Specific Process Knowledge/Thin film deposition/ALD Picosun R200/Al2O3 deposition using ALD

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The ALD window for depostion of aluminium dioxide (Al₂O₃) ranges from 150 ^oC to 350 ^oC. XPS measurements shows that at temperatures below 150 ^oC the Al₂O₃ layer will be contaminated by unreacted TMA molecules, and at temperatures above 350 ^oC the TMA decomposes.

All results shown on this page have been obtained using the "AL2O3" recipe on new Si(100) wafers with native oxide.

Al₂O₃ standard recipe

Recipe: AL2O3

Maximum deposition thickness: 100 nm

Temperature: 100 ^oC - 350 ^oC

	TMA	H2O
Nitrogen flow	150 sccm	200 sccm
Pulse time	0.1 s	0.1 s
Purge time	3.0 s	4.0 s

This is the standard recipe for deposition of Al₂O₃ on flat and high aspect ratio structures. For conformal passivation of porous materials, very narrow trenches etc. it is recomanded to use Al2O3T recipe instead. Recipe can be used for deposition in the range 100-350 ^oC. However, at 100 ^oC small amount of carbon impurities has been observed. It is not recomanded to use this recipe for deposition below 100 ^oC, since it also leads to accumulation of H₂O in the chamber.

Al₂O₃ deposition rates

The deposition rate for Al₂O₃ depends on the temperature, see the ALD-window graph below. The uniformity, thickness, refractive index has been obtained using Ellipsometer VASE.

• 
  ALD-window for Al₂O₃ deposition.
• 
  Typical uniformity profile across 100mm Si wafer based on 49 mesurement points.

In the graphs below the Al₂O₃ thickness as function of number of cycles for deposition temperatures between 100 ^oC and 350 ^oC can be seen. From the equations the number of cycles required for a certain thickess can be calculated.

• Aluminium oxide thickness as function of number of cycles
• 
  Temperature 100 ^oC.
• 
  Temperature 150 ^oC.
• 
  Temperature 200 ^oC.

• Aluminium oxide thickness as function of number of cycles
• 
  Temperature 250 ^oC.
• 
  Temperature 300 ^oC.
• 
  Temperature 350 ^oC.

Evgeniy Shkondin, DTU Danchip, 2014-2016.

Al₂O₃ standard recipe characterization across 100 mm Si <100> wafer

Al2O3 deposition at 100 oC and 150 oC

Deposition conditions at 100 oC Number of cycles Thickness (nm) Uniformity across 100mm Si substrate (%) Standard deviation error Refractive index @ 632.8 nm 150 14.11 2.18 0.225 1.56 300 25.94 0.68 0.14 1.59 500 41.35 1.87 0.60 1.59 800 65.05 2.28 1.13 1.59 1088 87.25 2.15 1.35 1.60 Deposition conditions at 150 oC Number of cycles Thickness (nm) Uniformity across 100mm Si substrate (%) Standard deviation error Refractive index @ 632.8 nm 150 15.38 1.72 0.18 1.61 300 28.67 1.73 0.36 1.62 500 46.93 1.75 0.57 1.62 800 73.46 1.75 0.92 1.63 1088 99.50 1.74 1.20 1.63

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Al2O3 deposition at 200 oC and 250 oC

Deposition conditions at 200 oC Number of cycles Thickness (nm) Uniformity across 100mm Si substrate (%) Standard deviation error Refractive index @ 632.8 nm 150 16.46 2.92 0.33 1.62 300 31.09 1.53 0.34 1.63 500 51.20 1.10 0.39 1.64 800 79.66 1.59 0.88 1.64 1088 107.69 1.41 1.04 1.64 Deposition conditions at 250 oC Number of cycles Thickness (nm) Uniformity across 100mm Si substrate (%) Standard deviation error Refractive index @ 632.8 nm 150 16.41 0.83 0.10 1.63 300 30.81 1.13 0.24 1.64 500 50.48 1.10 0.40 1.64 800 79.84 1.11 0.60 1.65 1088 108.03 1.11 0.61 1.65

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Al2O3 deposition at 300 oC and 350 oC

Deposition conditions at 300 oC Number of cycles Thickness (nm) Uniformity across 100mm Si substrate (%) Standard deviation error Refractive index @ 632.8 nm 150 15.59 2.11 0.24 1.63 300 29.00 0.79 0.17 1.65 500 47.86 1.71 0.26 1.64 800 75.04 0.90 0.55 1.65 1088 101.76 0.75 0.62 1.65 Deposition conditions at 350 oC Number of cycles Thickness (nm) Uniformity across 100mm Si substrate (%) Standard deviation error Refractive index @ 632.8 nm 150 13.88 0.69 0.06 1.67 300 26.70 0.62 0.12 1.64 500 43.70 0.42 0.15 1.64 800 68.77 0.65 0.37 1.65 1088 92.88 0.70 0.48 1.66

Evgeniy Shkondin, DTU Danchip, 2014-2016.

Al₂O₃ XPS investigation for elemental trace analysis

XPS profile for Al₂O₃ has been obtained using XPS-ThermoScientific. Al₂O₃ samples reveals chemically high quality films with no observable contaminations in temperature range 150 - 350 ^oC. At lower temperature (100 ^oC) the ALD reaction starts to become unsufficient and some amount of carbon from TMA precursor gets absorbed into the film.

• 
  Survey scan of Al₂O₃.
• 
  C 1s scan of Al₂O₃ film deposited at 100^oC. Shows clearly carbon impurities in the film
• 
  C 1s scan of Al₂O₃ film deposited between 150^oC - 350^oC. No carbon observes.

Evgeniy Shkondin, DTU Danchip, 2014-2016.

Al₂O₃ recipe for deposition on high aspect ratio structures

Recipe: AL2O3T

Maximum deposition thickness: 100 nm

Temperature: 100 ^oC - 350 ^oC

	TMA	TMA	H2O	H2O
Nitrogen flow	150 sccm	150 sccm	200 sccm	200 sccm
Pulse time	0.1 s	0.1 s	0.1 s	0.1 s
Purge time	0.5 s	20.0 s	0.5 s	20.0 s

The recipe is good for deposition on very high aspect ratio structures (with aspect ratio more then 1:20) such as deep trenches, pillars, pores etc. However, in most cases, including deposition on black silicon or other lower aspect ratio structures, the standard Al2O3 recipe is sufficient and should be used instead! A2O3T can also be used for deposition on polymers at low temperatures (80-120 ^oC). Deposition rate is approximately the same as for standard Al2O3 recipe.

Some some SEM images of Al₂O₃ deposited on a Si trenches at 150 ^oC temperature and 1000 cycles. Trenches prepered using DRIE-Pegasus. Research results based on this recipe can be found here: LINK (J. Vac. Sci. Technol. A 34(3), 2016 031605 )

• Al2O3 coatings on Si trenches
• 
  Temperature 150 ^oC, 1000 cycles.
• 
  Temperature 150 ^oC, 1000 cycles.
• 
  Temperature 150 ^oC, 1000 cycles.

• 
  Temperature 150 ^oC, 1000 cycles.
• 
  Temperature 150 ^oC, 1000 cycles.
• 
  Temperature 150 ^oC, 1000 cycles.

Evgeniy Shkondin, DTU Danchip, 2014-2016.

Al₂O₃ ozone recipe

Recipe: AL2O3 O3

Maximum deposition thickness: 100 nm

Temperature: 300 ^oC - 350 ^oC

	TMA	O3O
Nitrogen flow	150 sccm	200 sccm
Pulse time	0.1 s	0.2 s
Purge time	3.0 s	4.0 s

Oxidizing agent in this process is ozone instead of water. The advantage of using ozone is minimization of hydrogen impurities in the deposited film.

Al₂O₃ O₃ process deposition rates

The deposition of Al₂O₃ using O₃ can be done in the range between 300-350 ^oC. It is not recomanded to put temperature below 300^oC since it leads to very poor uniformity, which is somewhat lower compared with water process even at 300^oC (data obtained using Ellipsometer VASE). This recipe is not sutable for deposition on high aspect ratio structures (use recipe Al2O3 or Al2O3T instead).

• 
  Thickness distriburion across 100mm Si wafer (300^oC).
• 
  Thickness distriburion across 100mm Si wafer (350^oC)

In the graphs below the Al₂O₃ thickness as function of number of cycles for deposition temperatures between 300 ^oC and 350 ^oC can be seen. From the equations the number of cycles required for a certain thickess can be calculated.

• Aluminium oxide thickness as function of number of cycles
• 
  Temperature 300 ^oC.
• 
  Temperature 350 ^oC.

Evgeniy Shkondin, DTU Danchip, 2014-2016.

Al₂O₃ O₃ recipe characterization across 100 mm Si <100> wafer

Al2O3 deposition at 100 oC and 150 oC

Deposition conditions at 300 oC Number of cycles Thickness (nm) Uniformity across 100mm Si substrate (%) Standard deviation error Refractive index @ 632.8 nm 250 18.47 4.04 2.93 1.64 500 40.28 1.49 2.25 1.64 750 54.63 3.50 7.86 1.64 1000 77.86 1.83 5.48 1.64 1220 94.12 2.28 7.32 1.65 Deposition conditions at 350 oC Number of cycles Thickness (nm) Uniformity across 100mm Si substrate (%) Standard deviation error Refractive index @ 632.8 nm 250 19.58 2.23 0.35 1.66 500 37.94 2.09 0.60 1.65 750 56.52 1.85 0.81 1.65 1000 75.91 1.49 0.59 1.65

Evgeniy Shkondin, DTU Danchip, 2014-2016.