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Wafer Manufacturing Farshid Karbassian. 2 OutlineOutline Semiconductor Materials Semiconductor Materials Purification Purification Crystal pulling Crystal.

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Presentation on theme: "Wafer Manufacturing Farshid Karbassian. 2 OutlineOutline Semiconductor Materials Semiconductor Materials Purification Purification Crystal pulling Crystal."— Presentation transcript:

1 Wafer Manufacturing Farshid Karbassian

2 2 OutlineOutline Semiconductor Materials Semiconductor Materials Purification Purification Crystal pulling Crystal pulling Czochralski Czochralski Float-Zone Float-Zone Grinding Grinding Slicing Slicing

3 3 OutlineOutline Edge Rounding Edge Rounding Lapping Lapping Etching Etching Chemical Mechanical Polishing (CMP) Chemical Mechanical Polishing (CMP) Epitaxial Deposition Epitaxial Deposition

4 4 Semiconductor Materials Elemental Elemental Si, Ge Binary Compounds Binary Compounds IV-IV SiC III-V AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InP, InAs, InSb II-VI ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS IV-VIPbS,PbSe,PbTe

5 5 Semiconductor Materials Ternary Compound Ternary Compound Al x Ga 1-x As, Al x In 1-x As, GaAs 1-x P x, Ga x In 1-x As, Ga x In 1-x P Ga x In 1-x As, Ga x In 1-x P Quaternary Compound Quaternary Compound Al x Ga 1-x As 1-y Sb y, Ga x In 1-x As 1-y P y Al x Ga 1-x As 1-y Sb y, Ga x In 1-x As 1-y P y

6 6 Crystal Growth Shaping Wafer Slicing Wafer Lapping and Edge Grind Etching Polishing Cleaning Inspection Packaging Purification Basic Process Steps

7 1.Crystal Growth 2.Single Crystal Ingot 3.Crystal Trimming and Diameter Grind 4.Flat Grinding 5.Wafer Slicing 6.Edge Rounding 6.Edge Rounding 7.Lapping 7.Lapping 8.Wafer Etching 8.Wafer Etching 9.Polishing 9.Polishing 10.Wafer Inspection Slurry Polishing table Polishing head Polysilicon Seed crystal Heater Crucible

8 8 Purification of Silicon Common quartz sand is mainly silicon dioxide, which can react with carbon at high temperatures. Common quartz sand is mainly silicon dioxide, which can react with carbon at high temperatures. Carbon used doesn't need very high purity; it can be in the form of coal, coke or even pieces of wood. Carbon used doesn't need very high purity; it can be in the form of coal, coke or even pieces of wood. At a high temperature carbon starts to react with SiO 2 to form carbon mono or dioxide. At a high temperature carbon starts to react with SiO 2 to form carbon mono or dioxide.

9 9 Purification of Silicon This process generates polysilicon with about 98% to 99% purity called crude silicon or MGS. This process generates polysilicon with about 98% to 99% purity called crude silicon or MGS. MGS has high impurities that makes it inconvenient for electronic applications. MGS has high impurities that makes it inconvenient for electronic applications. To purify MGS, the crude silicon is ground into fine powder. Then the powder is introduced into a reactor to react with HCl vapor, forming any of a number of SiHCl. To purify MGS, the crude silicon is ground into fine powder. Then the powder is introduced into a reactor to react with HCl vapor, forming any of a number of SiHCl. MGS: Metallurgical-Grade Silicon

10 10 Purification of Silicon The chemical reaction can be expressed as: The chemical reaction can be expressed as: TCS (SiHCl 3 ) vapor then goes through a series of filters, condensers and purifiers to get ultrahigh-purity liquid TCS. (9s!) TCS (SiHCl 3 ) vapor then goes through a series of filters, condensers and purifiers to get ultrahigh-purity liquid TCS. (9s!) TCS now has less than one impurity per billion atoms. TCS now has less than one impurity per billion atoms.

11 11 Purification of Silicon Purified polysilicon is obtained from TCS which is purified earlier by fractional distillation, in a large CVD reactor. Purified polysilicon is obtained from TCS which is purified earlier by fractional distillation, in a large CVD reactor. The high purity polysilicon is called electronic-grade silicon, or EGS. The high purity polysilicon is called electronic-grade silicon, or EGS.

12 12 Purification of Silicon (cont.)

13 13 Crystal Pulling The EGS which is obtained from CVD has polycrystalline structure whereas Si which is used in fabrication of electronic devices is single crystal. The EGS which is obtained from CVD has polycrystalline structure whereas Si which is used in fabrication of electronic devices is single crystal. The resulting polysilicon may be broken up into pieces to load into crucibles for Czochralski crystal growth or the poly rod itself could be used as the starting material for float-zone crystal growth. The resulting polysilicon may be broken up into pieces to load into crucibles for Czochralski crystal growth or the poly rod itself could be used as the starting material for float-zone crystal growth.

14 14 Crystal Pulling (cont.) Crystallization methods: Crystallization methods: –Czochralski (CZ) –Float-zone (FZ)

15 15 Czochralski Crystal Growth

16 16 During CZ crystal growth, the seed and the crucible are normally rotated in opposite directions to promote mixing the liquid and more uniform growth. During CZ crystal growth, the seed and the crucible are normally rotated in opposite directions to promote mixing the liquid and more uniform growth. Czochralski Crystal Growth

17 17 Czochralski Crystal Growth

18 Why CZ is much more common? The CZ process is cheaper. The CZ process is cheaper. It is capable of producing It is capable of producing large diameter crystals, large diameter crystals, from which large diameter from which large diameter wafers can be cut. wafers can be cut.

19 19 88 die 200-mm wafer 232 die 300-mm wafer Assume 1.5x1.5 cm 2 microprocessor Czochralski Crystal Growth

20 20 Czochralski Crystal Growth The only significant drawback to the CZ method is that the silicon is contained in liquid form in a crucible during growth and as a result, impurities from the crucible are incorporated in the growing crystal. The only significant drawback to the CZ method is that the silicon is contained in liquid form in a crucible during growth and as a result, impurities from the crucible are incorporated in the growing crystal.

21 21 Czochralski Crystal Growth Oxygen and carbon are the most significant contaminants. Oxygen and carbon are the most significant contaminants. To avoid additional impurities from the ambient, the growth is normally performed in an argon ambient. To avoid additional impurities from the ambient, the growth is normally performed in an argon ambient.

22 22 Float-Zone (cont.) RF Gas inlet (inert) Molten zone Traveling RF coil Polycrystalline rod (silicon) Seed crystal Inert gas out Chuck Chuck

23 23 Float-ZoneFloat-Zone

24 24 Float-ZoneFloat-Zone Not to use any crucible in the FZ method impurity levels particularly oxygen is much lowered in the Not to use any crucible in the FZ method impurity levels particularly oxygen is much lowered in the resulting crystal. And it resulting crystal. And it makes easier to grow makes easier to grow high-resistivity material. high-resistivity material. Thus the FZ process is Thus the FZ process is used when only high used when only high resistivity, low oxygen resistivity, low oxygen content or both is required. content or both is required.

25 25 GrindingGrinding The boule is placed in a lathelike machine to grind with a diamond wheel into a perfect cylinder. The boule is placed in a lathelike machine to grind with a diamond wheel into a perfect cylinder. After the boule is ground to an appropriate diameter one or more flats are normally ground along its length. After the boule is ground to an appropriate diameter one or more flats are normally ground along its length.

26 26 Flat grind Diameter grind Preparing crystal ingot for grinding GrindingGrinding Internal diameter wafer saw

27 27 GrindingGrinding

28 28 SlicingSlicing The boule is sliced into individual wafers by a rapid-rotating, inward-diameter diamond-coated saw which cuts on its inside edge. The boule is sliced into individual wafers by a rapid-rotating, inward-diameter diamond-coated saw which cuts on its inside edge.

29 29 SlicingSlicing

30 30 Edge Rounding After sawing, preventing the wafer chipping during the mechanical handling, the wafer edge is ground in a mechanical process to round the sharp edges created in the slicing process. After sawing, preventing the wafer chipping during the mechanical handling, the wafer edge is ground in a mechanical process to round the sharp edges created in the slicing process.

31 31 Edge Rounding

32 32 LappingLapping The lapping operation is done under pressure using a mixture of alumina (Al 2 O 3 ), water and glycerine to improve the flatness of the wafer to about ±2 µm, removing most of the taper and bow that results from the sawing operation. The lapping operation is done under pressure using a mixture of alumina (Al 2 O 3 ), water and glycerine to improve the flatness of the wafer to about ±2 µm, removing most of the taper and bow that results from the sawing operation. This process removes about 50 µm from both sides of the wafer This process removes about 50 µm from both sides of the wafer

33 33 LappingLapping

34 34 EtchingEtching To remove any particles and damages that many still remain from sawing and lapping steps chemical etching is done as a batch process, with the wafers are loaded into cassettes and immersed in a mixture of nitric, hydrofluoric and acetic acids. To remove any particles and damages that many still remain from sawing and lapping steps chemical etching is done as a batch process, with the wafers are loaded into cassettes and immersed in a mixture of nitric, hydrofluoric and acetic acids.

35 35 Etching (cont.)

36 36 Chemical Mechanical Polishing As the wafers are need to have one mirror finish at least, CMP is the next step. As the wafers are need to have one mirror finish at least, CMP is the next step. Upper polishing pad Lower polishing pad Wafer Slurry

37 37 Chemical Mechanical Polishing The slurry consists of a suspension of fine silica particles in an aqueous solution of NaOH. The slurry consists of a suspension of fine silica particles in an aqueous solution of NaOH. The rotation and pressure generate heat that drives a chemical reaction in which OH¯ from the NaOH oxidize the silicon. The SiO 2 particles abrade the oxide away. The rotation and pressure generate heat that drives a chemical reaction in which OH¯ from the NaOH oxidize the silicon. The SiO 2 particles abrade the oxide away.

38 38 CMPCMP

39 39 Growth of Epitaxial Silicon In some purposes to increase the purity of where devices are supposed to be fabricated, an epitaxial layer of silicon is grown on the wafer. In some purposes to increase the purity of where devices are supposed to be fabricated, an epitaxial layer of silicon is grown on the wafer.

40 40 Growth of Epitaxial Silicon

41 41 Wafer Inspection Physical dimension Physical dimension Flatness Flatness Microroughness Microroughness Crystal defects Crystal defects Resistivity Resistivity Contaminations Contaminations

42 Notch Scribed identification number Tracking Number

43 43 Wafers Ready for Fabrication Process

44 44 Dopant Concentration Nomenclature

45 mm 100 mm 125 mm 150 mm 200 mm 300 mm Evolution of Wafer Size

46 46 Evolution of Wafer Size (cont.)

47 47 Improving Si Wafer Requirements

48 Any questions?


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