AZO靶材热压致密化过程中晶粒生长规律研究

分别以98:2(质量比)的ZnO–Al_2O_3混合粉体和预处理粉体为原料,在不同热压温度、压力、保温时间下,采用原位热压工艺制备铝掺杂氧化锌(Al-doped ZnO,AZO)靶材。通过扫描电子显微镜和透射电子显微镜观察靶材晶粒形貌、阿基米德法测定试样密度、X射线衍射仪分析物相组成以及晶粒大小,四探针测试电阻率,研究靶材热压致密化过程中的晶粒生长规律及细晶高密靶材的制备工艺。结果表明:热压温度为900℃时,晶粒尺寸与原料粉体接近,颗粒之间只形成烧结颈,扩散反应不完全,掺杂替位效应弱,电阻率为0.284W×cm;热压温度上升至1000℃时,ZnO蒸发凝聚形成众多小颗粒导致衍射峰宽化,颗粒之间逐渐结合紧密,Al原子替位效应增强,电阻率降低至0.093W×cm;在热压温度为1100~1150℃时,靶材相对密度不断上升,体系中形成众多的岛状细晶,电阻率下降至1.5′10~(-4)W×cm;在温度1100℃时,随着压力的升高,靶材相对密度从15 MPa时的88.00%上升到35 MPa时的95.60%,晶粒尺寸略有减小;在热压温度1150℃时,随着保温时间的延长,晶粒尺寸生长有限,靶材的反致密化现象与晶粒生长无关。煅烧混合粉体在热压温度1150℃,压力18 MPa,保温时间90 min时,靶材相对密度最高达96.28%,电阻率低至1.6′10~(-4)W×cm,扫描电子显微镜观察晶粒细小,满足溅射靶材的性能要求。

Study on grain growth of AZO target during densification process by hot pressing

Al-doped ZnO targets were prepared byin-situ hot-pressing using ZnO and Al2O3 mixture powders (98:2 by mass) and the pretreatment powder as raw materials at different hot pressing (HP) temperatures, pressures, and holding times. Studies on the grain growth during HP densification and the HP process parameters of fine grain and high density target were carried out. The grain microstructures of target were observed by transmission electron microscope (TEM) and scanning electron microscopy (SEM). The density of target was measured by Archimedes method. The phase structure and grain size were measured by X-ray diffraction (XRD). The resistivity was measured by Four-probe tester. The results are as follows, when the HP temperature is 900℃ , the grain size is close to the raw material powder and the sintered neck is just formed between the particles. The resistivity of target is only 0.284Ω·cm, because the diffusion reaction is not completed and the doping effect is weak. When the HP temperature rises to 1000℃ , ZnO evaporates and agglomerates to many small particles, resulting in the broad of diffraction peak. Then, the particles are gradually combined more closely. The substitution effect of Al atom is enhanced, so the resistivity reduces to 0.093Ω·cm. When the HP temperature is 1100~1150℃ , the target density is increasing. Many fine crystals are formed in the system and the resistivity decreases to 1.5×10-4Ω·cm. When the temperature is 1100℃ , with the increase ofpressure, the grain size decreases when the target relative density increases from 88.00% (15 MPa) to 95.60% (35 MPa). When the temperature is 1150℃ , the grain growth is limited with the extension of holding time. The anti-densification phenomenon is not related to the grain growth. Under such HP process parameters (1150℃ / 18 MPa / 90 min), the relative density of the AZO target using pretreatment powders is highest (96.28%), this target has fine grain size and lower resistivity (1.6×10-4Ω·cm), meeting the performance requirements of AZO sputtering target