Patent Application
20100024847
In manufacturing micro-scale devices from semiconductor wafers and similar workpieces, it is often necessary clean the wafer surface, before, during and/or after various processing steps.
In the past, surface cleaning has been performed in manual or automated wet benches using the well known RCA clean immersion process. The RCA clean process (originally developed at RCA or Radio Corporation of America) involves three basic immersion steps: removal of organic contaminants (known as organic clean), removal of a thin oxide layer (known as oxide strip), and then removal of ionic contamination (known as ionic clean).
The organic clean step typically uses a heated solution of ammonia (NH4OH), hydrogen peroxide (H2O2) and water. The second step typically uses a brief immersion in a solution of hydrofluoric acid (HF) and water. The third step typically uses a heated solution of hydrochloric acid (HCl), hydrogen peroxide and water. The hydrofluoric and hydrochloric acids generally are highly concentrated. Dilutions on the order of 10:1 are representative, although there are many variations of the basic RCA clean process.
Wet benches typically have a row of immersion tanks, and a mechanism for sequentially immersing a batch a workpieces into each tank. However, these systems have several disadvantages including relatively large consumption of process chemicals, such as acids, and large consumption of water, e.g., 30-35 liters for each wet bench tank, with a bath life of for example 2-4 hours. This consumption of process chemicals increases manufacturing costs, which ultimately increases the cost of the final product. Wet benches also generally require a large amount of clean room space. This results in higher manufacturing costs and other disadvantages. Wet bench processing can also typically be relatively slow and require extensive wafer movement, as the wafers must be moved between several different tanks to complete a single processing step. This tends to add to total production time.
Many chemicals used in wet bench processing, such as HF, HCl, H2SO4, and H2O2, are toxic, highly corrosive, expensive, and/or difficult to handle and dispose of. As a result, complex draining, recycling, and removal systems are often required for effectively handling and disposing of these used chemicals. Moreover, even when proper disposal procedures are followed, there is still a potential for the used chemicals to have a negative environmental impact. Accordingly, there is a need for processing machines and methods having less reliance on these types of chemicals.
Reducing consumption of water is also beneficial, especially in areas where clean water is becoming increasingly scarce. Disposing of waste water from manufacturing operations, in environmentally friendly ways, can often be difficult or costly. Accordingly, reducing water consumption in the manufacturing process is also important.
Spin/spray systems have also been used for wafer cleaning. In these types of systems, typically wafers are held in a spinning rotor and sprayed with chemical liquids and gases. Spin spray systems generally can require less space and use smaller amounts of chemicals in comparison to wet benches. However, even spin/spray systems still tend to use significant amounts of chemicals.
Accordingly, it is an object of the invention to provide an improved spin/spray wafer cleaning system.
New cleaning or processing systems and methods, have now been invented to overcome the disadvantages described above. These new systems and methods provide for rapid and efficient wafer cleaning with far less chemical consumption in comparison to existing systems. The invention therefore provides for significant advances in the technology of manufacturing semiconductor wafers and similar workpieces. In a new wafer cleaning method, one or more wafers are placed into a rotor in a process chamber. The rotor spins the wafers. De-ionized water and ultra-dilute hydrofluoric acid are sprayed onto the wafers. Ozone gas is introduced into the process chamber. The wafers are then sprayed with an ultra-dilute solution of hydrochloric acid. Ozone gas is purged from the chamber and the wafers are rinsed and dried.
The invention resides as well in sub-combinations of the features described and in the individual components.
In the drawings, wherein the same reference number denotes the same element throughout the several views:
Turning now in detail to the drawings, as shown in
A middle section or module 14 may include a processing chamber assembly 20, as illustrated in
A rotor 40, as illustrated in
Various types of rotors may be used. Generally, the rotor 40 is designed to hold one or more wafer containers or cassettes. Alternatively, the rotor 40 may be designed to hold wafers directly, without any container or cassette in the rotor. In this case, the rotor may be provided with combs or similar elements for holding the edges of the wafers directly. In either case, the wafers 55 are spaced apart from each other within the rotor, to allow sprayed in liquids and/or gases to contact substantially all surfaces of the wafers 55.
For processing with acids, the rotor 40 and the chamber 22 are made of a corrosion resistant material, such as Teflon (fluorine resins). Other components of the system that may come into contact with acids, or acid vapors, including the containers or cassettes, and the cabinet structure, may similarly be made from these types of materials. Alternatively, external components of the system, having little of no contact with process acids, may be made of e.g., stainless steel, with a plastic or Teflon insert or liner.
As illustrated in
Referring to
In the chamber 22, the nozzles may be spaced apart along substantially entire length of the processing chamber 22. The manifolds 80, 82 and 84 have spray nozzles or other openings directed into the processing chamber 22 for spraying liquids or gases towards the rotor, generally in a radially inwardly direction. An exhaust duct 63 is preferably included to exhaust gases or vapors from the processing chamber 22. A drain 47 removes liquids from the processing chamber 22.
The processing chamber 22 may further include various other components to enhance processing of the wafers 55. For example, the processing chamber 22 may heaters to heat the workpieces 55 and/or the processing and or rinsing liquids. An anti-static generator may be provided in the nitrogen gas supply to reduce static electricity within the chamber 22.
In the design shown in the drawings, the third module 16 contains an ozone generator 70 connected to the gas spray manifold 80 in the processing chamber 22 via one or more ozone delivery lines. The ozone generator 70 may generate up to 300 gm/cubic meter of ozone, or approximately 90 gm/hour of ozone. As shown in
The HF source 92 and the HCl source 94 may be set up to provide ultra-dilute acid. For example, the HF may be diluted down to 1 part source acid to 100 to 1500, 200-1200 or 400 to 1100 parts de-ionized water. Source acid, as used here, means the standard acid as provided by the manufacturer. In the case of HF, source acid is a 49% by weight solution of HF in water. For most applications, the HF concentration ratio (water to acid) may be in the range of 800-1200:1, 900-1100:1, or about 1000:1. Since the source acid is 49% HF, the final actual HF concentration is about 2000:1. The HCl may be provided with similar concentrations. Source hydrochloric acid is a 38% by weight solution of hydrochloric acid in water. Consequently, the final actual HCl concentration is about 3000:1. Correspondingly, the final actual concentrations ranges given above for the source acid (100 to 1500, 200-1200 or 400 to 1100) parts de-ionized water to acid are about 50-3000, 100-2400 or 200-2200 for HF, and about 33-4500, 66-3600 or 130-3300. The claims describe final actual concentrations, regardless of the concentration of the source chemical.
The liquid chemical supplies 92, 94, and 96 of HF, HCl and NH4OH (if used), respectively, may be provided in bulk from sources in the facility, or they may be provided via bottles stored within the system 10. As used here, the term ultra-dilute means 1 part acid (or other chemical as provided by the manufacturer for semiconductor manufacturing use in standard concentration) mixed with at least 100 parts of de-ionized water. Accordingly, with source HF provided at a 49% concentration, ultra-dilute HF is about one part HF to 200 or more parts water.
In use, wafers 55 are typically provided in a container or cassette 54. A standard type of cassette 54 holds 25 200 mm diameter wafers. The door 64 of the processing chamber 22 is opened. One or more cassettes 54 loaded with wafers is placed into the rotor 40, as described in U.S. Pat. No. 6,418,945, incorporated by reference. In the design shown, the rotor 40 is designed to hold two cassettes 54. The door 64 is closed and may generally provide a liquid and gas tight seal with the chamber.
A processing sequence can be preprogrammed into the system controller, or can be set up or selected by the operator using the control panel and display 18.
In a typical cleaning application, for example in front end of the line (FEOL) clean with low silicon loss, in an initial step, the motor 44 is turned on to spin the rotor 44. De-ionized water may then be briefly sprayed onto the spinning wafers via the nozzles 83 of the de-ionized water spray manifold 82. The rotor 44 and cassettes 54 have a generally open structure, allowing liquids and gases sprayed out from the nozzles to directly impact on the wafers.
In step 2 in
Next, in step 3, the supply of ozone gas is stopped, but without purging the chamber. Hot de-ionized water (at e.g., 30-99° C.) is sprayed onto the spinning wafers along with a dilute solution of HCl. The HCl chemically reacts with the wafer surface in the presence of the remaining ozone gas. This removes metal contaminants from the wafer surface.
In step 4, de-ionized water heated to a lower temperature is sprayed into the chamber along with ozone gas. Step 4 is the final chemical process step. The remaining steps 6-11 are cooling, purging, rinsing and drying steps, and may be varied as desired.
In step 5, still cooler de-ionized water is briefly sprayed onto the wafers. In step 6, the chamber is briefly purged by providing nitrogen gas and de-ionized water into the chamber. Steps 7 and 8 are progressive cooling steps conducted by spraying progressively cooler water onto the spinning wafers. In steps 9-11 the chamber is again briefly purged, and the wafers are sprayed with nitrogen gas while spinning at high speeds, to dry the wafers.
As shown in
The processing system 10 provides several advantages over existing processing systems. First, the system 10 is compact and does not require large amounts of space in a clean room environment in comparison to a wet bench Overall, the processing system 10 also uses less chemicals, in comparison to traditional RCA wet bench cleaning. The processing system 10 also uses much less de-ionized water. For example, consumption of de-ionized water per wafer is 0.34 liter per wafer in the
The process in
The apparatus and methods described above may reclaim and reuse one or more of the substances used in processing. However, since very low concentrations of chemicals are used. the apparatus and methods may also be economically operated on a single use basis, with out reusing chemicals, and with minimal or no environmental affects. This can provide for a higher level of clean, since potential for contamination from reused chemicals is avoided.
While discussed primarily in relation to silicon wafers, the invention relates as well to similar workpieces, such as flat panel displays, glass masks, rigid disk or optical media, thin film heads, or other workpieces formed from a substrate on which microelectronic circuits, data storage elements, layers, or micro-mechanical/micro-electro-mechanical elements may be formed. These and similar articles are collectively referred to here as a wafer or workpiece.
Thus, novel apparatus and methods have been shown and described. Various changes and substitutions may of course be made without departing from the spirit and scope of the invention. The invention, therefore, should not be limited except by the following claims and their equivalents.
