Definition
A homogenizer, also known as a spin coater, is a laboratory or industrial equipment used to prepare uniform films on a flat substrate. Its core function is to evenly spread the liquid material (such as photoresist, polymer solution, etc.) coated on the substrate surface through the centrifugal force generated by high-speed rotation and control the thickness and uniformity of the final film.
Principle
The working principle of the homogenizer is based on rotary coating technology. The process is mainly divided into two stages: the first stage is dripping and rotating at low speed, so that the liquid initially covers the substrate surface; The second stage is high-speed rotation, which throws excess liquid away from the substrate through centrifugal force while the solvent volatilizes, eventually forming a uniform solid or liquid film. The film thickness mainly depends on the rotation speed, solution viscosity, concentration, and rotation time, and the relationship can be roughly described by empirical formulas. For example, for Newtonian fluids, the final thickness is inversely proportional to the square root of the angular velocity of rotation and can be expressed as:h ∝ 1/√ω, where h is the film thickness and ω is the angular velocity.
Measurement method
The film quality prepared by the homogenizer is mainly evaluated by film thickness and uniformity. The measurement of film thickness is often done using a step meter or ellipsometer. The step meter measures directly by scanning the step height formed by the thin film with the substrate; The ellipsometer calculates the film thickness and optical constant by analyzing the state change of polarized light after reflection on the surface of the film. Uniformity evaluation involves multi-point thickness measurements at different locations of the substrate and calculation of the standard deviation or thickness extreme of its thickness distribution.
Influencing factors
The final quality of the film is affected by multiple factors. In terms of process parameters, rotation speed is the key to controlling film thickness, and the higher the speed, the thinner the film thickness. acceleration affects the uniformity at the initial stage of spreading; The spin time should ensure that the solvent is fully volatilized. In terms of solution properties, the viscosity of the solution directly affects the film thickness, and the higher the viscosity, the larger the film thickness. The volatilization rate of the solvent needs to match the rotation process. In terms of environmental conditions, ambient temperature and humidity can affect the volatilization rate of solvents, which can cause film defects. In addition, the cleanliness, flatness, and hydrophilicity of the substrate also have a significant impact on the initial spread of the liquid.
Applications
The glue homogenizer has a wide range of applications in many scientific research and industrial fields. In microelectronics and semiconductor manufacturing, it is a key equipment for coating photoresists. In materials science research, it is used to prepare functional coatings such as polymer films, self-assembled monolayers, and organic photovoltaic materials. In the field of optics, it is used to coat optical films such as contrast enhancement films and filters. In addition, in the field of biotechnology, it is also used to prepare sensitive film layers for biosensor chips.
Equipment selection considerations
When choosing a glue homogenizer, it is necessary to comprehensively consider a number of technical parameters and actual needs. The core parameters include the maximum speed and speed control accuracy, which directly determine the achievable film thickness range and repeatability. The equipment should have programmable speed and time control to accommodate complex process recipes. For special applications, the ability to vacuum absorb the substrate for stability may need to be considered, or a cover cup to collect waste liquid and control volatile atmospheres. In terms of compatibility, it is necessary to confirm the size and shape of the substrate that the equipment can handle. In addition, the reliability of the equipment, the ease of operation, and the technical support and service of the manufacturer are also important considerations.