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|標題:||Phase Transformation in Chromium Nitride Films
|關鍵字:||Chromium Nitride;氮化鉻;Stress;Phase Transformation;Young''s Modulus;應力;相變化;楊氏係數||出版社:||材料工程學研究所||摘要:||
將氮化鉻鍍膜於真空下退火，在500°C以上會出現氮化亞鉻，而在900°C則產生二矽化鉻。氮化亞鉻之生成量在500°C-600°C間，會隨溫度先增加，並在600°C時達到峰值，隨後隨溫度而減少，但在溫度大於750°C，其生成量會再次地隨溫度而增加。這亦可證實低溫的相變非熱力學因素所控制。繞射峰之偏移量與殘留應力的變化趨勢與該薄膜置於前述控制氣氛下退火時相同。本研究亦將氮化鉻粉末置於真空下退火，在750°C以上時，其真空度會逐漸地增加三個數量級，達10-2 torr，但在降溫時又會逐漸地回復到高真空 (10-5 torr)，此為高溫相變化釋放氮氣所致。另由理論計算相變化時所需的應力鬆弛量，與實驗量測結果所得到之應力鬆弛量相當一致。
The phase transformation of CrN films was investigated over various temperature ranges using X-ray diffraction and stress measurements. CrN films were deposited on (100) Si wafers by cathodic arc plasma deposition. After that, the films were annealed between 400°C and 1200°C for 2 h in air, N2, and N2/H2=9, which possess dramatically different pN2 and pO2. XRD results showed that oxidation of CrN films occurred above 700°C in all gases but the relative amount of the resultant oxide Cr2O3 decreased with rising (pN2/pO2) ratio in the gases for a given temperature. An additional Cr2N phase appears at temperatures above 1100°C, as well as between 500°C and 700°C. The formation of Cr2N at high temperatures is consistent with the thermodynamic prediction on the phase transformation of CrN and the reaction between CrN and Si. The later reaction would also result in the formation of CrSi2. Thermodynamics can successfully explain the phase transformation occurring at high temperature but not that in the low temperature range where Cr2N is not thermodynamic stable.
Peak shift of CrN (220) is found to be negative and its absolute value decreases with increasing temperature at low temperatures. The residual stresses of the films measured by a scanning laser curvature technique are found to be compressive and tend to relax rapidly with increasing temperature. Large stress relaxation results in the formation of Cr2N at such low temperatures. Unrelaxed as-deposited specimens and near completely relaxed annealed specimens were placed in the same annealing batch, which renders different results in the presence of Cr2N and could further confirm that the stress relaxation governs the phase transformation. Hence, the stress relaxation-induced phase transformation should be the governing mechanism of forming Cr2N in the low temperature range.
When CrN films annealed in vacuum, Cr2N appeared above 500°C whereas CrSi2 showed up at 900°C. The Cr2N ramped with temperature between 500°C and 600°C, after which Cr2N deceased with temperature up to 750°C. The absolute values of peak shift decreased between 400°C and 600°C, meanwhile the amount of Cr2N increased rapidly. The CrN powders annealed vacuum, the pressure of which is in situ monitored. The vacuum pressure was almost unchanged below 750°C. However, the pressure increased more than three orders, 10-2 torr, above 750°C. During cooling period, the pressure decreased to 10-5 torr. Such pressure changes indicated that the occurrence of phase transformation above 750°C was thermodynamically-nitrogen release. The phase transformation associated with stress relaxation was estimated by thermodynamics. The critical stress, above which the phase transformation occurred, was consistent with experimentally.
The Young's modulus of chromium nitride (CrN) films usually determined by complex and destructive techniques was obtained from this study. The CrN films were annealed in a N2/H2=9 reducing atmosphere between 300°C and 900°C. X-ray diffraction spectra revealed that the CrN main (220) peak was shifted from lower diffraction angles toward higher diffraction angles and then back to the standard reference angle with increasing temperature. Strains of the films were calculated from the corresponding interplannar spacing change associated with the peak shift. Residual stresses were determined by the curvature changes resulted from the annealing-induced stress relaxation. Young's modulus of CrN films was then deduced from the linear relation of stresses and strains by considering residual stresses as plane stresses. The obtained Young's modulus was 190±50 GPa, which is comparable with those reported in the literature.
|Appears in Collections:||材料科學與工程學系|
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