Method for cleaning semiconductor wafers

Abstract

The present invention relates to a method for cleaning the surface of a semiconductor wafer, comprising the following steps in a given sequence: (1) a first cleaning step for a cleaning process using ozone water, followed by a rinsing step using clean water, (2) a second cleaning step including a treatment step using ozone water, which is followed by a treatment step using a HF-containing liquid, and the second cleaning step can be repeated several times, (3) a third cleaning step for a cleaning process using ozone water, followed by a rinsing step using clean water, and (4) a drying step for drying the surface of the semiconductor wafer. The present invention is characterized in that a pre-cleaning step using water is carried out immediately before the first cleaning step, so that the surface of the semiconductor wafer is still wet when the first cleaning step begins.

Description

[Technical Field]

[0001] The subject of the present invention is a process for cleaning semiconductor wafers. [Background technology]

[0002] Conventional technology For example, semiconductor wafers, usually silicon wafers, which serve as substrates for the fabrication of microelectronic components, are cleaned using wet chemical processes after polishing and coating (e.g., by epitaxial deposition) or heat treatment steps ("annealing"), and / or before high-temperature working steps. The purpose of cleaning is to remove as much as possible of contamination of the semiconductor wafer, for example, by metals such as copper or organics, and also to remove as much as possible of particles adhering to the wafer surface, since such contamination can cause problems in the subsequent fabrication of components, such as uneven gate oxide growth or uneven deposition of polysilicon gates.

[0003] Processes used in this context include single-wafer cleaning processes in which a semiconductor wafer is rapidly rotated about its central axis and simultaneously first cleaned with one or more liquids, then rinsed with deionized water, and dried. The liquid is applied to the rotating semiconductor wafer and accelerated toward the wafer edge by centrifugal force, causing the liquid to flow outward, leaving a thin film covering nearly the entire surface of the wafer. The semiconductor wafer is then dried, for example, by applying vapor (e.g., isopropanol) that reduces the surface tension of the liquid film while the semiconductor wafer continues to rotate, causing the entire liquid film to flow outward. Such processes are described, for example, in U.S. Patent Application Publication No. 2004 / 0103915 and European Patent Application Publication No. 0905747.

[0004] US Patent Application Publication No. 2014 / 048100 discloses a process for cleaning semiconductor wafers using the following steps:

[0005] (1) a first cleaning step for cleaning with ozone water, followed by a rinsing step with purified water; (2) a second cleaning step including a treatment step with ozone water followed by a treatment step with a HF-containing liquid, which may be repeated multiple times; (3) a third cleaning step for cleaning with ozone water, followed by a rinsing step with purified water; (4) A drying process for drying the surface of the semiconductor wafer. Summary of the Invention [Problem to be solved by the invention]

[0006] In testing this process, the inventors discovered that defect patterns measurable by LLS measurements can occur on the wafers. These defects appear to preferentially occur in the center of the substrate and can adversely affect the behavior of affected semiconductor wafers in component manufacturing operations.

[0007] It is therefore an object of the present invention to provide a process that does not have these defects, or at least minimizes the likelihood of their occurrence. [Means for solving the problem]

[0008] The object is achieved by the process described in the claims. [Brief explanation of the drawings]

[0009] [Figure 1] 1 shows in exemplary form the radial defect density that can be measured after one semiconductor wafer has been treated by a process known from the prior art (A) and another semiconductor wafer has been cleaned by the process of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0010] It is clear that the process (B) of the present invention is better able to avoid defects in the center of the semiconductor wafer than the prior art process (A).

[0011] Detailed Description of Exemplary Embodiments of the Invention In testing a prior art process for cleaning semiconductor wafers using a single wafer cleaner apparatus, the inventors determined that defect patterns could potentially occur on the wafer that were measurable by LLS measurement.

[0012] These defect patterns can be visualized by light scattering measurements, for example using instruments from KLA-Tencor and Surfscan SP1 MX, and are therefore referred to as localized light scattering defects. International Publication No. 2005101483 discloses a technique for scattered light measurements of epitaxially coated semiconductor wafers.

[0013] These defects preferentially occur in the center of the semiconductor wafer, as shown in Figure 1. They can adversely affect the behavior of affected semiconductor wafers in component manufacturing operations.

[0014] In an attempt to eliminate the occurrence of these defects, the inventors have discovered that it is advantageous and therefore preferable to first perform a first cleaning step for cleaning with ozone water and a subsequent rinsing step with purified water, then perform a second cleaning step including a treatment step with ozone water and a subsequent treatment step with an HF-containing liquid, the second cleaning step may be repeated multiple times, then perform a third cleaning step for cleaning with ozone water and a subsequent rinsing step with purified water, and then perform a drying step for drying the surface of the semiconductor wafer.

[0015] Preferably, a water pre-cleaning step is performed immediately before the first cleaning step, where it is essential that the surface of the semiconductor wafer to be cleaned is still wet before the first cleaning step begins.

[0016] The inventors have further recognized that it is preferable if during the pre-cleaning step the proportion of ozone water increases from 0% at the start of the pre-cleaning step to 100% at the end of the pre-cleaning step, with the duration of the proportion less than 5% being less than 10 seconds and greater than 1 second.

[0017] This successive increase in the proportion of ozone water from the pre-cleaning step through the first cleaning step clearly has the effect of further reducing the number of defects found.

[0018] It is particularly preferred if the pre-cleaning step lasts for at least 1 to 15 seconds, and it is highly preferred if the step lasts for at least 3 to 8 seconds.

[0019] It is essential to the process that the surface of the semiconductor wafer to be cleaned be aligned horizontally and rotated during the pre-cleaning step at a speed greater than 500 rpm and less than 1000 rpm.

[0020] It is particularly preferred if a nozzle is used to add water in the pre-wash step, in which case the nozzle flow rate 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.

[0021] It is also preferred that the nozzle is 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°.

[0022] One particularly preferred embodiment of the process of the present invention is shown in Table 1.

[0023] [Table 1] [Explanation of symbols]

[0024] DIW Deionized water.

[0025] O3W Ozone water consisting of 15-20 ppm ozone (O3) dissolved in deionized water. SC1 "Standard Clean 1" containing 0.3% tetramethylammonium hydroxide (TMAH, [N(CH3)4]OH) and 0.7% hydrogen peroxide (H2O2) in deionized water.

[0026] HF 0.5% to 1% hydrogen fluoride (HF) dissolved in deionized water. DRY Drying operations carried out in a 100% nitrogen atmosphere (N2).

Claims

1. 1. A method for cleaning a surface of a semiconductor wafer, comprising: (1) a first cleaning step for cleaning with ozone water and a subsequent rinsing step with purified water; (2) A second cleaning step including a treatment step with ozone water and a subsequent treatment step with a HF-containing liquid is sequentially provided, and the second cleaning step may be repeated multiple times; (3) a third cleaning step for cleaning with ozone water, followed by a rinsing step with purified water; (4) a drying step of drying the surface of the semiconductor wafer, a pre-cleaning step using water immediately before the first cleaning step so that the surface of the semiconductor wafer is wet when the first cleaning step is started; During the pre-cleaning step, ozone water is added, and the ratio of the ozone water increases from the start of the pre-cleaning step to the end of the pre-cleaning step; A method in which less than 5% of the duration is less than 10 seconds and greater than 1 second.

2. The method of claim 1, wherein the pre-cleaning step lasts for at least 1 second to 15 seconds.

3. 2. The method of claim 1, wherein 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 precleaning step.

4. 2. The method of claim 1, wherein a nozzle is used to add the water in the pre-wash step, and wherein the nozzle has a flow velocity of 0.5 m / s to 2 m / s and a flow rate of 0.5 L / min to 1.5 L / min.

5. 5. The method of claim 4, wherein the nozzle is aligned such that a nozzle flow direction forms an angle α with the surface of the semiconductor wafer, the angle α being less than 70° and greater than 30°.

Images