Fujikin's advanced liquid vaporizer system "FALVS®" (Seven developers from the product and technology development department awarded the 2017 7th Monodzukuri Nippon Grand Award by the Minister of Economy, Trade and Industry) is the world's first system developed for semiconductor production to form a fixed amount of thin films on silicon wafers with precise control of pressure fluctuation, and can immediately vaporize liquid metal-organics without using carrier gases such as helium (further referred to as He). Compared to the conventional methods of dilution by carrier gases, productivity is greatly improved (100% concentration with a large flow rate supply, operating costs reduced, process time shortened, system downsizing), and contributes to the future production of semiconductors with large calibration for wafers and circuit integration, etc.
Digital video image quality is being enhanced with 4K and 8K televisions, and audio quality is also enhanced with high resolution players. These leave a strong impression on everyday life and is the accomplishment of semiconductor device innovation (circuit integration). Those semiconductor devices are produced by etching subtle details on many layers of thin films such as metal and are applied to silicon circuit boards. FALVS® contributes to the improvement of these important and essential processes (film formation and etching processes).
The FALVS® was developed as a system to efficiently vaporize metal-organics in chemical vapor deposition (CVD) equipment for the semiconductor manufacturing process. Please refer to diagram 1 which compares the conventional method with the new method. The conventional method bubbles/vaporizes the liquid metal organics with a carrier gas and then supplies it to the process chamber via heat insulated piping.
Diagram 1. Comparison of the conventional method and new method (FALVS®)
FALVS® is a new method of supplying liquid metal-organics by directly heating and vaporizing them. It is a system that does not require expensive carrier gases such as helium or insulation for piping, which saves resources and conserves energy. Immediately following the commencement of sales in 2014, it received a favorable reputation and more than 1500 units have already been shipped.
Diagram 2 shows the exterior and cross section structure of the FALVS®. Fujikin utilizes its skills to combine the flow rate controller with the newly developed compact vaporizer. We established structural design technology for the stable vaporization of pressure-fed metal-organics as a fluid and component technology such as pressure monitor sensors and control valves for the entire control technology. At the same time, we utilized Fujikin's specific skills in high precision pressure control with the flow rate control technology (FCS®-P technology) in the vaporizer and high temperature gas parts. The FALVS® was completed with a combination of this vaporizer and control technology.
Diagram 2. Exterior and cross section structure of the FALVS®
The FALVS® is a metal-organic supply unit that can be installed close to the CVD film forming equipment. Primarily, it is configured to efficiently vaporize liquid metal-organics and also control the flow rate of the vaporized metal-organics with high precision. Diagram 3 is a photo of the exterior of the FALVS®. Liquid metal-organics are supplied from "Source IN" and the vaporized metal-organics are supplied to the process chamber from "Gas OUT."
In order to apply high temperature heat to the entire product, a cartridge heater is utilized internally on the aluminum plate and a jacket made of heat insulating material covers the product to achieve high heat uniformity. Due to the maximum operation temperature of the control circuit board being low, the circuit board is designed to be installed in a case separate from the main FALVS® body. The P0 pressure sensor which supports high temperatures and monitors pressure inside the vaporizer is shown in the cross section structure image of diagram 2 (right), and is dedicated to detecting the pressure of high temperature gas inside the vaporizer.
By continuously reading the pressure levels inside the vaporizer with the pressure sensor, it is possible to check the remaining amount of liquid inside the vaporizer and liquid metal-organics can be supplied routinely to the vaporizer. Also, due to it being equipped with a preheater it is possible to support liquid metal-organics with a large heat capacity and latent heat of evaporation. Furthermore, due to an insulating layer being installed between the vaporizer and preheater, heat is prevented from being transferred away from the vaporizer to the preheater when the temperature setting of the preheater is lower than the vaporizer. This configuration prevents the temperature of the vaporizer from falling and improves the efficiency of the vaporization.
Diagram 3. FALVS® exterior
The maximum temperature of the gas that can be supplied to the FALVS® is 220℃, and vapor pressure is low (120℃ heat with 0.1kPa abs). Sufficient vapor pressure can be maintained even for metal-organic materials such as Si, Hf, Ta, Zr, Al, Ti, Zn, In, Ga, P, etc. and a precise and stable control of flow rate is possible. In order to fully utlize metal-organic materials, the precise control of the composition ratio is required for each element.
Since the FALVS® has no fluctuations in the control of the gas flow rate caused by external interference such as temperature and gas supply pressure variations, it is possible to precisely control the pressure and composition ratio of the gas which are important parameters for the compound semiconductor manufacturing process. Due to this, the range of metal-organic materials that can be used with high dielectric constants, ferroelectric/barrier metals, transparent conductive films and compound semiconductor materials is rapidly increasing. It can be said that a great number of possiblities are opened for new process developments.
Conventional technology takes 15 seconds to stabilize the flow rate of a liquid vaporization supply system, compared to less than 1 second for the FALVS®. In less than 1 second after receiving the control signal, the gas flow rate can be controlled with high speed and precision.
The advantage of having a fast response time is that the time to stabilize the control of the gas flow rate is shortened, which greatly reduces the amount of expensive metal-organic materials discarded, and by efficiently utilizing metal-organic gas, the process saves resources.
By using the FALVS®, a great improvement in resource saving can be implemented compared to the conventional process which had to discard 15 seconds of expensive metal-organic gases for a 60 second process.
With conventional technology, a large amount of helium gas is required as carrier gas for supplying liquid materials, but with the FALVS® helium gas is not required at all.
Due to this, running costs are drastically reduced.
The compact vaporizer supports high temperatures up to a maximum of 220℃, and due to the complete vaporization system, metal-organic materials are completely vaporized, which removes the cause of particle generation.
Recently, as the diameter of wafer circuit boards increase, a high flow rate is also required.
The FALVS® has the ability to supply 1.8 times more than conventional technology.
As described above, carrier gases are not required, and due to the 100% concentration of metal-oraganic gas supply with a complete vaporization system, a high flow rate is also possible.
Table 1 below compares the superior technology and creativity of the FALVS® against competing products.
Table 1. Comparison against conventional systems
The FALVS® utilizes a system to continuously detect the pressure inside the vaporizer which replenishes the liquid inside the vaporizer. The pressure sensor technology that is implemented supports the accumulated high temperatures.
The high temperature compatible pressure sensor responds in less than 1ms, and accurately controls the supply and suspension of liquid to the vaporizer.
The control sequence is shown in diagram 4. Points ①～⑤ in diagram 4 are explained below and detail the control operation for supplying liquid to the vaporizer, while continuously supplying gas to the process chamber.
Diagram 4. Pressure detection system for the control sequence
By repeating the control operations shown in ①～⑤, liquid is supplied routinely to the vaporizer. The pressure inside the vaporizer is continuously maintained above the minimum required supply pressure so that the flow rate controller can control the flow rate stably.
As shown above, the pressure inside the vaporizer continuously fluctuates. Fujikin has technology (FCS®-P technology) that absorbs these flucuations so that the gas can be supplied with a high precision flow rate without these flucuations.
The flow rate controller was developed so that it can utilize this technology with the FALVS®. As a result of this, the flow rate controller can be directly connected to the vaporizer, and a compact system is completed that can be installed in the direct vicinity of the process chamber.
With conventional systems, the liquid vaporizer supply system requires a carrier (primarily helium gas), but when using the FALVS®, a carrier gas is not required at all.
In a film forming process that uses the conventional system, 6 liters of helium gas is used continuously per minute. When using the FALVS® in the same process, around 4 million yen in gas fees can be saved in 1 year.
By unifying the vaporizer and flow rate controller in the FALVS®, the system becomes compact and reduces the footprint. This makes it possible to install it close to the process chamber.
Since the area that heat is applied to is reduced, an energy saving of up to 86% can be expected (diagram 1).
The FALVS® is also capable of supplying metal-organic gas at 100% concentration. Due to the FALVS® not requiring carrier gases which are indispensable in conventional systems, when comparing the same process of controlling the gas flow rate, the process time is reduced which contributes greatly to the improvement of the takt time.
This is because the supplied metal-organic gas is not diluted with helium gas. We evaluated that "the processing time of one wafer has improved by 12%."
Also, with conventional systems there were frequent occurrences of problems with the disintegrating and deposition of metal-organic materials and equipment maintenance was required every 3 months. With the FALVS® there are no such problems.
Since installation fees and production stop time for maintenance and replacements are not required, productivity is greatly improved and huge cost advantages can be expected.
Shipments and sales for the FALVS® have surpassed 1500 units and has become one of Fujikin's main products.
Domestically, we have received inquiries from multiple companies for uses such as fuel cell assessment systems, hard coating for surface cutting tools and concentrated H2O2 liquids for sterilization. We have also received inquiries and adoption with various new materials and the range of applications is increasing.
Looking ahead, we expect demand for installation in CVD process equipment for LEDs, solar cells, high frequency devices and power devices. We are also looking at expanding the applications to other processes such as atomic layer deposition (ALD), ashing, oxidization, diffusion and cleaning. We aim to sell a total of 3000 units after 3 years.