Patent Application
20130078810
The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. However, these advances have increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. In the course of integrated circuit evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased.
To fabricate these semiconductor devices, a plurality of semiconductor fabrication processes are performed. One of these processes is a chemical-mechanical-polishing (CMP) process, which is performed to polish a surface of a wafer. However, conventional CMP processes may have wafer scratch issues, which can lead to wafer acceptance test failure or low wafer yields.
Therefore, while existing CMP processes have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect.
Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
It is understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
During semiconductor fabrication, polishing processes such as chemical-mechanical-polishing (CMP) processes may be performed to polish and planarize the surface of a wafer. However, residue particles may be collected on the wafer from previous processes, for example from prior lithography or deposition processes. These particles may be difficult to remove, particularly if the particles are collected on a bevel region of a wafer (i.e., on the side of the wafer). This is at least in part due to the fact that the bevel regions of the wafer are less accessible and more difficult to rinse than the top and bottom surfaces of the wafer. Stated differently, a rinsing solution may be dispensed on the wafer's surface to wash away the particles or residue on the surface, but the same rinsing solution may not be able to reach the bevel regions effectively. Thus, the rinsing solution may not be able to efficiently and adequately wash away the particles or residue deposited on the bevel regions of the wafer. During the CMP process, these particles may come into contact with a polishing pad of a CMP polishing head and result in scratches of the wafer surface. The scratches on the wafer lead to wafer failures or reduced yields.
According to various aspects of the present disclosure, an improved method and apparatus of performing a wafer polishing process that substantially reduces the wafer scratches is discussed below.
The wafer 110 has bevel regions 110A, which include portions of the wafer 110 located on its sides. Residue or particles 115 are formed on the bevel regions 110A of the wafer 110 from prior fabrication processes. The residue or particles 115 may also be referred to as bevel defects 115. In the following paragraphs, a method and an apparatus of removing the bevel defects 115 (so as to avoid wafer scratching during polishing) are described in more detail.
The CMP polishing head includes a membrane 120 that is located above the wafer 110. The membrane 120 may include a flexible or pliable material, for example synthetic rubber. In an embodiment, the membrane 120 is pressed against the wafer 110 and makes contact with the wafer surface during polishing. The use of the membrane 120 during a wafer polishing process may reduce distortion of the wafer 110.
The CMP polishing head includes a retaining ring 130 (also referred to as a retainer ring). The wafer 110 is secured by the retaining ring 130 during the polishing process. The retaining ring 130 includes a material composition that is relatively hard, for example polyphenylene sulfide or polycarbonate with a stainless steel ring encapsulated therein. The hardness of the retaining ring 130 may cause problems if the retaining ring 130 were to make direct contact with the bevel region 110A of the wafer 110. For example, if the retaining ring 130 comes into physical contact with the bevel regions 110A of the wafer 110 while the bevel region is being polished, the wafer 110 may experience cracking. In addition, the bevel defects 110A would have been stuck between the retaining ring 130 and the bevel region 110A of the wafer 110 and as a result would have been inconvenient to remove. These are some of the problems facing conventional CMP polishing heads.
To address these shortcomings of conventional CMP polishing heads, the retaining ring 130 of the CMP polishing head 100 in
The retaining ring 130 is coupled to the rest of the CMP polishing head 100 through a rotationally flexible mechanism, for example cylinders 150. The cylinders 150 include a trackball therein, which is coupled to the retaining ring 130 and allows the retaining ring 130 to be rotated 360 degrees. The cylinders 150 also can move up and down to adjust the position of the retaining ring 130. The flexibility of the positional and rotational movements of the retaining ring 130 (enabled by the cylinders 150) allows the retaining ring 130 to be used to polish the bevel regions 110A of the wafer 110, so as to remove the bevel defects 115.
The CMP polishing head 100 also includes one or more spray nozzles 160. The spray nozzles 150 are positioned adjacent to the bevel regions 110A of the wafer 110. During a polishing process, the spray nozzles 160 are operable to dispense a cleaning solution, such as de-ionized water (DIW) or chemicals, to clean the bevel region 110A and rinse off the bevel defects 115.
The CMP polishing head 100 also includes an inner tube 170 which is a sensor component for pressure detection.
During the polishing process, a pressure may be delivered to the wafer 110 through the component 100A, and the CMP polishing head components 100A, 100B, and 100C can be combined together to perform a rotational movement of the polishing head. The polishing head may move across an upper (or lower) surface of the wafer 110 (
The process of polishing the bevel regions 110A of the wafer is illustrated in
While the bevel defects 115 are being loosened, the spray nozzles 160 (not illustrated in
The rotational flexibility of the rotatable mechanism 200 allows the retaining ring 130 to be rotated dynamically in a desired manner, for example rotated 360 degrees around the bevel regions 110A of the wafer 110 (
The cylinder 150 also includes a rod 210, through which the cylinder 150 is coupled to the CMP polishing head component 100A. In an embodiment, the rod 210 is retractable, which allows the cylinder 150 (and therefore the retaining ring 130) to be moved vertically up and down. For example, the retaining ring 130 may be moved up once the wafer bevel polishing process is completed.
Referring to
Referring to
In an embodiment, the following geometrical and dimensional conditions are true:
Referring to
During this stage, an inter platen 300 positioned underneath the wafer 110 may be operable to dispense a cleaning solution to the bottom surface or the back side of the wafer 110. The inter platen 300 may be equipped with rotationally flexible spray nozzles similar to the spray nozzles 160. The cleaning solution may be dispensed from these nozzles to wash the back side of the wafer 110 and remove defects disposed thereon.
Referring to
The CMP polishing head disclosed according to the various aspects of the present disclosure offer advantages over conventional CMP polishing heads, it being understood that other embodiments of the CMP polishing head may offer different advantages, and that no particular advantage is required for all embodiments. One of the advantages is offered by the soft material component embedded in the retaining ring. The soft material component can be used to grind the bevel region of a wafer. The softness of the embedded component reduces the likelihood of wafer cracking during the wafer bevel polishing process, thereby improving wafer yield.
Another advantage is offered by the rotationally flexible coupling mechanism (e.g., trackball) through which the retaining ring is coupled to the CMP polishing head. The rotationally flexible coupling mechanism allows the retaining ring to have dynamic rotational movements. Therefore, the retaining ring can be used to polish the bevel region of the wafer by rotating around the wafer and grinding the bevel region of the wafer with its embedded soft material component. The polishing of the bevel region loosens the bevel defects—which may be undesired particles or residue formed on the wafer from previous fabrication processes—so that they may be effectively removed later.
Yet another advantage is offered by the spray nozzle. According to the various aspects of the present disclosure, the spray nozzle is integrated into the CMP polishing head, for example it may be rotatably coupled to the CMP polishing head. Therefore, a cleaning solution can be dispensed on the wafer to wash away the defect particles during the wafer polishing process. In comparison, traditional CMP methods and apparatuses may require a separate cleaning polishing head to be used to clean the wafer surface. Thus, the integration of the spray nozzle herein shortens fabrication time and reduces fabrication costs. Furthermore, the spray nozzle may be coupled to the CMP polishing head through a rotationally flexible coupling mechanism, which allows the spray nozzle to point to a precise desired cleaning area and therefore clean that area effectively.
One of the broader forms of the present disclosure involves a semiconductor fabrication apparatus. The semiconductor fabrication apparatus includes: a polishing head; a retaining structure coupled to the polishing head, wherein the retaining structure is operable to hold a wafer in position; and a component embedded in the retaining structure, wherein the component is softer than the wafer, and wherein the component is operable to make contact with a bevel region of the wafer.
The polishing head includes: a retaining ring that is rotatably coupled to the polishing head, wherein the retaining ring is operable to secure the wafer to be polished; a soft material component located within the retaining ring, wherein the soft material component is softer than silicon, and wherein the soft material component is operable to grind a bevel region of the wafer during the polishing process; and a spray nozzle that is rotatably coupled to the polishing head, wherein the spray nozzle is operable to dispense a cleaning solution to the bevel region of the wafer during the polishing process.
Yet another one of the broader forms of the present disclosure involves a method of fabricating a semiconductor device. The method includes: placing a wafer within a retaining structure, the retaining structure including a component that is softer than the wafer and that is operable to make contact with a bevel region of the wafer; rotating the retaining structure around the bevel region of the wafer in a manner such that the bevel region of the wafer is polished by the component of the retaining structure; dispensing a cleaning solution to the wafer; and polishing a surface of the wafer.
The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the detailed description that follows. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.
