tightened by washers and nuts 217. Have. When clamping only the filament 116,
The screw 216 is slid into the first position 222. Screw 21
When turning 6 by 1/4 turn, jaw 202/206
Is forced open by the larger curved surface 220 of the screw 216. This operation is repeated with clamp 201 (see Figure 6). At this time, the filament 116 can be removed and repaired or replaced. To clamp the new filament 116 in place, the screw 216 is rotated another quarter turn, at which time each clamp 200 and 201 is retightened to retain the replacement filament 116.

When both the filament 116 and the surrounding reflector 118 are to be removed or replaced, the screw 21
Slide 6 into second position 224. 1 / screw 216
Both sets of jaws 202/206 and 2 when rotated 4 turns
04/208 opens, releasing both filament 116 and reflector 118. After the replacement, the screw 216 is rotated again by a quarter turn, and the filament 116 and the reflection device 1 are rotated.
Both 18 are clamped together and maintain their alignment.

The clamp system 124 allows for efficient removal of filaments and reflectors during maintenance of the ion source chamber. Reduces downtime, allows filaments and filament reflectors to be handled as a unit, which allows for rapid device replacement and reduces the risk of misalignment of filaments and filament reflectors or guides during reassembly To do.

The modification of the ion implanter described in this invention prolongs the life of the ion source, requires only a small amount of downtime for the device, and is the cause of misalignment of filaments and filament reflectors. To reduce the inoperable time. arc·
The use of a removable lining for the chamber improves ionization efficiency and reduces ion beam contamination depending on the materials used.

Although various examples of the systems and methods of this invention have been disclosed above, they have been presented by way of example only. Various modifications and variations will be apparent to those of ordinary skill in the art and are intended to be included herein without departing from the scope of the invention as claimed.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a prior art ion implanter beam line that is the preferred system environment for the ion source system and method of the present invention.

FIG. 2 is a schematic diagram of an ion source control and ion beam extraction system.

FIG. 3 is a side view of a Bernas ion source useful in the present invention.

FIG. 4 is an enlarged side view of a Bernas type filament.

FIG. 5 is an enlarged view of an insulator / shield assembly mounted outside the ion source chamber.

FIG. 6 is a top view of a pair of four-jaw integral clamps useful for gripping a Burnus filament.

7 is an exploded view of the clamp system of FIG.

Front Page Continuation (72) Inventor Paul Barfield United Kingdom Sussex Crawley Three Bridges Scarborough Road Farlands (No Address) (72) Inventor John Pontefract United Kingdom Sussex Acfield Manor Park Browns Lane 70 (72) Inventor Bernard Harrison United Kingdom West Sussex Earl H10 3 Eda Coptome Newlands Park 16 (72) Inventor Peter Mears United Kingdom West Sussex Henfield Parsonage Road 61 (72) Inventor David Virgin France Grenoble Mevran Breman Depressle 2 Bis Tamporozie 2 Apartments 1

Claims (25)

[Claims] 1. An arc chamber in which a plasma is generated, including a source of gas, a filament connected to a current source, an electrical insulator for the filament and the outlet opening, and an ion. An ion implanter comprising means for decomposing the beam to allow the preselected ion species to implant through the aperture into the target, the isolation between the reflector and the arc chamber. Mounting the filament and the reflector to maintain a gap, and mounting electrical insulation means for the filament on the source body, outside the arc chamber and spaced from the arc chamber. Characteristic ion implantation device. 2. The device of claim 1, wherein the insulator comprises a ceramic insulator material. 3. The device of claim 1, wherein the insulator comprises boron nitride or aluminum oxide. 4. The apparatus of claim 1, wherein the electrically insulating means comprises shield means surrounding the insulating means. 5. The device of claim 4, wherein the shield is in the form of a labyrinth. 6. The apparatus according to claim 1, wherein said electrically insulating means comprises an inert gas cloud surrounding said insulating means. 7. The apparatus of claim 4, wherein the electrically insulating means comprises an inert gas cloud surrounding the insulating means. 8. The device of claim 1, wherein the reflector comprises tungsten. 9. The apparatus of claim 1, wherein the arc chamber or a portion thereof comprises tungsten. 10. The apparatus of claim 1, wherein the arc chamber has a replaceable lining therein. 11. The apparatus of claim 10, wherein the lining comprises a refractory material selected from the group consisting of molybdenum, tungsten, vitreous carbon, carbon and silicon carbide. 12. The apparatus of claim 11, wherein the lining comprises tungsten. 13. The apparatus of claim 1, wherein the filament is a tungsten rod extending into the arc chamber. 14. The apparatus of claim 1, wherein the filament is a tungsten loop at one end of the arc chamber. 15. The apparatus of claim 1, wherein the filament and filament reflector are mounted in separate jaws of a unitary clamp. 16. The clamp has two pairs of jaws,
16. The set of jaws attached to the filament, the other set of jaws attached to the filament reflector, and the jaws attached to the filament can be opened independently. The described device. 17. An ion source including an arc chamber for producing an ion beam of a preselected species of a selected beam current level, and receiving the beam to select various ion species based on mass. In an ion implantation system consisting of a beam analysis means for spatially separating and producing an analyzed beam and a beam resolving means for allowing said separated species to reach a target to be implanted. An ion implantation system characterized by using tungsten as a part of the material. 18. The ion implantation system of claim 17, wherein one or more walls of the arc chamber are made of tungsten. 19. The ion implantation system of claim 17, wherein the arc chamber has a removable tungsten lining. 20. The ion implantation system of claim 18, wherein the arc chamber has a removable tungsten lining. 21. The ion implantation system of claim 17, wherein the arc chamber has a filament therein and a reflector therefor, the reflector comprising tungsten. 22. A method for improving the ionization efficiency of an ion source having an arc chamber containing a filament in an ion implanter, wherein the wall of the arc chamber is lined with a removable refractory material, the method comprising: Heat generated in the arc chamber when energized to the filament and plasma of the arc chamber is radiatively transferred by the lining to the wall of the arc chamber, thereby increasing the electron temperature of the arc chamber. A method characterized by. 23. The method of claim 22, wherein the lining is separated from the wall of the arc chamber by a gap of about 0.1 mm. 24. The method of claim 22, wherein the refractory material is selected from the group consisting of carbon, vitreous carbon, silicon carbide, molybdenum, and tungsten. 25. The method of claim 24, wherein the refractory material is tungsten.