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구리 합금을 이용한 확산 방지막 자가형성 공정 연구

Title
구리 합금을 이용한 확산 방지막 자가형성 공정 연구
Other Titles
Development of self-forming diffusion barrier process by Cu alloy
Author
문대용
Alternative Author(s)
Dae-Yong Moon
Advisor(s)
박종완
Issue Date
2013-02
Publisher
한양대학교
Degree
Doctor
Abstract
In the current processing technology for semiconductor devices, Cu is the material of choice for interconnects. However the high diffusion rate for Cu atoms in inter-metallic dielectric (IMD) requires barriers to prevent diffusion into the IMD and Ta or/and TaNx have been employed as a conventional barrier materials. These diffusion barrier layers have poor electrical conductivity and reduce the area for Cu line, and thereby increase the resistance of the interconnect. Therefore, there is a need to reduce the barrier thickness to the minimum required while still retaining good barrier properties. Self-forming diffusion barriers have the potential to overcome these difficulties. The formation process involves the deposition of Cu alloys directly onto the SiO2. After annealing, the alloying element chemically reacts with the SiO2 at the Cu/SiO2 interface and forms a uniform barrier layer. Also, as in the case of the conventional barrier and Cu seed layer, PVD of the Cu alloy seed layer will eventually encounter the difficulty in conformal deposition in narrow line trenches and via holes. Atomic layer deposition (ALD) has been known for its good step coverage and precise thickness control, and is a candidate technique for the formation of a thin conformal barrier layer and Cu seed layer. Nevertheless, there have not been previous reports of the use of the ALD Cu-Mn alloy film for the self-formed barrier process. Therefore, we have investigated plasma enhanced atomic layer deposition (PEALD) of Cu-Mn alloy films for a self-forming barrier process. In this work, we investigated the out-diffusion of alloying elements and the growth kinetics and thermal stability of the self-formed interlayer in Cu-Mn, Cu-V, and Cu-Nb alloys on SiO2, annealed under vacuum of 10-4 Pa to temperatures up to 500 ˚C. Transmission electron microscopy and electron energy loss spectroscopy were used to investigate the microstructure, composition profile, and oxidation state of the self-formed interlayer. The formation of interlayer obeyed the Cabrera-Mott theory, i.e. the oxide thickness increases linearly with a logarithm of annealing time. Also, interlayer growth rates were determined by the chemical states and diffusivity of Mn, V, and Nb ions in the interlayer. The V based interlayer was grown faster than Mn based interlayer because of the strong electric field between both sides of the interlayer due to V+5, compared to Mn+3, and the high diffusivity of V ions in the interlayer. To evaluate thermal stability, leakage currents of Cu alloys/interlayer/SiO2/Si (MOSs) formed by patterning the Cu-Mn, Cu-V, and Cu-Nb films on the SiO2/Si substrate were measured after annealing at 300 – 600 ˚C for 12 h. The results showed that all of the same thick interlayers (~2 nm) formed by Mn, V, and Nb were acted as a diffusion barrier with stability up to 450 ˚C and the Mn based interlayer was stable up to 500 ˚C. Further, the plasma enhanced atomic layer deposition of Cu-Mn alloy, in which the Mn contents was controlled from 0 to approximately 10 atomic % with various Mn precursor feeding times, was described. Low processing temperature using plasma allowed for the deposition of continuous and conductive Cu-Mn alloy several nanometers thick. The resistivity dramatically decreased with the annealing of the Cu-Mn alloy films due to out-diffusion of Mn atoms. Out-diffused Mn atoms were segregated to the interface between the Cu-Mn alloy and SiO2, resulting in self-formation of an interlayer approximately 3 nm thick, continuous MnSixOy. EELS analysis indicates that the chemical composition of the 2-3 nm self-formed interlayer contains primarily Mn in +2 and +3 oxidation states. The Mn based interlayer acted as a good diffusion barrier layer and adhesion layer with the Cu line and SiO2. |Cu가 기존 배선물질인 Al을 대체함에 따라 resistance-capacitance (RC) delay나 electromigration (EM) 등의 문제들이 어느 정도 해결되었다. 그러나 지속적인 배선 폭의 감소로 배선의 저항 증가, EM 현상 강화 그리고 stability 악화 등의 문제가 지속적으로 야기되고 있다. 이를 해결하기 위한 방법으로 atomic layer deposition (ALD) Cu alloy seed layer를 이용한 barrier 자가형성 공정에 대한 연구를 진행하였다. Barrier 자가 형성 공정은 Cu 합금을 seed layer로 사용하여 도금을 한 후 열처리를 통해 SiO2와의 계면에서 barrier를 자가 형성시키는 공정을 말한다. 이 공정은 매우 균일하고 얇은 barrier를 형성할 수 있고 별도의 barrier와 glue layer를 형성하지 않아 seed layer를 위한 공간을 추가로 확보할 수 있는 장점을 가지고 있다. 또한, via bottom에 barrier가 형성되지 않아 배선 전체 저항을 급격히 낮출 수 있다. 합금 물질로는 초기 Al이나 Mg에 대한 연구가 진행되었으나, 낮은 oxide formation energy로 인해 SiO2에 과도한 손상을 주는 문제점이 제기되었다. 최근 Mn을 합금 물질로 사용한 안정적인 barrier 형성 공정이 보고 되고 있다. 본 연구에서는 V과 Nb을 신규 합금 물질로 선정하여 그 barrier 형성 가능성을 판단하고 그 특성과 성장 거동을 Mn과 비교하였다. co-sputtering system을 사용하여 Cu-Mn, Cu-V 과 Cu-Nb 합금을 형성하고, barrier를 자가 형성을 위해 200 도에서 500 도까지 열처리 온도를 변화시키며 barrier 형성 양상과 그 특성을 관찰 하였다. 열처리 후 시편의 단면을 TEM 분석을 통해 Cu-V 박막과 SiO2 사이에 interlayer가 형성된 것을 확인 하였으며, 그 두께는 동일 함량과 열처리 조건에서 Cu-Mn 보다 두꺼 웠다. 다. 이는 V의 oxide formation energy와 interlayer 양단에서의 양이온 산화수가 영향을 미친 것으로 판단된다. 동일 두께에서 V 기반의 barrier가 Mn 기반의 barrier보다 열적으로 안정하지 않았으나, 200 도의 barrier 형성 온도에서는 빠른 성장 속도로 인해 더 높은 열적 안정성을 보였다. 또한, physical vapor deposition (PVD) 법의 단점을 극복하고자 atomic layer deposition (ALD) 법을 이용하여 Cu-Mn alloy를 형성하는 연구가 진행되었다. 120도의 저온에서 0-11.8 at. %의 다른 Mn 조성을 가지는 Cu-Mn ALD 공정이 확립되었다. Cu-Mn 박막의 전기 전도도는 박막 내 Mn 함량 이외에도 박막 형성 시 기판 온도에 의해 크게 영향을 받았다. 이는 높은 표면 에너지를 가지는 Cu-Mn 박막이 높은 기판온도에서 결정성이 향상됨에도 불구하고 조대한 island를 형성하며 치밀하지 못하게 성장했기 때문으로 판단된다. 결정성 측면을 고려한다면 높은 기판온도에서 seed layer를 형성하는 것이 바람직하나 전기적 특성과 표면 거칠기의 영향으로 120 도에서 형성된 Cu-Mn 박막이 seed layer로써 우수한 특성을 가진 것으로 판단된다. 약 5 nm의 ALD Cu-Mn 박막을 24 nm trench에 형성하고 이를 seed layer로 사용하여 전해도금을 실시한 결과 양호한 채움 특성을 얻을 수 있었다. 본 연구를 통해 V이 barrier 자가 형성 공정 시 온도를 감소시킬 수 있는 합금 물질로 평가 되었다. ALD Cu alloy 형성 시 저온 증착이 요구되는 만큼 저온 ALD가 가능한 V precursor가 설계될 경우 barrier 자가 형성 공정의 상용화에 큰 기여가 있을 것으로 판단된다.; In the current processing technology for semiconductor devices, Cu is the material of choice for interconnects. However the high diffusion rate for Cu atoms in inter-metallic dielectric (IMD) requires barriers to prevent diffusion into the IMD and Ta or/and TaNx have been employed as a conventional barrier materials. These diffusion barrier layers have poor electrical conductivity and reduce the area for Cu line, and thereby increase the resistance of the interconnect. Therefore, there is a need to reduce the barrier thickness to the minimum required while still retaining good barrier properties. Self-forming diffusion barriers have the potential to overcome these difficulties. The formation process involves the deposition of Cu alloys directly onto the SiO2. After annealing, the alloying element chemically reacts with the SiO2 at the Cu/SiO2 interface and forms a uniform barrier layer. Also, as in the case of the conventional barrier and Cu seed layer, PVD of the Cu alloy seed layer will eventually encounter the difficulty in conformal deposition in narrow line trenches and via holes. Atomic layer deposition (ALD) has been known for its good step coverage and precise thickness control, and is a candidate technique for the formation of a thin conformal barrier layer and Cu seed layer. Nevertheless, there have not been previous reports of the use of the ALD Cu-Mn alloy film for the self-formed barrier process. Therefore, we have investigated plasma enhanced atomic layer deposition (PEALD) of Cu-Mn alloy films for a self-forming barrier process. In this work, we investigated the out-diffusion of alloying elements and the growth kinetics and thermal stability of the self-formed interlayer in Cu-Mn, Cu-V, and Cu-Nb alloys on SiO2, annealed under vacuum of 10-4 Pa to temperatures up to 500 ˚C. Transmission electron microscopy and electron energy loss spectroscopy were used to investigate the microstructure, composition profile, and oxidation state of the self-formed interlayer. The formation of interlayer obeyed the Cabrera-Mott theory, i.e. the oxide thickness increases linearly with a logarithm of annealing time. Also, interlayer growth rates were determined by the chemical states and diffusivity of Mn, V, and Nb ions in the interlayer. The V based interlayer was grown faster than Mn based interlayer because of the strong electric field between both sides of the interlayer due to V+5, compared to Mn+3, and the high diffusivity of V ions in the interlayer. To evaluate thermal stability, leakage currents of Cu alloys/interlayer/SiO2/Si (MOSs) formed by patterning the Cu-Mn, Cu-V, and Cu-Nb films on the SiO2/Si substrate were measured after annealing at 300 – 600 ˚C for 12 h. The results showed that all of the same thick interlayers (~2 nm) formed by Mn, V, and Nb were acted as a diffusion barrier with stability up to 450 ˚C and the Mn based interlayer was stable up to 500 ˚C. Further, the plasma enhanced atomic layer deposition of Cu-Mn alloy, in which the Mn contents was controlled from 0 to approximately 10 atomic % with various Mn precursor feeding times, was described. Low processing temperature using plasma allowed for the deposition of continuous and conductive Cu-Mn alloy several nanometers thick. The resistivity dramatically decreased with the annealing of the Cu-Mn alloy films due to out-diffusion of Mn atoms. Out-diffused Mn atoms were segregated to the interface between the Cu-Mn alloy and SiO2, resulting in self-formation of an interlayer approximately 3 nm thick, continuous MnSixOy. EELS analysis indicates that the chemical composition of the 2-3 nm self-formed interlayer contains primarily Mn in +2 and +3 oxidation states. The Mn based interlayer acted as a good diffusion barrier layer and adhesion layer with the Cu line and SiO2.
URI
https://repository.hanyang.ac.kr/handle/20.500.11754/134265http://hanyang.dcollection.net/common/orgView/200000421160
Appears in Collections:
GRADUATE SCHOOL[S](대학원) > NANOSCALE SEMICONDUCTOR ENGINEERING(나노반도체공학과) > Theses (Ph.D.)
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