碳離子佈植對鎳化矽熱穩定性與碳化矽形成影響之研究

Abstract

本篇論文中,我們使用電漿浸潤式碳離子佈植(CPIII)與低溫碳離子佈植兩種製程作為碳離子佈植的方式。分別將此兩種碳離子佈植技術應用於兩個方向，分別為改善矽晶圓表面形成之鎳化矽薄膜之熱穩定性以及在碳離子佈植入矽晶圓以後經後續之退火製程形成碳化矽。 在CPIII的研究上，首先我們發現在經過CPIII製程之後，N+P接面的漏電並沒有明顯增加，此結果減少了我們對CPIII可能傷害N+P接面的疑慮。在經過一分鐘能量5keV的CPIII製程之後，未經砷參雜的NiSi薄膜之結塊溫度可以上升到800℃，但經過砷參雜之後的試片， CPIII並沒有增加熱穩定性的效果。我們也發現CPIII在製程中會在表面沉積一層碳薄膜，若離子佈植過程後剩餘的碳膜太厚，將會影響NiSi的形成。CPIII應用在碳化矽形成上的結果較不理想，佈植時間五分鐘能量3keV之CPIII製程的試片在做過650℃120秒鐘的退火之後，在替代位置上的碳原子百分濃度僅有0.301%，這是因為CPIII在製程中所形成的表面非晶層過少且非晶程度低的緣故。 低溫碳離子佈植的好處是能夠在表面形成厚且非晶程度高的非晶層，在載台溫度15℃下經過能量7keV劑量5×1015 cm-2 碳離子佈植的試片具有約49奈米接近完全非晶化的非晶層。碳離子佈植也被發現可以使矽基板中的磷離子在經過退火之後的分佈變的比退火之前淺，此項特性有助於實現超淺接面結構。在增加NiSi熱穩定性上，低溫碳離子的表現和CPIII類似，對於經過磷離子佈植的試片低溫碳離子佈植並不能增加NiSi的熱穩定性。在碳化矽形成的應用上，低溫碳離子佈植因為能夠形成非晶程度高且後的非晶層而具有優勢。我們針對離子佈植的能量、劑量及載台溫度上的不同分別進行實驗後，發現佈植能量7keV劑量5×1015 cm-2為較佳的佈植條件。而當載台溫度介於5℃與15℃之間時，其對退火後在替代位置上的碳原子濃度影響不明顯。我們也針對碳化矽形成所需的退火製程條件如第一階段退火的溫度及秒數和第二階段退火的方式進行實驗。在實驗結果中可發現第一階段退火的條件以溫度750℃時間120秒較佳，過高的溫度或過久的秒數反會使替代位置上的碳原子濃度降低。第二階段的退火的溫度需要很高以增加在過飽和狀態下的固態溶解度，但退火的時間需遠低於1秒，否則亦會使替代位置上的碳原子濃度降低。雷射退火因為其單一脈衝的退火時間僅25奈秒,故為一種十分具有潛力的第二階段退火方式。綜合以上各項理想的製程參數，我們使用載台溫度-15℃，佈植能量7keV劑量5×1015 cm-2的試片，在經過第一階段退火溫度750℃時間120秒及第二階段能量350 mj/cm2，五個脈衝的雷射退火後，替代位置上的碳原子濃度可以達到1.091%。

In this thesis, we use carbon plasma immersion ion implantation (CPIII) and low temperature carbon ion implantation as carbon implantation source. We applied the two processes on the application of increase NiSi thermal stability and Si-C formation. On the research of CPIII, first we find the leakage current of N+P junction after CPIII process didn’t increase. This result is beneficial for application on junction structure. After CPIII at 5 keV for 1 minute, the agglomeration temperature of NiSi thin film without arsenic doping could increase to 800 ℃. But on the arsenic doped sample, CPIII could not increase NiSi thermal stability. We also find CPIII will deposit a carbon thin film on the surface during process, if the carbon film is too thick after all ion implantation process, it will affect the formation of NiSi. The result of CPIII application on Si-C formation is not ideal, the substitutional carbon density of sample that performed CPIII at 3 keV for 5 minutes then annealing at 650 ℃ for 120 sec is only 0.301 %. That is because the surface amorphous layer produced by CPIII is not thick enough and the level of amorphous is low. The benefit of low temperature carbon ion implantation is it can produce thick amorphous layer with high amorphous level after process. After implantation at 7kev with a dose of 5×1015 cm-2 on a -15℃ chuck, the surface amorphous layer is about 49 nm and is near totally amorphous. We also find the implanted phosphorous profile after annealing would be shallower than the profile of as-implanted sample. This characteristic is beneficial for application on ultra-shallow junction fabrication. On the NiSi thermal stability application, we find low temperature carbon ion implantation could not improve thermal stability of phosphorous implanted NiSi film, which is similar to CPIII. We find low temperature carbon ion implantation is promising on Si-C formation application because it can produce thick and high quality surface amorphous layer after process. We perform low temperature carbon ion implantation with different energy、dose and chuck temperature and try to find the ideal implantation condition. From the result we find implantation energy at 7keV with a dose of 5×1015 cm-2 is the most ideal condition. We also try different annealing condition including first step annealing temperature、time and second step annealing method to find the ideal annealing condition. For first step annealing, temperature at 750 ℃ for 120 sec is the ideal condition. If the temperature is too high or the time is toolong, the density of substitutional carbon would decrease. Second step annealing time should be very high to increase carbon solid state solubility in silicon under supersatuation state, but the annealing duration time should be much shorter than 1 sec or the substitutional carbon density will decrease, too. The time duration of PLA is only about 25 ns for each shot, which is a promising second step annealing technique. Finally, by combine the optimized process condition, sample implanted at 7keV with a dose of 5×1015 cm-2 on a -15℃ chuck after first step annealing at 750 ℃ for 120 second and second step annealing using PLA at energy 350 mj/cm2 for 5 shots, the substitutional carbon density can reach 1.091%.