Advancements in Inductively Coupled Plasma Chemical Vapour Deposition (ICPCVD) with a Focus on Temperature-Sensitive Devices

The capability of depositing high-density dielectric films at temperatures less than 150°C has been gaining traction, particularly in temperature-sensitive devices like OLEDs.

Deposition processes developed by Oxford Instruments using ICP-CVD techniques enable the depositing of high quality films with high-density plasma and at low deposition temperatures and pressures.

This capability results in improved film stoichiometry, minimal radiation damage through direct ion-surface interaction, reduced film contamination, and elimination of device degradation at elevated temperatures.

Previously, silane gas has been used as the silicon source to deposit materials using the ICP-CVD technique. However, recently Oxford Instruments has developed new materials and processes at temperatures less than 150°C based on its expertise in ICPCVD and its ability to handle non-gaseous precursors.

TEOS-based SiO2 in ICPCVD

Silicon dioxide (SiO2) deposition is a key process in the manufacture of devices. There are several techniques available, including PECVD, LPCVD, APCVD, for SiO2 deposition. N2O and silane are normally used in the deposition of the SiO2 layer. Pure oxygen is not used owing to its high reactivity with SiH4. SiO2 deposition with PECVD using silane gas is commonly employed for applications where conformality is secondary.

TEOS (tetraethoxysilane, tetraethyl orthosilicate) is used in place of silane to achieve good conformal coverage. Around 85% conformal step coverage can be achieved with TEOS-based PECVD, which is also capable of controlling the level of step coverage through control over the oxygen radicals in the plasma in order to change deposition directionality.

Oxford Instruments has used the ICPCVD technique in a similar way for SiO2 deposition using TEOS and oxygen at temperatures less than 150°C, which is much lower when compared to the PECVD technique.

Additionally, higher aspect ratio structures can be coated using the ICPCVD technique at low pressures and with the option of supplying RF bias to the lower electrode. Adjusting ICP/RF power enables controlling the stress of the TEOS-based SiO2 film from tensile to compressive. Typical results and properties of the ICPCVD-deposited TEOS-based SiO2 are presented in Figure 1 and Table 1.

SEM showing ICPCVD TEOS-based SiO2 deposited at 100°C on structures with trench width of ~12µm, depth of ~50µm, and hence aspect ratio of ~4:1.

Figure 1. SEM showing ICPCVD TEOS-based SiO2 deposited at 100°C on structures with trench width of ~12µm, depth of ~50µm, and hence aspect ratio of ~4:1.

Table 1. ICPCVD TEOS-based SiO2 - Typical film properties

Process Parameter TEOS based SiO2
Deposition Rate >15nm/min
Film thickness Uniformity <+/-5% (150mm)
Refractive Index 1.46
Film Stress ±300MPa
Wet Etch rates (10:1 BHF, 20°C)
<1.5µm/min at deposition temperature 100°C

TiO2 Deposition Using the ICPCVD Technique

The thermal- and chemical-resistance properties of titanium dioxide films make them suitable for a myriad of applications, including:

  • Biocompatible coatings
  • Surface passivation
  • Ultra-thin film high-k insulators in integrated circuits (ICs)

Antireflection coatings are applied on glass using TiO2, thanks to its high refractive index. TiO2 also holds potential to impart photocatalytic surface property, and to serve as a photoanode layer in nanocrystalline solar cells. Poly-crystalline TiO2 is the most commonly available form of TiO2. Many different vapour deposition techniques are available for the fabrication of high quality poly-crystalline TiO2 films.

Low film growth temperatures are one of the advantages of using the CVD technique. However, the process requires substrate heating or post-deposition annealing due to the formation of anatase and rutile at 350°C and 800°C, respectively. This requirement puts limitation on some of the applications of poly-crystalline TiO2, particularly for temperature-sensitive materials such as polymers.

Oxford Instruments has used the ICPCVD technique for amorphous TiO2 deposition at much lower temperatures of less than 100°C. Titanium (IV) Isopropoxide (TTIP) has been used as the source of Ti for the TiO2 layer deposition using oxygen. Typical results of the ICPCVD-deposited TiO2 layer are shown in Figure 2 and Table 2.

SEM showing ICPCVD TiO2 deposited at 80ºC on a structure with an isolated~1µm step height.

Figure 2. SEM showing ICPCVD TiO2 deposited at 80ºC on a structure with an isolated~1µm step height.

Table 2. TiO2 - Typical film properties

Process Parameter TiO2 at <100°C
Deposition Rate 3-6nm/min
Refractive Index 1.8-2.1
Film Stress
-200MPa compressive to +400MPa tensile

Conclusion

Oxford Instruments plans further research for layer deposition at temperatures nearing room temperature. The recent developments discussed in this article have demonstrated the ability of the ICPCVD technique to produce films with superior quality and properties at low temperatures. Many manufacturers have realized the advantages of the ICPCVD technique, and are showing interest to use this technique in place of the traditional PECVD technique.

This information has been sourced, reviewed and adapted from materials provided by Oxford Instruments Plasma Technology.

For more information on this source, please visit Oxford Instruments Plasma Technology.

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