Pyrolytic Boron Nitride crucibles are known to be competent in terms of performance and purity. Comparing with the standard crisoles de nitruro de boro, Crisoles PBN are distinct in many ways. It offers corrosion resistance, operates at higher temperature and are resistant to oxidation. Let’s discuss on PBN, the growth and its properties.
What are Pyrolytic Boron Nitride Crucible?
Crisoles PBN are advanced high temperature materials with a purity value of 99.9%. They are generally produced through the process of CVD. The production is done at vacuum conditions at high temperature. It uses ammonia and halides of Boron.
Crisoles PBN are good conductors of heat. It possesses higher thermal conductivity. Crisoles PBN remains unreactive at room temperature. Crucibles made up of BN are also known to have excellent anti oxidation properties below 1000 degC.
Estructura del nitruro de boro pirolítico
PBN is also known in the name of Boron Nitride formed from CVD. This ceramic material is generally prepared by high temperature pyrolysis. As we all know Boron Nitride predominantly has two main structures i.e. Hexagonal and Cubic.
Pyrolytic Boron Nitride is same as Nitruro de boro hexagonal with fewer disorientations in its layered structure. The major difference of pyrolytic Boron Nitride is the method of production which is CVD.
Property table of Pyrolytic Boron Nitride
Typical properties and values of pyrolytic Boron Nitride is given below for better understanding:
| PROPIEDADES |
VALUES |
| Density of PBN | 1.9 – 2.2 g/cm3 |
| Pureza | 99.99% |
| Maximum Operating temperature
(Air, Vacuum and Inert conditions) |
900, 2000, 2100 degC |
| Compression strength | 154 MPa |
| Resistencia a la flexión | 172 MPa |
| Resistencia a la tracción | 112 MPa |
| PBN Dielectric constant and strength | Constants are 5.2 and 3.7,
strength value is 2 x 105 DC volts / mm |
| Pyrolytic Boron Nitride Thermal conductivity | 60 W/m degC |
| General range of impurity in PBN | < 10 mm |
The shock resistance of PBN is crucial even at a temperature of around 2000 degC. It displays no sublimation point and decomposes to Boron and Nitrogen at a temperature of 3000 degC. Pyrolytic Boron Nitride holds higher electrical resistance and hence are good insulators. It has lesser pores on surface and offers smoothness and non-wettability.
Pyrolytic Boron Nitride Crucible Properties
The properties of PBN are categorised into physical, thermal, electrical and chemical in nature.
Physical properties of PBN Crucibles
- Crucibles of PBN possesses great machinability and can be used to make variety of geometries
- The density value is in between 1.9 to 2.3 g/cm3
- Crisoles PBN have good permeability with respect to Helium in the range of < 1 x 10^-10 cm/s
- Crisoles PBN possesses lesser moisture absorption and they offer good performance under vacuum conditions.
Thermal properties of PBN
- They are crack resistant once immersed in water even at a temperature of around 2000 degC.
- Crisoles PBN holds good thermal resistance
- Pyrolytic Boron Nitride thermal conductivity varies in the range of 2 – 60 W/degC depending upon the type of PBN.
Chemical properties of PBN material
- Crisoles PBN are generally inert in nature. They do not react with acids, alkalis and molten materials.
- At room temperature Pyrolytic Boron Nitride undergoes slightest corrosion however at elevated temperatures they remain inert and non-reactive.
- As per mass spectroscopy the purity range for PBN is around 99.99%.
Electrical properties of Pyrolytic Boron Nitride Crucibles
- PBN crucible has a volume resistivity in the range of 3.1 x 1018-ohm cm
- Their dielectric strength measured under room temperature is around 56000 V/cm
How are PBN Crucibles made?
The process of making Crisoles PBN are known to be chemical - meteorological deposition. It involves high temperature reaction of BCl3 and NH3. High purity grade of both BCl3 and NH3 are used at certain aspect ratio to produce Crisol PBN. The reactions take place in a high temperature compression chamber operating at a temperature of around 2000 degC.
Th
e chemical reaction for the growth of PBN is as follows: BCl3+ NH3 —àBN + 3HCl
During the process, Hexagonal PBN falls on the cold mould of graphite present. This process is referred as crystal metal growth of PBN where the accumulated layer gets thickened gradually. The process is also referred as nucleation.
Growth of PBN: CVD process
Chemical vapor deposition method is used for producing Crisol PBN. The simpler factor in such method includes, the process, the equipments involved and the operating principle of the system. The complex part are the ones that influences the process. The loading rate of material , the air intake into the system and the geometry are the other factors.
There are other influencing factors also in the process of making Crisol PBN such as temperature and pressure inside furnace. The temperature range chosen for CVD is around 1800 – 1900 degC and the pressure is kept around 1-2 mmHg. Generally, for PBN coatings low temperature is preferred and for generating defects high temperature conditions are applied.
Pyrolytic Boron Nitride uses
PBN crucibles are the ideal material for growth of semiconductor crystals. They are also used to purify elements. Some key examples of Pyrolytic Boron Nitride Crucible pertaining to the semiconductor industry is the crystal growth are GaAs and LnP.
- Crystal growth in semiconductor industries require stricter environments such as purity of medium and vessel and higher temperature. This makes Crisol PBN much demanding in the regime.
- Crisoles BN are widely used in semiconductor industry to produce crystals using LEC. The other method used is Breman method
- Crisoles PBN are also ideal for III – IV and II -VI semiconductors. The popular method of synthesis is molecule Beam epitaxy. In molecular beam epitaxy Crisol PBN act as the source to keep materials for vaporization.
- They are also used in evaporation of elements or compounds in OLED process
- Rings and Sheets of PBN are majorly used as supporting elements in OLED and other syntheses.
- PBN is also a good coating material popularly applied on top of graphite heaters. This will prevent the vaporization of volatile components at higher temperature.
Pyrolytic Boron Nitride Crucibles: Types
OLED PBN crucible
As the name indicates these OLED deposition used Crisoles PBN. They offer performance at elevated temperature, are chemically inert and is known for its higher thermal stability.
Application: Metal and semiconductor industry
MBE crucible of PBN
MBE crucible is used for Molecular beam epitaxy process. The PBN properties are advantageous such as inertness and thermal stability. Such crucibles retard the release of gases during chemical reactions.
VGF Pyrolytic Boron Nitride Crucibles
This is used to synthesise GaAs, Ge etc. VGF based Crisoles PBN withstand high temperature and offer the growth of crystals in a controlled manner. This helps in the reduction of defects and offers better uniformity.
LEC BN crucible
The growth of GaAs and InP is majorly utilised LEC Crisol BN. The method used is Liquid encapsulated Czochralski process. The PBN LEC crucible are chemically stable and are corrosion resistant. They are not prone to any erosion by the encapsulants and ensures slow extraction of metals as single crystals.
Concluding Remarks
Crisoles PBN are of no doubt an advanced ceramic material with greater impact on the semiconductor industry. The machinability and the competitive thermal, chemical and physical properties make them a better choice in precision industry. The Crisoles PBN are often available under distinct spec and geometry and the suitable selection makes them applicable.