materials ALD films
Signatone 4-point probe connected to a Keithley 2410 Source meter
Figure 2 gives the growth rate (GR) and resistivity of platinum films using ALD cycle numbers up to 2250. It is found that GR of Pt increases slightly for long deposition, but is still around 0.45-0.475Å/cycle. The resistivity of Pt films are in a range of 14.1 to 12.8µΩ-cm from 500 to 2250 cycles and the resistivity of the Pt layer on Si was found to be slightly reduced with increasing Pt thickness, the lowest resistivity of 12.8 µΩ.cm were measured with a Pt thickness of 100nm on Si substrates. The Pt nucleation and growth in ALD processes was investigated by SEM.
The nucleation delay in thermal ALD of Pt was found to be approximately 70 cycles from Figure 3, which has been confirmed by SEM observations. Elam reported the nucleation behaviors of Pd and Pt on various substrates. [15, 16] They found that the Pt films deposited concurrently on Si (100) substrates showed Pt particles that increase in size with the number of Pt ALD cycles performed such that the Pt film is nearly continuous after 75-100 cycles. [16]
Platinum by plasma-ALD Figure 4 shows the growth rate of platinum films by plasma-ALD against precursor dose-time at 300°C. The growth rates of 0.43-0.45 Å/cycle were
Figure 3,thickness of platinum films by thermal-ALD vs cycle number at 300o
the nucleation delay of Pt thermal-ALD to be found is around 70 cycles
Figure 5,thickness and resistivity of platinum films by plasma-ALD vs cycle number at 300o
C and
the nucleation delay of Pt plasma-ALD is around 20
cycles.Comparing to the nucleation delay of Pt thermal-ALD of 70 cycles,it shows that plasma-ALD can reduce nucleation delay of Pt
obtained, which is comparable to that of thermal ALD.
C and
The thickness and resistivity of platinum films by plasma-ALD with cycle number at 300°C are shown Figure 5. The resistivity of the platinum films is below 14.5 µΩ.cm after plasma ALD of 500 cycles and the nucleation delay of Pt plasma-ALD is around 20 cycles. Comparing to the nucleation delay of Pt thermal-ALD of 70 cycles, it shows that plasma-ALD can reduce the nucleation delay of Pt.
The remote plasma enhanced ALD Pt films showed a short nucleation delay on all the different types of substrates, and an active nucleation behaviour which resulted in a very smooth film surface morphology. AES profile scanning and EDX testing were applied for the elemental analysis in the film and interfaces. AES studies revealed high quality Pt films deposited by both thermal and plasma ALD with carbon impurity less than 1.5% and oxygen found only in the interface (Fig.7).
Pt islands and nucleation delay Our initial Pt thermal ALD experiments on Si surfaces revealed nucleation and growth behaviour of forming Pt nanoparticle islands. Figure 8(a) and 8(b) show a similar SEM cross-section thickness of Pt-ALD films grown by using plasma and thermal ALD for 500 cycles at 300°C. The particle-size measurement was based on SEM and SE.
Figure 4,growth rate of platinum films by plasma-ALD at 300O vs precursor dose-time
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www.siliconsemiconductor.net Issue III 2012
One example of average Pt-size of 5.5 nm grown on Si by thermal ALD for 150 cycles at 300°C is shown in Figure 8(d). The detailed measurements showed that the average nano-particle island size of Pt
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