How to reduce the cost of using a large amount of high-purity acid in the silicon wafer production process?----Nanjing Binglab

A large number of different types of high-purity electronic chemicals, both liquid and gaseous, are used in the semiconductor manufacturing process.

Liquid process chemicals mainly fall into the following categories: acids, bases, and solvents.

Electronic-grade high-purity reagents currently mainly rely on imports (such as: Merck), and there has always been a problem of high costs. In recent years, due to the instability of the global supply chain, users are faced with not only high costs, but also the predicament that the delivery time is too long and cannot meet the needs of the production line.

Here, we will discuss with you a method that can independently prepare high-purity acid and greatly reduce the purchase cost – sub-boiling acid distillation purification.

Take our SCH series sub-boiling distillation and purification equipment as an example, the user usually can recover the purchase cost within a few months, and even within a few weeks if the amount of acid used is large.

Purification by sub-boiling acid distillation can purify 1ppb acid to 10ppt level, which can fully meet the standard of commercially available imported high-purity acid.

The following are some commonly used acids and their uses in silicon wafer processing:

1. HF etching silicon dioxide and cleaning quartz vessels

2. HCL wet cleaning chemical, part of No. 2 standard solution, used to remove precious metal elements in silicon

3. H2SO4 cleaning silicon wafers; 7 parts of sulfuric acid and 3 parts of 30% hydrogen peroxide to prepare piranhai solution for etching silicon dioxide film on silicon wafers

4. H3PO4 etching silicon nitride

5. Etch PSG with HNO3, and etch silicate glass with a mixed solution of hydrofluoric acid and nitric acid. According to the characteristics of the semiconductor industry, for HF, HCL, and HNO3, it is recommended to use high-purity PFA as the main body, small-range temperature zone, surrounding heating and natural cooling sub-boiling distillation purification equipment; for H2SO4, it is recommended to use quartz as the main body Sub-boiling distillation and purification equipment in the high temperature section.

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Why choose sub-boiling distillation and purification equipment with high-purity PFA as the main body:

First of all, fluoropolymer, as the only material in the semiconductor manufacturing industry that can accommodate and transport the high-purity chemicals used in the manufacturing process, can achieve the extremely high stability and purity required for semiconductor manufacturing. Two special types of fluoropolymers are commonly used: Polymer Tetrafluoroethylene (PTFE) and soluble polytetrafluoroethylene (PFA). Since the molecular structure of PFA allows melt processing, it can be manufactured by traditional single-process processes such as injection molding, making the surface roughness of PFA products almost impossible to measure, and the finished product does not need any subsequent processing to prevent the introduction of pollution. Therefore, PFA can provide more safety protection for semiconductor process chemicals than PTFE, and is more suitable for the semiconductor industry. PFA material can maintain stable performance at a high temperature of 200 degrees. The sub-boiling purification temperature of HF, HCL, and HNO3 does not exceed 90 degrees, which can fully guarantee the stable performance and no impurity precipitation during the working process.

Why choose sub-boiling distillation and purification equipment with a small temperature range:

Sub-boiling means distillation below the boiling point of the acid liquid, except for H2SO4, which needs to be purified at a sub-boiling temperature above 200 degrees Celsius, and the sub-boiling purification temperature of HF, HCL, and HNO3 is all below 90 degrees Celsius, and electronic equipment has a certain failure rate, if the temperature range is too large, once a temperature out-of-control failure occurs, not only will the purpose of purification not be achieved, but it may also cause immeasurable safety accidents. The small-range temperature zone ensures that the maximum temperature of the equipment will not exceed 90 degrees Celsius from the design source, which not only effectively guarantees the purification effect, but also avoids the occurrence of safety accidents to the greatest extent. For H2SO4, you can choose high temperature resistant quartz sub-boiling distillation purification equipment.

Why choose large-capacity sub-boiling distillation purification equipment:

This is obvious, because electronic-grade chemicals used in semiconductor manufacturing processes are not only laboratory testing reagents, but also widely used in production lines. Only large and fast purification can meet the practical application of production. Taking SCH-VI as an example, the maximum distillable acid liquid in a single operation is 6L, which can produce 130mL of acid per hour

Sub-boiling distillation pays attention to “cutting the head and removing the tail”. Only when the whole body is heated evenly and at a uniform temperature can impurities be effectively removed during the process of cutting the head and removing the tail.

The picture on the left shows that metal impurities enter the distilled liquid through boiling and splashing in the boiling state; the picture on the right shows that in the sub-boiling state, it can be seen that the metal impurities are all retained in the original liquid

Why choose natural cooling sub-boiling distillation purification equipment:

First of all, it must be admitted that natural cooling is relatively slow in collecting acid compared to water cooling, but it has been mentioned above that it needs to be fast. Why is water cooling still not recommended, but natural cooling? First, natural cooling equipment has low requirements for laboratory decoration conditions, and does not need to install water and sewage. Even if a mature laboratory adds equipment during operation, it only needs to prepare a chemical fume hood, and there is no need for waterway transformation at all, save worry and effort and save money; Secondly, from the perspective of purity, the fewer accessories, the simpler the process, and the fewer impurities that may be introduced. Purity is our first priority. Take our SCH sub-boiling distillation acid purification equipment as an example, usually 3 CH-I or 2 SCH-II can be placed in a fume hood with a width of 1.5 meters.

Installation site example

A large number of pure electronic chemicals, both liquid and gaseous, are used in the semiconductor manufacturing process. Adhere to the principle of simpler, safer and purer, and no recommendations are made here.

Of course, there is another reason, which is cost. The more complex the functional design, the higher its cost. What users need most is real purity, efficiency and economic benefits. The sub-boiling purification of acid usually takes 2 to 3 times. In order to ensure the purity and efficiency and save a lot of cleaning time, users often buy several equipments after several distillations. The price difference is very obvious when the purchase volume is large. And one of the important reasons for using sub-boiling distillation and purification equipment to make high-purity acid instead of buying commercially available high-purity acid is to save costs for enterprises.

Therefore, choosing a suitable subboiling acid distillation and purification equipment is the best choice for the future semiconductor wet etching process and silicon wafer production process, high-purity chemicals in semiconductor manufacturing process, semi-finished products and finished product quality inspection in each link.