materials  ALD films


connected to an in-situ ellipsometer and an inductively coupled plasma (ICP) source, which gives the ability to run both thermal and remote plasma ALD modes within a single system.


The pump unit consisted of a turbo molecular pump and a dry pump reaching a base pressure of 1 x 10-6 mbar. Trimethyl (methylcyclopentadienyl)


platinum(IV) (MeCpPtMe3) (SAFC, Sigma-Aldrich) in a stainless steel bubbler, heated to 70°C, was used as Pt- precursor and vapor drawn into the chamber.


The deposition of Pt films was carried out by both


thermal and remote O2-plasma ALD at 300°C, using methylcyclopentadienyltrimethyl platinum


(MeCpPtMe3) and O2 as precursors. The MeCpPtMe3 precursor was vaporized at 70°C using the vapour-draw method without bubbling gas and using 200sccm of Ar gas flow as purge gas.


To maximise precursor usage, the first half-cycle consisted of MeCpPtMe3 precursor dosing with the bottom valve closed (no pumping) a holding for


5-10 seconds, in the process investigation. Si (100) with native oxide layer was used as the substrate. For the oxide samples, Si (100) substrates were first coated prior to the Pt metal ALD with 10-20 nm of


ALD Al2O3, HfO2 and SiO2 using alternating ALD processes of TMA(trimethylaluminium)/O2-plasma, TEMAH [Tetrakis(ethylmethylamino) hafnium]/O2- plasma and TRDMAS [tris(dimethylamino)


silane]/O2-plasma, respectively. Table 1 shows the details of the four types of substrates used, namely:


Si wafers, SiO2, Al2O3 and high-k dielectric HfO2 ALD films on Si substrates. ALD chamber pressure


was varied from 10 to 40 millitorr during the process steps. Not only the wafer holder stage was heated but also the chamber wall and delivery line were heated to a temperature of 120°C and 80°C, respectively, to prevent the precursor condensation and make the sample surface temperature the


same. The remote O2 plasma was generated by a radio frequency (rf) induction-type plasma generator (ICP). The plasma power was 300 W.


The thickness and the refractive index of the ALD films were measured using a J.A. Woollam M2000V spectroscopic ellipsometer (370nm-1000nm


wavelengths) and also confirmed by cross sectional SEM (Zeiss, SUPRA-25). Energy dispersive X-ray (EDX) (INCA-7426, Oxford Instruments) and Auger Electron Spectroscopy (AES) were used for determining the chemical composition and element profile of the ALD films.


A 4-point probe (Signatone 4 point probe with a Keithley 2410 Source) was applied for testing the electrical property of the film.


Outcomes


Figure 1 shows the growth rate and resistivity of platinum films by thermal-ALD against the precursor dose-time for 600 cycles at 300°C. The growth rate of 0.45-0.47 Å/cycle and the resistivity of platinum films of about 13.5µΩ-cm from 600 cycles were obtained. To confirm the growth rate and to investigate the relationship of resistivity and film thickness of the platinum films by thermal-ALD,


Figure 2,growth rate (GR) and resistivity of platinum films by thermal-ALD vs cycle number and it is found that a GR of Pt thermal-ALD is around 0.45-0.47Å/cycle and the resistivity range of 14.1 to 12.8 µΩ-cm from 500 cycle to 2250 cycle


Figure 1,growth rate and resistivity of platinum films by thermal-ALD at 300o


C


vs precursor dose-time for 600 cycles


Table 1,the substrates used for ALD-Pt film deposition Issue III 2012 www.siliconsemiconductor.net 15


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