分子流モジュール

真空システムの低圧気体流をモデル化するソフトウェア

分子流モジュール

イオン注入機では、ビーム経路に沿ったガス放出分子の平均数密度を、設計を評価する性能指数として使用します。平均数密度は、ウエハー角度の関数として、1 軸を中心とした回転で計算します。

Understanding and Predicting Free Molecular Flows

Vacuum engineers and scientists use the Molecular Flow Module to design vacuum systems and to understand and predict low-pressure gas flows. The use of simulation tools in the design cycle has become more widespread as these tools improve understanding, reduce prototyping costs, and speed up development. Vacuum systems are usually expensive to prototype. Therefore, an increased use of simulation in the design process can result in substantial cost savings. The gas flows that occur inside vacuum systems are described by different physics than conventional fluid flow problems. At low pressures, the mean free path of the gas molecules becomes comparable to the size of the system and gas rarefaction becomes important. Flow regimes are categorized quantitatively via the Knudsen number (Kn), which represents the ratio of the molecular mean free path to the flow geometry size for gases:

流れのタイプ クヌーセン数
Continuum flow Kn < 0.01
Slip flow 0.01 < Kn < 0.1
Transitional flow 0.1 < Kn < 10
Free molecular flow Kn > 10

While the Microfluidics Module is used for modeling slip and continuum flows, the Molecular Flow Module is designed for accurately simulating flows in the free molecular flow regime. Historically, flows in this regime have been modeled by the direct simulation Monte Carlo (DSMC) method. This computes the trajectories of large numbers of randomized particles through the system, but introduces statistical noise into the modeling process. For low-velocity flows, such as those encountered in vacuum systems, the noise introduced by DSMC renders the simulations unfeasible.

事例紹介

  • 自由分子流インタフェースで利用できる角度係数手法と、数学的粒子トレーシングインタフェースを使用するモンテカルロ法の両方を使用した RF カプラーの通過確率 (粒子トレーシングモジュールが必要)。 自由分子流インタフェースで利用できる角度係数手法と、数学的粒子トレーシングインタフェースを使用するモンテカルロ法の両方を使用した RF カプラーの通過確率 (粒子トレーシングモジュールが必要)。

Accurate Modeling of Low-Pressure, Low-Velocity Gas Flows

The Molecular Flow Module is designed to offer previously unavailable simulation capabilities for the accurate modeling of low-pressure gas flows in complex geometries. It is ideal for the simulation of vacuum systems, including those used in semiconductor processing, particle accelerators, and mass spectrometers. Small channel applications (e.g., shale gas exploration and flow in nanoporous materials) may also be addressed. The Molecular Flow Module uses the angular coefficient method to simulate steady-state free molecular flows, allowing the molecular flux, pressure, number density, and heat flux to be computed on surfaces. The number density can be reconstructed on domains, surfaces, edges, and points from the molecular flux on the surrounding surfaces. You can model isothermal and nonisothermal molecular flows and calculate the heat flux contribution from the gas molecules.

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Differential Pumping

Molecular Flow in an Ion-Implant Vacuum System

Outgassing Pipes

Molecular Flow Through an RF Coupler

Rotating Plate in a Unidirectional Molecular Flow

Molecular Flow Through a Microcapillary

Adsorption and Desorption of Water in a Load Lock Vacuum System

Charge Exchange Cell Simulator