Research Of The Growth And Defects Of Czochralski Silicon Crystals

Semiconductor silicon is the basis material for micro-electronic industry.In the foreseeable future,it will still play an extremely important role in the information society.On one hand,the decreasing feature size of integrated circuits(ICs) demands Czochralski(CZ) silicon wafers to be of large diameter and to be defect-free.Presently,300 mm CZ silicon wafers are the mainstream materials for ICs.In order for the active areas of ICs to be defect-free,a technological strategy of nitrogen-codoping has been recently presented for CZ silicon.Accordingly,the development of 300 mm nitrogen-doped CZ silicon will provide high quality starting materials for ICs.On the other hand,as an important part of discrete semiconductor devices,the power electronic devices have found extensive applications in automobile,computer and consumer electronics.They contribute significantly to the growth of microelectronic industry.Most of the power electronic devices are fabricated using the silicon epitaxial wafers of N/N~+ structure.In this case,the forward power dissipation of the devices is close related to the resistivity of the substrates for epitaxial wafers.Therefore,the substrate resistivity should be minimized in order to reduce the power dissipation of the devices.Inthis context,developing heavily doped N-type CZ silicon with extremely low resistivity is of practical significance.Addressing the above-mentioned aspects,in this dissertation the growth technologies for 300 mm nitrogen doped CZ(NCZ) silicon and 150 mm heavily arsenic/phosphorus doped CZ silicon with extremely low resistivity have been exploited.Moreover,the formation,annihilation and manipulation of the defects in the aforementioned CZ silicon crystals have been investigated.The primary results achieved in this dissertation are described as follows.1.On the basis of designing desirable hot zone and optimizing the crystal growth process parameters(including pulling rate,seed and crucible rotation,crucible position,protective gas flow rate and working pressure),300 mm NCZ silicon crystal has been successively grown for the first time in our country by adopting a proprietary technology of nitrogen gas doping.This work has laid the foundation of developing high quality silicon wafers used for ultra large scale integrated(ULSI) circuits.2.The formation of grown-in oxygen precipitates in 300 mm NCZ silicon has been investigated. In this work,the ramping anneal i.e.,the isothermal anneal at an elevated temperature of 1150℃ramped up from a starting temperature(600～1000℃) was employed to enable the growth of the grown-in oxygen precipitates larger than the critical size of the starting temperature so that Flourier transformation infrared spectroscopy and scanning infrared microscopy could be used to measure the amount of precipitated oxygen and oxygen precipitate density,respectively.In such a way,the radial distribution of grown-in oxygen precipitates in 300 mm NCZ silicon wafer was qualitatively investigated.It is revealed that the grown-in oxygen precipitate density in the abnormal oxygen precipitation region (generally refers to P-region) is much higher than that in the vacancy-type defect region (generally refers to V-region).Moreover,the grown-in oxygen precipitates in the V-region exhibit as the large-sized precipitates formed at high temperatures and small-sized ones formed at low temperatures.While,the grown-in oxygen precipitates in the P-region are continuously formed from high to low temperatures,thus leading to a continuous size distribution.Such results have been tentatively explained in terms of the formation mechanisms for grown-in oxygen precipitates generated in the V- and P- regions.3.The annihilation of void defects in 300 mm NCZ silicon wafers has been investigated by revealing the evolution of flow pattern defects(FPDs) delineated by preferential etching with the high temperature annealing.It is indicated that the void defects can be remarkably annihilated by the conventional furnace annealing at 1200℃for 4 h or by the rapid thermal annealing at 1200℃for 30 s with a cooling rate of 50℃/s in Ar ambient.4.The internal gettering(IG) process for 300 mm NCZ silicon wafers based on ramping anneal has been developed.Herein,a simple anneal ramping from low temperature to elevated temperature and then with a final isothermal anneal is employed to create denuded zone(DZ) and bulk microdefecs(BMDs) region within NCZ silicon wafer.In the present IG process, considerable amount of grown-in oxygen precipitates are ramped and then involved in oxygen precipitation during the isothermal anneal at elevated temperature,which introduces a large number of BMDs.Moreover,DZ is simultaneously formed by the isothermal anneal at elevated temperature.SIRM and preferential etching indicate that an appropriate ramping anneal indeed enables NCZ silicon wafers to form DZ and BMD region,thus possessing IG capability.It is found that the terminal temperature of ramping anneal should be high enough to create DZ,as a result of the dissolution of oxygen precipitates and the simultaneous oxygen out-diffusion occurring in the near-surface region of wafer.On the other hand,the starting temperature of the ramping anneal should be low enough in order to form appreciably high density of BMDs.However,with a given terminally high temperature,if the starting temperature is too low,the DZ can not form.It should be stated that with respect to the conventional high-low-high three-step IG process,the ramping anneal based IG process features a relatively low thermal budget.5.In order to lower the forward power dissipation of power electronic devices made of N/N~+ epitaxial silicon wafers,the resistivity of substrate silicon wafers should be minimized. Therefore,developing heavily As-/P- doped CZ silicon crystals with ultra low resistivity is of practical significance.In this dissertation,the technology strategies for the growth of heavily As- and P- doped CZ silicon crystals with a seed resistivity respectively lower than 0.003Ω.cm and 0.0015Ω.cm have been proposed.For solving the issues such as the serious volatilization of dopant,constitutional supercooling and the difficulty of changing solid-liquid interface,which are arisen from the ultra heavy doping,the guidelines for designing the hot zone and doping tool have been put forward.Moreover,the crystal growth process parameters are optimized addressing the specific issues as mentioned above.As a consequence,the heavily As-/P- doped CZ silicon crystals with ultra low resistivity have been successfully grown.In addition,the nitrogen-doping has been proved to be an effective pathway to enhance oxygen precipitation in the heavily As-/P- doped CZ silicon.Furthermore,the epitaxial silicon wafers of strong IG capability using the nitrogen co-doped heavily As-/Pdoped silicon wafers as the substrates have been fabricated.The MOSFET devices made of such specific epitaxial silicon wafers feature smaller leakage currents with respect to those made of the conventional epitaxial silicon wafers.The above-mentioned technologies related to the heavily As-/P- doped CZ silicon have been issued three patents.They have been extensively employed in large scale production,bring about significant profit.