Plasma for Frontend

Our plasma systems represent a crucial processing step in wafer manufacturing. They are used to remove photoresists, oxide layers, and both organic and inorganic contaminants, as well as to activate surfaces for further processing. Only after these steps can additional layers be applied and further lithography processes performed.

During the process, wafers are exposed to a reactive gas mixture under vacuum, which treats the surfaces or layers according to the specific requirements.

PVA TePla offers a wide range of solutions, from small manual systems to fully automated, turnkey systems.

Cleanliness, process stability, sophisticated parameterization of the process gases, and extensive process experience are key factors.

PVA TePla has the most extensive expertise in the field and has been established in the market with its plasma systems for over 25 years. We provide solutions worldwide to help our customers realize their key technologies for wafer manufacturing.

Many of our systems achieve operational lifetimes of over 20 years, which is a testament to their outstanding quality.

Photoresist is removed via a plasma process, usually with excitation by microwaves. This configuration provides the best removal rate along with minimal damage to the components in the plasma.

Processing of a large number of wafers in a batch is the most cost-effective variant with regard to costs per wafer, and enables the PR to be removed from both sides simultaneously. However, the results are limited in terms of homogeneity of removal due to the geometry of wafer loading. Even so, this effect is barely relevant in a process with pure oxygen with total removal of the PR, as this process stops automatically at the inorganic layer underneath.

The removal rate in the oxygen process gets higher as the temperature of the wafers rises. To limit this procedure, we have developed a process that takes place at a consistent temperature. The advantage is attainment of the highest possible removal rate without exceeding the preset wafer temperature. Temperature monitoring is carried out by an infrared thermometer with corresponding control of the microwave output.

In descumming, a very small layer of the photoresist is removed in a very uniform way in order to prepare the exposed substrate surface for the subsequent step of galvanization or a lift-off process. In both cases, a clearly defined resist profile and a substrate surface with no organic impurities is required so that the subsequent metallization results in good adhesion and has the desired profiles.

Smaller substrates can be processed well and cost-effectively in a batch process, e.g. when manufacturing optoelectronic components or SAW filters. To this end, in line with the substrate size and the requirements of the components, we can structure the process chamber and the loading options and develop special processes with multiple steps using special gases.

Larger wafers can only be processed in the single-wafer process due to the strict requirements, for example in the bumping process. Uniformity of 5% can be attained on a 300 mm silicon wafer here with a corresponding design of the chamber and process.

The plasma systems for the batch process of PVA TePla all follow the same principle of plasma generation: direct coupling of the highly-frequency stimulation of the atmospheric side into the vacuum chamber. The gas inlet is situated on one side of the chamber and the vacuum suction on the opposite side. This chamber geometry achieves a particularly consistent process outcome.

The modular control system uses a latest-generation processor, a Windows-based platform as the operating system, and a graphical user interface (GUI). Consequently, the processes can be controlled both manually and fully automatically, and the process gases are controlled via MFCs. During the process, all parameters are written into a recipe and stored in the database. In parallel with this, the current values for pressure, gas flow, output, etc. are shown on a display that triggers a corresponding alarm in the event of deviations from the target value.

The plasma systems for single-wafer operation are combined in the GIGAfab product range. These systems are available in various configurations depending on the type of substrate or the customer’s application requirement—from the manually loaded system to the fully automatic version. Depending on the application, these systems can be equipped with various types of plasma sources: from simple and cost-effective microwave sources and large-scale sources to radical sources with a remote plasma for temperature-sensitive silicon etching processes for thinned wafers. The wafer can be tempered with various concepts here.

In the manually loaded systems, the chamber has a pull-out door, and the wafers are placed on the heating or cooling plate mounted on the door. In the automatic systems, the wafers are loaded into the chamber with a robot system by means of on-the-fly alignment.