Research On Annealing Of Ion Implanted Silicon And Thermodynamics In The Process Of Annealing

Ion implantation and annealing technology is an important means in the impurity of semiconductor and an important technology link of LSI,VLSI and LEI, it also plays a special role in the "impurity engineering" and "energy band engineering". but, for many years, most of researcher's spirit and interest focus in the field of experiment and technology, theoretical research is not enough, it is, of course, unfavarable to study deeply on ion implantation and annealing. It makes me try to reform this situation to some extent.In this thesis, I give a comprehensive summary about ion implanted Si and annealing, including development process, way and method and applied field and prospect ect, and make systematic study to several theoretical problems refering to annealing of ion implanted Si, which include 3 major part as follow:1. Temperature calculation on annealing process of ion implanted Si.According to the balance between incident energy and sbsorbed,conducted or radiated energy, temperature clculation, including 3 modes (adiabatic, heat flux and isothermal) and 2 mechanisms (liquid and solid phase), are performed at the first.Adiabatic mode is suitable for annealing of pulse laser or clectron beam. Because there is no enough time for heat dissipate or diffuse, so, it can be all used to raise temperature of superficial layer or melt it. According to such a thought, we give the relationship between annealing temperature on surface and incident energy flow density, specifically, we calculate that the laser energy flow density needed by annealing is approximately 107W/cm2 when it's pulse length is 100ns, and its order is 106～107 W/cm2 if superficial layer of 100～500nm thick melt. Furthermore, on the basis of balance between latent heat of transition and heat flux flowing into substrate, we get a result that the speed of liquid/solid interface is about 8×102cm/s, from which we give such a conclusion that for annealing of adiabatic mode, it's machanism is merely recrystallization from liquid phase.In the case of heat flux mode, absorbed heat on surface conduct into substrate, two different case are considered: 1) Diffusion length of heat is much less than thickness of Si wafer, so it can be taken as unlimited, we introduce analytic solution about relationship between temperature and time,depth, and reach such a conclusion that when the absorb length of heat is much less than it's diffusion length, heat flux mode can transit to adiabatic mode; 2) As to so-called cw laser annealing which irradiating time is order of ms and diffusion length of heat is approximately the thickness of Si wafer, we give differential equation of heat conduction as well as corresponding boundary and initial condition, and get series solution about temperature distribution, we also calculate specifically function relationship between rising of annealing temperature on surface and incident power density, as well as function curve of temperature rising(ΔT) vs depth (x) when temperatune increasing on surface is 1400℃(approach melting point of Si)Under the isothermal mode, temperature gradient in inner of material disappear, the energy absorbed on surface is merely lost by radiation. In the light of balance between incident and radiative power density, especially aimed at self-made annealing instrument with iodine-tungsten lamp, we calculate the relationship between annealing temperature and lamp power along with substrate temperature, and reach a conclusion that the maximum power of iodine-tungsten lamp is 2.6kW, the result of calculation is well coincident with experimental data.2. Recrystallization in the process of annealing of ion implanted SiAccording to the thermodynamical theory of nucleation, we study deeply liquid and solid phase recrystallization.1) Recrystallization in liquid phase:On the basis of theory of bulk nucleation, we put our emphasis on calculation of critical nucleus in the case of planar nucleation, including its radius,nucleation work and maximum nucleation rate etc. Nucleus is assumed to be cylinder, two cases:rod-like and plate-like, are discussed. Concerning rod-like nucleus, we can reach following conclusion:compared with bulk nucleation, the radius of critical nucleus decrease by a half, the supercooling corresponding to the maximum of nucleation rate is Tm/2, which is less than the value of bulk nucleation(2/3 Tm), the critical nucleation work is directly proportional to its height. As to plate-like nucleus, the critical radius and nucleation work all increase, the height of nucleus corresponding to the maximum nucleation rate is 0.35nm which is approximately diameter of a Si atom. It is indicated that nucleation become more difficulty when superficial energy increase with increasing surface area, no matter what nucleus form is, we can draw the same conclusion as follow:compared with bulk nucleation, planar nucleation become easier owing to solid substrate can be taken as natural two dimensional nucleus, but, the probability forming rod-like nucleus is larger, recrystallization process of Si wafer from liquid phase is performed layer by layer.2) Recrystallization in solid phase:At first, we do some calculation for bulk nucleation about critical nucleus according to the difference of free energy between amorphous and crystal Si as well as the value of superficial energy, including its radius,the number of atom,nucleation barrier and the maximum of nucleation rate. Then we extend it to the sit-uation of planar nucleation in solid phase, following main conclusion are reached:most of nucleus are rod-like, for critical nucleus, its radius,the number of atoms decrease, and nucleation barrier lower compared with bulk nucleation, the probability of nucleation is inversely proportional to its height. Taking SiGe semiconductor as an example, we also get the value of its elastic strain energy isεc=0.03eV/atom, that is 30% of bulk free energy (0.1eV/atom), it become a factor which can not be neglected in the process of crystallization study, more rational result be reached after considering effect of elastic strain energy.3. Research on Ge+implantation into SiRapid thermal annealing, in different time and temperature, is performed to Si sample implanted with high dose Ge+(100keV, 5.3×1016/cm2). Then, we make some analysis to XRD and RBS curves and reach following conclusions:when annealing time is not long enough (1000℃,5min), most of implanted Ge+ are not able to situated in substitutional position and crystallization on surface is not perfect. On the other hand, while annealing temperature is too high or time is too long, crystal effect become worse too. We determine that the most properly annealing temperature and time is 1000℃,30min according to experimental result, the calculation data indicate too that more than 80% implanted Ge+ are situated in substitutional position in the case of above annealing condition, coherent factor is 0.438. But owing to serious lattice damage caused by high dose Ge+ implantation as well as a large number of dislocation and defect liberation in the course of strain and relaxation, crystal quality is not perfect.In the end of this thesis, we explain frankly the shortage in our research and offer our suggestion on further study.