【作者】 符黎明；

【导师】 阙端麟； 杨德仁；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2008， 博士

【摘要】 集成电路特征线宽的不断减小对直拉（CZ）单晶硅片中的缺陷控制和内吸杂技术提出了愈来愈高的要求。在这种情况下,基于氧沉淀的内吸杂工艺在不断地改进。国际著名的硅片供应商——美国的MEMC公司近年来提出的基于快速热处理（RTP）的内吸杂工艺,是一个有里程碑意义的突破。它不仅具有技术上的重要性,而且还引发了一个基本的科学问题,即:RTP对直拉硅片的氧沉淀是如何影响的。在这个问题上的研究尽管已经取得了很大的进展,但是RTP对不同的直拉硅片及其在不同的热工艺过程中的氧沉淀行为的影响并没有彻底弄清楚。本论文详细地研究了不同种类的直拉硅片在各种条件下的RTP预处理和后续热处理过程中的氧沉淀行为,以及基于RTP的内吸杂工艺,获得了如下有创新意义的结果:研究了普通直拉硅片和掺氮直拉硅片在经过高温RTP预处理后,再经过不同的低一高两步热处理后的氧沉淀行为。结果表明:（1）在CZ硅片中由RTP引入的空位在800℃时增强氧沉淀形核的作用最强,而在NCZ硅片中氮和由RTP引入的空位在800～1000℃温度范围内可以发生协同作用,更强烈地促进氧沉淀的形核。（2）在900℃以上,氮比空位有更强的促进氧沉淀形核的能力,但有空位存在时,氮促进氧沉淀形核的能力被进一步增强。根据RTP对掺氮直拉硅片和普通直拉硅片的氧沉淀影响的不同,提出掺氮直拉硅片的基于RTP的内吸杂工艺应该有别于普通直拉硅片的,即:掺氮直拉硅片的工艺为在1250℃的RTP处理后,从800℃以1℃/min速率升温至1000℃并保温16小时;而普通直拉硅片的工艺则为在1250℃的RTP处理后,再经过800℃/4 h+1000℃/16 h两步处理。研究了N₂气氛下的RTP预处理的温度和降温速率,对硅片经低—高两步退火后氧沉淀和洁净区形成的影响,提出了直拉硅片的基于N₂气氛下RTP的内吸杂工艺。与Ar气氛下的RTP相比,较低温度的N₂气氛下的RTP预处理就能使硅片在随后的低—高两步退火过程中形成高密度的氧沉淀。当减小RTP的降温速率时,在硅片近表面能形成洁净区。在合适的降温速率下,RTP的温度越低,硅片中形成的洁净区宽度越大,但体微缺陷（BMD）密度越低。因此,选择合适的RTP温度和降温速率,结合后续低—高两步热处理,就可以在硅片内形成一定宽度的洁净区和合适密度的BMD区。上述结果纠正了以前国际上普遍接受的“N₂气氛下的RTP预处理不能用于直拉硅片的内吸杂工艺”的观点。研究了在不同气氛下两步高温RTP预处理对轻掺硼和重掺硼CZ硅片在后续热处理中氧沉淀和洁净区形成的影响。对于轻掺硼硅片来说,如果硅片先在Ar气氛下进行第一步RTP时,第二步RTP的气氛决定了氧沉淀和洁净区的形成;如果在N₂或O₂气氛下进行第一步RTP,则第二步RTP无论在哪种气氛下进行,经过后续低—高两步热处理后都能获得洁净区和高密度的BMD区,只是DZ宽度有所差异。对于重掺硼CZ硅片来说,只经过一步Ar气氛下的RTP预处理后,再通过低一高两步退火,硅片内仅形成高密度的BMD区而不能形成洁净区;而当RTP预处理的气氛变为O₂时,硅片内的BMD密度则很低。折衷上述两种情况,重掺硼CZ硅片经历先在Ar气氛紧接着在O₂气氛下的高温RTP预处理后,再通过低—高两步热处理,即可形成高密度的BMD区和一定宽度的洁净区。研究了表面有氮化硅薄膜的直拉硅片经历高温RTP后,在随后的低—高两步退火中BMD和洁净区的形成情况。结果表明:与通常的硅片经过1250℃的RTP预处理的情况相比,有氮化硅薄膜的硅片经过1200℃的RTP后,在随后的低—高两步热处理中产生的氧沉淀量与前者的相当,并能形成一定宽度的洁净区。初步认为:在RTP过程中,氮化硅薄膜的硅-氮键发生断裂,随后氮原子从硅片表面向体内扩散。在空位和氮的共同作用下,硅片的氧沉淀被显著地促进。研究了轻掺硼CZ硅片和重掺硼CZ硅片经过两种氧沉淀形核热处理,即:同在800℃的常规炉退火和RTP后,在1000℃热处理时氧沉淀的情况。对于轻掺硼硅片而言,RTP处理1小时和常规热处理4小时导致相当的氧沉淀量,表明RTP的光辐照促进了氧沉淀的形核过程,这可能与氧扩散被增强有关。对于重掺硼CZ硅片而言,RTP与常规炉退火相比,前者不仅促进了氧沉淀的形核,而且使后续高温热处理形成的氧沉淀及其诱生缺陷在硅片截面上的分布情况发生了改变,与常规炉退火导致的BMD在硅片截面上均匀分布的情况不同,它具体表现为:在硅片的近表面区域形成了大量的氧沉淀、位错环以及尺寸较大的层错,而在体内区域形成的是大量的氧沉淀以及少量的层错和伴生位错环的大尺寸氧沉淀。研究了CZ硅中的氧沉淀在RTP和常规炉退火过程中的消融以及在后续常规炉退火过程中的氧沉淀的再生长。结果表明:从间隙氧浓度升高的角度来看,RTP在短时间内消融氧沉淀的效果可以与长时间的常规炉退火的相比拟;另一方面,氧沉淀经两种热处理方式消融后再生长的情况也有所不同,具体表现为:经RTP消融处理后,由于小的氧沉淀未被完全消融,在氧沉淀再生长退火过程中,未消融的小的氧沉淀和较大的氧沉淀能够同时长大,因而BMD密度显著增加;而经常规炉退火消融处理后,小的氧沉淀被完全消融,体内残留较大的氧沉淀,它们作为氧沉淀再生长的核心,所以经过氧沉淀再生长退火后,BMD密度基本不变,但氧沉淀尺寸显著增大。更多还原

【Abstract】 The ever-smaller feature size of integrated circuit imposes on increasingly stringent requirements on the defect control and internal gettering（IG）capability of Czochralski（CZ）silicon wafers.Under the circumstance,the IG process based on oxygen precipitation in CZ silicon wafers has been continuously improved.In recent years,the MEMC company in America,a leading silicon supplier,has presented a patented IG process based on rapid thermal process（RTP）,which is believed to be a milestone in the defect engineering of silicon wafers.Such a process is not only of technological importance but also arouses a fundamental issue on the effect of RTP on oxygen precipitation in CZ silicon.Despite the great progress made in the research on this issue,the exact effects of RTP on oxygen precipitation in different kinds of CZ silicon wafers subjected to various thermal cycles have not substantially clarified.In this dissertation,the oxygen precipitation behaviors in CZ silicon wafers subjected to different RTPs and subsequent thermal anneals and,moreover,the RTP-based IG processes have been detailedly investigated.In the following,the primary results achieved herein are listed.The effects of prior RTP at high temperatures on the oxygen behaviors in CZ and NCZ silicon wafers subjected to low-high（L-H）two-step anneal were investigated.It was shown that:（1）.The RTP-induced vacancies in CZ silicon enhanced the nucleation for oxygen precipitation most significantly at 800℃,while,for NCZ silicon,the vacancies coact with the nitrogen atoms to enhance the nucleation for oxygen precipitation most significantly in the temperature range of 800～1000℃.（2）. At temperatures above 900℃,the nitrogen atoms are superior to the vacancies in terms of the enhancement of nucleation for oxygen precipitation and,moreover,the co-existing of nitrogen atoms and vacancies in CZ silicon will more significantly enhance the nucleation for oxygen precipitation.In view of the different effects of RTP-induced vacancies on the oxygen precipitation behaviors in CZ and NCZ silicon wafers,it is believed that the RTP-based IG process for NCZ silicon wafer should be somewhat different from that for CZ silicon wafer,that is,the one for NCZ silicon wafer is RTP at 1250℃followed by the ramping anneal from 800 to 1000℃with a rate of 1℃/min and then with a 16 h isothermal anneal;while,that for CZ silicon wafer is RTP at 1250℃followed by 800℃/4 h + 1000℃/16 h anneal. The influences of temperature and cooling rate of RTP under N₂ ambient on oxygen precipitation and formation of DZ in CZ silicon wafers subjected to the subsequent L-H two-step anneal were investigated,as a result,the IG process based on the RTP under N₂ ambient for CZ silicon wafers was proposed.In comparison with the RTP under Ar ambient,the RTP under Ar ambient at the lower temperatures could lead to high density of oxygen precipitates generated in CZ silicon wafer subjected to the subsequent L-H two-step anneal.Moreover,with a low cooling rate of RTP,a DZ could be formed in the near-surface region with CZ silicon wafer.With an appropriate cooling rate,the RTP at lower temperatures led to a wider DZ but a lower density of bulk microdefects（BMDs）.Accordingly,the RTP under N₂ ambient at appropriate temperatures and with desirable cooling rates could result in a width of DZ and an appropriate density of BMDs in CZ silicon wafers subjected to the subsequent L-H two-step anneal.This result reclaims the formerly widespread accepted viewpoint that the RTP under N₂ ambient cannot be applied to the IG process for CZ silicon wafers.The effect of two consecutive RTP under different ambients on oxygen precipitation and formation of DZ during the subsequent thermal cycles for the lightly and heavily boron-doped CZ silicon wafers were investigated.Regarding the lightly boron-doped CZ silicon wafers,if the first-step RTP was performed under Ar ambient, then the oxygen precipitation and formation of DZ were determined by the second-step RTP ambient;while,if the first-step RTP was performed under N₂ or O₂ ambient,then high density of BMDs and DZ could be formed during the L-H two-step anneal subsequent to the RTP under any ambient,but the width of DZ were different. As for the heavily boron-doped CZ silicon wafers,if with only one-step RTP under Ar ambient,then a high density of BMDs was formed but DZ was not generated after the subsequent L-H two-step anneal;however,if the RTP ambient was changed as O₂,the density of BMDs formed by the subsequent L-H two-step anneal was quite low.Therefore,for the heavily boron-doped CZ silicon wafers,making a trade-off between the above two cases,a width of DZ and a high density of BMDs could be formed by the L-H two-step anneal subsequent to the two-step RTP consecutively performed under Ar and O2 ambients.The formation of BMDs and DZ in the silicon nitride film coated CZ silicon wafers subjected to the high temperature RTP followed with L-H two-step anneal was investigated.With the same L-H two-step anneal,the amount of precipitated oxygen （△[O_i]）in the silicon nitride film coated CZ silicon wafers with a prior RTP at 1200℃was comparable to that in the silicon wafers with a prior RTP at 1250℃and, moreover,a width of DZ was generated in the silicon nitride film coated CZ silicon wafers.It is preliminarily believed that the silicon-nitrogen bonds within the silicon nitride film were broken by the RTP and,moreover,the released nitrogen atoms diffused into the silicon wafers.Furthermore,due to the coaction of in-diffused nitrogen atoms and the vacancies induced by the RTP,oxygen precipitation in silicon wafers was significantly enhanced.Oxygen precipitation during the 1000℃anneal subsequent to the nucleation anneal at 800℃by the RTP or conventional furnace anneal（CFA）for the lightly and heavily boron-doped CZ silicon wafers were respectively investigated.Regarding the lightly boron-doped CZ silicon wafers,the RTP at 800℃for 1 h and the CFA at 800℃for 4 h led to the comparative△[O_i],indicating that the optical radiation of RTP enhanced the nucleation of oxygen precipitates most likely due to the enhanced oxygen diffusion.As for the heavily boron-doped CZ silicon wafer,compared with the CFA, the RTP not only enhanced the nucleation of oxygen precipitates but also altered the cross-sectional distribution of BMDs formed in the subsequent 1000℃anneal. Concretely speaking,the nucleation by the CFA led to quite uniform distribution of BMDs across the silicon wafer,whereas,the nucleation by the RTP resulted in not uniform cross-sectional distribution of BMDs,that is,a large number of oxygen precipitates and dislocation loops as well as large-sized stacking faults formed in the near-surface region of silicon wafer,while,a large number of oxygen precipitates and a small amount of staking faults as well as large-sized oxygen precipitates accompanied with dislocation loops were generated in the bulk region.The dissolution of oxygen precipitates in CZ silicon by the high temperature RTP and CFA and the regrowth of oxygen precipitates during the subsequent CFA were investigated.In terms of the increase in[O_i],the effect of RTP for a short period of time on the dissolution of oxygen precipitates could be equivalent to that of CFA for a long time.On the other hand,the regrowth of oxygen precipitates after the RTP was quite different from that after the CFA.For the dissolution of oxygen precipitates by the RTP,due to the very short period of thermal cycle,even for the small-sized oxygen precipitates,they were not dissolved completely.Therefore,for the regrowth of oxygen precipitates,the undissolved small and large sized oxygen precipitates simultaneously acted as the nuclei,thus leading to increased number of BMDs.While, for the dissolution of oxygen precipitates by the CFA,the small-sized oxygen precipitates were substantially dissolved.Thus,during the regrowth of oxygen precipitates,only the residual large sized oxygen precipitates acted as the nuclei. Consequently,the resulting BMDs kept nearly the same density as those after the dissolution by CFA.更多还原