# Furnaces

| Furnaces for thermal oxidation, but also simply for annealing or for CDV processes are complicated and expensive pieces of equipments.
|  | While horizontal furnaces dominated the scene for 150 mm wafers or smaller, with 200 mm wafers a switch to vertical furnaces took place
|  | Below two pictures showing a horizontal and a vertical furncace for 200 mm or 300 mm wafer, respectively. Of course, you don't see much; nevertheless, they are big pieces of equipment.
Horizontal oxidation furnace; three tubes | ASM A412 300mm twin vertical furnace system for high temperature atmospheric pressure oxidation and LPCVD processing of polysilicon
| Here is a comparison between horizontal and vertical fucnaces, taken straight form the homepage of a major furncae manufactorer.
|  | ## Comparison Vertical vs. Horizontal Furnaces Koyo Thermo Systems manufactures numerous versions of vertical furnaces and horizontal furnaces with full automation or manual loading. Smaller versions for pilot and laboratory applications are available. We are frequently asked for the differences of vertical furnaces and horizontal furnace and for a justification of the higher price of vertical systems. Therefore we worked out the following table sheet. We hope that this overview, this comparison sheet will help you to make a proper planning. We compare in this sheet a horizontal furnace with a vertical furnace for mass production (VF5300) and with our small vertical furnace VF1000, which is a good alternative to horizontal systems for small companies as well as for research institutes.
#### Feature | #### 3- or 4-Tube Horizontal Furnace e.g. Model 206 | #### Vertical Furnace for Production e.g. VF5300 | #### Vertical furnace for RD e.g. VF1000
Heat up speed | slower | faster | faster
Quartz boat loading time | slower | faster | faster
Cool down speed | equal | equal | equal
Max. temperature using KLL's advanced LGO heaters | 1100°C | 1250°C | 1250°C
Temperature uniformity | lower | higher | higher
Temperature interference between the tubes | 1 - 2 °C | none | none
Oxygen concentration tube center (end open) | 16% | 0,1% | 0,1%
Oxygen concentration tube end (end open) | high | 500ppm | 500ppm
Oxygen concentration tube center (end closed) | 0,1% | 300ppm | 300ppm
Oxygen concentration tube end (end closed) | 10 - 30 ppm | 10ppm | 10ppm
Air tight process chamber (atmospheric process) | no | yes | yes
HCl leak free | no | yes | yes
Cross contamination | possible | not possible | not possible
Process independence | not completely | yes | yes
Particle data | worse | very good | better
Flexibility: Run mixed diameter of wafers in one run | possible | not possible | not possible
Flexibility: Run different diameter of wafers run to run | possible | not possible | possible
Flexibility: Range of wafer diameters that can be processed | 3" - 6" (8") | 4" - 300mm | 3" - 300mm
Stock wafer cassettes | no | yes | no
Automation level | lower | very high | higher
Thickness uniformity wet oxidation 10nm, 8" wafer | no data | ± 0.9 % | ± 0.9 %
Thickness uniformity dry oxidation 20nm, 8" wafer | ± 2.4 % | ± 1.2 % | ± 1.2 %
Thickness uniformity poly-Silicon 400nm, 8" wafer | ± 2.0 % | ± 1.0 % | ± 1.0 %
Thickness uniformity Nitride100nm, 8" wafer | ± 2.5 % | ± 1.5 % | ± 1.5 %
Capacity | 150 wafer | 100 - 150 wafer | 25 wafers
Power consumption | high | lower | very low
Maintenance independence | no | yes | yes
Maintenance work, necessary | higher | lower | very low
Footprint / tube | 2.6 - 3.4 m2 (partially cleanroom) | 3.0 m2 (grey room) | 1.5 m2 (grey room)
Price | low | high | low
Nowadays, mass production of semiconductor chips happens with silicon wafers with 200mm or 300mm diameter. Vertical furnaces are used almost exclusively. Only in older factories, which still use smaller wafer diameters, horizontal furnaces are still common. For wafer diameters until 150 mm the performance of such systems is in many cases still good enough to fulfil the customer requests. However, the advantages of vertical systems are already evident for this wafer size. The result of this situation on the oven market was, that almost all large furnace manufacturers stopped the further development of horizontal furnaces. Development work is done today almost only for vertical systems. Therefore vertical furnaces are superior to horizontal ones not only for physical reasons, but also because they are the more modern production tool. Their performance is much higher. A main issue is furnace automation. Automation for horizontal furnaces means mainly the installation of an elevator system for the loading of the boat on the cantilever arm. The loading area is open to the clean room. Vertical furnaces however are closed system with clean room class 1 inside. The loading happens fully automatically from the cassette by advanced robot systems. Other technical advantages of the vertical furnaces are the better gas tight sealing of the furnace tube, as well as several options, availabe only on vertical furnaces like improved temperature uniformity by boat rotation or nitrogen load lock chamber.

With frame

6.1.1 Si Oxide

© H. Föll (Semiconductor Technology - Script)