Effects of RF Sputtering Parameters on C-axis Aligned Crystalline (CAAC) InGaZnO₄Films Using Design of Experiment (DOE) Approach

Abstract

The influence of deposition parameters on the properties of RF sputter deposited c-axis aligned crystalline (CAAC) IGZO was studied using both single parameter and design of experiment (DOE) analysis (target composition near InGaZnO 4 ). Use of a 3-level, 6 factor Box-Behnken DOE enabled efficient sampling of the large processing parameter space. Deposition temperature and power, oxygen fraction in the sputter gas, and the ensuing Zn composition were identified as the key parameters correlated with c-axis texture in the films. CAAC formation commenced at a deposition temperature of 250 • C reaching maximum surface normal alignment near 315 • C. Crystallinity and alignment increased rapidly with oxygen fraction becoming nearly independent of fraction between 10% and 50%. Zinc loss during deposition at high temperatures and low oxygen partial pressures correlated with lower crystallinity, suggesting a strong composition dependence of CAAC formation in IGZO alloys. In contrast, increased deposition power improved alignment. Optimal deposition conditions were identified and related to a proposed nucleation and growth model.

Systematic Study on the Amorphous, C-Axis-Aligned Crystalline, and Protocrystalline Phases in In–Ga–Zn Oxide Thin-Film Transistors

“…The 2θ peak at 30° is a signature of CAAC IGZO. ,, This shift of the weak diffraction peak in the T sub range between 100 and 200 °C indicates a transition between a-IGZO and CAAC IGZO, pointing to a gradual enhancement of the c -axis-aligned crystallinity in the amorphous phase with T sub . Upon further T sub increase up to 300 °C, the CAAC IGZO peak at 30° increases in intensity while remaining substantially broad, which is in line with previous reports. ,, To sum up, when T sub varies from 25 to 300 °C while sputtering 50 nm thick IGZO films, we observe different IGZO phases: spinel IGZO, a-IGZO, CAAC IGZO, and the transition between them.…”

“…However, a fully distinct peak at 35° was never reported for sputtered films. ,,,, With a further increase of R O 2 , the intensity of the CAAC IGZO XRD peak increases and reaches its highest value at R O 2 = 80%. This corresponds to an increase of the c -axis-aligned crystallinity with R O 2 , which has been reported multiple times in the literature. ,,, At R O 2 = 0%, we see the weak diffraction with a maximum at ∼32°, indicative of a-IGZO.…”

“…Figure 1 shows that only weak diffraction with a maximum position at 2θ ∼ 32°is present at T sub = 25 °C. This weak signature is attributed to a-IGZO 46,47 based as well on simulated XRD. 48 Note that previous reports have observed that such a-IGZO can present a certain compositional ordering at the nanoscale, 23,49 but this is not resolved in the present study.…”

“…Upon further T sub increase up to 300 °C, the CAAC IGZO peak at 30°i ncreases in intensity while remaining substantially broad, which is in line with previous reports. 46,47,50 To sum up, when T sub varies from 25 to 300 °C while sputtering 50 nm thick IGZO films, we observe different IGZO phases: spinel IGZO, a-IGZO, CAAC IGZO, and the transition between them.…”

Improving Performance of Tin-Doped-Zinc-Oxide Thin-Film Transistors by Optimizing Channel Structure

“…7c has one prominent peak at 34.3°, indicating Sn atoms can successfully replace Zn sites in the lattice and form C-axis-aligned crystalline (CAAC). [39][40][41] The average grain size of the TZO film is estimated to be 17.1 nm using the Scherer formula, this can also be confirmed by the SEM image shown in Fig. 7d.…”