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An electron beam lithography tool with a Schottky emitter for wide range applications
Microelectronic Elsevier
Engineering
81
23 (1994) 81-84
An electron beam lithography tool with a Schottky emitter for wide range applications B.H. Koeka, T. Chisholma, a Leica Cambridge
A.J. v. Runb, J. Romijnb,
Ltd., Clifton Road, Cambridge
and J.P. Davcy”
CBl 3QH, United Kingdom
bDelft Institute of Microelectronics and Submicron Technology (DIMES), Delft University of Technology, P.O.Box 5053,260OGB Delft, The Ncthcrlands
An electron beam lithography tool with a Schottky field emitter source has been designed. The electron beam column can produce beam diameters between 6 nm and 250 nm, with corresponding currents up to 250 nA at 20, 50 and 100 kV accelerating voltage. It has been demonstrated that the tool is suitable for both very high resolution and fast reticle production. Feature sizes below 15 nm were resolved in resist after exposing with a calculated spot of 5.6 nm at 50 kV. Masks were produced with a 250 nm / 250 nA beam at 50 kV. The overlay between three masks was measured to bc 78 nm over a 100 mm arca and the placement accuracy in each mask was better than 60 nm. The stability at 50 kV was below 30 rim/h in position and around 1 %/h in current. 100 kV measurements showed an open loop position stability of better than 20 rim/h and 3 %/h current variation.
1. INTRODUCTION The user requirements of lithography tools arc constantly moving towards smaller dimensions and higher throughput, both coupled with high accuracy. Pfeiffer and Groves [ 11 have predicted that by the end of the century X-ray masks will demand minimum features of about 120nm with overlay values of 25 nm. Also users are confident that optical lithography will be used for the production of 1Gb DRAMS. This requires 5X-retitles with 175 nm minimum feature size and 35 nm overlay, all written with acceptable speed. High brightness Schottky, thermal field, emitters have proven to be successful in improving the speed of electron beam lithography systems [2-31. The performance has been reported for both high resolution [4] and mask making applications [5]. The designs described there arc mainly for one or the other application. We have designed a new source and column configuration (FEG) which is suitable for high resolution applications and an alternative version of the column with a modified deflection system particularly for reticle writing. Both concepts can be applied to the current Leica range of ebeam tools. The design work, which has been described by Koek et al. [6], was part of a European ESPRIT project (FREE) to dcvclop a lithography tool which could write the rcticlc for a poly-silicon layer of a dual 64 Mb DRAM in 30 minutes. 2. SOURCE
AND
COLUMN
DESIGN
The source is a commercially available zirconiated tungsten emitter; as reported by Tuggle et al. [73, these emitters operate at a current density in ex-
cess of 104 A/cm* coupled with an effective source diameter of a few tens of nanometers. In addition to the source the new designed optical module consists of a suppressor, extractor and focus electrode. The extractor and focus electrode together with the anode form an clcctrostatic lens (Cl). A larger solid angle of emission, 0.001 sterad, is transmitted so that, at an emission density of 1 mA/sterad, a beam of 1 pA is transmitted down the column. The prototype module has been integrated into a modified EBPG-5HR column located in DIMES. The beam emerging from the source module is aligned with the column axis by double aligners befort cntcring the second lens (C2). This magnetic lens which, together with Cl, forms a zoom system allowing the beam diameter to be continuously variable bctwecn 6 nm and 250 nm, with corresponding currents up to 250 nA at 50 kV. The zoom lens image is focused in the centre of the beam blanker in order to have conjugate blanking. The final double elccuomagnetic lens (C3) focuses the spot onto the substrate and corrects both static and dynamic focus and astigmatism variations. In order to maintain conjugate blanking, the on axis setting of C3 should bc kept constant and only correctcd for the substrate height. This sets extra requirements to the automatic column set-up and focusing routines. On axis focusing should be performed by using the zoom lenses. This will however inlluence the actual beam current or spot size and an iterative process is necessary to compensate for focusing induced beam variation. Dynamic, offaxis, focus is still corrected by C3. In the high resolution column, a double mainfield and a single sub-field deflector unit is positioned between the beam blanker and C3. The maximum deflection main-field size is 800pm square at
0167-9317/94/!$07.00 0 1994 - El sevier Science B.V. All rights reserved.
B.H. Koek et al. I An e-beam lithography tool with a Schottky emitter
82
L_zl-
I
50 kV and 56Opm square al 100 kV. Figure 1 shows a schematical cross-section of the high resolution column. Figure 2 shows the theoretical spot size of the HR column against beam current for an angular emission density of 1 mA/stcrad and acceleration voltages of 20, 50 and 100 kV. The spot size is defined as the diameter containing 50 o/o of the total current. The curves differ from those presented in (6). The stochastic broadening in the short distances from the source to Cl and from C3 to the substrate cannot bc ncglcctcd. Also WC have made some changes to the manner of combining the contributions in various sections of the column. In the fast reticle column the double pre-lens deflcctor is replaced by a single post lens deflector and the working dislance is increased from 40 to 75 mm. The increased working distance together with better control over deflection distortions allows for a larger field size than the HR version (4000pm square at 30 kV and 3(X)0 pm at 50 kV).
Cl primary plane
Gun alignment coils
-
C2 primary plane
--
II
A --
Beam blanker
1st Main deflection Sub-field deflection 2nd Main deflection
II I I:--
’
v[ EE -
3:
3.
C3 primary plane
Figure 1. Schematical resolution column.
Mask making The FREE rcquircmcnts for the accuracy and speed are listed in Table 1. In order to achieve the throughput spccil‘ication, i.c. dual 64Mb DRAM poly-silicon layer cxposcd in 30 minutes, a beam step size of 250nm is necessary, with a deflection speed of 25 MHz. The typical beam current for reticle production is cxpcctcd to bc around 250nA.
cross-section
of the high
100 kV E : R ‘5 5 fz
100:
-
50kV
-
20kV
Table 1. FREE main specifications 10 1
Edge roughness (pp) Placcmcnt (30) Overlay 30) 1
!
. . . ...
.1
..I
.
.
.
.
. . ‘I
.
.
.
. .
10
I
Beam
current
. ..I
100
.
Table 2. Calculated and experimental sity of 0.38 mA/sterad.
;:;
C3 (A) Diameter (nm) Current (nA)
1000
(nA)
01
column characteristics
2.787 110 0.625
Table 2 shows the thcorctical and experimental set-up for a 250nm spot size. This spot size vs. beam currcnl relation can be obtained with an emission density of only 0.38 mA/stcrad.
at 50 kV, 400 pm final aperture and an emission current den-
High resolution Theoretical Experimental 0.636 2267 20.620 100 2.816 5.61 0.625
and FEG performance FREE FEG 25 nm 40 nm 50 nm 60 nm 70 nm 78nm
.~.--4
Figure 2. Theoretical spot size vs. beam current the HR column at 1 mA/sterad emission density.
::
RESULTS
3.1.
1
.
EXPERIME:N’I’AL
Mask making Thcorctical Experimental 0.995 3238 0.950 3235 2.816 187 250
2.787 250 250
B./i. Koek et al. I An e-beam lithography
diamctcr can only bc obtained the source. This sets cstr;t condilions to the susccplibilily of the column to cxternal elcctrom~tgnctic ficlds and vi brations. C;trcl.u I analysis of all the noise compon~*nts on the beam rcsullcd in an inventory of all noise sources. The required
by actually
bcatn
magnifying
Removal of the predominant internal sourccs rcsulted in a reduction of the position noise LO less than 30 nm al 250 nm spot size. The main contribution to the remaining noise is an 1.S mGauss horizontal, external, field around the top of the column. Extra p-melal shielding in the aligncr section will be installed to reduce the influcncc even further. Three test masks wcrc cxposcd under Lhcsc conditions. The exposure Gmc for each mask was 30 min. The position- and beam current slabilily for this column set-up arc shown in Figure 3 and 4. From this figure it can bc derived that the stability is sufficicnt to fulfil the FREE rcquircmcnLs for ovcrlaq and critical dimension. The edge roughness, rcgi?;trution and ova-lay wcrc mcasurcd and arc lislcd in Table 1. 50 ,
40 f
tool with a Schottky
83
emitter
17.-. _
tligh resolution Writing high resolution patkrns rcquircs not only a sm:;ll b&n diamctcr, but also placement accuracy and stabilily in the same order of magniwdc oC the l’caturc six and prcl’cr:rbly cvcn smaller. The column is dcsigncd Lo product beam diamctcrs bclow 6 nnl. Lithography cspcrimcnls using a calculated beam diamctcr ol 5.6 nm and a 5 nm barn step size wcrc pcrl‘ormcd. Figure 5 shows a SEM micrograph of lines smaller than 1.S nm obtained in 100 nm thick PhlhlA (05OK) using a lint charge of 2 nC/cm. Table 2 shows the c:llculatcd and cxpcrimcnlal dalii for lhis scl-up. Figure 6 shows the open loop @lion stability of this column s&up. The measured instabilily over ;I period of one hour is close lo Lhc laser intcrfcrorncter resolution (5.3 nn~).
1
1--t
0
X position variation (nm) Y position variation (nm)
10
20
30
40
50
60
Time (minutes) Figure 3. Posttion conditions.
stability
from
rcticlc
writing
Figure lh:lll
2
5. SEbI IS 11111.
30
I
20 -1 10 -
0
, 10
.
,
.
20
,
.
30
,
.
40
, 50
.
1 60
-
-
stability
I‘rom
Y position variation (nm)
1
-““I
Time (minutes) Figure 4. Current conditions.
200
Time rcticlc
writing
smaller
0
-lOz .ZZ .: -2oa -21.
lines
X positton variation (nm)
r
.z .!? 2
o!’ cxposcd
I
5 6
image
Figure 6. Position \vrlting.
300
(minutes)
stability
l‘or high
rcsolulion
B.H. Koek et al. I An e-beam lithography tool with a Schottky emitter
84
In Figure 5 clearly field boundaries can bc observed in the exposed lines. The stitching errors are measured to be 15 nm for the main- and approximately 7 nm for the sub-field. A further invcstigation is necessary in order to improve the stitching performance for very high resoluLion applications. 100 kV operation The source module and column arc designed for 100 kV accelerating voltage. The micro gcomctry of the tip can easily be destroyed by high voltage discharges. The main cause for discharges is found to be contamination on the source module and the inside of the emission chamber. 100 kV operation rcquires a far more stringent cleaning procedure than stable 50 kV operation. After cleaning, the system was set to 100 kV. A full charactcrisation is currently in progress and Figure 7 shows the first rcsuits from position and Figure 8 Lhc currc.nt stability measurements. For the measurcmcnts a beam current of 1.3 nA was used. From Figure 8 it can be seen that both the beam and extractor current arc still varying. This may bc caused by formation of the tip. The mcasurcmcnls were performed wilh a newly installed tip. 3.3.
a8
-20 -
y
. _ -30
variation
(nm)
I 100
0
CONCLUSIONS
An clcctron beam column with a Schottky field emission source has been designed for both high resolution and high throughput mask production. The spot size range which can bc obtained with this ith to 250 nm column is calculated to be from an effccLivc brightness of 1.5~10 7 A/sterad.cm 7 at 50 kV. The thcorctical and cxperimcntal column sctup at 50 kV are in rcasonablc agreement. The ability to produce small spots has been dcmonstratcd in lithography experiments. A line width of less than 15 nm was obtained in 100 nm PMMA using a, theoretically predicted, 5.6 nm spot size. The position stability for this column set-up showed an accuracy in the order of the laser interfcromctcr rcsolulion (5.3 run). Masks wcrc exposed using 250 nA at 50 kV. The mcasurcd currcnl stability is around 1 %/h (open loop). The position stability was mcasurcd to be bet&r than 30 rim/h (open loop). The placcmcnt accuracy in three masks was mcasurcd to bc 60nm (30) and the overlay 78 nm (30) over a 5 inch area. The cdpc roughness of 1.Opm lines was better than 40 nm (peak LOpeak). Operation of the column at 100 kV showed a position drift 01’20 rim/h and beam current variations of less than 3 %/h.
WC wish LO thank our collcagucs in Leica Cambridge who have conuibutcd to the success of this projccl. Prof. J. Orloff for cncouragcment and valuable advice in the early stage of Ihe developmcnt. WC thank the EEC for funding of the FREE project and our partners for Lhcir collaboration.
X-positionvariation (nm) Y-position
1.
200
Time (minutes)
Figure 7. Position
stability
I.
at 100 kV.
7
I
J
Beam current _
Extractor current
7 -.
3.
4.
5. I
6.
100 Time
(minutes)
7. Figure 8. Current
stability
at 100 kV.
H. Pfciffcr, R. Butsch, and T. Groves, Microclcctronic Engineering 13 (1991) 141. J. Kelly, T. Groves, and H. Kuo, J. Vat. Sci. Tcchnol. Is19 (1981) 936. N. Samoto, R. Shim& H. Hashimoto, N. Tamura, K. Gamo, and S. Namba, Jpn. J. of Appl. Phys. 2.4 (1985) 766. H. Nakazawa, H. Takemura, M. Isobc, Nakagawa, M. Hasscl Shcarcr, and Y. W. Thompson J. Vat. Sci. Technol I$6 (1988) 2019. M. Gcslcy J. Vat. Sci. Tcchnol. 1%‘)(1991) 2949. B.H. Kock, T. Chisholm, J.P. Davcy, J. Romijn, and A.J. v. Run Microproccss Confcrcncc, Hiroshima, July 1993. D.W. Tugglc and L.W. Swanson. J. Vat. Sci. Tcchnol. I$3 (1985) 220.
Engineering
81
23 (1994) 81-84
An electron beam lithography tool with a Schottky emitter for wide range applications B.H. Koeka, T. Chisholma, a Leica Cambridge
A.J. v. Runb, J. Romijnb,
Ltd., Clifton Road, Cambridge
and J.P. Davcy”
CBl 3QH, United Kingdom
bDelft Institute of Microelectronics and Submicron Technology (DIMES), Delft University of Technology, P.O.Box 5053,260OGB Delft, The Ncthcrlands
An electron beam lithography tool with a Schottky field emitter source has been designed. The electron beam column can produce beam diameters between 6 nm and 250 nm, with corresponding currents up to 250 nA at 20, 50 and 100 kV accelerating voltage. It has been demonstrated that the tool is suitable for both very high resolution and fast reticle production. Feature sizes below 15 nm were resolved in resist after exposing with a calculated spot of 5.6 nm at 50 kV. Masks were produced with a 250 nm / 250 nA beam at 50 kV. The overlay between three masks was measured to bc 78 nm over a 100 mm arca and the placement accuracy in each mask was better than 60 nm. The stability at 50 kV was below 30 rim/h in position and around 1 %/h in current. 100 kV measurements showed an open loop position stability of better than 20 rim/h and 3 %/h current variation.
1. INTRODUCTION The user requirements of lithography tools arc constantly moving towards smaller dimensions and higher throughput, both coupled with high accuracy. Pfeiffer and Groves [ 11 have predicted that by the end of the century X-ray masks will demand minimum features of about 120nm with overlay values of 25 nm. Also users are confident that optical lithography will be used for the production of 1Gb DRAMS. This requires 5X-retitles with 175 nm minimum feature size and 35 nm overlay, all written with acceptable speed. High brightness Schottky, thermal field, emitters have proven to be successful in improving the speed of electron beam lithography systems [2-31. The performance has been reported for both high resolution [4] and mask making applications [5]. The designs described there arc mainly for one or the other application. We have designed a new source and column configuration (FEG) which is suitable for high resolution applications and an alternative version of the column with a modified deflection system particularly for reticle writing. Both concepts can be applied to the current Leica range of ebeam tools. The design work, which has been described by Koek et al. [6], was part of a European ESPRIT project (FREE) to dcvclop a lithography tool which could write the rcticlc for a poly-silicon layer of a dual 64 Mb DRAM in 30 minutes. 2. SOURCE
AND
COLUMN
DESIGN
The source is a commercially available zirconiated tungsten emitter; as reported by Tuggle et al. [73, these emitters operate at a current density in ex-
cess of 104 A/cm* coupled with an effective source diameter of a few tens of nanometers. In addition to the source the new designed optical module consists of a suppressor, extractor and focus electrode. The extractor and focus electrode together with the anode form an clcctrostatic lens (Cl). A larger solid angle of emission, 0.001 sterad, is transmitted so that, at an emission density of 1 mA/sterad, a beam of 1 pA is transmitted down the column. The prototype module has been integrated into a modified EBPG-5HR column located in DIMES. The beam emerging from the source module is aligned with the column axis by double aligners befort cntcring the second lens (C2). This magnetic lens which, together with Cl, forms a zoom system allowing the beam diameter to be continuously variable bctwecn 6 nm and 250 nm, with corresponding currents up to 250 nA at 50 kV. The zoom lens image is focused in the centre of the beam blanker in order to have conjugate blanking. The final double elccuomagnetic lens (C3) focuses the spot onto the substrate and corrects both static and dynamic focus and astigmatism variations. In order to maintain conjugate blanking, the on axis setting of C3 should bc kept constant and only correctcd for the substrate height. This sets extra requirements to the automatic column set-up and focusing routines. On axis focusing should be performed by using the zoom lenses. This will however inlluence the actual beam current or spot size and an iterative process is necessary to compensate for focusing induced beam variation. Dynamic, offaxis, focus is still corrected by C3. In the high resolution column, a double mainfield and a single sub-field deflector unit is positioned between the beam blanker and C3. The maximum deflection main-field size is 800pm square at
0167-9317/94/!$07.00 0 1994 - El sevier Science B.V. All rights reserved.
B.H. Koek et al. I An e-beam lithography tool with a Schottky emitter
82
L_zl-
I
50 kV and 56Opm square al 100 kV. Figure 1 shows a schematical cross-section of the high resolution column. Figure 2 shows the theoretical spot size of the HR column against beam current for an angular emission density of 1 mA/stcrad and acceleration voltages of 20, 50 and 100 kV. The spot size is defined as the diameter containing 50 o/o of the total current. The curves differ from those presented in (6). The stochastic broadening in the short distances from the source to Cl and from C3 to the substrate cannot bc ncglcctcd. Also WC have made some changes to the manner of combining the contributions in various sections of the column. In the fast reticle column the double pre-lens deflcctor is replaced by a single post lens deflector and the working dislance is increased from 40 to 75 mm. The increased working distance together with better control over deflection distortions allows for a larger field size than the HR version (4000pm square at 30 kV and 3(X)0 pm at 50 kV).
Cl primary plane
Gun alignment coils
-
C2 primary plane
--
II
A --
Beam blanker
1st Main deflection Sub-field deflection 2nd Main deflection
II I I:--
’
v[ EE -
3:
3.
C3 primary plane
Figure 1. Schematical resolution column.
Mask making The FREE rcquircmcnts for the accuracy and speed are listed in Table 1. In order to achieve the throughput spccil‘ication, i.c. dual 64Mb DRAM poly-silicon layer cxposcd in 30 minutes, a beam step size of 250nm is necessary, with a deflection speed of 25 MHz. The typical beam current for reticle production is cxpcctcd to bc around 250nA.
cross-section
of the high
100 kV E : R ‘5 5 fz
100:
-
50kV
-
20kV
Table 1. FREE main specifications 10 1
Edge roughness (pp) Placcmcnt (30) Overlay 30) 1
!
. . . ...
.1
..I
.
.
.
.
. . ‘I
.
.
.
. .
10
I
Beam
current
. ..I
100
.
Table 2. Calculated and experimental sity of 0.38 mA/sterad.
;:;
C3 (A) Diameter (nm) Current (nA)
1000
(nA)
01
column characteristics
2.787 110 0.625
Table 2 shows the thcorctical and experimental set-up for a 250nm spot size. This spot size vs. beam currcnl relation can be obtained with an emission density of only 0.38 mA/stcrad.
at 50 kV, 400 pm final aperture and an emission current den-
High resolution Theoretical Experimental 0.636 2267 20.620 100 2.816 5.61 0.625
and FEG performance FREE FEG 25 nm 40 nm 50 nm 60 nm 70 nm 78nm
.~.--4
Figure 2. Theoretical spot size vs. beam current the HR column at 1 mA/sterad emission density.
::
RESULTS
3.1.
1
.
EXPERIME:N’I’AL
Mask making Thcorctical Experimental 0.995 3238 0.950 3235 2.816 187 250
2.787 250 250
B./i. Koek et al. I An e-beam lithography
diamctcr can only bc obtained the source. This sets cstr;t condilions to the susccplibilily of the column to cxternal elcctrom~tgnctic ficlds and vi brations. C;trcl.u I analysis of all the noise compon~*nts on the beam rcsullcd in an inventory of all noise sources. The required
by actually
bcatn
magnifying
Removal of the predominant internal sourccs rcsulted in a reduction of the position noise LO less than 30 nm al 250 nm spot size. The main contribution to the remaining noise is an 1.S mGauss horizontal, external, field around the top of the column. Extra p-melal shielding in the aligncr section will be installed to reduce the influcncc even further. Three test masks wcrc cxposcd under Lhcsc conditions. The exposure Gmc for each mask was 30 min. The position- and beam current slabilily for this column set-up arc shown in Figure 3 and 4. From this figure it can bc derived that the stability is sufficicnt to fulfil the FREE rcquircmcnLs for ovcrlaq and critical dimension. The edge roughness, rcgi?;trution and ova-lay wcrc mcasurcd and arc lislcd in Table 1. 50 ,
40 f
tool with a Schottky
83
emitter
17.-. _
tligh resolution Writing high resolution patkrns rcquircs not only a sm:;ll b&n diamctcr, but also placement accuracy and stabilily in the same order of magniwdc oC the l’caturc six and prcl’cr:rbly cvcn smaller. The column is dcsigncd Lo product beam diamctcrs bclow 6 nnl. Lithography cspcrimcnls using a calculated beam diamctcr ol 5.6 nm and a 5 nm barn step size wcrc pcrl‘ormcd. Figure 5 shows a SEM micrograph of lines smaller than 1.S nm obtained in 100 nm thick PhlhlA (05OK) using a lint charge of 2 nC/cm. Table 2 shows the c:llculatcd and cxpcrimcnlal dalii for lhis scl-up. Figure 6 shows the open loop @lion stability of this column s&up. The measured instabilily over ;I period of one hour is close lo Lhc laser intcrfcrorncter resolution (5.3 nn~).
1
1--t
0
X position variation (nm) Y position variation (nm)
10
20
30
40
50
60
Time (minutes) Figure 3. Posttion conditions.
stability
from
rcticlc
writing
Figure lh:lll
2
5. SEbI IS 11111.
30
I
20 -1 10 -
0
, 10
.
,
.
20
,
.
30
,
.
40
, 50
.
1 60
-
-
stability
I‘rom
Y position variation (nm)
1
-““I
Time (minutes) Figure 4. Current conditions.
200
Time rcticlc
writing
smaller
0
-lOz .ZZ .: -2oa -21.
lines
X positton variation (nm)
r
.z .!? 2
o!’ cxposcd
I
5 6
image
Figure 6. Position \vrlting.
300
(minutes)
stability
l‘or high
rcsolulion
B.H. Koek et al. I An e-beam lithography tool with a Schottky emitter
84
In Figure 5 clearly field boundaries can bc observed in the exposed lines. The stitching errors are measured to be 15 nm for the main- and approximately 7 nm for the sub-field. A further invcstigation is necessary in order to improve the stitching performance for very high resoluLion applications. 100 kV operation The source module and column arc designed for 100 kV accelerating voltage. The micro gcomctry of the tip can easily be destroyed by high voltage discharges. The main cause for discharges is found to be contamination on the source module and the inside of the emission chamber. 100 kV operation rcquires a far more stringent cleaning procedure than stable 50 kV operation. After cleaning, the system was set to 100 kV. A full charactcrisation is currently in progress and Figure 7 shows the first rcsuits from position and Figure 8 Lhc currc.nt stability measurements. For the measurcmcnts a beam current of 1.3 nA was used. From Figure 8 it can be seen that both the beam and extractor current arc still varying. This may bc caused by formation of the tip. The mcasurcmcnls were performed wilh a newly installed tip. 3.3.
a8
-20 -
y
. _ -30
variation
(nm)
I 100
0
CONCLUSIONS
An clcctron beam column with a Schottky field emission source has been designed for both high resolution and high throughput mask production. The spot size range which can bc obtained with this ith to 250 nm column is calculated to be from an effccLivc brightness of 1.5~10 7 A/sterad.cm 7 at 50 kV. The thcorctical and cxperimcntal column sctup at 50 kV are in rcasonablc agreement. The ability to produce small spots has been dcmonstratcd in lithography experiments. A line width of less than 15 nm was obtained in 100 nm PMMA using a, theoretically predicted, 5.6 nm spot size. The position stability for this column set-up showed an accuracy in the order of the laser interfcromctcr rcsolulion (5.3 run). Masks wcrc exposed using 250 nA at 50 kV. The mcasurcd currcnl stability is around 1 %/h (open loop). The position stability was mcasurcd to be bet&r than 30 rim/h (open loop). The placcmcnt accuracy in three masks was mcasurcd to bc 60nm (30) and the overlay 78 nm (30) over a 5 inch area. The cdpc roughness of 1.Opm lines was better than 40 nm (peak LOpeak). Operation of the column at 100 kV showed a position drift 01’20 rim/h and beam current variations of less than 3 %/h.
WC wish LO thank our collcagucs in Leica Cambridge who have conuibutcd to the success of this projccl. Prof. J. Orloff for cncouragcment and valuable advice in the early stage of Ihe developmcnt. WC thank the EEC for funding of the FREE project and our partners for Lhcir collaboration.
X-positionvariation (nm) Y-position
1.
200
Time (minutes)
Figure 7. Position
stability
I.
at 100 kV.
7
I
J
Beam current _
Extractor current
7 -.
3.
4.
5. I
6.
100 Time
(minutes)
7. Figure 8. Current
stability
at 100 kV.
H. Pfciffcr, R. Butsch, and T. Groves, Microclcctronic Engineering 13 (1991) 141. J. Kelly, T. Groves, and H. Kuo, J. Vat. Sci. Tcchnol. Is19 (1981) 936. N. Samoto, R. Shim& H. Hashimoto, N. Tamura, K. Gamo, and S. Namba, Jpn. J. of Appl. Phys. 2.4 (1985) 766. H. Nakazawa, H. Takemura, M. Isobc, Nakagawa, M. Hasscl Shcarcr, and Y. W. Thompson J. Vat. Sci. Technol I$6 (1988) 2019. M. Gcslcy J. Vat. Sci. Tcchnol. 1%‘)(1991) 2949. B.H. Kock, T. Chisholm, J.P. Davcy, J. Romijn, and A.J. v. Run Microproccss Confcrcncc, Hiroshima, July 1993. D.W. Tugglc and L.W. Swanson. J. Vat. Sci. Tcchnol. I$3 (1985) 220.