CZ md_ppt_mj_unit-1.pptx

CZ method for Si wafer_IC Technology

1. ITS Engineering College, Gr Noida Topic: Crystal Growth Technique (Czochralski method)

2. Con t en t s CRYSTAL GROWTH CONDITION OF CRYSTAL GROWTH CRYSTAL GROWTH TECHNIQUE CZOCHRALSKI METHOD ADVANTAGES AND DISADVANTAGES

3. Crystal Growth growth is Crystal ex i st i ng c r y s t al b e co m es the process l a r ger a s more where growth a pr e - un i ts ( e .g. molecules, ions) add in their positions in the crystal lattice or a solution is developed into a crystal and further growth is processed. Nucleation and Growth are the main factors of crystal growth. If nucleation rates are slow and growth is rapid, large crystals will result. On the other hand, if nucleation is rapid, relative to growth, small crystals or even polycrystalline samples will result. The growth of crystals generally occurs by means of following: ---- diffusion of the molecule of the crystallizing ---- Substance through the surrounding environment

4. Condition of Crystal Growth Achi e v em e n t super cooling Formation of super s a tu r a t i on or of c r y s t al n u c l e u s of microscopic size Succes s i v e g r o w th of c r y s t als t o y i eld distinct faces

5. Basic growth methods available for crystal growth Th e ba s ic g r o w th m e th o ds a v ailable f or crystal growth are broadly Growth from melt. Growth from vapour . Growth from solution. Growth from solid.

6. Crystal Growth Techniques Bridgmann method Czochralski method Vernuil method Zone melting method Kyropoulos technique. Skull melting.

7. Bulk Crystal Growth Techniques Czochralski Growth (Most Used; and used for both Si and GaAs) Floating Zone Method (very pure but high cost) Bridgeman technique (for compound semiconductors)

8. Czochralski Growth Single crystal Si is produced by melting polycrystalline Si and then resolidifying it. Electronic grade silicon is loaded into quartz crucible and heated to ~ 1500 o C in presence of Ar inert gas T m = 1414 o C

9. Czochralski Growth A seed crystal with the desired orientation is lowered into the melt and rotated ccw slowly while crucible is rotated cw A neck region (“tang”) is produced to trap dislocations in the seed The pull rate is ~ 1/diameter. The “Shoulder” is formed by lowering the pull rate.

10. The “Boule”

11. Wafers Boule is ground from the sides, cut into disks with a diamond saw and polished on one or both sides. Thickness (0.5-1 mm) Currently 8” (200 mm) and 12” (300 mm) diameter wafers are used for production

12. Czochralski method Used for crystal growth to obtain single crystals of semiconductors (e.g. silicon, germaniu m, GaAS ), metals (e.g. palladium, platinum, silver, gold), salts and synthetic gemstones. It is also known as Pulling Technique In the Czochralski process a  seed crystal  is required to create a larger crystal, or ingot. This seed crystal is dipped into the pure molten silicon and slowly extracted. The molten silicon grows on the seed crystal in a crystalline fashion. As the seed is extracted the silicon solidifies and eventually a large, cylindrical boule is produced . [3] In this method the charge is melted and maintained at a temperature slightly above the melting point. The pulling rod is lowered to just touch the melt. Since the rod is at lower temperature of melt occurs at the point tip of the pulling rod. The crystal is pulled slowly.

13. Czochralski method The rate of pulling depend upon various factors like thermal conductivity, latent heat of fusion of charge and rate of cooling of the pulling rod. The seed is rotated to keep the grow crystal uniform and cylindrical. A seed crystal is attached to a rod, which is rotated slowly. The seed crystal is dipped into a melt held at a temperature slightly above the melting point. A temperature gradient is set up by cooling the rod and slowly withdrawing it from the melt (the surrounding atmosphere is cooler than the melt) Decreasing the speed with which the crystal is pulled from the melt, increases the quality of the crystals (fewer defects) but decreases the growth rate.

14. Czochralski method 1. A  boule  is a  single-crystal   ingot  produced by synthetic means. [1] 2. A boule of  silicon  is the starting material for most of the  integrated circuits  used today. 3. In the  semiconductor  industry synthetic boules can be made by a number of methods, such as the  Bridgman technique [2]  and the  Czochralski process , which result in a cylindrical rod of material. In the Czochralski process a  seed crystal  is required to create a larger crystal, or ingot. This seed crystal is dipped into the pure molten silicon and slowly extracted. The molten silicon grows on the seed crystal in a crystalline fashion. As the seed is extracted the silicon solidifies and eventually a large, cylindrical boule is produced. [3] A semiconductor crystal boule is normally cut into circular  wafers  using an inside hole  diamond saw  or diamond  wire saw , and each wafer is  lapped  and polished to provide substrates suitable for the fabrication of  semiconductor devices  on its surface. [4]

15. Czochralski Process

16. Czochralski Crystal Growth Process

17. APPLICATION The most important application of the Czochralski Process may be the growth of large cylindrical ingots, or boules, of single crystal silicon used in the electronics industry to make semiconductor devices like integrated circuits. Other semiconductors, such as gallium arsenide can also be grown by this method. Monoc r y st al l i ne si l i c o n ( m on o -Si) gr o wn b y t he method is often referred to as monocrystalline silicon ( C z -Si ) . It i s t he b a sic m a t er i al i n t he Czoc h ralski Czoc h ralski production of integrated circuits used in computers, TVs, mobile phones and all types of electronic equipment and semiconductor devices. Monocrystalline silicon is also used in large quantities by the photovoltaic industry for the production of conventional mono- Si solar cells. The almost perfect crystal structure yields the highest light-to-electricity conversion efficiency for silicon.

18. Advantages This method is used to grow large single crystals. Thus it is used extensively in the semiconductor industry. There is no direct contact between the crucible walls and the crystal which helps to produce unstressed single crystal.

19. Disadvantages In general this method is not suitable for incongruently melting compounds and of course the need for a seed crystal of the same composition limits is used as tool for exploratory synthetic research.