Cleaning and liquid contact with solids – Apparatus – With plural means for supplying or applying different fluids...
Reexamination Certificate
2001-04-17
2003-07-01
Markoff, Alexander (Department: 1746)
Cleaning and liquid contact with solids
Apparatus
With plural means for supplying or applying different fluids...
C134S018000, C134S0570DL, C134S902000
Reexamination Certificate
active
06584989
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to semiconductor processing, and more particularly to a process and an apparatus for wet cleaning a wafer using a dilute cleaning solution that achieves and maintains the desired characteristics of the cleaning solution.
BACKGROUND OF THE INVENTION
In the manufacturing of semiconductor devices, wafers must be cleaned at various stages in processing. For example, a reactive ion etching (RIE) process may leave inorganic polymer residues on the substrate which would cause electrical or mechanical defects in the semiconductor device if not removed.
RIE is often used to form patterns of metal lines (for example, aluminum, copper, and alloys as known in the art) in a conductive film or layer which will act as wiring or interconnection (for example, terminal vias) for a semiconductor circuit. RIE processes typically involve patterning the conductive layer with a photoresist, and then using a reactive ion etch, where a plasma environment is formed from chemical species including, for example, boron trichloride, HCl gas, Cl
2
, or other reactive species which etch exposed portions of the conductive layer. However, the RIE process typically leaves a residue around the metal, which, for the example of aluminum lines, includes complex polymeric oxides of aluminum along with chlorine incorporated into the inorganic matrix. This is often referred to as sidewall polymer residue, and its presence is a source of corrosion of the metal lines when exposed to air or humidity. In addition, after a RIE process, sidewall polymers remain on the semiconductor wafer surface. These sidewall polymers, known as “polymer rails” are inorganic in nature and may have various chemical constituents, including aluminum, silicon, titanium, oxygen, carbon and chlorine. Since each of these constituents tend to react and/or interfere with the function of the semiconductor, removal of the sidewall polymers is therefore desirable.
Some prior art cleaning processes used chromium-based phosphoric acid (CP) solutions or other heavy-metal solvents to clean wire and terminal vias after a RIE process. However, such heavy-metal solutions require special handling and associated costs to avoid environmental and health impacts.
More recently, solutions that contain more than eighty percent water by volume are being used, which are both environmentally safer and less costly than heavy-metal (e.g. chromium) based solutions. The primary additional components include sulfuric acid and hydrogen peroxide, and the resulting solution is often referred to as dilute sulfuric peroxide (DSP). Other oxidants, such as ozone, may also be used instead of hydrogen peroxide. For example, Delehanty et al. (U.S. Pat. No. 5,780,363, hereinafter referred to as the Delehanty patent) discloses an aqueous etchant solution containing about 0.01% to about 15% by weight of sulfuric acid, and about 0.01% to about 20% by weight of hydrogen peroxide or about 1 ppm to 30 ppm of ozone, which is effective to remove polymer residues from a substrate, particularly from a chip having aluminum lines. A typical DSP solution may be obtained by mixing about 50 parts deionized water, about 7 parts of standard 30% dilute hydrogen peroxide, and about 3 parts concentrated sulfuric acid, or roughly 92 wt % water, 3 wt % peroxide, and 5 wt % sulfuric acid. However, such mixtures have not been successful in removing all types of polymer rails.
It has been found that the addition of a small amount of hydrofluoric acid (HF) in the range of about 0.1 to about 100 ppm, and preferably about 8 to 10 ppm to create a dilute sulfuric peroxide, hydrofluoric acid (DSPHF) solution, is sufficient to improve the etch rate, and results in more complete removal of sidewall polymers from metal after RIE processing, effectively cleans metal contacts, and can be used for specific applications in copper technology as well as aluminum. However, the small amount of HF in the DSPHF solution may be depleted over time, reducing the effectiveness of the bath, and achieving a relatively constant level of HF concentration over time is difficult to do manually. For example, a DSPHF cleaning solution is disclosed in copending U.S. patent application Ser. No. 08/975,755 filed on Nov. 21, 1997 entitled “Etching Composition and Use Thereof,” assigned to the present assignee and which is incorporated by reference in its entirety.
Teruhito et al. (European Patent Application Publication 0 618 612 A3, hereinafter referred to as Teruhito) discloses a method and apparatus for cleaning residues from a semiconductor substrate with the purpose of preventing the cleaning solution from degrading with time. Teruhito appears to describe a concentrated cleaning solution including a sulfuric acid to hydrogen peroxide mixture in the ratio 5:1, with the addition of fluorosulfuric acid (HSO
3
F) or SO
2
F
2
, and further discloses the use of the cleaning solution at a temperature in the range of 80° C. to 130° C., and preferably at about 100° C. Teruhito discloses that using HSO
3
F or SO
2
F
2
, used in preference to HF, acts to release hydrofluoric acid and fluorine ions when the vaporization decreases the amount of fluorine ions which tends to stabilize the etch rate in the preferred range of 0.5-2 nm per minute. Teruhito does not suggest that a very dilute solution containing at least 80% water would be appropriate for cleaning polymer residues on a semiconductor substrate. Teruhito does disclose the use of an infrared detector to monitor fluorine concentration, and a controller which acts to add fluorosulfuric acid for specified periods of time order to maintain the concentration of fluorine at an approximately constant value. However, fluorosulfuric acid is not a commonly available chemical compared to HF. In addition, the monitoring device, controller, and valve mechanism disclosed in Teruhito does not appear to be suitable for accurately detecting and controlling very small amounts of fluorine ion concentrations, for example, in the range of about 5 ppm to about 12 ppm. For example, Teruhito appears to disclose the addition of fluorosulfuric acid to a small reservoir adjacent to the main process tank, and measuring the ion concentration as the fluid circulates through a tube from the small reservoir to the process tank. The applicants of the present invention have found that such an arrangement would not accurately reflect and suggest inaccurately high concentration levels of fluorine ions in the process tank where cleaning would take place. In addition, applicants are not aware of an infra-red detector that is capable of accurately monitoring fluorine ion concentrations in the range of 5 ppm to about 12 ppm.
Kamikawa et al. (U.S. Pat. No. 6,158,447, hereinafter referred to as the Kamikawa patent) discloses a cleaning apparatus that includes a cleaning bath for dipping a semiconductor wafer. The equipment includes chemical supply pipes and a pump for injecting a predetermined amount of chemical, such as dilute hydrofluoric acid (HF), into water. The temperature of the solution is monitored by a sensor, and on the basis of a signal output from the temperature sensor, a diaphram pump is controlled to inject an amount of chemical so that the concentration of the chemical is at a predetermined concentration. However, for the purposes of cleaning polymer residues left over from RIE processing, very small quantities, for example, in the range of 6 ppm to 12 ppm of HF are required, and diaphram pumps as known in the art are not capable of controlling the addition of HF in such small controlled amounts. The Kamikawa patent also does not suggest the need for monitoring the HF concentration.
McConnell et al. (U.S. Pat. No. 4,899,767, hereinafter referred to as the McConnell '767 patent) discloses a system for treating semiconductor wafers using a plurality of different treatment fluids. Sensors are provided to detect fluid level, temperature, and electrical conductivity of the fluids. A metering pump may be included which controls injection of chemicals, and provide f
McCullough Kenneth J.
Ouimet George F.
Rath David L.
Taft Charles J.
Zigner, Jr. Robert W.
C. Li Todd M.
International Business Machines - Corporation
Markoff Alexander
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