POLITECNICO DI MILANO. Contents 1. Introduction 2. Semiconductor Process Gases 2.1. Methods of...

POLITECNICO DI MILANO

Fluorinated Compounds for Semiconductor

Industry


Contents

1. Introduction

2. Semiconductor Process Gases2.1. Methods of preparing 2.2. The use of Fluorinated Compounds in

semiconductor industry

3. Fluorinated Compounds and Environmental Effects


Introduction

Fluorine as a Useful Element

Fluorine is a very reactive element.

It is the 13th most common element in the Earth's crust. Most fluorine is used is in the form of a fluorine compound, which is made of fluorine and other atoms.


Introduction ……

Uses of elemental fluorine and fluorine compounds:

Uses of Elemental Fluorine

• In rocket fuels, where it works in a manner similar to oxygen and helps the other materials in the fuel to burn.

Uses of Fluorine Compounds

The uses of fluorinated compounds are practically limitless;• used to create a number of different polymers and plastics, designed to withstand high temperatures or large amounts of stress without melting or breaking.


Some Uses of Fluorine Compounds…..• Refrigerants and cooling solutions

• In glass etching, where hydrofluoric acid is used by a number of industries. In addition to decorative etching on glassware, this acid can also be used to mark light bulbs and other highly-sensitive glass pieces that would be much too thin for other etching methods to be used.

• Fluoride has been proven to help prevent tooth decay, added to toothpaste and a number of mouth washes.


Fluorinated Compounds in Semiconductor Industry

• The electronics industry uses multiple long-lived fluorinated greenhouse gases (fluorinated GHGs).

• First began to occur in the late 1970’s

The rapid growth in fluorinated compound use is due to:

Increased worldwide demand for semiconductor devices, The increase in semiconductor device complexity, and The lack of viable alternatives to fluorinated compounds.


Fluorinated compounds widely used by the semiconductor industry:

Tetrafluoromethane (CF4)

Hexafluoroethane (C2F6)

Octafluororopane (C3F8)

Octafluorobutane (c-C4F8)

Sulfur hexafluoride (SF6)

Nitrogen trifluoride (NF3) and

Trifluoromethane (CHF3)


C-F bonds are strongest in Tetrafluoromethane.

Prepared by the reaction of silicon carbide with F2

SiC + 2 F2 → CF4 + Si

Reaction with F2 and dichlorodifluoromethane or

chlorotrifluoromethane

During the electrolysis of metal fluorides MF, MF2 using a carbon electrode.

Perfluoromethane


Hexafluoroethane is versatile etchant for many substrates in semiconductor manufacturing.

Due to high energy of C-F bonds, hexafluoroethane it is very inert and an extremely stable greenhouse gas.

Perfluoroethane


CF4 C2 F6

(A)Direct fluorination of carbon

(B) Fluorination or disproportionation of chlorofluoroalkane

(C) Fluorination or decarbonization of perfluoroalkene.

METHOD OF PREPARING FLUORINATED COMPOUNDS


(A) Direct fluorination of carbon;

Granulated carbon is fluorinated in the presence of fused metal in the presence of chlorine C+2CaF 2 +2Cl 2 ➝CF 4 +2CaCl 2

Difficult to control the reaction. Complicated processTemperature ?

METHOD OF PREPARING…. CF4 AND C2 F6


(B) Fluorination or disproportionation of chlorofluoroalkane;

Chlorofluoromethane is fluorinated in the vapor phase by using chromium fluoride as catalyst and hydrogen fluoride as fluorinating agentCCl2F2 +HF➝CClF3 +CF4 +HCl

Chlorofluoromethane is disproportionated by using aluminum fluoride as CCl2 F2 ➝CF3 Cl+CF4 +CFCl3 +CCl4



(C) Fluorination or decarbonization of perfluoroalkene• To obtain CF 4 from TFE is the decomposition reaction of TFE through disproportionation:C 2 F 4 ➝CF 4 +C

Explosive nature Large amounts of heat Great deal of carbon

Other reactions C 2 F 4 +O 2 ➝CF 4 +CO 2

C 2 F 4 +2F 2 ➝2CF 4



Manufacturing CF4 and/or C2F6 free from defects by • reacting a mixture of gaseous (TFE) and (CO2 )

• at a mol ratio of less than 4:1 • at a temperature higher than 950° C.

CO 2 acts as a diluent for TFE reducing the chance of explosion lowering the reaction heat carbon is not produced



Product obtained is easily determined by simply changing reaction conditions;

C 2 F 4 +CO 2 ➝CF 4 +2CO …* And

3C 2 F 4 +2CO 2 ➝2C 2 F 6 +4CO …. **

These reactions are affected by temperature, and mixture ratio of TFE and CO 2 used as raw materials.



C3F8 Octafluoropropane

(a) Introducing a first gaseous reactant stream comprising F2 into an elongated inner zone surrounded by porous member which is substantially resistant to F2 corrosion;

(b) Introducing a second gaseous reactant stream outside the porous member comprising a three C compound selected from the group consisting of (F)propane, (F)propene and hexafluoropropene;

(c) Recovering Octafluoropropane from the effluent outside the porous member;

METHOD OF PREPARING…. C3F8


TrifluoromethaneFluoroform is the chemical compound with the formula CHF3.

"haloforms", a class of compounds with the formula CHX3 (X = halogen).

Produced as a by-product of the manufacture of PTFE By decarboxylation of trifluoroacetic acid


Nitrogen TrifluorideInorganic compound with the formula NF3.Is a colorless, toxic, odorless, nonflammable gas.

prepared both by direct reaction (electric discharge) of ammonia and fluorine and

by a variation of Ruff's method (prepared nitrogen trifluoride by the electrolysis of a molten mixture of ammonium fluoride and hydrogen fluoride).


Two critical Applications:

For cleaning (CVD) chambers and For dry etching.

Plasma etching will generate volatile etch products at room temperature from the chemical reactions between the elements of the material etched and the reactive species generated by the plasma.

• The atoms of the shot element embed themselves at the surface of the target, thus modifying the physical properties of the target


CVD is a process where one or more volatile inorganic, metal-organic, or organometallic precursors are transported in the vapor phase, often in a carrier gas, to the reactor chamber where they decompose on a heated substrate and subsequently deposit a solid film along with volatile byproducts.

To eliminate buildup of deposited CVD films include polycrystalline silicon, silicon nitride, silicon dioxide, and metals such as tungsten.

CF4, C2F6, C3F8 and NF3

For chamber cleaning.

APPLICATIONS CONT…


• Etch processes are used to• Etch wires into the insulating layers

• CF4, CHF3, C2F6, C3F8, c-C4F8, NF3 and SF6 are etching gases• Certain CF-containing polymers are formed on surfaces,

permits highly selective and directional removal of film material.

APPLICATIONS CONT…


• Of the total fluorinated compound emissions from semiconductor manufacturing, roughly •(million metric tons of carbon equivalent)

Chamber CleaningPlasma Etching

40%

60%


Depending on the concentration, Inhalation cause headaches, Nausea, Dizziness and Damage to the cardiovascular systemCF4, C2F6

Suffocation – C3F8

FLUORINATED COMPOUNDS AND THE ENVIRONMENT


• A main industrial emission of C2F6 in semiconductor manufacturing is CF4.

ENVIRONMENT CONT….


Each layer of metal (wiring) and dielectric (insulating) material that is deposited and patterned upon the wafer requires specific fluorinated compound process steps.

The complexity of a semiconductor product qualitatively correlates with the required number of CVD and etch process steps.

Generally, as semiconductor devices increase incomplexity, so does the quantity of fluorinated compounds required for manufacture.

SUMMARY


Handbook of Chemicals and Gases for the SEMICONDUCTOR INDUSTRY, Misra, Hogan, Chorush.

Introduction to Microfabrication, Sami Franssila, Director of Microelectronics, Centre, Helsinki University of Technology, Finland.

United Nations Framework Convention on Climate change (UNFCCC),

Wikipedia, the free encyclopedia,

Other related websites.

References


END


•TH is the time horizon• ax is the radiative efficiency due to a unit increase in atmospheric abundance of the substance• [x(t)] is the time-dependent decay in abundance of the substance

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