Kye Hyun Baek

Chamber maintenance and fault detection technique for a gate etch process via self-excited electron resonance spectroscopy

With the introduction of 300mm wafer and sub-100nm technology processes, semiconductor manufacturers are gradually paying attention to efficient methods for process and equipment control, which is conventionally called advanced process control (APC) and advanced equipment control (AEC). As a potential strategy, an APC∕AEC technique by self-excited electron resonance spectroscopy (SEERS) was evaluated in a dynamic random access memory gate etch process, in terms of chamber maintenance and process control. Small changes in the chamber conditions after wet cleaning, which could not be detected under conventional monitoring methods, were identified by analyzing the electron collision rate of plasma. This event justifies that plasma monitoring is inevitable in chamber maintenance, especially considering that process results gradually tend to be affected by even small chamber changes in sub-100nm technology process era. Also, the first wafer effect, one of the most serious process drifts in an etch process, cou...

Role of O2 in Aluminum Etching with BCl3/Cl2/O2 Plasma in High Density Plasma Reactor

Role of O2 in aluminum etching process using BCl3/Cl2/O2 plasma was investigated in inductively coupled plasma (ICP) etching system. Optical emission spectroscopy (OES) of BCl3/Cl2/O2 plasmas shows that reaction between oxygen and boron chloride occurs in the presence of O2. This reaction seems to result in increase of aluminum etchant chlorine radicals and generation of BxOy species. Increase of chlorine radicals may play role to enhance aluminum etch rate at relatively low O2 concentration (≤6%). As the concentration of O2 increased, local etch stop of aluminum was observed along the aluminum grain boundary at 9% O2 and it was extended to cause etch stop on all exposed surface at 15% O2. Two possible causes of etch stop (i.e. deposition of reaction byproduct BxOy species and surface oxidation of aluminum) were postulated and examined. Investigation of these possibilities shows that the major cause of etch retardation, in the presence of O2, is surface oxidation of aluminum rather than the formation of inhibitor layer via the deposition of BxOy species.

Effects of gas species on charging induced tungsten plug corrosion during post metal etch process

Effects of gas species on charging induced tungsten plug corrosion during post metal etch process have been investigated. It was found that the O2 plasma in the dry strip process induces considerable charge build-up, which subsequently results in the tungsten plug corrosion in the solvent with pH value larger than 4.0. Experiments were performed in various strip chambers in order to find effective methods to avoid the charging by the O2 plasma. Adding H2 or H2O to the O2 plasma during the strip process or additional H2O plasma treatment right after the O2 plasma strip process were proven to be an effective way to prevents the charge build-up by the O2 plasma. Mechanisms for the charge build-up by the O2 plasma and the drastic reduction of the charging by H-related compounds are discussed.

An effective procedure for sensor variable selection and utilization in plasma etching for semiconductor manufacturing

Abstract Plasma etching processes have a potentially large number of sensor variables to be utilized, and the number of the sensor variables is growing due to advances in real-time sensors. In addition, the sensor variables from plasma sensors require additional knowledge about plasmas, which becomes a big burden for engineers to utilize them in this filed. Thus an effective procedure for sensor variable selection with minimum plasma knowledge is needed to develop in plasma etching. The integrated squared response (ISR) based sensor variable selection method which facilitates collecting and analyzing sensor data at one time with regard to manipulated variables (MVs) is suggested in this paper. The reference sensor library as well as sensor ranking tables constructed on the basis of ISR can give insight into plasma sensors. The ISR based sensor variable selection method is incorporated with relative gain array (RGA) or non-square relative gain array (NRGA) for effective variable selection in building a virtual metrology (VM) system to predict critical dimension (CD) in plasma etching. The application of the technique introduced in this paper is shown to be effective in the CD prediction in plasma etching for a dynamic random access memory (DRAM) manufacturing. The procedure for sensor variable selection introduced in this paper can be a starting point for various sensor-related applications in semiconductor manufacturing.

Implementation of a robust virtual metrology for plasma etching through effective variable selection and recursive update technology

Virtual metrology (VM) is attracting much interest from semiconductor manufacturers because of its potential advantages for quality control. Plasma etching equipment with state-of-the-art plasma sensors are attractive for implementing VM. However, the plasma sensors requiring physical understanding make it difficult to select input parameters for VM. In addition, those sensors with high sensitivity frequently cause several issues in terms of VM performance. This paper will address plasma sensor issues in implementing a robust VM, where self-excited electron resonance spectroscopy, optical emission spectroscopy, and VI-probe are utilized for critical dimension prediction in a plasma etching process. An optimum sensor selection technique which can give insight into effectiveness of plasma sensors is introduced. In this technique, a numerical criterion, integrated squared response, is proposed for effective selection of important sensors for particular manipulated variables. Sensor data shift across equipmen...

Effects of N2 Addition on Aluminum Alloy Etching in Inductively Coupled Plasma Source

Addition of N2 to the plasma activated with Cl2, BCl3, or their mixtures in an inductively coupled plasma source induces drastic changes in the plasma state. These N2-related changes in the plasma state sometimes result in abnormal phenomena in aluminum alloy etching, like the wave-like fringes on the sidewalls of patterned metal lines. Optical emission spectroscopy revealed that admixing small amounts of N2 to the plasma activated with Cl2, BCl3, or their mixtures generally expedites dissociation processes to increase the density of Cl* radicals within it. On the other hand, N2 addition also accelerates the formation of passivation polymers via carbon species sputtered from patterned photo-resists. The polymers adhere to the sidewalls of patterned metal lines and protect them against the lateral attacks of deflected etchants such as Cl* radicals. Our studies tell that the relative abundance of Cl* radicals within the plasma over the passivation polymers, which is controlled by the amount of N2 addition, seems to be a critical factor in determining the occurrence of the wave-like fringes on the sidewalls of patterned metal lines.

Multiple input multiple output controller design to match chamber performance in plasma etching for semiconductor manufacturing

In semiconductor manufacturing, multiple chambers utilized for the same process step often experience performance variation. This chamber to chamber performance variation has affected the yield of wafers, but there are no standard procedures to reduce them in semiconductor manufacturing. This paper introduces chamber matching in plasma etching as one of the core issues in semiconductor manufacturing and suggests a step-by-step procedure to address chamber matching issues. A brief review of two approaches, fault detection and classification and equipment control, is given and a step-by-step procedure of the equipment control approach is introduced. To design a multiple input-multiple output controller, a decomposed etch rate map makes it possible to analyze etch rate performance between chambers and to define controlled variables. Optimum variable selection techniques, such as singular value analysis and relative gain array methods, and dynamic optimization with constraints are suggested in this paper. In ...

Comprehensive understanding of chamber conditioning effects on plasma characteristics in an advanced capacitively coupled plasma etcher

An advanced capacitively coupled plasma etcher with two frequencies and additional direct current is characterized with complementary sensors. Due to the restrictive boundary conditions of the manufacturing environment, which the authors had to take into account, applicable plasma sensors are limited. Thus, the plasma parameters depending on the center, wall, sheath, and cathode regions are extracted separately based on the tool parameters, optical emission spectroscopy, and self-excited electron spectroscopy. One main target of this investigation is a cross verification of complementary sensor data and a deeper understanding. Due to the complex chamber setup, the authors use a chemically simple system of an Ar plasma with a blank Si wafer as the substrate. It is found that the removal of SiO2 and sputtering Si from the cathode and wafer changes the chamber condition and thus causes changes in the plasma characteristics. The established plasma process model comprises a change in secondary electron emission caused by changing the surface condition and a subsequent change in collisionless electron heating, in particular, in the case of applied low frequency power. Current electron heating models and conditioning models are used for cross verification of the plasma process model. It indicates that both chemical and electrical aspects to chamber conditioning should be considered in multiple frequency driven plasma etchers. The results presented in this paper are expected to contribute to the understanding of the interaction of the chamber conditioning effects and plasma parameters in advanced plasma etchers for sub-20 nm devices.

Multi-mode operation of principal component analysis with k-nearest neighbor algorithm to monitor compressors for liquefied natural gas mixed refrigerant processes

Abstract LNG mixed refrigeration (MR) process is usually used for liquefying natural gas. The compressors for refrigerant compression are associated with the high-speed rotating parts to create a high-pressure. However, any malfunction in the compressors can lead to significant process downtime, catastrophic damage to equipment and potential safety consequences. The existing methodology assumes that the process has a single mode of operation, which makes it difficult to distinguish between a malfunction of the process and a change in mode of operation. Therefore, k -nearest neighbor algorithm ( k -NN) is employed to classify the operation modes, which is integrated into multi-mode principal component analysis (MPCA) for process monitoring and fault detection. When the fault detection performance is evaluated with real LNG MR process data, the proposed methodology shows more accurate and early detection capability than conventional PCA. Consequently, proposed k-NN integrated multi-mode PCA methodology will play an important role in monitoring the LNG process.

Process and chamber health monitoring of plasma enhanced ti deposition process through high performance VI-probe

As an alternative to plasma sensors, high performance VI probe was evaluated in a plasma enhanced Ti deposition process. Its utilization was focused on finding any reasonable differences between good and bad chambers classified in terms of end of line yield data. Some differences of delivered power and time trace current signal between chambers were found, which well matches the good and bad chamber classification. Also, a fault detection and classification algorithm to handle huge amount of raw VI-probe data was evaluated. The algorithm estimates deviation of TiCl4 content in plasma occurs right after preventive maintenance, which might be considered as a chamber conditioning procedure. Despite requiring additional evaluations, the combination of VI-probe and well-developed algorithm might be a feasible solution where conventional plasma sensors can not be applied.