Micro-fabrication Process

1. Micro-fabrication Process

2. Clean Room

3. Clean room classifications and applications

4. Clear room classification • Class 1000: fewer than 1,000 particles (>0.5μm) in 1 cubic foot of air • Class 100: fewer than 1,00 particles (>0.5μm) in 1 cubic foot of air

5. Micromachining Materials • Substrates: • Silicon • GaAs • Other elemental or compound semiconductors • Metals (bulk and foils) • Glasses • Quartz • Sapphire • Ceramics • Plastics, polymers and other organics

6. Micromachining Materials • Additive Materials: • Silicon (amorphous, polycrystalline, epitaxial) • Silicon compounds (oxides, nitrides, carbides, …) • Metals and metal compounds • Glass • Ceramics • Polymers and other organics • Biomaterials

7. Silicon Crystallography

8. Cubic Lattices • Simplest arrangements of atoms in three dimension in which the unit cell is a cubic volume • Simple Cubic (sc) structure has an atom located at each corner of the unit cell • Body Centered Cubic (bcc) has an additional atom at the center of the cube • Face Centered Cubic (fcc)unit cell has atoms at the eight corners and on the six faces.

9. sc bcc fcc Cubic Lattices a is lattice constant • How is the arrangement of atoms in Silicon? • Silicon has fcc + (1/4x, 1/4y, 1/4z) fcc structure

10. Si crystal structure Si crystal= fcc +1/4(x,y,z)fcc

11. c (214) plane b a Planes and directions Lattice vector R= r*a+ s*b+ t*c, r, s & t are integers We can define a plane in a crystal lattice with three integer, called Miller indices • 1. Find the intercepts of the plane in terms of integral multiples of the basis vectors • [Fig2, 4, 1] • Take the reciprocal of the integers and reduce to smallest set of integers h, k, l, in this case 2,1,4 • Label the plan (214) & direction is <214>

12. Blue is (010) plane, yellow arrow is <010> dirn c c c Blue is (100) plane, yellow arrow is <100> dirn Blue is (110) plane, yellow arrow is <110> dirn b b b a a a Planes and directions

13. 晶圓製作流程

14. Czochralski Method • For growing single-crystalline ingot

15. CZ晶體提拉過程

16. Floating Zone Method(FZ)

17. 懸浮帶區法(FZ法) • 因CZ法缺點，乃因坩鍋內的氧原子會滲入單晶錠長晶過程中。 • FZ法可以生產含氧量非常低的單晶錠。 • 先以模子鑄出含摻雜物多晶矽棒。 • 種晶被熔融並接合於棒的下端。 • 射頻(RF)加熱線圈沿軸向上移動，多晶棒熔融，原子排成種晶方向。 • 缺點 –無法生成大直徑晶錠。 –差排(dislocation)密度較高。 • 生成的晶錠以製造 –功率晶體(thyristor) 。 –大功率整流元件(rectifier) 等為主要目的。

18. 比較柴氏和浮動區長晶法 兩法之比較 • 柴氏法(Czochralski) –較普遍、便宜。 –較大晶圓尺寸 (300 mm in production) 。 –原料可再度使用。 • 懸浮帶區法(FZ法) –純矽晶(無坩堝) 。 –較昂貴，晶圓尺寸較小(150 mm) 。 –主要用來製造分離式功率元件所需晶圓。

19. 比較柴氏和浮動區長晶法

20. 晶圓的備製 • 去除末端：用鋸將晶錠的兩端(頸及尾)切除。 • 研磨直徑尺寸：用無心研磨機(centerless grinder)。 • 檢測結晶方向、導電形式，以及阻抗性結晶方向檢測方法-X光繞射(diffraction)、平行(collimated)光束折射。 • 晶錠刻意偏移主方向(off-orientation)幾度：離子植入。

21. 晶塊修整 • “裁切”錐形的晶塊與錐體末端。 • 驗證程序控制以控制小塊金屬或雜質。 晶塊本體研磨至所需直徑，並加上平的或槽口記號。

26. Silicon Wafer Cuts Miller indices indicated by ground edges called “flats”. “n”-type and “p”-type refer to “doping”. N means “negative” (phosphorous) and P means “positive” (boron).

27. Photolithography

28. Lithography devices

29. Lithography process

30. Lithography process-cont.

31. Positive/negative resist

32. Positive/negative resist-cont.

33. Positive/negative resist-cont.

34. Masking and Exposure

35. Mask fabrication process

36. Lithographic masks

37. Lithographic light source

38. Exposure Light Source (UV)

39. Development

40. Developing the pattern (C)

41. Oven Baking

42. Lithographic processing: Repeat process

43. Etching

44. Etching Mechanism • Etching type Wet etching Dry etching • Etching steps Oxidation Reaction Remove products

45. Factors in Wet Etching • Limited • Reaction limited • Diffusion limited • Factors • Concentration • Temperature • Stirring 

46. HNA system Anisotropic Wetting Etching

47. Anisotropic Etch

48. Anisotropic Etchants

49. Wet anisotropic etching

50. Etch the material