JP2837023B2 - Ion implanter with improved ion source life - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an improved system and method for implanting preselected ions into a target. In particular, the present invention relates to an apparatus for implanting preselected ions into a target that has improved ion source life and reduced ion beam contamination.

[0002]

2. Description of the Related Art In the manufacture of semiconductor devices, various types of hardware are manufactured 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 a semiconductor device becomes smaller as in the case of manufacturing LSIs and VLSIs, interconnections between them become closer to each other. As a result, while the wafer is used efficiently and the operating speed of the apparatus is increased, the arrangement of the conductivity correcting means must be further increased accordingly. Improvements have also been made to the equipment used to perform the doping.

[0003] Diffusion involves placing conductivity modifying ions on the surface of the wafer and driving them into the wafer with heat, but the diffusion process drives the ions both laterally and vertically into the wafer. Therefore, there are limitations in tightly controlling the shape. Therefore, ion implantation that can anisotropically implant ions into the wafer,
It is the method of adding impurities that is used favorably in the manufacture of the latest equipment.

[0004] Various ion implanters using several types of ion sources are known. An ion beam of a preselected species is created by applying a current to a filament in a controlled ion source chamber provided with a power source and a gas that is an ion precursor. The ions are extracted through an opening in the ion source chamber by a voltage between the ion source chamber that is positive and the extraction means. An associated acceleration system, a magnetic analysis stage that separates desired ions from undesired ions based on mass and focuses the ion beam, and directs desired ions at a desired beam current level to a target or substrate wafer. After the acceleration stage, the system is completed. 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. State of the art ion implantation systems are described in U.S. Pat. No. 4,754,200 to Plumbal et al. And U.S. Pat. No. 4,578,589 to Aitken, both of which are described. Is incorporated herein by reference.

[0005] The most common type of commercially used ion source is known as the Freeman source. In the Freeman source, the filament, or cathode, is a straight rod that can be made from tungsten or an alloy of tungsten or other known source materials, such as iridium, which is 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 And a power supply connected from the filament to the arc chamber.

[0007] When power is applied to the filament, the filament temperature rises until it emits electrons, which bombard and destroy 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 are selectively passed to a target. The filament is insulated with an electrical insulator that also serves to support the filament. The insulator is, for example, made of high temperature ceramic material such as alumina or boron nitride, which is resistant to high temperatures and a corrosive atmosphere generated from the precursor gas species and fragments thereof, such as BF ₃ or SiF ₄ . It can be seen that the insulator severely limits the life of the ion source. Although the exact number and type of ions generated in the ion source chamber are not known with certainty, the various ions generated in the chamber are both the graphite walls of the chamber and other ions in the chamber. May form a reaction product, which adheres to the insulator walls to form a conductive coating. For example, when BF ₃ is supplied to the ion source chamber, the chemical reaction of the graphite with carbon and fluorine from the chamber walls, for example, C
It occurs various fluorocarbon such as F and CF _2, which becomes a fine dust react further, which covers the insulator. Conducting compounds can also be produced from other parts of the ion source chamber. Even very thin conductive coatings may short out the arc source, hindering 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 insulation and filament must be reconditioned or replaced. This is the most common and most frequent cause of ion implanters.

Some prior art researchers have made proposals to prevent the formation of this conductive coating on insulators. For example, it is known to alter the shape of the electrical insulator in the arc chamber to reduce the formation of coatings, but this does not significantly extend the life of the device. Others have proposed shields to protect the insulator from the formation of a conductive coating, which itself increases system instability. Although a cleaning discharge to etch away the coating inside the chamber has also been attempted, a degree of success has been achieved since other ions can be formed during the etch and introduce other instability and unwanted ions into the chamber. Was miscellaneous.

Thus, there is a method of reducing or eliminating the formation of a conductive coating on a filament insulator, thereby increasing the time between repairs of the arc chamber and reducing the downtime of the ion implanter. Highly desired. Further, 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 apparatus of the present invention places an electrical insulator for the filament outside the arc chamber while maintaining the ion source body's ability to insulate the filament. Although it can be mounted where it can travel, it is no longer possible for the insulator to form a conductive coating quickly because the insulator is no longer located within the arc chamber itself and is therefore not exposed to ionic species. Absent. Thus, the life of the ion source is greatly extended compared to conventional ion beam devices.

[0011] To further prevent the filament insulation from forming a conductive coating from the gas in the arc chamber, further protecting the insulation from the chamber gas by at least one of a shield and an inert gas spill. Can be done. Contamination of the ion beam by contaminants from the material in the arc chamber can be reduced by making the arc chamber itself, a portion thereof, or its removable lining of tungsten.

Since the ionization efficiency of the arc chamber is improved by using a removable refractory lining,
The heat generated in the chamber when power is supplied to the filament is transmitted by radiation to the chamber walls, increasing the electron temperature during operation.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a freeman ion implanter according to the prior art. Ions are generated in the arc chamber 15 of the Freeman ion source. Extraction electrode assembly 1
3 is a rectangular opening 15A at the front of the arc chamber 15.
To extract a beam of ions. The ion beam is extracted and accelerated toward the mass spectrometry system 20, which includes an ion beam flight tube 21 that provides a path between the poles of the 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 strikes the beam stop 51. The suppression magnet 52 of the beam stop device 51 generates a magnetic field that is directed to ensure an accurate measurement of the resulting beam current by blocking electrons arriving and exiting the beam stop. Let it.

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

As shown in FIG. 2, the Freeman ion source is activated from an electrical point of view by coupling a filament power supply 60 to the filament 15B to supply a large current to the filament at a low voltage. . Arc power supply 61 applies a voltage between filament 15B and arc chamber 15 that is typically clamped to a maximum of about 120 volts, with arc chamber 15 acting as an anode. The filament 15B generates thermionic electrons which are accelerated through the gas species in the arc chamber toward the arc chamber walls to create a plasma of the ionic species in the arc chamber 15.
This ion implanter is more fully disclosed in U.S. Pat. No. 4,754,200, which is hereby incorporated by reference in its entirety.

FIG. 3 is a side view of a burner type ion source according to the present invention. A Bernas ion source differs from a 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 a Bernas type ion source and a Freeman type ion source.

Referring to FIG. 3, ion arc chamber 110 is an almost closed chamber having 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. An evaporable metal source such as antimony, arsenic or phosphorus is evaporated in a high temperature oven and then
It can be sent into the chamber 110. The arc chamber 110 also has an exit opening 114 through which the ion beam generated in the arc chamber 110 exits, is focused, and is accelerated to a desired target. A coiled filament 116 is at one end of the arc chamber 110. Filament 1
An enlarged 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 and reflects the electrons generated in 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 the arc chamber mounting can maintain a gap between them to prevent the reflector 118 from contacting the arc chamber 110 and the lining 134, but such contact may cause a short circuit. Becomes A refractory electron reflecting device 120 is located at the other end of the arc chamber and 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 more detail below. Insulation 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 prevents gas molecules from reaching the insulator 128 from zero. The insulator 128 is located 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,
The filament is electrically insulated in the chamber 110. FIG. 5 shows the insulator / shield assembly 128 /
FIG. 4 is an enlarged detail view of 130 with the same numbers used in the same parts as in FIG. One or more shields 130 that form a labyrinth around the insulator 128 allow the insulator 12 to be isolated from gaseous species released from the arc chamber 110.
8 can be further protected. The gas type is insulator 12
This labyrinth furthermore has to hit the wall of the labyrinth several times before reaching
Protect 8 The more surfaces around the insulator 128, the more
The likelihood of gas species from the arc chamber 110 coalescing and condensing before reaching the insulator 128 is increased.
The shield 130 can be made from a metal such as stainless steel.

Another method of protecting the electrical insulator 128 is
Flowing an inert gas over insulator 128 to prevent gaseous species from reaching insulator 128.
The cloud of inert gas around insulator 128
Acts as an additional barrier to prevent the diffusion of gas species toward the To enhance the protection of the electrical insulator 128 located outside the arc chamber 110, one or both, preferably both, of the shielding means 130 and the inert gas barrier means (not shown) may be used. I can do it.

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

The efficiency of the ion source is part of the input material (precursor gas) to the ion source that is ionized and extracted from the ion source. The higher this efficiency, the less material is needed to produce a given extraction current or ion beam. Thus, there are several advantages to increasing ionization efficiency. That is, the amount of gaseous ion source material that needs to be supplied to the arc chamber 110 is reduced, the vacuum level that must be used is reduced, and contamination of unwanted ionic species that occurs is reduced. This may also reduce the total usable gas species that may coat or enrich inside or outside 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 conveniently made of tungsten. The material of the lining is important because there is a risk of contaminating the target or substrate that is implanted by the molecules or ions of the lining. For example, Mo ²⁺ (MW9
8) cannot be decomposed from the impurity source ion BF ₂ (MW49), and cannot be separated from the impurity ions during mass spectrometry, and is sent as a contaminant during boron ion implantation. As another example, the reaction between a carbon arc chamber and plasma fluorine atoms is CF
(MW31) causing ions and CF ₂ (MW50) ions, the mass is the same as the common impurities such as P (MW31) and BF ₂ (MW50). Since these fluorocarbon ions are not completely separated from the impurity ions,
Boron and phosphorus ion implantation also become contaminants.

[0024] Tungsten linings are convenient to use because they do not contaminate the wafer or other substrate to be implanted. In fact, in our research on tungsten lining, the same advantage of low contamination of the implant by 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. In general, conventionally, the arc chamber was made of carbon or molybdenum, which, as described above, may include various ion implantations such as boron and phosphorus, for example, Mo.
There is a problem in that ionic species contaminated by ⁺² and CF or CF ₂ are generated. Thus, by making the arc chamber itself, or a portion of the arc chamber, for example, a wall having an exit opening, of tungsten, it may be used with or without a lining, and with a tungsten lining. Even without use, contamination of the ion implant by the material in the arc chamber is reduced. Advantageously, other parts, such as the reflector for the filament, are also made of tungsten. As mentioned in detail above, the insulator
The same applies to the case inside or outside the chamber.
Therefore, it is conceivable that the whole or a part of the arc chamber or a part such as a reflection device in the arc chamber is made of tungsten using the conventional ion implantation apparatus or the ion implantation apparatus 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. SiF ₄ in the case of toxic or corrosive strong input precursor gases, such as or BF _3, lower the required vacuum level in the system by reducing the total amount of the required gas is highly desirable. Problems associated with vacuum, such as collisions with natural gas species that would create unwanted ionic species in the ion beam, resulting in the implantation of unwanted species, are reduced. 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 onto the outer surface of the arc chamber. The risk of condensation is also reduced. This also reduces other sources of ion beam instability and increases the period between required oven refills.

Another advantage is that higher temperatures produce higher levels of desired ions, and thus higher wall temperatures increase the yield of certain ionic species. For example, the ratio of desired B ₁₁ ion formation to ion formation, such as unwanted BF ₂ , increases from about 1.5: 1 to about 2: 1. This is a surprising increase in ionization efficiency. The device of the present invention
Significantly increasing the time for forming the conductive coating on the electrical insulator extends the life of the ion source by a factor of two to four, and also reduces the inoperable time of the ion implanter. . The lining 134 is removable so that it can be replaced as desired during maintenance of the arc chamber. Because the number of times that the ion source is maintained is reduced, not only is the time between maintenances increased, but also the opportunity for erroneous reassembly that causes other failures of the ion implanter.

The maintainability of the ion implanter is also enhanced 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 clamp both ends of a Bernas 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
Engage simultaneously with both 16 and the filament reflector or guide 118 to maintain their relative alignment. Each clamp 200, 201 forms one integral assembly 4
Two jaws 202, 204, 206, 208 and a straight slot 2 in the upper jaw pair 202/206.
09. The upper jaws 202, 206 have a smaller opening 210 for clamping one end of the filament 116. Lower jaws 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 change, or both pairs of jaws
02/206 and 204/208 with Allen Key 214
Can be opened together.

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. Having. 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, the jaws 202/206
Is forcibly opened by the larger curved surface 220 of the screw 216. This operation is repeated with clamp 201 (see FIG. 6). At this time, the filament 116 can be removed for repair or replacement. To clamp the new filament 116 in place, the screw 216 is turned another ４ turn, at which time each clamp 200 and 201 retightens to hold the replacement filament 116.

When removing or replacing both the filament 116 and the reflector 118 around it, the screw 21
6 into the second position 224. Screw 216
Four turns will result in both sets of jaws 202/206 and 2
04/208 opens to release both filament 116 and reflector 118. After the replacement, the screw 216 is again rotated by 1/4 turn, and the filament 116 and the reflecting device 1
18 are clamped together to maintain their alignment.

This clamping system 124 allows for efficient removal of filaments and reflectors during maintenance of the ion source chamber. Reduces downtime, allows the filament and filament reflector to be handled as a single unit, which allows for quick replacement of the device and reduces the risk of filament and filament reflector or guide misalignment during reassembly I do.

The modification of the ion implanter described in the present invention extends the life of the ion source, requires only a small amount of downtime for the device and is a source of misalignment of the filament and the filament reflector. Is eliminated, and the inoperable time is further reduced. arc·
The use of a removable lining in the chamber can improve ionization efficiency and reduce ion beam contamination depending on the material used.

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

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a prior art ion implanter beamline that is a 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 burner type filament.

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

FIG. 6 is a top view of a pair of four-jaw integrated clamps that assist in gripping a Bernas-type filament.

FIG. 7 is an exploded view of the clamping system of FIG. 6;

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Paul Barfield United Kingdom Sussex Crawley Three Bridges Scarous Road Far Farns (no address) (72) Inventor John Pontefract United Kingdom Sussex Ackfield de Manor Park Browns Lane 70 (72) ) Inventor Bernard Harrison England West Sussex Ar Ruhr 103 3 EW Coptomet Newlands Park 16 (72) Inventor Peter Mears England West Sussex Hen Field Personage Road 61 (72) Inventor David Virgin France Grenoble Mevran Bleman Depressle 2 Screw tampo lodge 2 Apartment 1 (56) References JP-A-1-95454 (JP, A) JP-A-54-139000 (JP, A) JP-A-2-1383839 (JP, U) (58) Fields investigated (Int. . ^6, DB name) H01J 27/00 - 27/26 H01J 37/08 H01J 37/317

Claims (4)

(57) [Claims] 1. An arc chamber for generating a plasma having an opening for emitting an ion beam on one surface, a filament connected to a current source, and generation of a plasma precursor gas. An electrical insulator for said filament is mounted outside said arc chamber;
And wherein the filament is surrounded by a reflector or shield mounted around the filament such that an insulating gap is maintained between the reflector or shield and the wall of the arc chamber. Ion implantation equipment. 2. The arc chamber further comprises a replaceable liner made of tungsten, the liner and the liner of the chamber being heated such that walls of the chamber are heated by radiation from the liner. The ion implanter of claim 1, wherein the ion implanter is mounted to maintain a gap between the wall and the wall. 3. The ion implanter according to claim 1, wherein said filament, said arc chamber and said liner are all made of tungsten. 4. The ion implanter of claim 1, wherein a unitary clamp grips the filament and the reflector to maintain alignment thereof.