Impact of Transition-Metal Contamination on Oxygen Precipitation in Czochralski Silicon Under Rapid Thermal Processing

研究了快速热处理工艺下直拉单晶硅中过渡族金属铜、镍对内吸杂工艺中氧沉淀形成规律的影响.实验结果表明:在快速热处理工艺下,间隙铜对氧沉淀几乎没有影响,铜沉淀却能显著地促进氧沉淀的形成;而间隙镍或镍沉淀对氧沉淀的形成都没有影响.基于实验结果并结合氧沉淀的形核理论,对金属铜、镍对氧沉淀的影响机理进行了解释.     

Effect of Nickel Contamination on Formation of Denuded Zone in Czochralski Silicon

研究了过渡族金属镍在快速热处理作用下对直拉单晶硅中洁净区形成的影响.实验结果发现:硅中魔幻洁净区(MDZ)形成后,氧沉淀及其诱生缺陷能有效地吸杂金属镍;而沾污金属镍的硅中,随后的快速热处理工艺不能形成MDZ,硅片近表面出现大量沉淀.采用传统的内吸杂工艺,镍沾污的次序对洁净区的形成没有影响.实验表明由于硅片表面形成的镍硅化合物的晶格常数比硅小,所以在硅片近表面产生高浓度的空位,导致近表面的氧依然能够在MDZ工艺中形成沉淀.     

单晶硅中过渡族金属镍对洁净区形成的影响

研究了过渡族金属镍在快速热处理作用下对直拉单晶硅中洁净区形成的影响.实验结果发现:硅中魔幻洁净区(MDZ)形成后,氧沉淀及其诱生缺陷能有效地吸杂金属镍;而沾污金属镍的硅中,随后的快速热处理工艺不能形成MDZ,硅片近表面出现大量沉淀.采用传统的内吸杂工艺,镍沾污的次序对洁净区的形成没有影响.实验表明由于硅片表面形成的镍硅化合物的晶格常数比硅小,所以在硅片近表面产生高浓度的空位,导致近表面的氧依然能够在MDZ工艺中形成沉淀.     

氮对直拉硅片中氧沉淀分布的影响

研究了氮在退火过程中对直拉硅片中的氧沉淀分布的影响.实验结果表明,三步退火后在掺氮硅片截面形成特殊的M形的氧沉淀密度分布,即表面形成没有氧沉淀的洁净区(DZ),体内靠近DZ区域形成高密度、小尺寸的氧沉淀,而在硅片的中心处形成低密度、大尺寸的氧沉淀.分析认为,由于在第一步高温退火过程中氮在硅片表面外扩散,同时在硅片体内促进氧沉淀,改变了间隙氧的分布,从而导致在随后的热处理过程中氧沉淀的特殊分布行为.     

氮对直拉硅片中氧沉淀分布的影响

研究了氮在退火过程中对直拉硅片中的氧沉淀分布的影响.实验结果表明,三步退火后在掺氮硅片截面形成特殊的M形的氧沉淀密度分布,即表面形成没有氧沉淀的洁净区(DZ) ,体内靠近DZ区域形成高密度、小尺寸的氧沉淀,而在硅片的中心处形成低密度、大尺寸的氧沉淀.分析认为,由于在第一步高温退火过程中氮在硅片表面外扩散,同时在硅片体内促进氧沉淀,改变了间隙氧的分布,从而导致在随后的热处理过程中氧沉淀的特殊分布行为     

硅中碳含量对缺陷成核的影响

本文研究了直拉硅单晶的氧内吸杂(IG)工艺中,单晶的碳含量对缺陷形成的影响.实验表明,碳含量较高的硅片虽然在750℃热处理时,氧的沉淀速率较高,但是经IG处理后,硅片体内仅观条到较少的缺陷.本文详细地研究了导致上述现象的原因,指出碳含量较高的硅片,在750℃处理时氧、碳同时沉淀,并以C-O复合体的形式存在.但是该类氧沉淀在高于900℃,将因分解而消失,因此对IG 硅片中缺陷的形成没有贡献.本文提供了有关实验结果,指出450℃下形成的SiO_x复合团,是IG硅片体内缺陷的主要成核部位.碳含量对低温形成SiO_x复合团的抑制作用,是高碳含量硅片在IG处理中,仅形成较少缺陷的直接原因.     

高温快速热处理对氧沉淀消融的作用

通过对已经过两步(低-高)退火的大直径直拉硅单晶片进行高温快速热处理,研究硅中氧沉淀被高温快速热处理消融的情况.研究证实:高温快速热处理可以显著地消融氧沉淀,氧沉淀消融的决定性因素是热处理温度.另外,讨论了快速热处理消融氧沉淀的物理机制.     

高温快速热处理对氧沉淀消融的作用

通过对已经过两步(低-高)退火的大直径直拉硅单晶片进行高温快速热处理,研究硅中氧沉淀被高温快速热处理消融的情况.研究证实:高温快速热处理可以显著地消融氧沉淀,氧沉淀消融的决定性因素是热处理温度.另外,讨论了快速热处理消融氧沉淀的物理机制.     

大直径直拉硅片的快速热处理

主要研究了快速热处理( RTP)对大直径直拉( CZ)硅片的清洁区( DZ)和氧沉淀的影响.通过在Ar、N2 、O2 三种不同气氛中,在不同温度下RTP发现在大直径CZ硅片中氧沉淀的行为及DZ的宽度与RTP的温度、气氛有很大关系.在实验的基础上,讨论了在大直径CZ硅中RTP对氧沉淀和DZ的影响机理.     

大直径直拉硅片的快速热处理

主要研究了快速热处理(RTP)对大直径直拉(CZ)硅片的清洁区(DZ)和氧沉淀的影响.通过在Ar、N2、O2三种不同气氛中,在不同温度下RTP发现在大直径CZ硅片中氧沉淀的行为及DZ的宽度与RTP的温度、气氛有很大关系.在实验的基础上,讨论了在大直径CZ硅中RTP对氧沉淀和DZ的影响机理.     

铜镍共沉淀对直拉硅单晶中洁净区形成的影响

The influence of co-precipitation of copper and nickel on the formation of a denuded zone(DZ) in Czochralski silicon(Cz Si) was systematically investigated by means of etching and optical microscopy(OM).It was found that,for conventional high-low-high annealing(CFA),the DZ could be obtained in all specimens contaminated by copper and nickel co-impurity at different steps of the heat treatment,indicating that no copper precipitates or nickel precipitates were generated in the region just below the surface.However,for rapid thermal annealing(RTA)-low-high annealing,the tendency is not the same; the DZ could not be found in the specimen which was contaminated by copper and nickel contamination before the first RTA annealing.On the basis of the experimental results,it was supposed that the concentration and distribution of the vacancies generating during the RTA can influence the distribution of copper precipitation and nickel precipitation along the cross-section of Cz Si significantly,and thus influence the formation of the DZ to a great extent.     

Increased oxygen precipitation in CZ silicon wafers covered by polysilicon

Increased oxygen precipitation in CZ silicon wafers covered by a polysilicon layer has been observed after a high temperature anneal. This study established that the low temperature anneal, inherent in the LPCVD polysilicon deposition process, is so responsible for the enhanced oxygen precipitation effect. Temperature-time parameters were developed to match oxygen concentration in the wafer material with preannealing (polysilicon deposition) temperatures to achieve various degrees of oxygen precipitation. Data from this work show that interstitial oxygen reduction (δ C_ox) saturation can be achieved after 100 min oxidation at 1150°C, if the polysilicon deposition temperature is between 670–700°C (150 min for a 1.3 Μm polysilicon layer) and the interstitial oxygen concentration in the wafer is between 22 and 24 ppm. A denuded zone of 20 Μm was obtained and can be observed on a chemically etched cross section. Chemically etched and decorated defects in these samples with various degrees of oxygen precipitation are also displayed in these optical micrographs.     

Increasing bondability and ball-shear force of gold balls thermosonic bonding to flex substrates by depositing a nickel layer

To improve the bondability and ball-shear force of gold balls that are thermosonically bonded to copper electrodes over flex substrates, a nickel layer was deposited on the surface of the copper electrodes to increase their rigidity. A silver layer was then deposited on the nickel layer to prevent oxidation of the copper electrodes during the thermosonic bonding process. This nickel layer was expected to enhance the rigidity of copper electrodes over the flex substrates, increasing the thermosonic bonding efficiency of gold balls to copper electrodes over the flex substrates.Deposition the nickel layer on the copper electrodes improved the elastic modulus of the flex substrates, indicating that the nickel layer is effective in enhancing the rigidity of copper electrodes over the flex substrates. The bondability and ball-shear force of gold balls that are thermosonically bonded to copper electrodes increases with the thickness of the nickel layer given fixed bonding parameters. One hundred percent bondability and high ball-shear force can be achieved when gold balls are thermosonically bonded to copper electrodes with the deposition of a 0.5 μm-thick nickel layer. Herein, the ball-shear force was higher than that specified in JEDEC standards. Furthermore, gold balls that were thermosonically bonded to copper electrodes with a nickel layer had a large bonded area with an extensive scrape, while gold balls that were thermosonically bonded to copper electrodes without a nickel layer had a blank surface morphology. This experimental result was similar to that of tests of the elastic modulus of flex substrates, similarity can be used to explain that the effectiveness of the nickel layer in increasing the rigidity of copper electrodes, increasing the bonding efficiency at the bonding interface between gold balls and copper electrodes during thermosonic bonding process. After ball-shear test, a layer that was stuck on the ball bond was observed at the location of fracture of the ball bonds for gold balls they were thermosonically boned on copper electrodes with 0.5 μm-thick nickel layer. This observation implies that the ball-shear force of the gold balls that were bonded on the copper electrodes exceeded even the adhesive force of the layers that were deposited on the copper electrodes.The deposition of a 0.5 μm-thick nickel layer on copper electrodes over flex substrates improved the rigidity of the copper electrodes; the ultrasonic power could be propagated to the bonding interface between the gold balls and the copper electrodes, increasing the bondability and ball-shear force.     

Interstitial carbon formation in irradiated copper-doped silicon

The influence of a copper impurity on the spectrum of defects induced in p-Si crystals containing a low oxygen concentration by irradiation with electrons with an energy of 5 MeV at room temperature is studied by deep-level transient spectroscopy. It is found that interstitial carbon atoms (C _i ) which are the dominant defects in irradiated samples free of copper are unobservable immediately after irradiation, if the concentration of mobile interstitial copper atoms (Cu _i ) is higher than the concentration of radiation defects. This phenomenon is attributed to the formation of {Cu _i , C _i } complexes, which do not introduce levels into the lower half of the band gap. It is shown that these complexes dissociate upon annealing at temperatures of 300–340 K and, thus, bring about the appearance of interstitial carbon.

     

重掺硅衬底材料中氧沉淀研究进展

对国内外在重掺硅中氧沉淀方面的研究做了综合阐述,对氧沉淀研究现状和存在问题进行了讨论,同时就热处理,掺杂剂对氧沉淀的影响做了浅析,使人们对重掺硅衬底中氧沉淀这一领域有更深的认识.     

Transmission electron microscope study of oxidation-induced

Boron-implanted silicon devices have been shown to be affected by the ambient conditions during implantation, anneal and drive-in diffusion. The presence of oxygen appears to be of major significance. This study was undertaken to observe directly by transmission electron microscopy defects existing in silicon implanted and annealed under varying conditions which might account for changes in device characteristics. Boron ions at doses of 10¹³ to 10¹⁶ B⁺ /cm² were implanted at 180KeV into silicon through 2000Å. thick oxide layers formed by steam at 950°C or dry oxygen at 1150°C. After implantation specimens were annealed to 950° or 1000°C for 1/2 hour periods in dry nitrogen or argon. At 950°C precipitate colonies were found in the steam-oxidized specimens and were also present in those annealed to 1000 C, whereas, to date, no such colonies were found on the specimens which had been oxidized in dry oxygen at 1150°C. Energy dispersive x-ray analysis in an electron microscope shows that the particles contain copper and are possibly a copper suicide. Precipitation occurs only along dislocations formed on annealing the ion-damaged specimens Colonies were found as deep as 0.5μm below the oxide film. Tentatively, it is proposed that precipitation of the copper is observed only in specimens implanted through the steam formed oxide because of an increase in the number of silicon oxide nuclei due to the faster rate of oxidation. These nuclei form at dislocations and become nucleation sites for copper precipitation. The source of the copper contamination has not yet been determined.