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A universal high-current implanter for surface modification of materials
MaterialsScienceand Engineering, A 116 (1989) 193-196
193
A Universal High-Current Implanter for Surface Modification of Materials* B. R. NIELSEN, P. ABRAHAMSENand S. ERIKSEN DanJ),sikA IS, DK-4040Jyllinge (Denmark) (ReceivedSeptember 16, 1988)
Abstract
A new high-current implanter dedicated for surface modification of materials has been developed and is now in operation at the Danish Tribology Centre in Aarhus, Denmark. The implanter contains a high-current multipole reflex-discharge ion source (CHORDIS) and produces mass analysed beam currents on the samples in the 5-1O mA range at energies up to 200 keV. A versatile ion beam focusing system combined with two-dimensional magnetic beam scanning offers high flexibility in the shaping of the implantation area (maximum 1600 cm:) and control of local current densities. The large target chamber contains a remote-controlled water-cooled sample manipulator with one linear and two rotational movements. Continuous monitoring of the sample temperature and interlocks prevents overheating of surfaces during implantation, 7he paper describes the general design of the implanter as well as ion beam performance and operational experience from implantations of "industrial" samples, 1. Introduction Although high-dose implantation of nitrogen has proven successful in improving the tribological properties of steel there exists considerable evidence that in some cases nitrogen has no effect or even a negative effect. In such cases the implantation of different ions, e.g. Ti +, Ta +, Cr +, B +, C + etc., may be used with success [1]. With such ions the implantation process can hardly be quantitatively controlled without mass analysis of the beam. Furthermore, the prevailing uncertainty *Paper presented at the Sixth International Conference on Surface Modification of Metals by lon Beams, Riva del Garda, Italy,September 12-16, 1988. 0921-5093/89/$3.50
in the theoretical understanding of ion-beaminduced modifications of material properties calls for better control of implantation parameters such as beam purity, beam energy, implantation dose, vacuum environment, sample temperature, etc. in research and development as well as in service work [2]. Recently Danfysik A/S has developed a Universal High-Current Implanter (Model 1090) which can serve as a research and development machine and at the same time have sufficient throughput capacity to work as a service implantation facility. The basic design criteria for this implanter were as follows: versatility in the choice of ion species: high currents; large range of beam energy: isotopically pure beams; beam shaping to optimise current density on target; beam scanning over large implant area; remotely controlled manipulation of complex samples; active cooling of samples; fast pump-down time; safety against improper implant conditions; personnel and equipment safety. One implanter is now in operation at the Danish Tribology Centre, a collaboration between Jutland Technological Institute, Aarhus, The Institute of Physics at Aarhus University and Danfysik A/S [3]. The aim of this centre is to transfer the ion beam surface modification technology to the Danish manufacturing industry. This will be pursued by (a) offering implantation and consultation services and (b) developing processing techniques and implantation hardware. Another implanter for similar purposes is presently under construction for the Euratom, Joint Research Centre at Ispra, Italy. © Elsevier Sequoia/Printed in The Netherlands
194
In the following some of the design features and operational characteristics of the 1090 Universal High Current Implanter will be presented, 2. Description of the implanter The implanter is shown in Figs. 1 and 2. The layout is "conventional" with mass separation at the extraction level and subsequent post-acceleration to the final beam energy. With this configuration the beam current loading of the accelerating section is reduced to a minimum which has many advantages such as reduction of space charge effects, HV supply rating, impurity beam power and radiation level, The ion optical system is designed for maximum transmission of the extracted beam to the target. Furthermore, care has been taken to ensure space charge compensation wherever possible in
!
~
~
iiiiiiiiiliiiii!!Lii iil ii !! ! iii ii:: ill
'"" ~iiiiiii~iiii
,
i:~ i
Fig. 1. Model 1090 high current implanter installation at
Jutland Technological Institute showing beam handling system with target chamber.
..............................
beam power. After post-acceleration the beam is focused and/or scanned by means of a quadrupole triplet magnet and an electromagnetic two-dimensional beam-scanning system. The beam may be focused to a minimum beam spot 10-20 mm in diameter or, if instantaneous power deposition on the
~III~IHVPROTECT/ONCAGE
I !
t00kvIMPLANTEU ~NIT
order to avoid beam instabilities and to maintain control of the beam. Thus the extraction and acceleration structures are compressed to a minimum length and include electron suppression electrodes to avoid electrons being drained from the beam plasma. For the same reason all beamhandling components such as analysers, lenses, scanners and steerers are magnetic. The ion source (Fig. 3) is a magnetic multicusp high-current ion source (CHORDIS) originally developed at GSI, Darmstadt [4, 5]. It produces a quiet, cold and stable plasma with densities suitable for forming high-current, high-brightness ion beams. In the single-aperture extraction version used in the implanter it produces stable beam currents in the range 5-40 mA. Charge materials may be gases, vapours, chemical compounds or solid elemental materials with a vapour pressure of 2 mbar at 1000 °C. Furthermore, an operation mode based on the sputtering technique to produce ions from pure high-melting-point elemental materials is presently under investigation with promising results [6, 7]. The extracted beam at 50 keV max is analysed in a double-focusing 90 ° analysing magnet with mass resolution of M/AM=250, and the analysed beam is post-accelerated to a maximum of 200 keV for singly charged ions. The implanter produces a maximum analysed beam current of 10 mA at 200 keV, corresponding to 2 kW of
BEAM SCANNING /MAGNE[S
, ',
i'
Fig. 2. Layout of the Model 1090 high current implanter.
:i iiiiiiiii~iiiii# i m
i
Fig. 3. The CHORDIS ion source, oven version.
195
target surface is of concern, defocused to larger circular or oblong dimensions (e.g. 100 mm in diameter or 50 mm x 400 mm). The scanning covers an area up to 40 cm x 40 cm and at maximum scan width moves the beam across the sample at a speed of 4 m s- ~ in one direction and 0.4 m s I in the other. Hence, with a well-focused beam a "point" on the surface of a stationary target will be exposed to the beam for approximately 5 ms with an average interval of 1 s. However, with a maximum beam power density of 2 kW cm 2 this may be too long an exposure time for thin and long samples or samples with sharp edges [8]. In such cases the defocusing of the beam may be applied for a more "gentle" treatment of the samples, At the entrance to the target chamber two large water-cooled hinged plates act as a beam stop which will allow the beam-focusing and scanning parameters to be set without the beam hitting the sample. A set of two magnetically suppressed Faraday cups may be used for checking the implant profile. One cup may be used for dose measurements during implantation by overscanning the beam so that it intercepts the beam. The target chamber (Fig. 4) is a vacuum box of approximate dimensions 0.7 m x 0.7 m x 0.7 m with several ports for diagnostics and adaptation of auxiliary equipment. It contains a sample manipulator which can rotate, tilt and move the samples up and down continuously or in a programmed way during implantation. The mechanical sample movements are slow compared with the beam scanning movements, typically a few rev min- t for the rotation and a few centimetres per
I .....
........
....It
second for the linear movement. The rotating sample holder is directly water cooled with sufficient flow rate to cool away the maximum beam power. To avoid accidental overheating of samples the temperature of the sample surface is continuously monitored by a dual-wavelength IR thermometer during implantation, and the process is automatically interrupted in case a preset upper (or lower)temperature limit is exceeded. In the standard version of the implanter the vacuum pumps in the source region and beam line are oil diffusion pumps. The target chamber has a 40 m 3 h J roughing pump and a 700 1 s diffusion pump with cryobaffie and separate backing pump. The pumping speed for water vapour is 2000 1 s 1. Since the various apertures, slits and lens chamber act as pumping restrictions, and the target chamber pump with cryobaffle is positioned upstream of the target, contamination by pumping oil into the target chamber is minimised. Several interlock systems for vacuum, high voltage, radiation and beam heating are adapted to the implanter to ensure personnel, equipment and sample safety.
3. Operational details The implanter at The Danish Tribology Centre has now been in operation since November 1987 and service implantations for industrial customers started in January 1988. So far the implanter has been operated with nitrogen, argon, sulphur, carbon, oxygen and titanium ions with analysed beam currents on target ranging from 1 to 6.5 mA. Since the recordings were made during service implantations or initial tests, these are not maximum-obtainable beam currents [4]. With these intensities a dose of 2 x 10 ~7 cm- 2 N + is obtained within 8 min for a small sample (100 cm 2) whereas a full batch
, 000 cm , wou, be imp,anted in 0 m,n !
he
Fig. 4. Interior of the target chamber showing the watercooled sample manipulator and mounting disc. The move-
corresponding times for Ti + implantation are 55 rain and 9 h. The base vacuum in the implanter is 5 x 10 7 mbar in the source and beam line regions and in the target chamber 3 x 10 ~ mbar. The pressure rise during operation depends on the beam intensity and whether a large "impurity" beam is dumped on the analysing magnet liner. Typically the vacuum in the source region is ( 2 - 4 ) x 10 5 mbar, in the beam line ( 2 - 5 ) x 1() -6 mbar and at
remotely bycomputer,
the target 0.5-2 x 10 5 mbar during implanta-
~i ............. i
ments are controlled either locally by push buttons or
196
tion. The target chamber is roughed down to 10 -2 mbar in 7 min and with cold cryobaffie 1 x 10 -5 mbar is obtained after a further 10 min pumping with the diffusion pump. Although the sample holder is directly water cooled the fast scanning and the possibility of shaping medium- and high-power beams has proved absolutely necessary because of the limited heat conductivity of many samples. Furthermore the continuous monitoring of the sample temperature is a very useful independent quality control check of the processing. The feedback from industrial users of implanted tools and samples has up to now been mostly positive. Several different types of component and steel types and alloys have been implanted. Many of these tools are still being tested in the production environment and final results are only available for a limited number of cases [3]. The improvements recorded up to now range from a factor of 1.3 to 6 with an average factor of 3.
target chambers on a switching magnet. In such a system one batch could be prepared and mounted in one chamber while another batch is being implanted in the other. With the expected close to doubling of the sample handling capacity an extra ion source would be needed in standby position for maximum efficiency. Since most electronics and part of the vacuum equipment may be shared between the two end stations the additional investment is relatively small for a large increase of efficiency. Finally, a "universal" implanter for surface modification should also include the option of combining evaporation or sputter deposition with ion implantation for ion beam mixing and ionbeam assisted deposition. The implanter now in production will be prepared for electron beam evaporation in the target chamber. Furthermore, it will also be possible in that system to combine laser surface treatments with ion implantation.
Acknowledgments 4. Future developments The practical experience obtained so far with service implantation has demonstrated the desirability of modification in two regions. Both have to do with increasing the throughput efficiency of the equipment. Firstly, the need for implantation of high-melting-point materials such as titanium, tantalum and chromium implies that any increase in the beam current of these elements is highly desirable because of the reduced implantation time. A joint development program between Danfysik and GSI, Darmstadt, on developing the sputtering technique for the ion source aims at producing ion beams of such elements in the range 2-5 mA. Secondly, even if the pump downtime of the sample chamber is short the time needed for mounting the samples with good heat contact to the cooling plate is time consuming and takes considerably more time than the pump-down and sometimes more than the implantation time. One way to improve this effectively is to mount two
The authors wish to thank Drs. C. A. Str~ede and S. Eskildsen of Jutland Technological Institute for providing information on the operational experience with the implanter.
References 1 Nucl. Instrum. Methods B, 19/20 (1987); Mater. Sci. Eng., 90 (1987); Nucl. Instrum. Methods B, 39 (1989). 2 G.D. Lempert, Surf. Coat. Technol., 34 (1988) 185. 3 C.A. Stra~de, Wear, 130 (1989) 1l 3. 4 R. Keller, P. Sp~idtkeand F. Nrhmayer, Proc. Int. lon Eng. Congr., Kyoto, Institute of Electrical Engineers of Japan, Tokyo, 1983,p. 25. 5 Manufactured by Danfysik A/S under license from GSI, Darmstadt (patented). 6 R. Keller, B. R. Nielsen and B. Torp, Nucl. lnstrum. MethodsB, 37/38 (1989) 74.
7 H. Emig, D. Prick, P. Sp~idtke, B. H. Wolf and B. Torp, Mater. Sci. Eng.,All6(1989)205.
8 K. S. Grabowski and R. A. Kant, in H. Ryssel and H. Glawishnig (eds.), Proc. 4th Int. Conf. on Ion Implantation." E q u i p m e n tand Techniques, Springer, Berlin, 1983, p.364.
193
A Universal High-Current Implanter for Surface Modification of Materials* B. R. NIELSEN, P. ABRAHAMSENand S. ERIKSEN DanJ),sikA IS, DK-4040Jyllinge (Denmark) (ReceivedSeptember 16, 1988)
Abstract
A new high-current implanter dedicated for surface modification of materials has been developed and is now in operation at the Danish Tribology Centre in Aarhus, Denmark. The implanter contains a high-current multipole reflex-discharge ion source (CHORDIS) and produces mass analysed beam currents on the samples in the 5-1O mA range at energies up to 200 keV. A versatile ion beam focusing system combined with two-dimensional magnetic beam scanning offers high flexibility in the shaping of the implantation area (maximum 1600 cm:) and control of local current densities. The large target chamber contains a remote-controlled water-cooled sample manipulator with one linear and two rotational movements. Continuous monitoring of the sample temperature and interlocks prevents overheating of surfaces during implantation, 7he paper describes the general design of the implanter as well as ion beam performance and operational experience from implantations of "industrial" samples, 1. Introduction Although high-dose implantation of nitrogen has proven successful in improving the tribological properties of steel there exists considerable evidence that in some cases nitrogen has no effect or even a negative effect. In such cases the implantation of different ions, e.g. Ti +, Ta +, Cr +, B +, C + etc., may be used with success [1]. With such ions the implantation process can hardly be quantitatively controlled without mass analysis of the beam. Furthermore, the prevailing uncertainty *Paper presented at the Sixth International Conference on Surface Modification of Metals by lon Beams, Riva del Garda, Italy,September 12-16, 1988. 0921-5093/89/$3.50
in the theoretical understanding of ion-beaminduced modifications of material properties calls for better control of implantation parameters such as beam purity, beam energy, implantation dose, vacuum environment, sample temperature, etc. in research and development as well as in service work [2]. Recently Danfysik A/S has developed a Universal High-Current Implanter (Model 1090) which can serve as a research and development machine and at the same time have sufficient throughput capacity to work as a service implantation facility. The basic design criteria for this implanter were as follows: versatility in the choice of ion species: high currents; large range of beam energy: isotopically pure beams; beam shaping to optimise current density on target; beam scanning over large implant area; remotely controlled manipulation of complex samples; active cooling of samples; fast pump-down time; safety against improper implant conditions; personnel and equipment safety. One implanter is now in operation at the Danish Tribology Centre, a collaboration between Jutland Technological Institute, Aarhus, The Institute of Physics at Aarhus University and Danfysik A/S [3]. The aim of this centre is to transfer the ion beam surface modification technology to the Danish manufacturing industry. This will be pursued by (a) offering implantation and consultation services and (b) developing processing techniques and implantation hardware. Another implanter for similar purposes is presently under construction for the Euratom, Joint Research Centre at Ispra, Italy. © Elsevier Sequoia/Printed in The Netherlands
194
In the following some of the design features and operational characteristics of the 1090 Universal High Current Implanter will be presented, 2. Description of the implanter The implanter is shown in Figs. 1 and 2. The layout is "conventional" with mass separation at the extraction level and subsequent post-acceleration to the final beam energy. With this configuration the beam current loading of the accelerating section is reduced to a minimum which has many advantages such as reduction of space charge effects, HV supply rating, impurity beam power and radiation level, The ion optical system is designed for maximum transmission of the extracted beam to the target. Furthermore, care has been taken to ensure space charge compensation wherever possible in
!
~
~
iiiiiiiiiliiiii!!Lii iil ii !! ! iii ii:: ill
'"" ~iiiiiii~iiii
,
i:~ i
Fig. 1. Model 1090 high current implanter installation at
Jutland Technological Institute showing beam handling system with target chamber.
..............................
beam power. After post-acceleration the beam is focused and/or scanned by means of a quadrupole triplet magnet and an electromagnetic two-dimensional beam-scanning system. The beam may be focused to a minimum beam spot 10-20 mm in diameter or, if instantaneous power deposition on the
~III~IHVPROTECT/ONCAGE
I !
t00kvIMPLANTEU ~NIT
order to avoid beam instabilities and to maintain control of the beam. Thus the extraction and acceleration structures are compressed to a minimum length and include electron suppression electrodes to avoid electrons being drained from the beam plasma. For the same reason all beamhandling components such as analysers, lenses, scanners and steerers are magnetic. The ion source (Fig. 3) is a magnetic multicusp high-current ion source (CHORDIS) originally developed at GSI, Darmstadt [4, 5]. It produces a quiet, cold and stable plasma with densities suitable for forming high-current, high-brightness ion beams. In the single-aperture extraction version used in the implanter it produces stable beam currents in the range 5-40 mA. Charge materials may be gases, vapours, chemical compounds or solid elemental materials with a vapour pressure of 2 mbar at 1000 °C. Furthermore, an operation mode based on the sputtering technique to produce ions from pure high-melting-point elemental materials is presently under investigation with promising results [6, 7]. The extracted beam at 50 keV max is analysed in a double-focusing 90 ° analysing magnet with mass resolution of M/AM=250, and the analysed beam is post-accelerated to a maximum of 200 keV for singly charged ions. The implanter produces a maximum analysed beam current of 10 mA at 200 keV, corresponding to 2 kW of
BEAM SCANNING /MAGNE[S
, ',
i'
Fig. 2. Layout of the Model 1090 high current implanter.
:i iiiiiiiii~iiiii# i m
i
Fig. 3. The CHORDIS ion source, oven version.
195
target surface is of concern, defocused to larger circular or oblong dimensions (e.g. 100 mm in diameter or 50 mm x 400 mm). The scanning covers an area up to 40 cm x 40 cm and at maximum scan width moves the beam across the sample at a speed of 4 m s- ~ in one direction and 0.4 m s I in the other. Hence, with a well-focused beam a "point" on the surface of a stationary target will be exposed to the beam for approximately 5 ms with an average interval of 1 s. However, with a maximum beam power density of 2 kW cm 2 this may be too long an exposure time for thin and long samples or samples with sharp edges [8]. In such cases the defocusing of the beam may be applied for a more "gentle" treatment of the samples, At the entrance to the target chamber two large water-cooled hinged plates act as a beam stop which will allow the beam-focusing and scanning parameters to be set without the beam hitting the sample. A set of two magnetically suppressed Faraday cups may be used for checking the implant profile. One cup may be used for dose measurements during implantation by overscanning the beam so that it intercepts the beam. The target chamber (Fig. 4) is a vacuum box of approximate dimensions 0.7 m x 0.7 m x 0.7 m with several ports for diagnostics and adaptation of auxiliary equipment. It contains a sample manipulator which can rotate, tilt and move the samples up and down continuously or in a programmed way during implantation. The mechanical sample movements are slow compared with the beam scanning movements, typically a few rev min- t for the rotation and a few centimetres per
I .....
........
....It
second for the linear movement. The rotating sample holder is directly water cooled with sufficient flow rate to cool away the maximum beam power. To avoid accidental overheating of samples the temperature of the sample surface is continuously monitored by a dual-wavelength IR thermometer during implantation, and the process is automatically interrupted in case a preset upper (or lower)temperature limit is exceeded. In the standard version of the implanter the vacuum pumps in the source region and beam line are oil diffusion pumps. The target chamber has a 40 m 3 h J roughing pump and a 700 1 s diffusion pump with cryobaffie and separate backing pump. The pumping speed for water vapour is 2000 1 s 1. Since the various apertures, slits and lens chamber act as pumping restrictions, and the target chamber pump with cryobaffle is positioned upstream of the target, contamination by pumping oil into the target chamber is minimised. Several interlock systems for vacuum, high voltage, radiation and beam heating are adapted to the implanter to ensure personnel, equipment and sample safety.
3. Operational details The implanter at The Danish Tribology Centre has now been in operation since November 1987 and service implantations for industrial customers started in January 1988. So far the implanter has been operated with nitrogen, argon, sulphur, carbon, oxygen and titanium ions with analysed beam currents on target ranging from 1 to 6.5 mA. Since the recordings were made during service implantations or initial tests, these are not maximum-obtainable beam currents [4]. With these intensities a dose of 2 x 10 ~7 cm- 2 N + is obtained within 8 min for a small sample (100 cm 2) whereas a full batch
, 000 cm , wou, be imp,anted in 0 m,n !
he
Fig. 4. Interior of the target chamber showing the watercooled sample manipulator and mounting disc. The move-
corresponding times for Ti + implantation are 55 rain and 9 h. The base vacuum in the implanter is 5 x 10 7 mbar in the source and beam line regions and in the target chamber 3 x 10 ~ mbar. The pressure rise during operation depends on the beam intensity and whether a large "impurity" beam is dumped on the analysing magnet liner. Typically the vacuum in the source region is ( 2 - 4 ) x 10 5 mbar, in the beam line ( 2 - 5 ) x 1() -6 mbar and at
remotely bycomputer,
the target 0.5-2 x 10 5 mbar during implanta-
~i ............. i
ments are controlled either locally by push buttons or
196
tion. The target chamber is roughed down to 10 -2 mbar in 7 min and with cold cryobaffie 1 x 10 -5 mbar is obtained after a further 10 min pumping with the diffusion pump. Although the sample holder is directly water cooled the fast scanning and the possibility of shaping medium- and high-power beams has proved absolutely necessary because of the limited heat conductivity of many samples. Furthermore the continuous monitoring of the sample temperature is a very useful independent quality control check of the processing. The feedback from industrial users of implanted tools and samples has up to now been mostly positive. Several different types of component and steel types and alloys have been implanted. Many of these tools are still being tested in the production environment and final results are only available for a limited number of cases [3]. The improvements recorded up to now range from a factor of 1.3 to 6 with an average factor of 3.
target chambers on a switching magnet. In such a system one batch could be prepared and mounted in one chamber while another batch is being implanted in the other. With the expected close to doubling of the sample handling capacity an extra ion source would be needed in standby position for maximum efficiency. Since most electronics and part of the vacuum equipment may be shared between the two end stations the additional investment is relatively small for a large increase of efficiency. Finally, a "universal" implanter for surface modification should also include the option of combining evaporation or sputter deposition with ion implantation for ion beam mixing and ionbeam assisted deposition. The implanter now in production will be prepared for electron beam evaporation in the target chamber. Furthermore, it will also be possible in that system to combine laser surface treatments with ion implantation.
Acknowledgments 4. Future developments The practical experience obtained so far with service implantation has demonstrated the desirability of modification in two regions. Both have to do with increasing the throughput efficiency of the equipment. Firstly, the need for implantation of high-melting-point materials such as titanium, tantalum and chromium implies that any increase in the beam current of these elements is highly desirable because of the reduced implantation time. A joint development program between Danfysik and GSI, Darmstadt, on developing the sputtering technique for the ion source aims at producing ion beams of such elements in the range 2-5 mA. Secondly, even if the pump downtime of the sample chamber is short the time needed for mounting the samples with good heat contact to the cooling plate is time consuming and takes considerably more time than the pump-down and sometimes more than the implantation time. One way to improve this effectively is to mount two
The authors wish to thank Drs. C. A. Str~ede and S. Eskildsen of Jutland Technological Institute for providing information on the operational experience with the implanter.
References 1 Nucl. Instrum. Methods B, 19/20 (1987); Mater. Sci. Eng., 90 (1987); Nucl. Instrum. Methods B, 39 (1989). 2 G.D. Lempert, Surf. Coat. Technol., 34 (1988) 185. 3 C.A. Stra~de, Wear, 130 (1989) 1l 3. 4 R. Keller, P. Sp~idtkeand F. Nrhmayer, Proc. Int. lon Eng. Congr., Kyoto, Institute of Electrical Engineers of Japan, Tokyo, 1983,p. 25. 5 Manufactured by Danfysik A/S under license from GSI, Darmstadt (patented). 6 R. Keller, B. R. Nielsen and B. Torp, Nucl. lnstrum. MethodsB, 37/38 (1989) 74.
7 H. Emig, D. Prick, P. Sp~idtke, B. H. Wolf and B. Torp, Mater. Sci. Eng.,All6(1989)205.
8 K. S. Grabowski and R. A. Kant, in H. Ryssel and H. Glawishnig (eds.), Proc. 4th Int. Conf. on Ion Implantation." E q u i p m e n tand Techniques, Springer, Berlin, 1983, p.364.