半導體設備硅刻蝕機概述Overview of silicon etcher for semiconductor equipment

在眾多半導體工藝中，刻蝕是決定特征尺寸的核心工藝技術之一?？涛g分為濕法刻蝕和干法刻蝕。濕法刻蝕采用化學腐蝕進行，是傳統的刻蝕工藝。它具有各向同性的缺點，即在刻蝕過程中不但有所需要的縱向刻蝕，也有不需要的橫向刻蝕，因而精度差，線寬一般在3um以上。干法刻蝕是因大規模集成電路生產的需要而開發的精細加工技術，它具有各向異性特點，在Z大限度上保證了縱向刻蝕，還可以控制橫向刻蝕。本節介紹的硅等離子刻蝕機就是屬于干法ICP（Inductively Coupled Plasma）刻蝕系統。它被廣泛應用在微處理器（CPU）、存儲（DRAM）和各種邏輯電路的制造中。

典型的硅刻蝕機系統結構如下圖2-1所示。整個系統分為傳輸模塊（Transfer Module）、工藝模塊（Process Module）等。

圖2-1 典型的硅刻蝕機系統結構  傳輸模塊由Loadport、機械手（Robot）、硅片中心檢測器等主要部件組成，其功能是完成硅片從硅片盒到PM的傳輸。Loadport用于裝載硅片盒，機械手負責硅片的傳入和傳出。在傳送過程中，中心檢測器會自動檢測硅片中心在機械手上的位置，進而補償機械手伸展和旋轉的步數以保證硅片被放置在PM靜電卡盤的中心。  工藝模塊（PM，如圖2-2所示）是整個系統的核心，刻蝕工藝就在PM中完成。一個機臺可以帶2－4個工藝模塊，工藝模塊包括反應腔室、真空及壓力控制系統、射頻（RF）系統、靜電卡盤和硅片溫度控制系統、氣體流量控制系統以及刻蝕終點檢測系統等。其反應原理概述如下：  刻蝕氣體（主要是F基和Cl基的氣體）通過氣體流量控制系統通入反應腔室，在高頻電場（頻率通常為13.56MHZ）作用下產生輝光放電，使氣體分子或原子發生電離，形成“等離子體”（Plasma）。在等離子體中，包含由正離子（Ion＋ ）、負離子（Ion－ ）、游離基（Radical）和自由電子（e）。游離基在化學上很活波、它與被刻蝕的材料發生化學反應，生成能夠由氣流帶走的揮發性化合物，從而實現化學刻蝕。另一方面，如圖2-2所示，反應離子刻蝕腔室采用了陰極面積小，陽極面積大的不對稱設計。在射頻電源所產生的電場作用下帶負電的自由電子因質量小，運動速度快，很快到達陰極；而正離子則由于質量大，速度慢不能在相同的時間內到達陰極，從而使陰極附近形成了帶負電的鞘層電壓。同時由于反應腔室的工作氣壓在10－3 ～10－2 Torr，這樣正離子在陰極附近得到非常有效的加速，垂直轟擊放置于陰極表面的硅片，這種離子轟擊可大大加快表面的化學反應以及反應生產物的脫附，從而導致很高的刻蝕速率。正是由于離子轟擊的存在才使得各向異性刻蝕得以實現。

In many semiconductor processes, etching is one of the key technologies to determine the feature size. Etching can be divided into wet etching and dry etching. Wet etching is a traditional etching process, which is carried out by chemical etching. It has the disadvantage of isotropy, that is, in the etching process, there are not only longitudinal etching but also transverse etching, so the accuracy is poor, and the linewidth is generally more than 3um. Dry etching is a fine machining technology developed for the needs of large-scale integrated circuit production. It has anisotropic characteristics, which ensures the maximum vertical etching and can also control the horizontal etching. The silicon plasma etching machine described in this section belongs to the dry ICP (inductively coupled plasma) etching system. It is widely used in the manufacture of microprocessor (CPU), memory (DRAM) and various logic circuits.

 A typical silicon etcher system structure is shown in Figure 2-1. The whole system is divided into transfer module, process module and so on. 

Figure 2-1 typical silicon etcher system structure transmission module is composed of loadport, robot, silicon center detector and other main components, whose function is to complete the transmission of silicon from silicon box to PM. Loadport is used to load the silicon box, and the manipulator is responsible for the incoming and outgoing silicon. During the transfer process, the center detector will automatically detect the position of the silicon center on the manipulator, and then compensate the extension and rotation steps of the manipulator to ensure that the silicon is placed in the center of the PM electrostatic chuck. The process module (PM, as shown in Figure 2-2) is the core of the whole system, and the etching process is completed in PM. One machine can be equipped with 2-4 process modules, including reaction chamber, vacuum and pressure control system, radio frequency (RF) system, electrostatic chuck and silicon chip temperature control system, gas flow control system and etching end point detection system. The reaction principle is summarized as follows: etching gas (mainly F-based and Cl based gas) is introduced into the reaction chamber through the gas flow control system, and glow discharge is generated under the action of high frequency electric field (frequency is usually 13.56MHz), which ionizes the gas molecules or atoms and forms plasma. The plasma consists of positive ion (ion +, negative ion (ion -), free radical and free electron (E). Free radicals are chemically active. They react with the etched material to form volatile compounds that can be removed by the air flow, thus achieving chemical etching. On the other hand, as shown in Figure 2-2, the reactive ion etching chamber adopts the asymmetric design with small cathode area and large anode area. Under the action of the electric field produced by the RF power supply, the negative free electron has small mass, fast moving speed, and quickly reaches the cathode; while the positive ion can not reach the cathode in the same time due to its large mass, so the negative sheath electric pressure is formed near the cathode. At the same time, the working pressure of the reaction chamber is in the range of 10-3 ~ 10-2 Torr, so that the positive ions can be accelerated very effectively near the cathode. The vertical bombardment can greatly accelerate the chemical reaction on the surface and the desorption of the reaction products, resulting in a high etching rate. It is the ion bombardment that makes anisotropic etching possible.