Verification of GeSbTe composition in the high aspect holefilled by Chemical Vapor Deposition○Hideaki Machida2, Takafumi Horiike1, Seiti Hamada1, Tomohiro Uno1, Naomi Sawamoto1, Kohei
Suda1, Masato Ishikawa2, Hiroshi Sudo2, Yoshio Ohshita3, and Atsushi Ogura1

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School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, 214-8571, Japan

Gas-phase Growth Ltd., Nokohdai-Tamakoganei BP301, 2-24-16 Naka-cho, Koganei-shi, Tokyo, 184-0012, Japan
3Toyota Technological Institute, 2-12-1 Hisakata, Tenpaku, Nagoya 468-8511, Japan

E-mail: machida@kisoh-seicho.com
Large scale integrated memory devices require filling small holes with GST material, so chemicalvapor deposition (CVD) technology has been studied as a way to overcome this problem1. Recently, wesucceeded in obtain stoichiometric Ge2Sb2Te5 thin films on flat SiO2 and TiN substrates2 (Fig. 1.).
However, a basic experiment of filling is not performed enough, such as composition control in theholes. We are verifying of GeSbTe Composition and interaction of precursors in the high aspect hole byCVD method.
In this paper, we report on GST film deposition involving the use of appropriate precursors. The precursors have moderate vapor pressure and are in liquid state, thereby enabling easy control of film
composition. They also have low decomposition temperature to avoid carbon incorporation in the film.
Tert-butylgermanium [ t-C4H9GeH3, Fig. 2(A) ] was selected as the Ge precursor. A conventional Ge
precursor such as (CH3)4Ge has a strong Ge-C bond; thus, its decomposition temperature may be high,and many carbon impurities may be incorporated in its films.3) Low deposition temperature and lowcarbon impurity should be observed after using t-C4H9GeH 3 with one hydrogen atom of dangerous
GeH4 substituted for a bulky t-C4H9- group, which however can easily be removed. Triisopropylantimony [ (i-C3H7)3Sb, Fig. 2(B) ] and diisopropyltellurium [(i-C3H7)2Te, Fig. 2(C)] were selected as theSb and Te precursors.
A schematic diagram of the low-pressure CVD system used is shown in Fig. 3. The precursor vapors
were precisely controlled by adjusting H2 carrier gas flow rate, bottle temperature, and pressure. Afterthe SiO2 and TiN substrates were heated at the deposition temperature, vapors of the three precursors
were injected into the chamber. The typical experimental conditions are as follows. Deposition temperature and total pressure varied from200 to 350 °C and from 1 to 50 torr, respectively. The atomic
concentrations of Ge, Sb, Te, and C in the films were estimated using X-ray photoemission spectro-

scopy calibrated using Rutherford backscattering spectrometry (RBS) measurement. The film structures
were observed using scanning electron microscopy (SEM).
GST films of various compositions were deposited by controlling CVD conditions such as pressure,temperature, and the precursor supply ratio. The obtained films comparatively had a smooth surface
structure at 275 °C, 30 torr (Fig. 4). SEM image of the deposited GST film on patterned substrate by
CVD was shown in Fig. 5. High aspect hole was filled with GeSbTe materials. As a result, GST-CVD
can have a considerable expectation in the next generation's large capacitance PCRAM manufacturing.
The control in a high aspect hole is important. However, it is difficult to analyze the compositionalchange in the microscopical region as in the hole. Thus, we deposited GST films in a macro cavity with700 mm gap and more than 20 mm length for the purpose of achieving the composition control in theminute holes. Fig 6 shows some results of the composition in macro cavity with different depth from theentrance. The Ge composition increases toward the direction of depth of the hole and Sb decrease. We
therefore inferred from this result that there is some strong relationship between precursors in such anarrow space at deposition temperature. To fill the high aspect ratio hole with desired GeSbTe composition, it is necessary to make detailed CVD experiments in two precursor systems ( Ge-Sb, Ge-Te,Sb-Te ) and to control the fine CVD conditions based on this experimental results.	  The control of surface roughness is also important. Fig.7 shows that surface roughness increases by
the increase of Te concentration of the film. So we tried two-step deposition for small hole filling. Asfor 1st step low Te smooth film was deposited. Te dope by diisopropyltellurium vapor flow followed as
the 2nd step to achieve the desired Ge/Sb/Te ratio. We successfully filled under 150nm diameter hole bythis 2step method. (Fig.8)
References[1] J. I. Lee, H. Park, S. L. Cho, Y. L. Park, B. J. Bae, J. H. Park, J. S. Park, H. G. An, J. S. Bae, D. H.
Ahn, Y. T. Kim, H. Horii, S. A. Song, J. C. Shin, S. O. Park, H. S. Kim, U-In Chung, J. T. Moon, and B.
I. Ryu: VLSI Technology, 2007, p. 102.
[2] H Machida, S Hamada, T Horiike, M Ishikawa, A Ogura, Y Ohshita, and T Ohba, Japanese Journalof Applied Physics, 49 (2010) 05FF06.
[3] S. S. Bukalov, L. A. Mikhalitsyn, L. A. Leites, G. A. Domrachev, E. G. Domracheva, B. S. Kaverin, and A. M. Ob’yedkov: Mendeleev Commum. 13 (2003) No.6, 251.

Fig. 1. Composition diagram of obtained films. The red circle key is Ge2Sb2Te5. Other keys
denote various film compositions under different deposition conditions (pressure: 1-50 torr;
temperature: 200-350 °C).

Fig. 2. Structural formulae and vapor pressures of three precursors:(A)= t-C4H9GeH3, (B)= (i-C3H7)3Sb, (C)= (i-C3H7)2Te[ TEOS= Si(OC2H5)4 for comparison ].

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Fig. 3. Schematic diagram of CVD equipment.

Fig. 4. SEM image of obtained film surface.

Fig. 5. SEM image of the GST in the hole.

Fig. 6. Diagram of micro cavity and film compositions in the cavity.

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Fig. 7. Surface of various Ge/Sb/Te ratio films.

(a) 1st srep: Smooth Low Te film deposition (Ge/Sb/Te=57/41/2 at%)(b) 2nd step: composition control by Te dope (Ge/Sb/Te=19/27/54 at%)Fig. 8. Filling of small hole under 200nm diameter by two-step deposition.

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