Not Applicable.
Not Applicable.
The present invention relates generally to a process and apparatus for use with workpieces, such as semiconductor wafers, flat panel displays, rigid disk or optical media, thin film heads or other workpieces formed from a substrate on which microelectronic circuits, data storage elements or layers, or micro-mechanical elements may be formed. These and similar articles are collectively referred to herein as a “wafer” or “workpiece.” More specifically, the present invention relates to a process chamber and system for treating semiconductor workpieces. Such treatment generally relates to the surface preparation, cleaning, rinsing and drying of semiconductor workpieces.
State of the art electronics (e.g., cellular phones, personal digital assistants, and smart cards) demand thinner integrated circuit devices (“ICD”). In addition, advanced packaging of semiconductor devices (e.g., stacked dies or “flip-chips”) provide dimensional packaging constraints which require an ultra-thin die. Moreover, as operating speeds of ICDs continue to increase heat dissipation becomes increasingly important. This is in large part due to the fact that ICDs operated at extremely high speeds tend to generate large amounts of heat. That heat must be removed from the ICD to prevent device failure due to heat stress and to prevent degradation of the frequency response due to a decrease in carrier mobility. One way to enhance thermal transfer away from the ICD, thereby mitigating any deleterious temperature effects, is by thinning the semiconductor wafer from which the ICD is fabricated. Other reasons for thinning the semiconductor wafer include: optimization of signal transmission characteristics; formation of via holes in the die; and minimization of the effects of thermal coefficient of expansion between an individual semiconductor device and a package.
Semiconductor wafer thinning techniques have been developed in response to this ever increasing demand for smaller, higher performance ICDs. Typically, semiconductor devices are thinned while the devices are in wafer form. Conventional wafer thicknesses vary depending on the size of the wafer. For example, the thickness of a 150 mm diameter silicon semiconductor wafer is typically about 650 microns, while wafers having a diameter of 200 or 300 mm are generally about 725 microns thick. Mechanical grinding of the back side of a semiconductor is one standard method of thinning wafers. Such thinning is referred to as “back grinding.” Generally, the back grinding process employs methods to protect the front side or device side of the semiconductor wafer. Conventional methods of protection of the device side include the application of a protective tape or a photoresist layer to the device side of the wafer. The back side of the wafer is then ground until the wafer reaches a desired thickness.
However, conventional back grinding processes have drawbacks. Mechanical grinding induces stress in the surface and edge of the wafer, including micro-cracks and edge chipping. This induced wafer stress can lead to performance degradation and wafer breakage resulting in low yield. In addition, there is a limit to how much a semiconductor wafer can be thinned using a back grinding process. For example, semiconductor wafers having a conventional thickness (as mentioned above) can generally be thinned to a range of approximately 250-150 microns.
Accordingly, it is common to apply a wet chemical etch process to a semiconductor wafer after it has been thinned by back grinding. This process is commonly referred to as polishing. The polishing process relieves the induced stress in the wafer, removes grind marks from the back side of the wafer and results in a relatively uniform wafer thickness. Additionally, polishing after back grinding thins the semiconductor wafer beyond conventional back grinding capabilities. For example, utilizing a wet chemical etch process after back grinding allows standard 200 and 300 mm semiconductor wafers to be thinned to 100 microns or less. Wet chemical etching typically includes exposing the back side of the wafer to an oxidizing agent (e.g., HNO3, H3PO4, H2SO4) or alternatively to a caustic solution (e.g., KOH, NaOH, H2O2). Examples of wet chemical etching processes may be found in co-pending U.S. patent application Ser. No. 10/631,376, assigned to the assignee of the present invention. The teachings of patent application Ser. No. 10/631,376 are incorporated herein by reference.
Although methods for thinning semiconductor wafers are known, they are not without limitations. For example, mounting a semiconductor wafer to a submount or “chuck” (as it is commonly known) so that the wafer can be thinned requires expensive coating and bonding equipment and materials, increased processing time, and the potential for introducing contaminates into the process area. Additionally, adhesives for bonding a wafer to a chuck that may be useful in a mechanical grinding process will not withstand the chemical process fluids used in wet chemical etching. Furthermore, the current use of a photoresist or adhesive tape fails to provide mechanical support for very thin wafers either during the back grind process or in subsequent handling and processing. The use of tape also creates obstacles in the removal process. For example, tape removal may subject a wafer to unwanted bending stresses. In the case of a photoresist, the material is washed off the device side of a wafer with a solvent, adding to the processing time and use of chemicals, and increasing the risk of contamination.
Further, thinned semiconductor wafers are prone to warping and bowing. And because thinned semiconductor wafers can be extremely brittle, they are also prone to breakage when handled during further processing. Thinned semiconductor wafers (e.g., below 250 microns) also present complications in automated wafer handling because, in general, existing handling equipment has been designed to accommodate standard wafer thicknesses (e.g., 650 microns for 150 mm wafer and 725 microns for 200 and 300 mm wafers).
Accordingly there is a need for a process and equipment for producing thinner semiconductor workpieces. At the same time, there in a need to provide thinner workpieces that are strong enough to be handled by conventional equipment to minimize the threat of breakage. Finally, it would be advantageous to develop a system that reduces the number of processing steps for thinning a semiconductor workpiece.
The present invention provides a system and method for use in processing wafers. The system and apparatus includes a process chamber that allows for the batch production of thinner wafers, which at the same time remain strong. As a result, the wafers produced by the present process are less susceptible to breaking, they have a uniform, stress-free surface, and they have a more uniform total thickness variation. The batch processing system also offers improved processing steps and higher productivity since the overall cycle time is reduced. This results in, among other things, improved yields and improved process efficiency.
According to one aspect, one embodiment of the system includes a process chamber that allows for batch wet chemical thinning of semiconductor workpieces down to less than 125 microns. The process chamber comprises a chamber body having a first end, an outer wall, and an opening at the first end leading into a cavity. The process chamber is supported at an incline within the processing machine, and the semiconductor workpieces within the process chamber are similarly supported at an incline therein. A door assembly is provided adjacent the first end of the chamber body. The door assembly has a door that selectively closes the opening of the chamber body. The process chamber also has a spray assembly having a nozzle to spray a process fluid into the cavity of the chamber body and onto the exposed portions of the semiconductor workpieces therein. In one embodiment, the spray assembly has a dual inlet/outlet mechanism that introduces fluid into the process chamber from opposing directions.
According to another aspect, the process chamber has an exhaust vent and a exit port or drain. The exhaust vent exhausts gases and vapors from the cavity of the processing chamber. The drain removes excess and used process fluid from the cavity of the chamber body of the process chamber. The drain may be connected to a recirculation system to deliver the excess and used process fluid from the process chamber to a delivery tank. In a preferred embodiment, both the exhaust vent and the drain traverse about approximately the full length of the process chamber.
According to another aspect, the system includes a carrier assembly to retain a plurality of the workpieces. The carrier assembly is positioned in the cavity of the process chamber, and rotates within the process chamber to allow for better coverage for the sprayed process fluid on the workpieces. In one embodiment, the carrier assembly has a plurality of positioning members about a length of its body. The positioning members are used to retain the semiconductor workpieces in a specific location in the carrier assembly, and to provide a gap between adjacent semiconductor workpieces. Further, because of the geometry of the positioning members of the carrier assembly, the workpieces in the carrier assembly generally rotate both with the carrier assembly, and somewhat independently of the rotation of the carrier assembly.
According to another aspect, the workpieces are positioned in chucks that are placed in the carrier assembly. The chucks cover a peripheral portion of a backside of the workpieces. The chucks leave a majority of the surface area of the backside of the workpiece exposed for processing in the process chamber. In one embodiment, the chucks leave at least 95% of a surface area of the backside of the workpieces exposed.
According to another aspect, the system includes a rotor assembly. The rotor assembly is positioned within the cavity of the process chamber, and the carrier assembly is generally positioned within a cavity of the rotor assembly. A motor associated with the process chamber drives the rotor assembly to rotate the rotor assembly within the cavity of the chamber body. The rotor assembly subsequently provides rotational motion to the carrier assembly and the semiconductor workpieces therein.
According to another aspect, the system includes a delivery tank and a recirculation system. The delivery tank houses a volume of the process fluid and is in fluid communication with the process chamber. The recirculation system is in fluid communication with both an exit port of the process chamber and the delivery tank. The recirculation system communicates used process fluid from the process chamber to the delivery tank.
Several processes for thinning a batch of semiconductor workpieces are also provided. The process includes the step of placing the semiconductor workpieces into a chuck body so that a back side of the workpieces is exposed. Inserting a batch of the workpieces into the carrier assembly. Loading the carrier assembly into a rotor assembly such that the semiconductor pieces are positioned at an incline. Rotating the rotor assembly, which subsequently provides rotational motion to the carrier assembly and the workpieces therein, and spraying a process fluid on the exposed back sides of the workpieces. Through this system the back sides of the workpieces are then thinned to a desired thickness (preferably less than 125 microns). After the workpieces are thinned, the tool and system disclosed provide for rinsing and drying the workpieces. The system also provides for recirculating and recycling used process fluid.
These and other objects, features and advantages of this invention are evident from the following description of preferred embodiments of this invention, with reference to the accompanying drawings.
To understand the present invention, it will now be described by way of example, with reference to the accompanying drawings in which:
While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated.
Referring now to the Figures, and specifically to
As explained above, in the present system a plurality of workpieces 12 is thinned in the process chamber 20. In a preferred embodiment, prior to being placed in the process chamber 20 the workpiece 12 is mounted in a chuck 30 for processing. As shown in
As best shown in
The chuck 30 can be made from a number of different polymer materials that are stable and highly chemically resistant. The supporting body 32 preferably comprises polytetrafluoroethylene, and the retainer 34 preferably comprises a fluoropolymer such as polyvinylidene fluoride sold by Atofina Chemicals under the KYNAR tradename. In order to enhance the attachability of the retainer 34 to the supporting body 32 it is preferred that the supporting body 32 is comprised of a material having a Durometer hardness greater than the Durometer hardness of the material from which the retainer 34 is formed. Additionally, while the chuck 30 can be any shape (e.g., square, rectangular, circular, etc), in a preferred embodiment the chuck is disk-shaped and will have a diameter slightly larger than the diameter of the workpiece 12 to be processed.
Referring now to
The carrier assembly 52 has a central bore area 62. At a perimeter of the central bore area 62 the carrier assembly 52 has a plurality of positioning members 64 which position and retain the semiconductor workpieces 12 within the carrier assembly 52. The positioning members 64 generally extend radially inward from the support legs 58. Thus, the positioning members 64 provide a gap between adjacent workpieces 12 in the carrier assembly 52 to allow the process fluid to interact with the entire backside of the workpieces 12. As best shown in
Another carrier assembly 66 is shown in
After the appropriate carrier assembly (for purposes of example, this disclosure will utilize carrier assembly 52 in further discussions herein) is loaded with the workpieces 12, it is fitted into a rotor assembly 74 contained in the cavity 106 of the process chamber 20. An example of a rotor assembly 74 is shown in
Referring to
The process chamber 20 also has various assemblies connected thereto, including a door assembly 108 and a motor assembly 112. As shown in
The process chamber 20 also includes a spray assembly 110 to inject process fluid into the process chamber. In a preferred embodiment, the spray assembly 110 is integral with the process chamber 20. In a preferred embodiment as shown in
In a preferred embodiment, each of the manifolds 120 have inlet ports 121 at both the first end 98 and the second end 100 of the process chamber 20, and nozzles 122 extending substantially along the entire length of the process chamber 20. This provides for a dual inlet of process fluid in opposing directions about the manifold 120. By having a dual inlet of the process fluid in the manifolds 120, the pressure drop across the manifold 120 is decreased and the amount of flow or volume of fluid able to be introduced into the process chamber 20 is increased.
Referring to
As best shown in
While the process chamber 20 may be oriented horizontally, it is preferably orientated at an inclined angle. Moreover, in a preferred embodiment, the first end 98 of the chamber body 96 is inclined upwardly at an angle of, for example, 5 to 30°, and most preferably about 10°, so that the first end 98 of the process chamber 20 is at a higher elevation than the second end 100 of the processing chamber 20. To accomplish such an orientation, in a preferred embodiment the receiving members in the cabinet 14 are provided at the appropriate angle of inclination. The chamber body 96 of the process chamber 20 is connected to the receiving members via the mounting members 136 as described above. It is understood that the semiconductor workpieces are thus positioned at approximately the same angle of inclination as the process chamber 20.
As shown in
In a preferred embodiment, the process fluid utilized in the current system comprises one or more of: water, hydrogen peroxide, ozone, potassium hydroxide, sodium hydroxide, hydrofluoric acid, nitric acid, sulfuric acid, acidic acid and phosphoric acid. Other process fluids are also possible. The process fluid can be mixed and adjusted to address the specific needs of the system.
A volume of the process fluid is typically housed in the delivery tank 146 for delivery to the process chamber 20. Additional components, however, may be provided as part of an overall system in delivering fluids from the delivery tank 146 to the process chamber 20. An example of a fluid delivery schematic is shown in
The system may also include concentrated metering vessels 158 that contain concentrated volumes of the various processing fluids. For example, as shown in
As explained below in the method for processing the workpieces, various cleaning and etching steps are provided. For each step, a separate delivery tank 146 is typically provided. Accordingly, the processing fluid necessary for the pre-cleaning step 212 may be housed in one delivery tank 146, the processing fluid necessary for the coarse etching step 214 may be housed in a separate delivery tank 146, the processing fluid necessary for the polish etching step 216 may be housed in another separate delivery tank 146, and the processing fluid necessary for the rinsing step 218 may be housed in yet another separate delivery tank 146. The metering vessels 158 may therefore be utilized to separately deliver fluid to the appropriate delivery tank 146 (only one delivery tank is shown in
One method for processing a batch of semiconductor workpieces is illustrated in
After the workpieces 12 are placed in the cavity 106 and the door 130 to the process chamber 20 is closed, the workpieces are prepared to be processed. Typically, the workpieces 12 are processed while rotating in the process chamber 20. Accordingly, at step 210, the motor 114 is charged to rotate the rotor assembly 74 within the process chamber 20. The workpieces 12 rotate with the carrier assembly 52 in the rotor assembly 74, however, the workpieces 12 also somewhat independently rotate and move axially as explained above. Next, process fluid is sprayed through the nozzles 122 of the spray assembly 110 onto the exposed portion of the workpieces in the carrier assembly 52 as they are rotated by the rotor assembly 74.
In one embodiment, a first pre-cleaning spray step (step 212) is performed. In this step 212, a cleaning fluid is sprayed through the spray assembly 110 and onto the exposed portion of the workpieces 12 in the process chamber 20 to remove surface contamination on the workpieces 12. The cleaning solution is housed in a first delivery tank and may comprise at least one of H2O, H2O2 and NH4OH. Next, a first coarse chemical etch is performed at step 214. In the first chemical etch step, an increased etch rate is utilized to remove larger quantities of the substrate from the workpiece 12. After the coarse chemical etch is performed on the workpieces 12, a polish chemical etch is performed on the workpieces 12 at step 216. The etch rate of the polish chemical etch is less than the etch rate of the coarse chemical etch. In a preferred embodiment, the step of chemically etching the workpieces 12 comprises applying a solution of HF, HNO3 and H3PO4 to the workpieces 12. Two different delivery tanks are used to house the fluid for the coarse and polish etching processes. Through these two steps the batch of workpieces 12 are thinned in the process chamber 20. The workpieces 12 may be thinned to a thickness of less than 100 microns. Next, the workpieces 12 are rinsed in the process chamber at step 218. Rinsing the workpieces 12 generally comprises applying a solution of H3PO4 to the workpieces 12 in the process chamber 20. This solution is housed in yet another delivery tank 146. During each of these steps, the used process fluid is typically reclaimed via the recirculation system 144, and delivered from the process chamber 20 to the appropriate delivery tank 146.
After the workpieces 12 have been thinned and rinsed, they are typically removed from the process chamber 20 at step 220. Generally, the workpieces 12 remain in the carrier assembly 52, and the carrier assembly 52 is removed from the rotor assembly 74 in the process chamber 20. At step 224, the carrier assembly 52, holding the workpieces 12, is placed in the secondary processing module 18 for drying and rinsing thereof. The step of drying and rinsing the workpieces 12 in the drying and rinsing chamber 22 generally comprises first applying deionized water to the workpieces 12 to rinse the workpieces 12, and then applying isopropylalcohol vapor or hot nitrogen gas to the workpieces to dry the workpieces 12, all while spinning the workpieces 12. Each of these fluids may be held in yet another delivery tank.
After the workpieces 12 have been cleaned and dried, the carrier assembly 52 is removed from the secondary process chamber 22 at step 226. At step 228 the workpieces 12 are removed from the carrier assembly 52, and finally at step 230 the workpieces 12 are removed from the chucks 30.
Several alternative embodiments and examples have been described and illustrated herein. A person of ordinary skill in the art would appreciate the features of the individual embodiments, and the possible combinations and variations of the components. A person of ordinary skill in the art would further appreciate that any of the embodiments could be provided in any combination with the other embodiments disclosed herein. Additionally, the terms “first,” “second,” “third,” and “fourth” as used herein are intended for illustrative purposes only and do not limit the embodiments in any way. Further, the term “plurality” as used herein indicates any number greater than one, either disjunctively or conjunctively, as necessary, up to an infinite number.
It will be understood that the invention may be embodied in other specific forms without departing from the spirit or central characteristics thereof. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein. Accordingly, while the specific embodiments have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention and the scope of protection is only limited by the scope of the accompanying Claims.