【作者】 殷桂琴；

【导师】 宁兆元；

【作者基本信息】 苏州大学 ， 凝聚态物理， 2008， 博士

【摘要】 自20世纪90年代以来,超大规模集成电路(ULSI)的特征尺寸按摩尔定律缩小。由于器件密度和连线密度增加、线宽减小,将导致阻容(RC)耦合增大,从而使信号传输延时、干扰噪声增强和功率耗散增大。未来的超大规模集成电路制造技术必须采用低介电常数(k)材料取代二氧化硅做层间介质来降低寄生电容,因此低介电常数材料(k <4)和超低介电材料(k <2)在今后的超大规模集成电路制造方面将占有重要的地位。本论文采用溶胶-凝胶法并与旋转涂敷工艺(SOD)相结合制备了硅基多孔低介电常数薄膜,系统地研究了制备多孔低介电薄膜的方法,并详细地分析了所制备薄膜的微结构,化学键和电学性质,得到了一些有价值的新结果。第一,首先,利用溶胶凝-胶法结合旋转涂敷工艺,制备了多孔低介电(k)的MSQ (methylsilsesquioxane甲基倍半硅氧烷)薄膜。本实验中,利用MTMS(甲基三甲氧基硅氧烷)做为主要原料,乙醇为溶剂,采用HCl为催化剂在常温下制备出MSQ胶体,然后用旋转涂敷工艺(SOD)将MSQ胶体制备成MSQ薄膜。由于MSQ的性质较为活泼,常规的制备方法难以控制,而本技术具有设备简单,工艺容易控制,掺杂方便等特点。解决了其他制备MSQ薄膜的方法所带来的困难。其次本文详细地分析了利用D4((八甲基环四硅氧烷)的低沸点和分子密度低的性质,将其作为致孔剂来制备多孔低介电的MSQ薄膜,并研究了退火温度和氛围对该多孔低介电薄膜的影响。对退火前后低介电薄膜样品的结构特点和电学性能进行了测试与分析。FTIR分析结果表明,合适的退火温度为500oC,合适的退火氛围是在氮气的保护下退火,所得到的薄膜经过退火处理后介电常数可达2.1,在氮气保护下400oC时退火之后的薄膜,它的漏电流密度比没有加D4的要低一个数量级。第二,本文详细地研究了不同气氛下退火处理对另一类硅基低介电薄膜—HSQ (hydrogensilsesquioxane)薄膜介电常数的影响。由于水的强极性键会导致介电常数和漏电流的增加,而Si-OH基易吸水,所以含有Si-OH键是低介电材料的不利因素。本论文发现了HSQ薄膜在氮气保护下并且在一定温度下退火可以有效地去除Si-OH基团,从而降低薄膜的介电常数及漏电流密度。同时又详细地介绍了用D5和D4分别作为致孔剂制备多孔低介电HSQ薄膜的技术,分析了该多孔低介电HSQ薄膜的结构变化,以及在不同氛围下退火后介电常数的变化。(1)FTIR结果发现,不加D4退火和加入D4在真空中退火后均会产生Si-OH基,而加入D4后在氮气保护下退火Si-OH基明显地被减弱。Si-OH基的出现,究其原因可能是由于Si-H和Si-O在温度的影响下被破坏,从而形成了Si-OH基。加入D4的样品在氮气保护下,温度为400oC时退火1.5小时后,-OH基团和C-H基团的吸收峰强度都有明显的减弱,表明水份和有机成分的大量流失。也就是说,在氮气的保护下退火可以有效地消减Si-OH基峰的强度。可能消减的原因可以用下面的脱水反应式来解释:Si-OH + HO-Si = Si-O-Si + H2O加入D4和未加入D4的样品,在不同的氛围下退火处理后其结构变化情况不同。加入D4的样品,并在氮气保护中,温度为400oC时退火1.5小时后的介电常数最低,加入D4,并且未经过任何处理的样品,这种薄膜的介电常数最高。加入D4,并在真空中,温度为400oC时退火1.5小时后,引起了Si-OH基的产生,造成了介电常数的增加。经过氧等离子体处理后的多孔HSQ薄膜的漏电流密度比未经过处理的多孔HSQ薄膜的漏电流密度几乎高了一个数量级。在电场强度为1 MV/cm时,经过氧气等离子体处理,又在氮气保护下,在350oC时退火1.5小时后的多孔HSQ薄膜的漏电流密度是3.0038×10-8 A/cm2,几乎是未经过处理的多孔HSQ薄膜的漏电流密度的两倍。由此可知,薄膜经退火处理之后,其漏电流密度有所改善。(2)加入D5 (十甲基环五硅氧烷)为致孔剂的多孔低介电HSQ薄膜退火处理工艺的分析。FTIR结构分析表明,在较高温度下有利于维持Si-H基,而Si-H基是构成低介电薄膜的主要基团。真空退火下出现了Si-OH基,所以真空退火不利于低介电薄膜。在温度为500oC时氮气氛围下退火1.5小时之后,由于脱水反应,Si-OH基的吸收峰强度很弱,同时由于D5分解的原因,D5分解后在薄膜中产生了孔隙,从而降低薄膜的分子密度,达到降低介电常数的目的。众所周知,Si-O键的笼式结构由于其特殊的结构有利于薄膜低介电性。而一定条件下的退火可以保持Si-H基和Si-O键的笼式结构,也就是有利于维持薄膜的低介电性。我们将在氮气保护下不同温度退火的多孔低介电HSQ薄膜与未处理的HSQ薄膜进行了介电特性测试。退火处理之后的HSQ薄膜的介电常数降低,并且介电常数随着退火温度的增加而增加。在温度为400oC时氮气氛围下退火1.5小时的薄膜样品的漏电流密度较大。其原因是在400oC时退火后,部分D5已经分解,产生了较大的孔隙,增加了漏电流密度。而在温度为500oC时,由于薄膜结构逐渐致密,变得均匀,所以漏电流密度降低。在温度为300oC时,溶剂和D5还未完全去除,故薄膜分子密度较大,所以其漏电流密度较低。在温度为400oC时退火后,Si-O-Si的笼式结构吸收峰强度大于在500oC和300oC的。第三,首次研究了甲烷等离子体表面处理对HSQ薄膜的结构和电学性能的影响。对HSQ薄膜进行了不同时间的甲烷等离子体处理,FTIR结果表明,处理时间对于单独使用甲烷等离子体处理后的HSQ薄膜结构没有太大的变化。但是,对于不同甲烷等离子体处理时间,又在氮气保护下,不同温度退火的HSQ薄膜而言,其结构有很大的变化。(1)随着甲烷等离子体处理时间的增加,Si-H键的含量在逐步增加,Si-O笼式结构得以保护,不会被破坏。Si-O笼式结构是维持低介电常数的主要结构,所以经过甲烷等离子体处理后的薄膜样品,可以保护低介电常数薄膜结构不被破坏。(2)随着退火温度的增加,Si-H键的含量也在逐步增加,而Si-O笼式结构容易遭到破坏,但随着甲烷等离子体处理时间的增加,破坏减小,Si-O笼式结构得以保护。因此,经过甲烷等离子体处理后的HSQ薄膜在高温退火后,可以保护Si-O笼式结构不遭到破坏,可以维持在高温退火后薄膜的低介电性能,从而保护退火薄膜的低介电性。更多还原

【Abstract】 Since 1920’s, the feature size of ULSI (Ultra-large scale integrate circuit) is scaling down to a very small value according to the prediction of so-called“Moore’s Law”. In order to reduce the RC sign delay, power dissipation and cross-link noise between metal and interconnects caused by size shrinking continuously, the porous low dielectric constant (low- k) and ultra-low dielectric constant (k <2) materials recently received much close attention. In this thesis, we focus our research on the sol-gel with spin-on (compatibility with existent ULSI technology) technology to prepare low- k thin films. To the best our knowledge, we systematically studied the properties of these Silicon based films, such as preparation, microstructure, chemical bonds and leakage current density. We achieved some valuable breakthrough.1. Through sol-gel method with spin-on technology, we deposited the porous low dielectric constant MSQ (methylsilsesquioxane) thin films. We use ethanol as solvent and HCl as the catalyzer and MTMS (methyltrimethoxysilane) as the main materials to prepare MSQ colloid in room temperature. We prepared the MSQ colloid into MSQ thin films by using SOD (Spin-on Deposition). The MSQ is difficult to prepare because the property of MSQ is very lively. As one of the many methods to prepare MSQ thin films, this method possesses many virtues, such as simple equipment, easy to be controlled, convenient adulteration. We analyzed detailedly the properties of low-k MSQ thin films which prepared by using D4 (Octamethyl cyclotetrasiloxane) as sacrificial porous materials. FTIR investigated that the proper annealing temperature is 500oC. The dielectric constant of the MSQ thin films reduced to k=2.1. The leakage current density of the thin films annealed at 400oC lowered one order of magnitude comparing with no D4. 2. The effect of dielectric constant of thin films was discussed detailedly in different annealing temperature. The contribution of the highly polarized Si-OH components to the orientation polarization will increase the k value of the thin films. Furthermore, the Si-OH bonds in the HSQ (hydrogensilsesquioxane ) films lead to moisture uptake, which is responsible for the increase of k value and leakage current density. In this thesis, the Si-OH bonds of HSQ films can be weaken after being annealed in N2, which is very valuable. We introduced the structural and dielectric varieties of these HSQ films which using D4 and D5 (decamethylcyclopentasiloxane) as sacrificial porous materials respectively. FTIR investigated that (1) the HSQ films of adding D4 and no D4 both produced Si-OH bonds after being annealed in vacuum, but they were weaken after being annealed in N2. The reason of the appearance of Si-OH bonds was that Si-H and Si-O bonds both were destroyed after being annealed. The -OH bonds and C-H bonds of the sample of adding D4 both were weaken after being annealed at 400oC for 1.5 h in N2. These results investigated that water and organic matter were disappeared. It can be explained with the following expression. Si-OH +HO-Si = Si-O-Si + H2OThe properties of sample of adding D4 and no D4 were different after being annealed in different condition. The dielectric constant of sample of adding D4 is the lowest than others after being annealed at 400oC for 1.5 h in N2. The dielectric constant of sample of no D4 without any treatment is the highest. The dielectric constant of sample of adding D4 was increased after being annealed at 400oC for 1.5 h in vacuum. The reason is that the Si-OH bonds appearaned after the thin films were annealed in vacuum. The leakage current density of samples with O2 plasma treatment is higher one order magnitude than others. When E =1 MV/cm , The leakage current density of samples is 3.0038×10-8 A/cm2 with O2 plasma treatment and followed to be annealed at 350oC for 1.5 h in N2.(2) The analysis of low-k HSQ thin films with adding D5, FTIR investigated that it is benefit to Si-H bonds at higher temperature. The proper annealing condition is in N2. As we all know, Si-O cage structure is good to lower the dielectric constant. The D5 was decomposed after being annealed at 500oC for 1.5 h in N2, which resulted in porous to reduce the density of HSQ thin films. It is benefit to Si-H bonds with higher temperature. Si-CH3 (~1260 cm-1) and C-H (~2960 cm-1) were broken to form Si-OH bonds after being annealed in vacuum.We compared the dielectric constant with annealed treatment and without treatment. The dielectric constant is lower after being annealed. The dielectric constant of thin films with annealed treatment increased with the increase of annealing temperature. The leakage current density of samples was higher after being annealed at 400oC for 1.5 h in N2, The reason is that the decomposition of D5 produced many porous. The leakage current density of samples was lower after being annealed at 500oC for 1.5 h in N2. The reason is that the structure of HSQ thin films became compact and uniformity after being annealed. The intensity of Si-O-Si cage structure at 400oC is greater than 500oC and 300oC3. We first use CH4 plasma treated the HSQ films then were annealed in N2. The structural change of these films was introduced. They changed little with different CH4 plasma treatment time. (1) From the FTIR results, the CH4 plasma treatment can resist the structure of HSQ films to be destroyed after being annealing with the increase of treatment time. (2) The CH4 plasma treatment can keep the characterization (low leakage current density and low dielectric constant) of HSQ films with the increase of annealing temperature.更多还原