Overview of core technologies of wafer transfer equipment

1 Introduction

Wafer transfer equipment, also known as wafer equipment front-end module (EFEM), is an important sub-segment of equipment. This type of equipment is basically monopolized by foreign equipment companies (such as Rorze, DAIHEN, Hirata, Fala, Sinfonia, Brooks and Nidec, etc.) and Taiwan, China. In addition, in recent years, foreign policy restrictions and technical blockades on China have made it impossible for domestic companies to open up advanced functions of foreign equipment. Faced with such a severe international situation, the founder of Guona led the team, combined with their own industry experience and technical strength, chose the field of wafer transfer, established the company, accelerated the pace of self-research, and was committed to solving the dependence on foreign equipment, accelerating the process of independent localization, and gradually breaking the embarrassing situation of existing domestic equipment assembling foreign core components, and truly began to fill the gap in domestic components.

Wafer transport equipment (EFEM) completes the functions of wafer sorting, pre-alignment and transport in the entire production line. It is a bridge connecting the material handling system and the wafer processing system, and is an indispensable and important part of the wafer production line [1]. EFEM has a high degree of integration and great flexibility. According to different user needs, modules with different functions can be reasonably arranged inside the equipment. EFEM can also provide an ultra-clean transmission environment.

2 Core technologies of wafer transfer equipment

The core components of wafer transfer equipment mainly include wafer loading device, wafer transport arm (Robot), wafer pre-alignment mechanism (Pre-Aligner) and air filter (FFU).

2.1 Wafer loading device

During the semiconductor production process, wafers need to be frequently switched between clean and ultra-clean environments. To ensure that the wafers are not attached to particles during the switching process, a wafer loader is required as the input and output of the environment switching [2]. It can be said that the wafer loader is an external device for the wafer. It is installed on the front side of the EFEM and is used as a window for the wafer to enter and exit the wafer transfer device, thereby realizing the wafer transportation between the tracks in the production workshop and the processing equipment.

The wafer loading device is generally composed of a support frame, a box opening device, a loading platform, a mechanism, etc. It can also be equipped with components with different functions according to the use requirements, such as a flip mechanism and a protective cover, etc. The working process of the wafer loading device is divided into two stages: the loading process and the unloading process of the wafer box. The loading or unloading work is completed by the overhead transport trolley (OHT) or manual transport of the wafer box to the loading platform.

During the wafer transfer process between different semiconductor manufacturing equipment, the wafer box can prevent the wafer in the wafer box from being attached by microparticles to a certain extent. From the beginning to the end of the semiconductor process, with the wafer being taken out of the wafer box and put back into the wafer box, in the above process, the wafer is switched between the clean and ultra-clean environment. The wafer box required for the conversion will vary depending on the process. Currently, the commonly used wafer boxes are FOUP, SMIF Pod, Open Casset, etc. The loading systems used by different types of wafer boxes are different. According to the type of wafer box, the wafer loading device is divided into wafer loading port Loport, SMIF, open wafer box loading platform OCS and special loading port, etc.

2.1.1 Wafer Loadport

The wafer loading port Loadport is used to load FOUP. FOUP is a front-opening wafer transfer box used to load 12-inch wafers. It can be said that the wafer loading port (Loadport) is the common name for 12-inch wafer loading in the industry.

Loadport is the medium between EFEM and Intrabay. The operation of the automated material handling system in the semiconductor factory is to assist the wafer to shuttle between different operation areas (bays) according to its processing path. After the wafer operation is completed in a certain operation area, it is transmitted from the Loadport in front of the EFEM to the Intrabay handling system, and then the transmission destination is determined according to the next operation area. If the destination is in a different operation area, the Wr is first stored in the Stocker, and then transmitted to the Stocker of the destination through the Interbay system. Finally, the Intrabay system of the destination transmits the wafer box to the Loadport of the front-end module of the semiconductor equipment, so that the wafer can smoothly enter the process chamber for processing.

The specific working steps of Loadport for loading and unloading wafer boxes are: OHT or manual transport of wafer boxes to the loading platform → the clamping mechanism on the loading platform locks the wafer box → the box opening device adsorbs or clamps the wafer box door → the wafer box door is separated from the wafer box → the detection mechanism moves in the vertical direction and scans and detects the wafers in the box → the transport robot transports the wafers → after the wafers in the box are transported, the box opening device merges the wafer box door and the wafer box → the clamping mechanism unlocks the wafer box → OHT or manual removal of the wafer box.

2.1.2 SMIF

SMIF is the abbreviation of Standard Mechanal Interface. It is a standard machine. Using SMIF can greatly improve production efficiency. SMIF is used to load SMIF Pod. SMIF Pod is a transfer box with a built-in wafer boat and an external wafer box cover. The wafer box cover needs to be opened upwards. Its wafer loading size includes 6 inches and 8 inches.

The function of SMIF is basically the same as that of Loadport. SMIF supports E84 protocol and can correspond to AGV and OHT. The difference lies in the box opening method of SMIF. The box opening device is set on the loading platform of SMIF. The box opening device includes a frame surrounding the SMIF Pod, and a wafer detection mechanism is installed on the frame. The SMIF Pod is fastened on the loading platform, and the crystal box cover of the SMIF Pod is clamped on the frame of the box opening device. The box opening device is gradually lifted up to separate the crystal box cover from the wafer boat. During the lifting process, the detection mechanism installed on the frame of the box opening device scans and detects the wafers in the wafer boat. It can be seen that the box opening and wafer detection of the SMIF Pod are completed synchronously.

2.1.3 Open Wafer Cassette Loading Platform OCS

The structure and function of the open wafer box loading platform OCS are similar to the wafer loading port Loadport. The difference is that the open wafer box loading platform OCS is used to load the Open Cassette. The Open Cassette is an open wafer box. The OCS independently developed by Guona Semiconductor can adapt to 6-inch, 8-inch or 12-inch Open Cassette according to needs. There is no wafer box door at the front opening, which is open, and the rear end is semi-open. In order to prevent particles in the air from entering the wafer box and contaminating the wafer, a protective cover is installed at the placement position of the Open Cassette. Before and after each loading and unloading of the Open Cassette, the protective cover can be opened or closed manually or automatically.

2.1.4 Special loading ports

In the semiconductor manufacturing process, different processes have different requirements for wafer transmission and require different loading systems. In the later stages of semiconductor manufacturing, packaged wafers need to be transmitted. The wafers are placed in a wafer frame to form a whole sheet material, which is loaded in a specific sheet material box (Frame box) for transmission. The loading system used is a loading port with special functions.

The special loading port developed by Shanghai Guona Semiconductor Technology Co., Ltd. is used to load the above-mentioned sheet materials. It has special functions such as wafer box flipping and wafer movement. It includes a wafer box flipping mechanism, a wafer moving mechanism, a loading platform, a detection mechanism, and a port door opening mechanism, etc. It mainly uses manual transportation of the wafer box to the loading platform for transportation. The loading work steps are as follows: manually transport the wafer box to the loading platform and place it with the opening facing upward → manually remove the wafer box cover with the opening facing upward → the clamping mechanism on the loading platform locks the wafer box → the flipping mechanism flips the wafer box 90° so that the wafer box opening faces the loading port → the wafer moving mechanism clamps all the wafers in the box and moves toward the loading port → opens the loading port door seal → the detection mechanism moves in the vertical direction and scans and detects the wafers in the box → the transport manipulator transports the wafers. The loading port can realize the automatic loading, flipping and transmission of sheet materials, which can improve the processing efficiency of wafers.

2.2 Wafer Transport Robot

Wafer transfer robots are responsible for the precise positioning of wafers and for the rapid and smooth handling of wafers. They are the most commonly used robotic equipment in semiconductor manufacturing equipment, and their performance is crucial to the development of the semiconductor industry. The transfer of wafers in wafer transfer equipment needs to be completed by wafer transfer robots. The positioning and transmission accuracy of wafer transfer robots directly determines the wafer transfer accuracy of the entire wafer transfer equipment system. The smooth and vibration-free movement of the robot also affects the accuracy of wafer transfer. The cleanliness of the robot itself and the amount of particles generated during operation determine the cleanliness of the wafer processing environment. The transmission speed of the robot determines the production efficiency of the entire production line. Therefore, wafer transfer robots need to have the characteristics of high reliability, high speed, and smooth and vibration-free wafer transfer [3].