Atmospheric Processes


TYTAN Furnace systems can be used for all conventional atmospheric pressure processes employed in the semiconductor industry. Processes run at temperatures above 1150°C require a thicker wall quartz tube, a SiC liner for the tube, SiC wafer boats, and SiC cantilever rods.

Wet Oxidation

Wet oxidation is used for growing thicker (> 100 nm) layers of silicon dioxide for applications such as isolation (field oxides and local oxidation) and dopant diffusion barriers, in which oxide quality is less important.


There are three (3) popular methods of Wet Oxidation:

Option Advantages Disadvantages
Flash Vaporizer Oxidation Good for thick and thin oxides, good uniformity. Cost
Pyrogenic Oxidation Inexpensive, clean, all-gas system, good uniformity Not suitable for thick oxides because of torch burn. Incurs hydrogen's safety risks.
DI Water Bubbler Oxidation Moderate price, acceptable uniformity for thick oxides Thin oxides have non-uniformity issues. Cool water vapor causes temperature disturbances. Slower since process gas is only half steam.
  • Typical Film Thickness:
    • 500 nm at 1,000 °C (flat) using DI water method
    • < 50 nm at 1,000 (flat) using pyrogenic method
  • Maximum Film Thickness:
    • 20 μm at 1,000 °C (flat) using DI water bubbler
    • 3 μm at 1,000 °C (flat) using pyrogenic method
  • Batch Size:
    • 100 in 18 flat zone
    • 200 in 34 heater
  • Oxidation Rate: Standard Chart Rates Deal-Grove for both methods
  • Oxidation Gases: Hydrogen/Oxygen (Pyrogenic only), DI H2O Steam
  • Oxidation Temperature: 800 - 1250 °C
  • Refraction Index: 1.4 - 1.47
  • Uniformity
    • < 3% 1σ at thickness < 2000 Å
    • < 2% 1σ at thickness > 2000 Å

Applications: optical waveguides, insulation, isolation (field oxides and local oxidation), dopant diffusion barriers

Dry Oxidation with TLC Bubbler Cleaning Option

Dry oxidation is slower than the wet process due to oxygen's slower rate of diffusion through the silicon dioxide layer to the silicon/oxide interface where the oxidation reaction occurs. It produces a high-density pinhole-free oxide and is thus the preferred method for growing gate oxides and surface passivation oxides such as pad oxides for nitride stress buffering, screen oxides for ion implantation, sacrificial oxides for surface defect removal, and barrier oxides for shallow trench isolation. TLC (trans-1,2-dichloroethylene) is a non-ozone depleting source of chlorine for scavenging mobile metal ion contaminants that impair gate oxide integrity. It also increases the oxidation process growth rate by a few percent.

  • Typical Film Thickness:
    • 10 nm to 0.5 μm
    • 100 in 18 flat zone
  • Batch Size:
    • 200 in 34 heater
    • Standard Chart Rates Deal-Grove for both methods
  • Oxidation Rate: Oxygen, TLC (C2H2Cl2)
  • Oxidation Gases: 800 - 1250 °C
  • Oxidation Temperature: 1.45 - 1.47 at 550 nm
  • Refraction Index: < 5% 1σ for thickness of 100 to 500 Å
  • Uniformity:
    • < 3% 1σ for thickness > 500 Å
    • < 3% 1σ for thickness > 500 Å

Applications: gate oxides, surface passivation, nitride stress buffering, sacrificial oxides, barrier oxides


Note: Temperatures above 1,150 °C require silicon carbide cantilever rods, wafer boats, and tube liners.

Thick Thermal Oxides

For optical wave guide applications thick (>10 µm) silicon dioxide films of excellent thickness and index of refraction uniformity are required. Tystar Corporation has been offering process technology for these applications for several years. In semiconductor applications the most frequently used technology is based on a pyrogenic process, using the combustion of H2 and O2 in either an external heater or an internal furnace torch to generate the steam for the thermal oxidation process. Typical oxidation temperatures are in excess of 1,100 °C and oxidation times from several days to weeks to achieve the desired oxide thickness. Tystar's preferred approach is using a continuous D.I. water feed system in combination with a liquid flow controller and a flash vaporizer. The liquid flow controller has a flow range of up to 10 cm3 per minute. With a 4 cm3 per minute H2O flow, the system generates about 5-slpm steam.

The following wafer parameters for thick oxides (approximately 15 μm) grown in a TYTAN 2000 furnace system for up to 8"/200 mm wafers have been obtained:

  • Thickness Uniformity: < 1%, 2σ, within wafer, Wafer-to-Wafer, Run-to-Run
  • Refractive Index Uniformity: Better than 1 × 10-4, 2σ
  • Particle Density: 2 > 0.25 mm for a 5 hour process.

Diffusion of Solid Source Dopants

In this process, the wafers are loaded into boats along with solid sources that release B2O3 or P2O5 when heated. The dopant oxide condenses on the wafers and forms a borosilicate or phosphosilicate glass. Dopant atoms then diffuse into the silicon to dope it. Should the application require it, other dopants are available such as Sb2O3 and Zn3P2.

  • Sheet Resistance: 1-100 Ω/□
  • Batch Size: 26
  • Gases: Nitrogen, Oxygen, Hydrogen
  • Uniformity: < 4%

The Sb2O3 solid source requires a separate source furnace with operating temperatures from 620 - 660 °C. At those temperatures the vapor pressure of Sb2O3is sufficient for a carrier gas to sweep it into the actual diffusion zone where the silicon wafers are located. The Sb concentration in silicon, or the sheet resistance of the diffused Sb layer, which can be attained depends on:

    Sb2O3 vapor pressure or Sb2O3 source temperature Silicon wafer or diffusion temperature Diffusion time

Antimony diffused layers with sheet resistances of 10 to 60 Ω/□ or surface concentrations from 5 × 1018 to 5 × 1019/cm3 are typically attained. The Sb2O3 diffusion temperature is typically between 1230 °C and 1280 °C and thus requires the high-temperature materials specified above. The gas inlet part of the process tube is extended beyond the actual diffusion zone and extends through a source furnace (a small 3-zone heater), which is attached to the diffusion zone heater. It is essential to have a smooth temperature transition from the source furnace to the diffusion zone. There can be no dip in the temperature or the Sb2O3 vapor concentration cannot be controlled. The temperature in the diffusion zone is controlled to < 1 °C in the diffusion zone over a distance of 34"/860 mm, and in the source heater over a distance of 6"/150 mm.


The Sb2O3 material is introduced into the source furnace in a quartz boat, which is loaded from the gas inlet port of the extended diffusion tube. A tapered quartz flange or a ball joint is used to connect the gas inlet to the process tube. Process gases used for the Sb2O3 diffusion are either a combination of N2 with O2 or pure, dry Argon. The Argon process minimizes the oxidation of Sb2O3 into Sb2O4, which has a much lower vapor pressure than Sb2O3 and results in a reduced consumption of Sb2O3. Several wafer loads can be processed with one charge of Sb2O3 in the source furnace. At the exhaust part of the process tube the Sb2O3 and Sb2O4 condense and can present a particulate problem when the wafers are loaded and unloaded. A condensing cup is normally attached to the source end to capture the condensed Sb2O3 and Sb2O4.

  • Sheet Resistance: 5%
  • Oxide Thickness: 3%
  • Junction Depth: 5%

POCL3 or BBR3 Liquid Source Dopant Diffusion

In these processes, nitrogen carries the liquid source from a bubbler to the process tube where it reacts with oxygen to form a borosilicate or phosphosilicate glass. Dopant atoms then diffuse into the silicon to dope it.

  • Sheet Resistance: 1-100 Ω/□
  • Batch Size: 26
  • Gases: Nitrogen, Oxygen, Hydrogen
  • Uniformity: < 4%

Anneal

Annealing is used for purposes such as dopant diffusion/activation, oxide/glass densification, repair of damage done to crystal structure by ion implantation, silicide formation, reflow of PSG and BPSG to smoothen and flatten the surface, and film stress release. It is typically done in an atmosphere of either nitrogen, argon, or forming gas (hydrogen in nitrogen). The hydrogen in the forming gas passivates the substrate's surface and deactivates interface carrier traps.

  • Batch size: 100 in 18 flat zone or 200 in 34 heater
  • Process Gases: Nitrogen, forming gas (N2 / H2), Argon
  • Process Temperature: 400 - 1100 °C
  • Process Duration: 1 - 180 min.

Applications: stress relief, oxide/glass densification, glass reflow, dopant diffusion/activation, passivation

Nano Materials LPCVD

Tystar Corporation has been working with universities and national labs to develop recipes for nano materials CVD for the past 30 years. A variety of nano materials can be produced using Tystar furnaces or non-thermal reactors either either under LPCVD or APCVD conditions.

For the details of other nano materials CVD, please contact 7050 Lampson Avenue Garden Grove, CA 92841 | Tel: (310) 781-9219 or write to sales@tystar.com