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Thermal stability and gap-fill properties of spin-on MSQ low-k dielectrics
Microelectronic Engineering 84 (2007) 2606–2609 www.elsevier.com/locate/mee
Thermal stability and gap-fill properties of spin-on MSQ low-k dielectrics N. Ahner b
a,*
, S.E. Schulz
a,b
, F. Blaschta a, M. Rennau
a
a Chemnitz University of Technology, Center for Microtechnologies, Germany Fraunhofer Institute for Reliability and Microintegration IZM, Department Micro Devices and Equipment, Chemnitz, Germany
Received 6 June 2007; accepted 7 June 2007 Available online 22 June 2007
Abstract Looking onto integration of low-k materials within FEOL used processing temperatures in this field are much higher than within BEOL. In addition partly high aspect ratio features have to be filled without defects, e.g. within usage of spin-on low-k materials for shallow trench isolation. We evaluated two MSQ-based spin-on dielectrics, a porous ultralow-k material and a dense spin-on glass regarding their thermal stability and gap-fill behaviour. The films were annealed from standard curing temperatures up to temperatures of 850 °C and 900 °C, film thickness and refractive index were measured by spectral ellipsometry, electrical film properties were evaluated by a mercury probe measurement and changes within chemistry are studied by FTIR. Both low-k materials are thermally stable up to temperatures of 650–700 °C. Above this range the film thickness is rapidly decreasing, refractive index and corresponding to that the k-value are strongly increasing, as does the leakage current density. FTIR spectra show a shift within Si–O–Si backbone and Si–CH3 and CH3 bonds are vanishing, while OH groups are adsorbed, additionally leading to higher k-value and leakage currents. Both materials show very good gap-fill properties, filling features with aspect ratios up to 5 or 10 and Aluminium covered structures without any visible defects. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Low-k dielectrics; Spin-coating; Annealing; FTIR; Wetting behaviour; Surface energy
1. Introduction As device dimensions are further scaled down, RC delay of the interconnect system becomes more significant. Using low dielectric constant (k) materials for isolation, parasitic capacitances and thus signal delay and crosstalk can be reduced [1]. Dense and porous Methylsilsesquioxane (MSQ) based dielectrics both contain CH3-groups to lower permittivity and by addition of porogens a porous ultralow-k MSQ film can by fabricated. To initiate crosslinking of the Si–O–Si backbone and, in case of porous materials, to decompose and drive out the porogen, a curing step at elevated temperatures is necessary. Within BEOL processing temperature load is limited to values of about *
Corresponding author. E-mail address: [email protected] (N. Ahner).
0167-9317/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2007.06.007
400– 450 °C and so e.g. spin-on dielectrics are designed to achieve their desired electrical, optical and mechanical characteristics at curing temperatures within this range. Looking onto spin-on and low-k material application in the FEOL, higher processing temperatures and defect free filling of partly high aspect ratio features are two of the major challenges. Possible applications for spin-on dielectrics range from STI to low-k integration as premetal dielectric, e.g. to decrease word and bitline coupling in DRAM circuits and as isolating materials within Aluminium technology [2]. Spin-on precursors for low-k and ultralow-k dielectrics are liquids, mainly consisting of a solvent, solid parts which finally form the low-k film, and additives, e.g. porogens. Filling high aspect ratio gaps, defects like film cracking, mainly caused by shrinking, and formation of voids due to air inclusion can occur. The thicker the film the stronger it shrinks and so this defect can by overcome
N. Ahner et al. / Microelectronic Engineering 84 (2007) 2606–2609
e.g. by variation of the spin-on parameters like spin-speed. Void formation is mainly caused by poor wettability of the surface to be coated and wetting behaviour of the used precursor. Wetting behaviour strongly depends on the surface energies of the solid as well as of the liquid and therefore has to be evaluated to make any predictions if the gap-fill will be without defects. In this work the thermal stability of the electrical and optical parameters, the wetting behaviour and the high aspect ratio gap-fill ability of two spin-on MSQ materials has been evaluated.
2.2. Gap-fill properties of LK2000 and ACCUGLASSTM PE-CVD SiO2 with a film thickness of 500 nm and 900 nm has been deposited on 150 mm p-doped (1 0 0)Si substrates. The film was patterned and the structures were refilled with LP-CVD SiO2to produce aspect ratios from around 1 to 10. In addition some patterned samples have been coated with a 30 nm Aluminium film, produced by sputter deposition. The structures were filled with LK2000 and ACCUGLASSTM, both deposited by spincoating, cross-sectioned and inspected by SEM. The wetting behaviour of the SiO2 and Aluminium surface has been evaluated by contact angle measurement using several testing liquids and the precursor liquids, used for the gap-fill. The surface energy of the films was calculated using the method of Owens and Wendt by creating a Kaelble-plot [3].
2. Experimental The materials evaluated in this study are Rohm and Haas ZirkonÒ LK2000, a porous low-k dielectric (k 2.1), and Honeywell ACCUGLASSTM T-512B (k 3.2). After deposition by spin-on using a SUSS MicroTec RC8 spin-coater both materials were dried on hotplates and cured in N2 ambient using an ATV PEO 603 batch furnace (Table 1).
3. Results and discussion 3.1. Thermal stability of LK2000 and ACCUGLASSTM
2.1. Thermal stability of LK2000 and ACCUGLASSTM
Fig. 1a and b show the change in film thickness and refractive index for LK2000 and ACCUGLASSTM, respectively. At temperatures below 650 °C (LK2000) and 700 °C (ACCUGLASSTM) the film thickness is only slightly changing and the refractive index is almost constant. Above these temperatures thickness of the films is strongly decreasing and the refractive index is heavily increasing. Corresponding to the rising refractive index the k-value of both materials is increasing to values up to 10 for temperatures above 650 °C or 700 °C, while it stayed nearly constant at temperatures below this range. Leakage current density is showing the same behaviour, strongly increasing from temperatures above 650 °C for LK2000 and 700 °C for ACCUGLASSTM (Fig. 2a and b). The FTIR spectra (Figs. 3a and 3b) show the changes of the chemical structure of LK2000 (above 650 °C) and ACCUGLASSTM (above 700 °C), both with almost similar behaviour. The Si–C stretch peak at 780 cm 1 is reduced, as does the Si-CH3 peak at 840 cm 1. At 960 cm 1 a shoulder occurs which indicates the existence of Si-OH bonds.
Both materials were deposited on 150 mm p-doped Si(1 0 0) substrates, dried at standard parameters and cured applying temperatures from standard value up to 850 °C and 900 °C for LK2000 and ACCUGLASS, respectively, in steps of 100 °C for 1 h each. Changes in film thickness and refractive index were evaluated using spectral ellipsometry (Sentech SE 850), k-value and leakage current density were determined using a mercury-probe measurement. To detect changes within the chemical structure of the materials caused by applying high temperatures, a FTIR analysis using a Bruker IFS 66 spectrometer has been performed. Table 1 Standard drying and curing parameters for LK2000 and ACCUGLASSTM Curing (in N2)
85 °C (30 s) 150 °C (30 s) 150 °C (60 s)
450 °C, 1 h, 8 K/min ramp up 425 °C, 1 h, 8 K/min ramp up
Film thickness [nm]
a
1.4 1.38 1.36 1.34 1.32 1.3 1.28 1.26 1.24 1.22 1.2
220 200 180 160 140 120 100 450
550
650
750
Curing Temperature [°C]
850
b Film thickness [nm]
ACCUGLASSTM
Drying (Hotplate)
Refractive Index
LK2000
2607
450 400 350 300 250 200 300
400
500
600
700
800
1.56 1.54 1.52 1.5 1.48 1.46 1.44 1.42 1.4 1.38 1.36 900 1000
Curing Temperature [°C]
Fig. 1. (a) Film thickness and refractive index vs.curing temperature for LK2000. (b) Film thickness and refractive index vs. curing temperature for ACCUGLASS.
1,0E+00 1,0E-01 1,0E-02 1,0E-03 1,0E-04 1,0E-05 1,0E-06 1,0E-07 1,0E-08 1,0E-09 1,0E-10
11,00 10,00 9,00 8,00 7,00 6,00 5,00 4,00 3,00 2,00 1,00 0,00 450
550
650
750
b Leakage current density [A/cm²]
Leakage current density [A/cm²]
a
850
1 0,1 0,01 0,001 1E-04 1E-05 1E-06 1E-07 1E-08 1E-09 1E-10 1E-11 400
11 10 9 8 7 6 5 4 3 2 1 500
600
700
800
Permittivity
N. Ahner et al. / Microelectronic Engineering 84 (2007) 2606–2609
Permittivity
2608
900
Curing Temperature [°C]
Curing Temperature [°C]
Fig. 4 shows the contact angles of the testing liquids on SiO2 and Aluminium, arranged by the surface energy of the liquids, both with similar wetting behaviour. The calculation of the surface energy led to comparable results with 65.1 mN/m for the Aluminium surface and
Absorption (normalized)
Absorption (normalized)
2.5
1.5
2.0
1.5
1.0
0.5
1.0 0.0 1000
1100
1200 1300 Wave number (1/cm)
1400
20 15 10
0 20
30 LPCVD-Oxid
40
50
60
Fig. 4. Contact angles of several testing liquids on LP-CVD SiO2 and Aluminium.
64.9 mN/m for the LP-CVD SiO2 surface. From the contact angle measurements of the spin-on precursors of LK2000 and ACCUGLASSTM, which showed angles between 0° and 10°, no gap-fill defects resulting from poor wetting behaviour are expected. Gap-fill experiments with LK2000 and ACCUGLASSTM on structures with an aspect ratio of 1 and below (SiO2 surface) showed no visible defects, even when spun on at low speeds the thick films did not crack. Filling structures with
2.5
2.0
1.5
2.5 2.0 1.5 1.0 0.5 0.0 900
1.0
1000
1100 1200 1300 Wave number (1/cm)
1400
0.5
0.0 400 900
1400
1900
2400
2900
3400
Wave number (1/cm) 450°C
550°C
650°C
750°C
70
Surface energy of the testing liquids [mN/cm]
Al
0.5
0.0 400
Water
Glycerin Diiodmethan
DMSO
Benzylalkohol
Octanol
25
5
b
2.5
2.0
30
Absorption (normalized)
a
35
Absorption (normalized)
3.2. Gap-fill properties of LK2000 and ACCUGLASSTM
40
Contact angle [°]
The change within the Si–O–Si network is clearly visible in the range of 950 cm 1–1200 cm 1. The Si–O–Si stretch peak at 1080 cm 1 is reduced and the Si–O–Si cage peak at 1140 cm 1 is shifted to 1220 cm 1. The Si–CH3 vibration peak at 1275 cm 1 completely vanishes at high temperatures, as does the CH3-peak at 2975 cm 1. As seen at 960 cm 1 OH groups have been adsorbed as the broad shoulder around 3400 cm 1 is showing [4]. As shown in the spectra the Si–CH3 and CH3 bonds itself vanish and so the CH3 within MSQ materials is not stable at temperatures higher than 650–700 °C leading to an increase of the k-value, refractive index and leakage current density caused by the destruction of these groups. The materials become denser and so the film thickness is decreasing. The appearance of OH groups indicates a hydrophilization of the materials, which also causes higher k-values and leakage currents.
Ethylenglycol
Fig. 2. (a) Leakage current density and permittivity vs. curing temperature for LK2000. (b) Leakage current density and permittivity vs. curing temperature for ACCUGLASS.
900
1400
3900
1900
2400
2900
3400
Wave number (1/cm) 425°C
500°C
600°C
700°C
800°C
850°C
Fig. 3. FTIR spectra for (a) LK2000 and (b) ACCUGLASS for different curing temperatures.
900°C
3900
N. Ahner et al. / Microelectronic Engineering 84 (2007) 2606–2609
2609
Fig. 5. (a) Gap-fill (AR = 5) using LK2000, (b) gap-fill (AR = 10) using ACCUGLASS, (c) gap-fill (AR = 1.5) using LK2000 on Al.
an aspect ratio of 5 (LK2000) and 10 (ACCUGLASSTM) showed the very good gap-fill properties of both materials, also with no visible defects like cracks or failures caused by incomplete wetting of the deep gaps (Fig. 5a and b). Experiments on Aluminium-covered structures (AR = 1.5) using LK2000 also did not show any defects resulting from poor wetting or film shrinkage (Fig. 5c). 4. Conclusions The MSQ based dielectrics ZirkonÒ LK2000 and ACCUGLASSTM T-512B are thermally stable and therefore show potential for usage within processes applying temperatures up to 650 °C and 700 °C, respectively. For higher temperatures a degradation of the materials caused by the destruction of CH3 groups occurs and the surface becomes hydrophil. This leads to higher k-values and rising
leakage currents. The gap-fill experiments showed the very good gap-fill properties LK2000 and ACCUGLASSTM, filling structures with aspect ratios up to 5 and 10 without visible defects, respectively. The evaluation of the surface energy of LP-CVD SiO2 and Aluminium showed similar values, which could be due to the oxidized Aluminium surface. From these results no problems due to poor wettability of this surface were expected and the gap-fill with LK2000 of Aluminium covered structures actually was free from defects. References [1] [2] [3] [4]
The International Roadmap for Semiconductors, IRTS, 2006. A. Birner, A. Klipp, Proc. Electrochem. Soc. 4 (2004) 183–194. W. Preusser, C. Gierl, A. Rainer, J. Oberfl. Tech. 10 (2002) 106–108. S. Sivoththaman, R. Jeyakumar, J. Vac. Sci. Technol. A 20 (3) (2002) 106–108.
Thermal stability and gap-fill properties of spin-on MSQ low-k dielectrics N. Ahner b
a,*
, S.E. Schulz
a,b
, F. Blaschta a, M. Rennau
a
a Chemnitz University of Technology, Center for Microtechnologies, Germany Fraunhofer Institute for Reliability and Microintegration IZM, Department Micro Devices and Equipment, Chemnitz, Germany
Received 6 June 2007; accepted 7 June 2007 Available online 22 June 2007
Abstract Looking onto integration of low-k materials within FEOL used processing temperatures in this field are much higher than within BEOL. In addition partly high aspect ratio features have to be filled without defects, e.g. within usage of spin-on low-k materials for shallow trench isolation. We evaluated two MSQ-based spin-on dielectrics, a porous ultralow-k material and a dense spin-on glass regarding their thermal stability and gap-fill behaviour. The films were annealed from standard curing temperatures up to temperatures of 850 °C and 900 °C, film thickness and refractive index were measured by spectral ellipsometry, electrical film properties were evaluated by a mercury probe measurement and changes within chemistry are studied by FTIR. Both low-k materials are thermally stable up to temperatures of 650–700 °C. Above this range the film thickness is rapidly decreasing, refractive index and corresponding to that the k-value are strongly increasing, as does the leakage current density. FTIR spectra show a shift within Si–O–Si backbone and Si–CH3 and CH3 bonds are vanishing, while OH groups are adsorbed, additionally leading to higher k-value and leakage currents. Both materials show very good gap-fill properties, filling features with aspect ratios up to 5 or 10 and Aluminium covered structures without any visible defects. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Low-k dielectrics; Spin-coating; Annealing; FTIR; Wetting behaviour; Surface energy
1. Introduction As device dimensions are further scaled down, RC delay of the interconnect system becomes more significant. Using low dielectric constant (k) materials for isolation, parasitic capacitances and thus signal delay and crosstalk can be reduced [1]. Dense and porous Methylsilsesquioxane (MSQ) based dielectrics both contain CH3-groups to lower permittivity and by addition of porogens a porous ultralow-k MSQ film can by fabricated. To initiate crosslinking of the Si–O–Si backbone and, in case of porous materials, to decompose and drive out the porogen, a curing step at elevated temperatures is necessary. Within BEOL processing temperature load is limited to values of about *
Corresponding author. E-mail address: [email protected] (N. Ahner).
0167-9317/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2007.06.007
400– 450 °C and so e.g. spin-on dielectrics are designed to achieve their desired electrical, optical and mechanical characteristics at curing temperatures within this range. Looking onto spin-on and low-k material application in the FEOL, higher processing temperatures and defect free filling of partly high aspect ratio features are two of the major challenges. Possible applications for spin-on dielectrics range from STI to low-k integration as premetal dielectric, e.g. to decrease word and bitline coupling in DRAM circuits and as isolating materials within Aluminium technology [2]. Spin-on precursors for low-k and ultralow-k dielectrics are liquids, mainly consisting of a solvent, solid parts which finally form the low-k film, and additives, e.g. porogens. Filling high aspect ratio gaps, defects like film cracking, mainly caused by shrinking, and formation of voids due to air inclusion can occur. The thicker the film the stronger it shrinks and so this defect can by overcome
N. Ahner et al. / Microelectronic Engineering 84 (2007) 2606–2609
e.g. by variation of the spin-on parameters like spin-speed. Void formation is mainly caused by poor wettability of the surface to be coated and wetting behaviour of the used precursor. Wetting behaviour strongly depends on the surface energies of the solid as well as of the liquid and therefore has to be evaluated to make any predictions if the gap-fill will be without defects. In this work the thermal stability of the electrical and optical parameters, the wetting behaviour and the high aspect ratio gap-fill ability of two spin-on MSQ materials has been evaluated.
2.2. Gap-fill properties of LK2000 and ACCUGLASSTM PE-CVD SiO2 with a film thickness of 500 nm and 900 nm has been deposited on 150 mm p-doped (1 0 0)Si substrates. The film was patterned and the structures were refilled with LP-CVD SiO2to produce aspect ratios from around 1 to 10. In addition some patterned samples have been coated with a 30 nm Aluminium film, produced by sputter deposition. The structures were filled with LK2000 and ACCUGLASSTM, both deposited by spincoating, cross-sectioned and inspected by SEM. The wetting behaviour of the SiO2 and Aluminium surface has been evaluated by contact angle measurement using several testing liquids and the precursor liquids, used for the gap-fill. The surface energy of the films was calculated using the method of Owens and Wendt by creating a Kaelble-plot [3].
2. Experimental The materials evaluated in this study are Rohm and Haas ZirkonÒ LK2000, a porous low-k dielectric (k 2.1), and Honeywell ACCUGLASSTM T-512B (k 3.2). After deposition by spin-on using a SUSS MicroTec RC8 spin-coater both materials were dried on hotplates and cured in N2 ambient using an ATV PEO 603 batch furnace (Table 1).
3. Results and discussion 3.1. Thermal stability of LK2000 and ACCUGLASSTM
2.1. Thermal stability of LK2000 and ACCUGLASSTM
Fig. 1a and b show the change in film thickness and refractive index for LK2000 and ACCUGLASSTM, respectively. At temperatures below 650 °C (LK2000) and 700 °C (ACCUGLASSTM) the film thickness is only slightly changing and the refractive index is almost constant. Above these temperatures thickness of the films is strongly decreasing and the refractive index is heavily increasing. Corresponding to the rising refractive index the k-value of both materials is increasing to values up to 10 for temperatures above 650 °C or 700 °C, while it stayed nearly constant at temperatures below this range. Leakage current density is showing the same behaviour, strongly increasing from temperatures above 650 °C for LK2000 and 700 °C for ACCUGLASSTM (Fig. 2a and b). The FTIR spectra (Figs. 3a and 3b) show the changes of the chemical structure of LK2000 (above 650 °C) and ACCUGLASSTM (above 700 °C), both with almost similar behaviour. The Si–C stretch peak at 780 cm 1 is reduced, as does the Si-CH3 peak at 840 cm 1. At 960 cm 1 a shoulder occurs which indicates the existence of Si-OH bonds.
Both materials were deposited on 150 mm p-doped Si(1 0 0) substrates, dried at standard parameters and cured applying temperatures from standard value up to 850 °C and 900 °C for LK2000 and ACCUGLASS, respectively, in steps of 100 °C for 1 h each. Changes in film thickness and refractive index were evaluated using spectral ellipsometry (Sentech SE 850), k-value and leakage current density were determined using a mercury-probe measurement. To detect changes within the chemical structure of the materials caused by applying high temperatures, a FTIR analysis using a Bruker IFS 66 spectrometer has been performed. Table 1 Standard drying and curing parameters for LK2000 and ACCUGLASSTM Curing (in N2)
85 °C (30 s) 150 °C (30 s) 150 °C (60 s)
450 °C, 1 h, 8 K/min ramp up 425 °C, 1 h, 8 K/min ramp up
Film thickness [nm]
a
1.4 1.38 1.36 1.34 1.32 1.3 1.28 1.26 1.24 1.22 1.2
220 200 180 160 140 120 100 450
550
650
750
Curing Temperature [°C]
850
b Film thickness [nm]
ACCUGLASSTM
Drying (Hotplate)
Refractive Index
LK2000
2607
450 400 350 300 250 200 300
400
500
600
700
800
1.56 1.54 1.52 1.5 1.48 1.46 1.44 1.42 1.4 1.38 1.36 900 1000
Curing Temperature [°C]
Fig. 1. (a) Film thickness and refractive index vs.curing temperature for LK2000. (b) Film thickness and refractive index vs. curing temperature for ACCUGLASS.
1,0E+00 1,0E-01 1,0E-02 1,0E-03 1,0E-04 1,0E-05 1,0E-06 1,0E-07 1,0E-08 1,0E-09 1,0E-10
11,00 10,00 9,00 8,00 7,00 6,00 5,00 4,00 3,00 2,00 1,00 0,00 450
550
650
750
b Leakage current density [A/cm²]
Leakage current density [A/cm²]
a
850
1 0,1 0,01 0,001 1E-04 1E-05 1E-06 1E-07 1E-08 1E-09 1E-10 1E-11 400
11 10 9 8 7 6 5 4 3 2 1 500
600
700
800
Permittivity
N. Ahner et al. / Microelectronic Engineering 84 (2007) 2606–2609
Permittivity
2608
900
Curing Temperature [°C]
Curing Temperature [°C]
Fig. 4 shows the contact angles of the testing liquids on SiO2 and Aluminium, arranged by the surface energy of the liquids, both with similar wetting behaviour. The calculation of the surface energy led to comparable results with 65.1 mN/m for the Aluminium surface and
Absorption (normalized)
Absorption (normalized)
2.5
1.5
2.0
1.5
1.0
0.5
1.0 0.0 1000
1100
1200 1300 Wave number (1/cm)
1400
20 15 10
0 20
30 LPCVD-Oxid
40
50
60
Fig. 4. Contact angles of several testing liquids on LP-CVD SiO2 and Aluminium.
64.9 mN/m for the LP-CVD SiO2 surface. From the contact angle measurements of the spin-on precursors of LK2000 and ACCUGLASSTM, which showed angles between 0° and 10°, no gap-fill defects resulting from poor wetting behaviour are expected. Gap-fill experiments with LK2000 and ACCUGLASSTM on structures with an aspect ratio of 1 and below (SiO2 surface) showed no visible defects, even when spun on at low speeds the thick films did not crack. Filling structures with
2.5
2.0
1.5
2.5 2.0 1.5 1.0 0.5 0.0 900
1.0
1000
1100 1200 1300 Wave number (1/cm)
1400
0.5
0.0 400 900
1400
1900
2400
2900
3400
Wave number (1/cm) 450°C
550°C
650°C
750°C
70
Surface energy of the testing liquids [mN/cm]
Al
0.5
0.0 400
Water
Glycerin Diiodmethan
DMSO
Benzylalkohol
Octanol
25
5
b
2.5
2.0
30
Absorption (normalized)
a
35
Absorption (normalized)
3.2. Gap-fill properties of LK2000 and ACCUGLASSTM
40
Contact angle [°]
The change within the Si–O–Si network is clearly visible in the range of 950 cm 1–1200 cm 1. The Si–O–Si stretch peak at 1080 cm 1 is reduced and the Si–O–Si cage peak at 1140 cm 1 is shifted to 1220 cm 1. The Si–CH3 vibration peak at 1275 cm 1 completely vanishes at high temperatures, as does the CH3-peak at 2975 cm 1. As seen at 960 cm 1 OH groups have been adsorbed as the broad shoulder around 3400 cm 1 is showing [4]. As shown in the spectra the Si–CH3 and CH3 bonds itself vanish and so the CH3 within MSQ materials is not stable at temperatures higher than 650–700 °C leading to an increase of the k-value, refractive index and leakage current density caused by the destruction of these groups. The materials become denser and so the film thickness is decreasing. The appearance of OH groups indicates a hydrophilization of the materials, which also causes higher k-values and leakage currents.
Ethylenglycol
Fig. 2. (a) Leakage current density and permittivity vs. curing temperature for LK2000. (b) Leakage current density and permittivity vs. curing temperature for ACCUGLASS.
900
1400
3900
1900
2400
2900
3400
Wave number (1/cm) 425°C
500°C
600°C
700°C
800°C
850°C
Fig. 3. FTIR spectra for (a) LK2000 and (b) ACCUGLASS for different curing temperatures.
900°C
3900
N. Ahner et al. / Microelectronic Engineering 84 (2007) 2606–2609
2609
Fig. 5. (a) Gap-fill (AR = 5) using LK2000, (b) gap-fill (AR = 10) using ACCUGLASS, (c) gap-fill (AR = 1.5) using LK2000 on Al.
an aspect ratio of 5 (LK2000) and 10 (ACCUGLASSTM) showed the very good gap-fill properties of both materials, also with no visible defects like cracks or failures caused by incomplete wetting of the deep gaps (Fig. 5a and b). Experiments on Aluminium-covered structures (AR = 1.5) using LK2000 also did not show any defects resulting from poor wetting or film shrinkage (Fig. 5c). 4. Conclusions The MSQ based dielectrics ZirkonÒ LK2000 and ACCUGLASSTM T-512B are thermally stable and therefore show potential for usage within processes applying temperatures up to 650 °C and 700 °C, respectively. For higher temperatures a degradation of the materials caused by the destruction of CH3 groups occurs and the surface becomes hydrophil. This leads to higher k-values and rising
leakage currents. The gap-fill experiments showed the very good gap-fill properties LK2000 and ACCUGLASSTM, filling structures with aspect ratios up to 5 and 10 without visible defects, respectively. The evaluation of the surface energy of LP-CVD SiO2 and Aluminium showed similar values, which could be due to the oxidized Aluminium surface. From these results no problems due to poor wettability of this surface were expected and the gap-fill with LK2000 of Aluminium covered structures actually was free from defects. References [1] [2] [3] [4]
The International Roadmap for Semiconductors, IRTS, 2006. A. Birner, A. Klipp, Proc. Electrochem. Soc. 4 (2004) 183–194. W. Preusser, C. Gierl, A. Rainer, J. Oberfl. Tech. 10 (2002) 106–108. S. Sivoththaman, R. Jeyakumar, J. Vac. Sci. Technol. A 20 (3) (2002) 106–108.