Method for cleaning semiconductor wafers

Abstract

A method for cleaning the front and back surfaces of a semiconductor wafer is provided, comprising the step of cleaning the front surface of the semiconductor wafer, the step of cleaning the front surface of the semiconductor wafer comprising, in the given order, (1) a pre-cleaning step with water so that the front surface is still wet when the next cleaning step begins, (2) a first cleaning step for cleaning with ozone water followed by a rinsing step with purified water, (3) a second cleaning step including a treatment step with ozone water followed by a treatment step with an HF-containing liquid, and (4) a third cleaning step for cleaning with ozone water followed by a rinsing step with purified water, the method comprising cleaning both the front and back surfaces of the semiconductor wafer, a fourth cleaning step including a treatment step with ozone water followed by a treatment step with an HF-containing liquid, and a drying step for drying both surfaces of the semiconductor wafer.

Description

[Technical Field]

[0001] The present invention provides a method for cleaning a semiconductor wafer. [Background technology]

[0002] Prior art Semiconductor wafers, typically silicon wafers, which are used, for example, as substrates for the fabrication of microelectronic components, are cleaned by wet chemical methods after being polished, coated (for example by epitaxial deposition), or subjected to a heat treatment (annealing) step, and / or before high-temperature process steps.

[0003] The purpose of cleaning is to remove as much as possible of any contamination of the semiconductor wafer, for example, from metals such as copper or organic substances, and particles adhering to the wafer surface, since during subsequent component fabrication, such contamination can lead to problems, for example, uneven gate oxide growth or uneven deposition of polysilicon gates.

[0004] Employed cleaning methods include single-wafer methods in which a semiconductor wafer is first cleaned with one or more liquids, then rinsed with deionized water, and dried while being rapidly spun about its central axis. These liquids are applied to the spinning semiconductor wafer and accelerated toward the wafer edge by centrifugal force, causing the liquid to flow outward and form a generally blanket-like thin film on the wafer surface. Upon subsequent drying by further rotation of the semiconductor wafer, the liquid film is completely flowed outward, for example, by adding vapor (e.g., isopropanol vapor) that reduces the surface tension of the liquid film. Methods of this type are described, for example, in US 2004 / 0 103 915 A1 and EP 0 905 747 A1.

[0005] US2014 / 048 100 A1 discloses a method for cleaning semiconductor wafers, in which the following method steps are used:

[0006] (1) a first cleaning step for cleaning with ozone water, followed by a rinse step with purified water; (2) a second cleaning step, which may be repeated multiple times, including a treatment step with ozone water followed by a treatment step with a HF-containing liquid; (3) a third cleaning step for cleaning with ozonated water, followed by a rinse with purified water; (4) A drying step in which one side of the semiconductor wafer is dried.

[0007] While testing this method, the inventors discovered that a pattern of defects measurable by LLS measurements can occur on the wafer. These defects appear to occur preferentially in the center of the substrate and can adversely affect the behavior of the affected semiconductor wafer in the part fabrication process. When using this process, if both sides of a semiconductor wafer are processed, additional defects are generated in the edge region of the semiconductor wafer on each opposite side. For example, if the backside of a semiconductor wafer is cleaned using this method, particles can subsequently be generated in the edge region of the front side, which can disrupt semiconductor part processing. Summary of the Invention [Problem to be solved by the invention]

[0008] It is therefore an object of the present invention to provide a method that does not cause these defects, or at least minimizes the likelihood of these defects occurring. [Means for solving the problem]

[0009] This object is achieved by the method described in the claims. [Brief explanation of the drawings]

[0010] [Figure 1]1 is a diagram illustrating the number of defects D in relative units as a function of radius R of a semiconductor wafer having a nominal diameter of 300 mm, where the filled circles represent the number of defects obtained with cleaning according to the prior art and the open circles represent the defects obtained with cleaning according to the method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Detailed Description of the Preferred Embodiments of the Invention When testing a prior art method for cleaning semiconductor wafers using an apparatus for cleaning single wafers (single wafer cleaner), the inventors determined that defect patterns could be produced on the wafer that were measurable with LLS measurements.

[0012] These defect patterns can be visualized by scattered light measurements using, for example, a KLA-Tencor instrument using a Surfscan SP 1 MX, and are therefore also called local light scattering burdens. WO 2005 101 483 A1 discloses a method for scattered light measurements of epitaxially coated semiconductor wafers.

[0013] As shown in Figure 1, these defects occur preferentially at the edge of the semiconductor wafer. They can adversely affect the behavior of the semiconductor wafer as it is subjected to the part fabrication process. It can be clearly seen that the method of the present invention is better able to avoid defects at the edge of the semiconductor wafer than prior art methods.

[0014] When the backside of a semiconductor wafer is cleaned using methods known in the prior art, the semiconductor wafer has an increased defect density in the edge region of the front side, and the inventors have been able to demonstrate these defects using the described measurement techniques.

[0015] After cleaning, defects are unacceptable on either the front or back side of the semiconductor wafer and therefore must be minimized.

[0016] In an attempt to eliminate these defects, the inventors have discovered that it is necessary to first clean the front surface of the semiconductor wafer and then clean both sides.

[0017] According to the present invention, the surface of the semiconductor wafer is first subjected to a pre-cleaning step in which the liquid consists essentially of water, and the inventors have determined that it is essential that the surface remain wet before the subsequent first cleaning step for cleaning with ozone water (which may be followed by a rinse with purified water) begins.

[0018] According to the invention, a second cleaning step is then performed, which comprises a treatment step with ozone water followed by a treatment step with a HF-containing liquid.

[0019] After the second cleaning step, according to the invention, a third cleaning step is performed for cleaning with ozone water, followed by a rinse with purified water.

[0020] Thereafter, according to the present invention, a step of cleaning both the front and back surfaces of the semiconductor wafer is performed, which step includes a fourth cleaning step including a treatment step using ozone water followed by a treatment step using an HF-containing liquid, and a drying step of drying both surfaces of the semiconductor wafer.

[0021] Preferably, during the pre-clean step, the percentage of ozonated water increases from 0% at the beginning of the pre-clean step to 100% at the end of the pre-clean step, with the percentage being less than 5% for a duration of less than 10 seconds and greater than 1 second. This continuous increase in the percentage of ozonated water between the pre-clean step and the first cleaning step appears to have the effect of further reducing the number of defects found.

[0022] More preferably, the pre-wash step lasts for at least 1 second and no more than 15 seconds.

[0023] More preferably, the surface of the semiconductor wafer is aligned horizontally and rotated at a speed greater than 500 rpm and less than 1000 rpm during the pre-cleaning step.

[0024] More preferably, in the pre-wash step, the water is applied using a nozzle, where the nozzle flow is between 0.5 m / s and 2 m / s, and the associated flow rate is between 0.5 L / min and 1.5 L / min.

[0025] More preferably, the nozzles used are aligned so that the direction of the nozzle flow forms an angle α with the surface of the semiconductor wafer that is less than 70° and greater than 30°.

[0026] More preferably, the pre-wash step lasts for at least 1 second and not more than 15 seconds. Highly preferably, this step lasts for at least 3 seconds and not more than 8 seconds.

[0027] It is preferred for this method if the surface of the semiconductor wafer to be cleaned is aligned horizontally and rotated at a speed greater than 500 rpm and less than 1000 rpm during the pre-cleaning step.

[0028] It is more preferred if the water is applied using a nozzle in the pre-wash step, where the nozzle flow is more preferably between 0.5 m / s and 2 m / s, and the associated flow rate is preferably between 0.5 L / min and 1.5 L / min.

[0029] It is also preferred if the nozzles are aligned so that the direction of the nozzle flow forms an angle α with the surface of the semiconductor wafer that is less than 70° and greater than 30°.

[0030] One particularly preferred embodiment of the method of the present invention for cleaning a surface is shown in Table 1.

[0031] [Table 1]

[0032] Abbreviation DIW Deionized water.

[0033] O3W Ozonated water consisting of 15-20 ppm ozone (O3) dissolved in deionized water.

[0034] SC1 "Standard Clean 1" containing 0.3% tetramethylammonium hydroxide (TMAH, [N(CH3)4]OH) and 0.7% hydrogen peroxide (H2O2) in deionized water.

[0035] HF 0.5% to 1% hydrogen fluoride (HF) dissolved in deionized water. DRY A drying process carried out in a 100% nitrogen atmosphere (N2).

[0036] D Number of defects.

Claims

1. 1. A method for cleaning a front and back surface of a semiconductor wafer, comprising: cleaning the surface of the semiconductor wafer; The step of cleaning the surface of the semiconductor wafer comprises: (1) a pre-cleaning step with water so that the surface is still wet when the next cleaning step begins; (2) a first cleaning step for cleaning with ozone water, followed by a rinse with purified water; (3) a second cleaning step, which includes a treatment step with ozone water followed by a treatment step with a HF-containing liquid; (4) a third cleaning step for cleaning with ozone water, followed by a rinse with purified water, in the given order; cleaning both the front and back surfaces of the semiconductor wafer; a fourth cleaning step comprising a treatment step with ozone water followed by a treatment step with a HF-containing liquid; and drying both sides of the semiconductor wafer.

2. The method of claim 1 , wherein the second washing step is repeated multiple times.

3. 10. The method of claim 1, wherein the third cleaning step is followed by a drying step to dry the surface of the semiconductor wafer.

4. The method of claim 1 , wherein the fourth washing step is repeated multiple times.

5. The method of claim 1 , wherein the fourth washing step is repeated four or more times.

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