JP7056610B2 - Intentional contamination method for semiconductor wafers - Google Patents

Description

The present invention is a method for evaluating the performance of a semiconductor wafer for manufacturing a highly integrated device, and in particular, the behavior of a metal element that deteriorates the performance of a silicon wafer when present in a silicon wafer (semiconductor wafer). To know, it relates to a method for deliberately introducing a metal element into a silicon wafer.

With the increasing density and high integration of devices such as semiconductor integrated circuits, stabilization of device operation has been desired. In particular, improvement of characteristic values such as leakage current and withstand voltage of oxide film is an important issue.

However, if contaminants such as metal elements are mixed into the silicon wafer, which is an integrated circuit board, stable operation of the device manufactured thereafter cannot be expected. For example, it is widely known that a metal element introduced in a manufacturing process of a semiconductor integrated circuit adversely affects device characteristics depending on the type and concentration of the element.

Therefore, a technique for removing contaminants mixed in a silicon wafer, particularly a metal element, from a device active layer has been developed. This technique is called gettering, and IG (Internal Getting) that precipitates metal on the oxygen precipitate formed on the wafer bulk, or a polycrystalline silicon film is formed on the back surface of the wafer, and the metal is solid-dissolved in the polycrystalline film at a high concentration. A typical method is PBS (Poly-Si Back Seal).

When developing these gettering techniques and examining their capabilities, it has long been practiced to deliberately introduce metal elements into silicon wafers and investigate their behavior. For the investigation, it is necessary to intentionally contaminate the wafer with a metal element having a set concentration, and various methods are known as the intentional contamination method. For example, a method of dissolving a metal element in SC1 (Standard Cleaning 1, NH ₃ OH / H ₂ O ₂ / H ₂ O mixed solution) and immersing a silicon wafer in this solution heated to 70 to 100 ° C. An example is a spin coating method in which a solution prepared by diluting a standard solution for atomic absorption of an element with a solvent is applied to a hydrophilic wafer surface and spin-dried to intentionally contaminate the target concentration.

However, since all of these methods contaminate the entire surface of the wafer with a uniform concentration (uniform contamination method), when evaluating the gettering ability under conditions with different contamination concentrations, the required contamination concentration conditions are required. The number of wafers corresponding to the number is required.

In addition, the contamination that actually occurs is often local contamination that occurs when metal particles or the like partially come into contact with and adhere to the wafer. In this case, the contaminated part and the non-contaminated part form a boundary on the wafer, and the behavior of the boundary part changes and the diffusion in the radial direction of the wafer occurs. Therefore, the metal behavior caused by these local contaminations is investigated. However, the above-mentioned uniform contamination method cannot be used.

Japanese Unexamined Patent Publication No. 2016-44988 Japanese Unexamined Patent Publication No. 2014-41030 Japanese Unexamined Patent Publication No. 2002-270568

As described above, it has been impossible to investigate the metal behavior caused by local contamination by the conventional uniform contamination method. Although it has been reported that the surface of a wafer is locally contaminated (Patent Documents 1 to 3), these methods have, for example, concentrations of Fe, Cr, and Ni as a solution for intentional contamination. Prepares and uses a 5% nitrate-based mixed solution of 10 ppb (Patent Document 2). With such a method, it is difficult to control the contaminated area diameter and the contaminated concentration, and the workability is also poor. Met.

The present invention has been made in view of such problems, and provides a method for intentionally contaminating a limited local region of a wafer by controlling a desired metal element to a desired concentration with high precision. The purpose. It is also an object to improve work efficiency as compared with the conventional method.

In order to achieve the above object, the present invention is a method for intentionally contaminating a semiconductor wafer by intentionally introducing a desired metal element into a predetermined region on the surface of the semiconductor wafer in order to evaluate the performance of the semiconductor wafer.
A solution obtained by diluting a standard solution containing a metal element with a solvent consisting of a volatile liquid is used as a contaminating solution, and a contaminated region is formed at a predetermined position on the surface of the semiconductor wafer by dropping the standard solution at a predetermined position. Provided is a method for intentionally contaminating a semiconductor wafer.

With such a method, since the contaminated solution is prepared as a volatile liquid, the solvent volatilizes in a short time, and the contaminated area diameter and contamination of the local area in the wafer surface, which was difficult with the conventional method, are contaminated. The concentration can be controlled in a stable manner. Moreover, since the solvent volatilizes in a short time, the work efficiency can be improved as compared with the conventional case.

At this time, it is preferable to use alcohols as the solvent.
Alcohols are highly volatile and can be suitably used as a solvent in the method of the present invention.

At this time, it is preferable to use ethanol as the alcohol.
Ethanol is cost-effective among alcohols and can be more preferably used as a solvent in the method of the present invention.

Further, at this time, before the dropping is performed, the relationship between the amount of the dropped solution of the contaminated solution and the diameter of the contaminated area is obtained in advance according to the contaminated solution to be used and the method of the dropping, and the relationship is determined. Based on this, it is preferable to control the diameter of the contaminated area by the amount of the dropped solution.

With such a method, the diameter of the contaminated area can be controlled more reliably, so that local intentional contamination in the wafer surface can be carried out more stably.

In the method of the present invention, since the contaminated solution is prepared as a volatile liquid, the solvent volatilizes in a short time, which is difficult with the conventional method. The concentration can be controlled in a stable manner. Moreover, since the solvent volatilizes in a short time, the work efficiency can be improved as compared with the conventional case. Therefore, the performance of the semiconductor wafer can be appropriately evaluated.

It is a figure which shows the relationship between the dropping volume of the contaminated solution and the diameter of a contaminated area in Example 2 of this invention.

In order to solve the above problems, the present inventor is a method of intentionally contaminating a predetermined region on the surface of a semiconductor wafer with a desired metal element, and dilutes a standard solution containing the metal element with a solvent consisting of a volatile liquid. It has been found that if the intentional contamination method is to form a contaminated region at a predetermined position on the surface of the semiconductor wafer by dropping the prepared solution at a predetermined position, local intentional contamination can be stably carried out. The present invention has been completed.

That is, the present invention is a method for intentionally contaminating a semiconductor wafer by intentionally introducing a desired metal element into a predetermined region on the surface of the semiconductor wafer in order to evaluate the performance of the semiconductor wafer.
A solution obtained by diluting a standard solution containing a metal element with a solvent consisting of a volatile liquid is used as a contaminating solution, and a contaminated region is formed at a predetermined position on the surface of the semiconductor wafer by dropping the standard solution at a predetermined position. This is a method of intentionally contaminating semiconductor wafers.

Hereinafter, embodiments will be described.

In the present invention, a standard solution of a metal element is used to prepare a contaminated solution for locally contaminating a semiconductor wafer. Standard solutions with strict concentrations of metal elements are commercially available, and standard solutions for most of the elements to be investigated are available. For example, when Fe is targeted, a commercially available 0.2 mol / L nitric acid solution containing 0.38% of Fe (III) nitric acid (1000 mg / L = 1000 ppm as iron) can be used. can. Of course, the standard solution of the metal element may have a specified concentration of the metal element, and even if it is not commercially available, a solution having an adjusted concentration may be used. When such a standard solution was diluted with a volatile liquid, for example, ethanol, as a contaminated solution, dropped onto a wafer, and left at room temperature for several minutes, the volatile ethanol was lost by evaporation and dissolved. Only iron will remain on the wafer. Since the number of atoms of the residual iron can be regarded as the same as the number of iron atoms contained in the contaminated solution used at the time of dropping, it is possible to intentionally contaminate the desired number of iron atoms on the wafer.

The solvent used for dilution is preferably alcohols such as methanol and IPA (isopropyl alcohol) in addition to ethanol, but is not particularly limited as long as it is a volatile liquid. In addition, it is more preferable that the solvent is ethanol because it is advantageous in terms of cost.

When performing the above-mentioned local contamination, the area of the contaminated area is determined in proportion to the volume of the contaminated solution to be dropped. For example, when ethanol is used as a solvent and 10 μL of the solution is dropped using a micropipette or the like, the ethanol solution spreads in a region of a circle having a diameter of about 25 mm, and the ethanol evaporates in a short time. The area becomes the contaminated area of the target element. By reducing the amount of solution and dropping 2 μL, this contaminated area can be narrowed to a diameter of about 12 mm.

In this way, the diameter of the contaminated area can be controlled by the volume of the dropping solution. Here, when a different solvent is used or the dropping method is changed, the relationship between the dropping solution volume and the diameter of the contaminated area does not necessarily have the above relationship, but the dropping is performed in advance depending on the solution used and the dropping method. The relationship between the solution volume and the diameter of the contaminated area may be obtained.

At this time, the purity of the volatile liquid used as the solvent affects the control of the contaminated area diameter and the contaminated concentration, so a high-purity one is preferable, but the relationship between the amount of the dropped solution and the contaminated area diameter is obtained in advance. Thus, the purpose of local pollution can be achieved.

From the above, before performing the dropping, the relationship between the amount of the dropping solution of the contaminated solution and the diameter of the contaminated area is obtained in advance according to the contaminated solution to be used and the method of the dropping, and the relationship is established. Based on this, it is preferable to control the diameter of the contaminated area by the amount of the dropped solution. With such a method, the diameter of the contaminated area can be controlled more reliably, so that local intentional contamination in the wafer surface can be carried out more stably.

As described above, when the method of intentionally contaminating the semiconductor wafer of the present invention is used, it has been difficult to control the contaminated area diameter and the contaminated concentration due to the slow volatilization of the contaminated solution. In the intentional contamination method, since the contamination solution is prepared as a volatile liquid, the solvent volatilizes in a short time, and local intentional contamination in the wafer surface can be stably carried out. Moreover, since the solvent evaporates in a short time, the work efficiency can be improved as compared with the conventional case.

Further, with such a method, it is possible to form different intentionally contaminated regions (regions having different contamination concentrations, types of metal elements, etc.) in the radial direction of the same wafer. For example, in the case of an element having a small diffusion coefficient and diffusion in the radial direction of the wafer can be almost ignored, if a silicon wafer having a radius of 100 mm is used, a contaminated region having a diameter of 12 mm can be used to obtain up to eight contaminated regions having different concentrations. It will be possible to form.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited thereto.

(Example 1)
A silicon wafer was manufactured by processing a semiconductor silicon single crystal rod having a diameter of 8 inches (200 mm) pulled up by the CZ method. On the other hand, a 1000 ppm iron standard solution was diluted with high-purity ethanol to prepare a 0.5 ppb iron ethanol solution. 2 μL (2 microliters) of this iron ethanol solution was dropped with a micropipette at a position 40 mm from the notch formed at the end of the silicon wafer toward the center of the wafer. Next, 2 μL of a 5 ppb iron ethanol solution prepared in the same manner as above was added dropwise to a position 80 mm advanced from the notch portion toward the central portion. Subsequently, 2 μL of a 50 ppb iron ethanol solution prepared in the same manner as above was added dropwise to a position 120 mm ahead from the notch portion toward the central portion. Finally, 2 μL of a 500 ppb iron ethanol solution prepared in the same manner as above was added dropwise to a position 160 mm advanced from the notch portion toward the central portion. From the dropping point, the iron ethanol solution spread in the range of about 10 to 15 mm in diameter, and then the ethanol of the solvent evaporated and dried by holding at room temperature for several tens of seconds, and the local contamination of about 10 to 15 mm in diameter was completed.

In this way, after intentionally contaminating four points on the wafer surface with different concentrations, the iron concentration was measured at the four positions by the TXRF (total reflection fluorescent X-ray analysis) method, and the iron concentration was measured toward the central part. In order, iron having a concentration of 8 × 10 ⁹ , 1.2 × 10 ¹¹ , 9 × 10 ¹¹ , and 1.1 × 10 ¹³ cm ^-2 was detected. This is the concentration calculated assuming that all the iron atoms contained in the dropped contaminated solution remained in the region with an average diameter of 12 mm covered by the dropped ethanol, 9.5 × 10 ⁹ , 9.5 × 10 ¹⁰ , 9 It was almost the same as .5 × 10 ¹¹ and 9.5 × 10 ¹² cm ^-2 , and local intentional contamination was possible with the iron concentration as intended.

(Comparative Example 1)
A silicon wafer was manufactured by processing a semiconductor silicon single crystal rod having a diameter of 8 inches (200 mm) pulled up by the CZ method. On the other hand, 1000 ppm of iron standard solution was diluted with ion-exchanged water to prepare a 0.5 ppb iron aqueous solution. 2 μL of this aqueous iron solution was dropped from the notch at the end of the silicon wafer to the center of the wafer at a position of 40 mm with a micropipette. Next, 2 μL of a 5 ppb iron aqueous solution prepared in the same manner as above was added dropwise to a position 80 mm advanced from the notch portion toward the central portion. Subsequently, 2 μL of a 50 ppb iron aqueous solution prepared in the same manner as above was added dropwise to a position 120 mm ahead from the notch portion toward the central portion. Finally, 2 μL of a 500 ppb iron aqueous solution prepared in the same manner as above was added dropwise to a position 160 mm advanced from the notch portion toward the central portion. From that drip point, the aqueous iron solution spread over a range of about 3 mm in diameter and then held at room temperature for 10 to 15 minutes to evaporate and dry the solvent water, completing local contamination with a diameter of about 3 mm.

As described above, when water having low volatility is used as a solvent, it can be seen that the diameter of the contaminated area is small and the drying time is very long, and the workability is remarkably poor.

(Comparative Example 2)
A silicon wafer was manufactured by processing a semiconductor silicon single crystal rod having a diameter of 8 inches (200 mm) pulled up by the CZ method. On the other hand, 1000 ppm of iron standard solution was diluted with ion-exchanged water to prepare a 0.5 ppb iron aqueous solution. 100 μL of this aqueous iron solution was dropped from the notch at the end of the silicon wafer to the center of the wafer at a position of 40 mm with a micropipette. Next, 100 μL of a 5 ppb iron aqueous solution prepared in the same manner as above was added dropwise to a position 80 mm advanced from the notch portion toward the central portion. Subsequently, 100 μL of a 50 ppb iron aqueous solution prepared in the same manner as above was added dropwise to a position 120 mm ahead from the notch portion toward the central portion. Finally, 100 μL of a 500 ppb iron aqueous solution prepared in the same manner as above was added dropwise to a position 160 mm advanced from the notch portion toward the central portion. From the dropping point, the iron aqueous solution spread in the range of 10 to 20 mm in diameter, but after that, the solvent water evaporated and dried only after being left for 1 hour or more, and the local contamination of 10 to 20 mm in diameter was completed.

As described above, it can be seen that if the amount of the dropping liquid is increased so as to have the same contaminated area as the alcohol solvent, the drying time is further extended and the workability is significantly deteriorated. Further, the diameter of the contaminated area has a large variation of 10 to 20 mm in diameter, and it is difficult to control the diameter of the contaminated area and the contaminated concentration.

(Example 2)
A 1000 ppm iron standard solution was diluted with high-purity ethanol to prepare a 0.5 ppb iron ethanol solution. 2 μL, 4 μL, 6 μL, 8 μL, and 10 μL of this iron ethanol solution are dropped on the surface of the silicon wafer with a micropipette, and the diameter of the solution spread on the wafer surface (contaminated area diameter) is measured, and the dropped volume and the contaminated area diameter are measured. The relationship with was obtained and plotted in FIG. The plot in FIG. 1 shows the average value obtained by measuring three times for each volume.

As shown in FIG. 1, the relationship between the volume of the dropped solution and the diameter of the contaminated area is not always linear due to the surface tension of the solution used and the accuracy of the dropping operation, but it depends on the solution used and the dropping operation method. It was shown that if the relationship between the volume of the dropped solution and the diameter of the contaminated area is obtained in advance, it is possible to intentionally contaminate the target contaminated area (area) by controlling the volume of the dropped solution.

Next, 2 μL of the 0.5 ppb iron ethanol solution used for the preparation of FIG. 1 was added to a silicon wafer obtained by processing a semiconductor silicon single crystal rod having a diameter of 8 inches (200 mm) pulled up by the CZ method. A pipette was used to drop the silicon wafer from the notch at the end of the silicon wafer toward the center of the wafer at a position of 40 mm. Next, 6 μL of the same 0.5 ppb iron ethanol solution as described above was added dropwise to a position 80 mm ahead from the notch portion toward the central portion. Subsequently, 10 μL of the same 0.5 ppb iron ethanol solution as described above was added dropwise to a position 120 mm ahead from the notch portion toward the central portion.

The dropped iron ethanol solution spread over a range of about 12 mm, 24 mm, and 25 mm in diameter, respectively, and then the ethanol of the solvent evaporated and dried at room temperature for several tens of seconds, and the desired range of local contamination was completed.

In this way, after intentionally contaminating three points on the wafer surface with different contaminated areas, the iron concentration was measured at the three positions by the TXRF method. However, iron with a concentration of 8 × 10 ⁹ cm ^-2 was detected as intended. That is, by controlling the dropping volume, the target contaminated area (area) could be intentionally contaminated at the target concentration.

The present invention is not limited to the above embodiment. The above embodiment is an example, and any object having substantially the same structure as the technical idea described in the claims of the present invention and having the same effect and effect is the present invention. It is included in the technical scope of the invention.

Claims (3)

A method for intentionally contaminating a semiconductor wafer, in which a desired metal element is intentionally introduced into a predetermined region on the surface of the semiconductor wafer in order to evaluate the performance of the semiconductor wafer.
A solution obtained by diluting a standard solution containing a metal element with a solvent consisting of a volatile liquid is used as a contaminating solution, and a contaminated region is formed at a predetermined position on the surface of the semiconductor wafer by dropping it at a predetermined position .
Before performing the dropping, the relationship between the amount of the dropped solution of the contaminated solution and the diameter of the contaminated area is obtained in advance according to the contaminated solution to be used and the method of dropping, and the contamination is based on the relationship. A method for intentionally contaminating a semiconductor wafer , wherein the region diameter is controlled by the amount of the dropped solution . The method for intentionally contaminating a semiconductor wafer according to claim 1, wherein the solvent is alcohols. The method for intentionally contaminating a semiconductor wafer according to claim 2, wherein the alcohols are ethanol.

Images