Implementation of Fab light model in practice
To carry out comprehensive studies of heterostructures, the Institute has a section of molecular beam epitaxy (MBE) with the CNA-9 and Riber 32P systems. These MBE systems are designed for the epitaxial growth of thin layers of A3B5 compounds as a result of the reactions between thermally generated molecular beams of components and the surface of a substrate located in ultrahigh vacuum at high temperature. CNA-9 was manufactured by the now-closed NITI Ryazan. Riber 32P of the French company Riber has a growth chamber of horizontal geometry and is equipped with analytical modules. Both MBE systems were upgraded several times. Nano-heterostructures grown on them are the basis for the development of modern microwave transistors and MMIC.
The Plasmalab System 100 ICP 180 (Oxford Instruments) is used for plasma-chemical deposition of dielectric layers on up to 100 mm wafers. The technology of chemical vapor deposition with an inductively coupled plasma source (ICP-CVD) is characterized in that an inductive discharge plasma is used to decompose the reaction gas into active radicals. The substrate is placed on the electrode to which the RF voltage is applied to create an electrical bias that determines the energy and density of the ion flux on the surface of the wafer. Control of these parameters allows to realize low-temperature modes of deposition of dielectric layers. The substrate is fed through a vacuum load lock.
Low-energy plasma etching of materials is performed on the SI-500 ICP system (Sentech Instruments, Germany), which replaced the previously used plasma-chemical etching system based on electron cyclotron resonance (ECR). Sentech SI-500 ICP is a universal solution for high rate dry etching in inductively coupled plasma, which allows to work with A3B5 semiconductors, silicon, dielectrics, metals and other materials. The system is distinguished by the use of a patented ICP plasma source, helium backside cooling and the substrate electrode with dynamic temperature control that provide a constant temperature regardless of the plasma power, an effective two-stage vacuum system, and a reliable vacuum load lock. The main parameters of the etching process are controlled automatically. The maximum wafer size is 200 mm.
Russian producers of process equipment also took part in equipping the production of the IUHFSE RAS. The Semiteq STE EB715 system performs electron beam deposition of thin-film compositions in ultrahigh vacuum. The system has a stainless steel process chamber with integrated water cooling of walls, an oil-free pumping system based on an ion pump, a water-cooled screen to prevent the camera from contaminating by the evaporated materials. The thickness uniformity of the deposited materials is less than ±2% on up to 180 mm substrates. The material consumption can be optimized by changing the substrate-evaporator distance.
Logitech PM-5 with microprocessor control, built-in auto-feeding of abrasive mixture and electronic control of grinding plane is used for mechanical processing of wafers. This model is equipped with a precision holder, which ensures the flatness and parallelism of the processed wafers. All functions are controlled with the joystick, and the necessary information is displayed on the LCD display located on the front panel.
One of the know-how of IUHFSE RAS is the technology of forming a gate of a mushroom-like section. This form provides a reduction in capacitance and gate resistance, allowing to maximize the efficiency of the microwave transistor. Electron beam lithography is used to obtain the structural element of the required shape. The Institute became the first Russian and one of the first world users of high-resolution electron beam nanolithography equipment RAITH150-TWO and VOYAGER produced by Raith (Germany).
RAITH150-TWO has a beam energy up to 30 keV and allows the formation of structural elements with a size of less than 10 nm, exposing up to 200 mm wafers. A generator with a frequency of 20 MHz provides a fast creation of the pattern. The electron column is characterized by high stability of the beam current. The system provides high overlap accuracy at multilayer lithography and fine matching accuracy.
Installed in 2014, the VOYAGER is a system of the new generation, built on Raith eWRITE technology, which combines new electronic optics and an innovative pattern generator. The equipment is designed for exposing substrates up to 200 mm in size with a speed of more than 1 cm2/h. Automated calibration system "on the fly" provides high efficiency. The maximum resolution is less than 10 nm. Preliminary settings for high resolution and high performance modes are offered, as well as modes of continuous and seamless writing (traxx and periodixx) developed by Raith. The system is characterized by low sensitivity to environmental conditions and noise level. Due to the fact that the beam energy of VOYAGER reaches 50 keV, the formation of the "leg" and "cap" of the mushroom-like transistor gate can be performed in one cycle.
For the formation of other elements of microwave transistors, contact photolithography, in particular, the SUSS MJB4 IR mask aligner (SUSS MicroTec, Germany) is used in the IUHFSE RAS. This model provides high-precision alignment in the submicron range and is designed for up to 100 mm wafers.
As the director of IUHFSE RAS Sergey Gamkrelidze explains in an interview to our magazine (NANOINDUSTRY, No. 6(77), 2017, P. 8–15), plans for the development of the institute include the expansion of the equipment base, the beginning of small-scale production of microwave devices, the creation of a new generation of devices on nitride structures on silicon, the development of new frequency ranges and further development of combined systems on a chip. ■