Crystec Technology Trading GmbH

Diffusion and Doping

Doping can be achieved using solid dopant sources (dopant wafers), liquid dopants such as TMB (Trimethoxyborane, Trimethyl borate, (CH₃O)₃B) or TMP (Trimethylphosphite, (CH₃O)₃P) or phosphorus oxychloride POCl₃, and by dopant gases like borane BH₃, phosphine PH₃. TMB and TMP have become widely used. The advantages of these liquid dopants are easy handling, lower health risks for operators, and high purity. Annealing steps activate and diffuse dopants into silicon. By using LGO heating elements, JTEKT Thermo Systems achieves very good temperature uniformity in its furnaces and thus excellent process results.

Dry and wet oxidation

JTEKT Thermo Systems (formerly Koyo Thermo Systems) offers advanced furnace versions for dry and wet oxidation. Thin gate oxides can be produced with very high uniformity across the wafer and from wafer to wafer. Thicker field oxides or masking oxides are grown faster by wet oxidation. A flash gas burner with a very high safety level enables safe operation. HCl can be added to prevent metallic contamination and to avoid defects during oxide growth. A special gas-tight quartz-to-quartz seal prevents leakage of aggressive gases such as HCl and protects the tube exhaust from corrosion. Our furnaces demonstrate their high capability especially for producing thin oxides. We are happy to send you measurement data for layers produced by dry and wet oxidation, with or without HCl.

Of course we can also provide TCA (1,1,1-Trichloroethane) or trans-LC (Trans-1,2-dichloroethylene (DCE)) bubblers as liquid sources instead of an HCl gas supply. TCA and trans-LC are far less corrosive than HCl.

JTEKT Thermo Systems furnaces with LGO heating elements offer the greatest advantages in low-temperature processes. JTEKT has meanwhile developed a high-temperature version of the vertical furnace that can operate at temperatures up to 1350°C, uses special heating elements and is equipped with SiC tube and SiC boat.

Forming gas and hydrogen annealing

Hydrogen can passivate dangling bonds and heal defects. These processes are normally run at temperatures around 400°C, which is relatively low for a semiconductor tube furnace equipped with a standard heating element (HCG, heavy winding), and such furnaces are more difficult to control at these temperatures.

JTEKT Thermo Systems installs special LGO heating elements that have particularly low thermal mass and can be used already from 140°C. Using these LGO heaters leads to better temperature uniformity on the wafer and from wafer to wafer. The most important point for this process, however, is the reduced temperature overshoot of the furnace after inserting/removing the boat and during heating and cooling ramps. These furnaces can be offered with upper and lower process gas exhausts. A combination furnace for hydrogen annealing and polyimide curing is also available (see below).

Polyimide curing

JTEKT Thermo Systems is a specialist in polyimide curing. For non-photosensitive polyimides our CLH furnace can be used. There is a special version of this furnace specifically for polyimide curing.

Photosensitive polyimide, by contrast, has much better properties and helps to save process steps and thus cost. However, it produces decomposition products during curing that can deposit on furnace walls and are difficult to remove. Together with one of the largest manufacturers of photosensitive polyimide, Asahi Chemical Co., Japan, JTEKT Thermo Systems has developed a special vertical furnace. Special LGO heating elements enable excellent temperature control and ensure very uniform temperature distribution in the furnace at the low temperatures (350°C - 400°C) normally used for these curing processes. Furthermore, JTEKT Thermo Systems uses special quartz parts for this process that basically prevent deposition of decomposition products on the furnace wall.

The furnace is therefore maintenance-free. These extraordinary characteristics of the furnace are best demonstrated by the long reference list of satisfied customers. Please also visit our dedicated polyimide page.

A vertical furnace that can both cure polyimide and perform hydrogen anneals is also available (see below).

Hybrid furnace

Due to customer demand, JTEKT Thermo Systems has developed a vertical furnace that allows the combination of two processes. Polyimide curing and hydrogen annealing can in future be performed in a single furnace. The furnace can be converted from one process to the other in a short time. This reduces production peaks and keeps the total number of required furnaces small. At the same time, sufficient backup systems remain available. Maintaining spare capacity for safety reasons can be minimized. The new JTEKT Thermo Systems furnace therefore reduces costs. The cost savings have already been confirmed in our current installations.

Copper annealing

Copper interconnects are increasingly replacing aluminum in chip manufacturing, despite the increased contamination risk from copper, lower adhesion to dielectrics and increased corrosion compared to aluminum. Copper provides significantly better conductivity, which is decisive when shrinking device features. The electromigration effect is much smaller for copper than for aluminum.

To improve and stabilize the properties of the copper layer, annealing is essential. It has been found that the most favorable conditions to achieve good electrical properties and a high yield of functioning devices are longer anneals (45 s in RTP, or approx. 30 min in a furnace) at the lowest possible temperature (<200°C). Note that annealing in smaller structures requires more time than in larger structures. You can find further details on our web page about copper annealing.

Low-k annealing

Low-k materials can be applied either by spin coating or by CVD. For porous materials spin coating is mainly used. Careful control of solvent evaporation is required. The subsequent curing is usually done in a batch furnace. Today, vertical furnaces are commonly used for this application to achieve the high temperature uniformities required. The curing temperature is normally in the 350°C - 400°C range, which places high demands on a standard vertical furnace.

JTEKT Thermo Systems has long experience with the similar SOG curing process and has developed a special furnace with an LGO heating element that has particularly low thermal mass. JTEKT Thermo Systems has developed a furnace for curing low-k dielectrics. The LGO heater used has been successfully employed for years in JTEKT Thermo Systems furnaces for other low-temperature processes such as polyimide curing and hydrogen annealing. The atmospheric JTEKT Thermo Systems furnace can guarantee low oxygen levels of <20 ppm required for low-k curing (and also for polyimide curing). Expensive reduced-pressure solutions including vacuum pumps are not required here. You can find further details on our web page about low-k annealing.

poly-Silicon

Polycrystalline silicon layers can be used for gate electrodes, resistors and capacitors as well as getter layers. JTEKT Thermo Systems provides processes for undoped and doped poly-Si layers. By using LGO heating elements, excellent temperature uniformity is achieved in JTEKT Thermo Systems furnaces, which leads to very good process results for poly-Si deposition. We are happy to send test results upon request.

Silicon nitride

Silicon nitride is an excellent diffusion barrier. It can also be used for masking during oxidation processes, as a dielectric for capacitors and as a passivation layer. Due to the use of LGO heating elements and the resulting excellent temperature uniformity in the furnace, outstanding process results can also be achieved for silicon nitride deposition. Particle counts can still be kept low. We will gladly provide measurement results on request.

TEOS (tetraethyl orthosilicate)

Deposited oxide layers do not consume silicon from the wafer during growth. TEOS oxide is used for applications such as spacer formation or trench fill. TEOS is a stable, non-flammable and non-corrosive liquid and therefore a preferred alternative to processes using silane or chlorosilanes.

Thanks to the use of LGO heating elements and the resulting excellent temperature uniformity in the furnace, outstanding process results can be achieved for CVD oxide deposition as well. We are happy to provide measurement data on request.

BPSG (boron-phosphosilicate glass)

Phosphosilicate glass layers are used for doping and planarization. They flow already at 1000°C and also provide good gettering for alkali and heavy metals. TMB and TMP can be used to produce BSG, PSG or BPSG layers.

Thanks to the use of LGO heating elements and the resulting excellent temperature uniformity in the furnace, outstanding process results can be achieved for CVD oxide deposition as well. We are happy to provide measurement data on request.

SOG annealing

Spin-on glass (SOG) is produced by curing dissolved silicon tetraacetate. It serves planarization and partially doping purposes. Today, chemical-mechanical polishing (CMP) is a more common process.

This process belongs to low-temperature processes that particularly benefit from the properties of the LGO heating elements. These LGO heating elements (see image) have a very low thermal mass. Compared with furnaces equipped with standard heating elements, significantly better process results can be achieved.

Hydrogen annealing

Hydrogen annealing is sometimes performed under reduced pressure for specific applications. Recently JTEKT Thermo Systems has also begun offering combination furnaces for hydrogen annealing at atmospheric pressure and under reduced pressure. Switching between the two processes can be achieved by simply changing the process tube.