JP2004200314A - Method of manufacturing semiconductor wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain pollutant metals contained in a polishing slurry from being introduced into an SC-1 cleaning solution, and to specify the relation between the pollutant metal content of the SC-1 cleaning solution and the metal content inside a semiconductor wafer so as to improve the semicoductor wafer in quality and a semiconductor devices manufactured using the same in yield. <P>SOLUTION: An HF cleaning process of cleaning the semiconductor wafer with HF and an SC-1 (a mixture of NH<SB>4</SB>OH, H<SB>2</SB>O<SB>2</SB>and water) cleaning process of cleaning the semiconductor wafer with SC-1 are carried out after a polishing process of polishing the semiconductor wafer with the polishing slurry. The semiconductor wafer is cleaned with the SC-1 cleaning solution whose pollutant metal content is 50 ppt or below so as to set pollutant metals contained in the semiconductor wafer and separated out on its surface are set smaller than 10<SP>9</SP>atoms/cm<SP>2</SP>. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor wafer including a step of cleaning a surface of a semiconductor wafer such as a silicon wafer.
[0002]
[Prior art]
One of the steps for finally manufacturing a mirror-finished silicon wafer from a silicon ingot is a chamfering step. In the chamfering step, the end surface is mirror-polished using a polishing member such as a cloth or a buff while supplying polishing slurry to the end surface of the silicon wafer. Generally, a polishing slurry is obtained by dispersing silica (SiO ₂ ) particles (abrasive particles) having a particle size of about 50 to 100 nm in a colloidal form in an aqueous alkaline solution such as NaOH or KOH having a pH of about 10 to 11. Things.
[0003]
After the chamfering step, an SC-1 cleaning step is performed. In the SC-1 cleaning step,
Contaminants such as particles, organic matter, and metal impurities attached to the surface of the silicon wafer are removed by the chemical action of the SC-1 cleaning solution. The SC-1 cleaning was performed by mixing ammonia (NH ₄ OH), aqueous hydrogen peroxide (H ₂ O ₂ ), and water (H ₂ O) in a volume ratio of 1: 1 to 2: 7. This is a cleaning method in which a silicon wafer is immersed in a cleaning liquid at a temperature of approximately 70 to 90 ° C. for approximately 10 to 20 minutes to clean, and is particularly effective in removing adhered particles (fine particles).
[0004]
Note that a polishing step is performed after the SC-1 cleaning step. In the polishing step, a mount plate made of ceramic or the like is attached to the silicon wafer, and the mount plate is fixed to a polishing apparatus, and the surface of the silicon wafer is polished to a mirror surface.
[0005]
By the way, the polishing slurry contains a contaminant metal. Types of contaminant metals include copper (Cu), nickel (Ni), chromium (Cr), and iron (Fe). Contaminant metals such as copper and nickel enter as impurities from the outside in the process of producing silica particles from natural quartz.
[0006]
When a silicon wafer is polished using a polishing slurry containing such a contaminant metal, the contaminant metal diffuses into the bulk of the silicon wafer during polishing, thereby deteriorating the quality of the silicon wafer. When a semiconductor device is manufactured using such a deteriorated silicon wafer, the yield of the semiconductor device is adversely affected. Among the contaminating metals, copper, in particular, has the highest moving speed in the silicon wafer, and thus quickly penetrates deeply into the silicon wafer during the polishing process, and has a serious adverse effect on the yield of semiconductor devices.
[0007]
Therefore, a method of reducing the concentration of the contaminant metal in the polishing slurry to such a level as not to adversely affect the yield of the semiconductor device has been conventionally considered.
[0008]
As a method of reducing the concentration of the contaminant metal in the polishing slurry, it is conceivable to remove the contaminant metal by spending time and cost on a purification step in the polishing slurry manufacturing process. Certainly, the more time and cost is required for refining, the lower the concentration of contaminant metals such as copper is, but the work efficiency is poor and not practical.
[0009]
(Prior art 1)
Therefore, Patent Document 1 (Japanese Patent Application Laid-Open No. H11-186201) discloses that the concentration of copper and nickel in a polishing slurry is kept within a range of 0.01 to 1 ppb by a cation exchange resin, and the amount of an aqueous sodium hydroxide solution is adjusted. An invention is disclosed in which the pH of a polishing slurry is adjusted to be 11 or less to reduce the amount of copper and nickel contaminated in a silicon wafer during polishing.
[0010]
In the process of producing the SC-1 cleaning liquid, a contaminant metal such as copper may enter the liquid from the outside. When the SC-1 cleaning liquid is repeatedly used for cleaning, a contaminant metal such as copper may enter the liquid from the outside due to contact with jigs and the like. Types of contaminant metals include copper (Cu), nickel (Ni), chromium (Cr), and iron (Fe).
[0011]
(Prior art 2)
Here, when the SC-1 cleaning solution contains a contaminated metal, it has been conventionally known that the contaminated metal in an amount corresponding to the amount of the contaminated metal adheres to the surface of the silicon wafer immediately after cleaning. For example, this is described in the literature (Ryuta et. Al. Jpn. J. Appl. Pyys. 31 (1992) p2338).
[0012]
The contaminant metal adhering to the surface of the silicon wafer immediately after the SC-1 cleaning can be easily removed by cleaning or polishing again thereafter.
[0013]
As mentioned above,
1) The contaminant metal diffuses into the silicon wafer during polishing by the polishing slurry.
[0014]
2) Contaminated metal adheres to the surface of the silicon wafer by cleaning with the SC-1 cleaning solution.
[0015]
This is already known, and its countermeasures are already known.
[0016]
[Problems to be solved by the invention]
However, when the present inventors conducted experiments,
a) When SC-1 cleaning is performed using an SC-1 cleaning solution containing a contaminant metal, not only the contaminant metal adheres to the surface of the silicon wafer during the cleaning, but also a part of the contaminant metal adhered to the surface. Have found that they diffuse into the silicon wafer (in the bulk) and degrade the quality of the silicon wafer.
[0017]
b) In addition, the contaminated metal in the polishing slurry was carried into the SC-1 cleaning liquid while being attached to the surface of the silicon wafer, and it was discovered that most of the contamination was caused by the SC-1 cleaning liquid.
[0018]
The contaminated metal in the polishing slurry brought into the SC-1 cleaning liquid is diffused into the silicon wafer by performing the SC-1 cleaning, and the contaminated metal diffused inside the wafer is subjected to the above-described re-cleaning and the like. Even if implemented, it cannot be easily removed.
[0019]
When a semiconductor device is manufactured using a silicon wafer in which a contaminant metal is diffused inside, the yield of the semiconductor device is adversely affected. Among the contaminating metals, copper, in particular, has the highest diffusion rate in the silicon wafer, so that it quickly penetrates deeply into the silicon wafer during cleaning, and becomes extremely difficult to remove even if re-cleaning is performed immediately after cleaning. For this reason, a large amount of copper is contained in the mirror-finished silicon wafer manufactured through the final process, and when a semiconductor device is manufactured using this mirror-finished silicon wafer, the yield of the semiconductor device is greatly affected. For example, if a silicon wafer is cleaned using an SC-1 cleaning solution containing copper at a concentration exceeding 50 ppt, the amount of copper contamination (atoms / cm ² ) diffused into the silicon wafer is less than 10 ⁹ atoms / cm ² . Also shows a large value, which has a serious adverse effect on the yield of semiconductor devices. Here, the contamination amount (atoms / cm ² ) is evaluated by the number of atoms per unit area of the contaminant metal deposited on the surface of the cleaned silicon wafer when the silicon wafer is stored for a long time (for example, three months). is there.
[0020]
SUMMARY OF THE INVENTION The first solution of the present invention is to improve the quality of a semiconductor wafer and to improve the yield of semiconductor devices manufactured by using the SC-1 cleaning liquid by preventing the contamination metal in the polishing slurry from being introduced. It is an issue. Further, the present invention clarifies the relationship between the concentration of the contaminating metal in the SC-1 cleaning solution and the amount of metal contamination inside the semiconductor wafer, which was not previously known, and improves the quality of the semiconductor wafer using these relationships. A second object of the present invention is to improve the yield of semiconductor devices manufactured by using this.
[0021]
Means and effects for solving the problem
The first invention is
A polishing step of polishing a semiconductor wafer using a polishing slurry, and a semiconductor wafer manufacturing method including a step of cleaning the polished semiconductor wafer using a cleaning liquid,
After the polishing step,
An HF cleaning step of HF cleaning the semiconductor wafer;
And an SC-1 cleaning step of SC-1 cleaning the semiconductor wafer.
[0022]
The second invention is
A polishing step of polishing a semiconductor wafer using a polishing slurry, and a semiconductor wafer manufacturing method including a step of cleaning the polished semiconductor wafer using a cleaning liquid,
After the polishing step,
An HF cleaning step of HF cleaning the semiconductor wafer;
The semiconductor wafer is subjected to an SC-1 cleaning step of performing SC-1 cleaning using an SC-1 cleaning liquid having a contaminant metal concentration of 50 ppt or less.
[0023]
A third invention is the second invention,
The SC-1 cleaning solution is characterized by being changed in cycles where the concentration of the contaminant metal does not reach 50 ppt.
[0024]
According to the first invention, the second invention, and the third invention, the contaminated metal in the polishing slurry adhered to the surface of the semiconductor wafer in the polishing step is washed away by the HF cleaning liquid that does not affect the metal contamination of the semiconductor wafer. Therefore, the amount of contaminated metals brought into the SC-1 cleaning liquid can be reduced.
[0025]
Further, when the SC-1 cleaning solution itself is contaminated with a contaminant metal, if the SC-1 cleaning solution is replaced before reaching 50 ppt, metal contamination of the semiconductor wafer due to the SC-1 cleaning solution adversely affects the device yield. Can be maintained at a level that does not give
[0026]
The fourth invention is
In a method for manufacturing a semiconductor wafer including a step of cleaning the semiconductor wafer using an SC-1 cleaning solution,
The semiconductor wafer is cleaned using an SC-1 cleaning liquid having a concentration of the contaminant metal of 50 ppt or less so that the contaminant metal inside the semiconductor wafer is deposited at a surface of 10 ⁹ atoms / cm ² or less when deposited on the surface. And
[0027]
According to the fourth invention, as shown in FIG. 1, when the semiconductor wafer is cleaned using the SC-1 cleaning solution having a contaminant metal concentration of 50 ppt or less, when the contaminant metal inside the semiconductor wafer is deposited on the surface. The concentration is 10 ⁹ atoms / cm ² or less, and the contamination level which does not adversely affect the yield of semiconductor devices can be suppressed.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments will be described below with reference to the drawings. In the present embodiment, a silicon (Si) wafer is assumed as the semiconductor wafer, but the embodiments described below are also applicable to gallium arsenide wafers other than silicon wafers. In the present embodiment, copper (Cu) is assumed as the contaminant metal, but the present invention is also applicable to contaminant metals other than copper, such as nickel (Ni), chromium (Cr), and iron (Fe). In particular, nickel has a high diffusion rate in a silicon wafer like copper, and thus can be treated in the same manner as copper in the following embodiments.
[0029]
The manufacturing process of the silicon wafer of the present embodiment includes the following steps.
[0030]
(Chamfering process)
In this chamfering step, the end face is mirror-polished using a polishing member such as a cloth or buff while supplying polishing slurry to the end face of the silicon wafer. The polishing slurry is obtained by dispersing silica (SiO ₂ ) particles (abrasive particles) having a particle size of about 50 to 100 nm in a colloidal state in an aqueous alkaline solution such as NaOH or KOH having a pH of about 10 to 11.
[0031]
(HF cleaning step)
In the HF cleaning step, the silicon wafer is cleaned by immersing the silicon wafer in a DHF solution composed of, for example, a 1% hydrofluoric acid aqueous solution at room temperature for several tens of seconds.
[0032]
(SC-1 washing step)
In the SC-1 cleaning step, ammonia (NH ₄ OH), hydrogen peroxide solution (H ₂ O ₂ ), and water (H ₂ O) were mixed at a volume mixing ratio of 1: 1 to 2: 7. (1) The silicon wafer is immersed in the cleaning solution at a temperature of approximately 70 to 90 ° C. for approximately 10 to 20 minutes to clean the silicon wafer. Here, in the SC-1 cleaning step, the SC-1 cleaning is performed using an SC-1 cleaning liquid in which the concentration of copper in the liquid is 50 ppt or less. The SC-1 cleaning solution is replaced in a cycle in which the concentration of copper in the solution does not reach 50 ppt.
[0033]
One cycle of the chamfering step, the HF cleaning step, and the SC-1 cleaning step is defined as one batch.
[0034]
Note that a polishing step is performed after the SC-1 cleaning step. In the polishing step, the silicon wafer is attached to a mount plate made of ceramic or the like, the mount plate is fixed to a polishing device, and the surface of the silicon wafer is polished to a mirror surface.
[0035]
Next, the effects of the silicon wafer manufacturing method including the above-described steps will be described with reference to FIGS.
[0036]
2 to 5 show the experimental results when the HF cleaning solution and the SC-1 cleaning solution were not replaced.
[0037]
FIG. 2 shows the relationship between the number of batches (0 batches, 24 batches) and the concentration (ppt) of copper (Cu) in the HF cleaning solution. As shown in FIG. 2, it can be seen that as the number of batches increases, the concentration (ppt) of copper (Cu) in the HF cleaning solution increases. This is considered to be due to the fact that the copper in the polishing slurry adhered to the surface of the silicon wafer in the chamfering step was washed away in the solution by HF cleaning, and the copper concentration in the HF cleaning solution increased with the number of batches. .
[0038]
FIG. 3 shows the relationship between the number of batches (0 batches, 24 batches) and the concentration (ppt) of copper (Cu) in the SC-1 cleaning solution. However, this is a case where the SC-1 cleaning liquid is 54 liters. As shown in FIG. 3, as the number of batches increases, the concentration (ppt) of copper (Cu) in the SC-1 cleaning solution increases. This is because the copper in the polishing slurry adhered to the surface of the silicon wafer by the HF cleaning is washed away in the HF cleaning liquid, but the copper in the polishing slurry that cannot be removed by the HF cleaning is brought into the SC-1 cleaning liquid, and the batch is removed. It is considered that the copper concentration in the SC-1 cleaning solution increased as the number increased.
[0039]
From FIG. 3, a trial calculation of the amount of copper brought in per batch is as follows.
[0040]
Since the SC-1 cleaning solution is 54 liters and the copper concentration of the SC-1 cleaning solution is already 42.10 ppt in the case of 0 batch and the copper concentration of the SC-1 cleaning solution in the case of 24 batches is 165.54 ppt,
54 × 10 ³ (g) × (165.54-42.10) × 10 ⁻⁹ ÷ 24 (batch) = 0.278 (mg) / batch.
[0041]
FIG. 4 is an experimental result showing that copper in the polishing slurry and copper in the SC-1 cleaning solution affect copper contamination of the silicon wafer.
[0042]
The experimental results on the left in FIG. 4 show the amount of copper contamination LN1 on the surface of the silicon wafer and the amount of copper contamination inside the silicon wafer when the chamfering process, the HF cleaning process, and the SC-1 cleaning process were performed in one batch and 24 batches. LN2 is shown. In addition, the experimental result on the right in FIG.
The copper contamination amount LN3 on the surface of the silicon wafer and the copper contamination amount LN4 inside the silicon wafer when the HF cleaning step and the SC-1 cleaning step are performed in one batch and 24 batches without performing the chamfering step are shown. In the case of the right side in FIG. 4, a “Cu-less silicon wafer” in which copper inside the silicon wafer was almost completely deposited on the surface and copper on the surface was removed by etching was used.
[0043]
Here, the copper contamination amount on the silicon wafer surface indicates the copper contamination amount on the wafer surface in terms of area density (atoms / cm ² ). The copper contamination inside the silicon wafer indicates the amount of copper contamination when the copper inside the wafer is deposited on the wafer surface, in terms of area density (atoms / cm ² ).
[0044]
As shown in FIG. 4, when the chamfering step is performed (left in FIG. 4), the silicon wafer in the initial batch (one batch) is compared with the case where the chamfering step is not performed (right in FIG. 4). The copper contamination amount shows a high value both on the wafer surface and inside the wafer (LN1 and LN2 show higher values than LN3 and LN4, respectively). This indicates that the polishing slurry containing copper is adhered to the silicon wafer during the chamfering process, so that both the wafer surface and the inside of the silicon are contaminated with copper. That is, in the initial batch, it is considered that copper in the polishing slurry used in the chamfering step affects copper contamination of the silicon wafer.
[0045]
In the 24 batches, when the chamfering step was not performed (right in FIG. 4), the silicon wafer was made of copper on both the wafer surface and silicon inside to the same level as when the chamfering step was performed (left in FIG. 4). Contaminated. This is considered that the copper concentration in the SC-1 cleaning solution increased due to the increase in the number of batches, and the copper contamination of the SC-1 cleaning solution itself affected the copper contamination of the silicon wafer.
[0046]
The experimental results on the left in FIG. 5 show the amount of copper contamination LN5 on the surface of the silicon wafer and the amount of copper contamination inside the silicon wafer when only one batch and 24 batches of HF cleaning were performed using the above-mentioned Cu-less silicon wafer. LN6 is shown. The experimental results on the right side of the drawing in FIG. 5 show the amount of copper contamination LN7 on the surface of the silicon wafer and the copper inside the silicon wafer when only one batch of SC-1 cleaning and 24 batches were performed using a Cu-less silicon wafer. This shows the contamination amount LN8.
[0047]
Although the amount of copper contamination of the HF cleaning solution itself increases with the number of batches as described above with reference to FIG. 2, the experimental results on the left side of FIG. 5 show that the copper contamination of the HF cleaning solution itself affects the copper contamination of the silicon wafer. Is not affected. On the other hand, as already described with reference to FIG. 3, the amount of copper contamination of the SC-1 cleaning solution itself increases as the number of batches increases, and the experimental results on the right in FIG. It can be seen that the increase in the amount of copper contamination with the increase in the amount of copper affects the copper contamination of the silicon wafer.
[0048]
From the above experimental results, copper in the polishing slurry in the chamfering step was prevented from being brought into the SC-1 cleaning solution, and when the SC-1 cleaning solution was contaminated with copper, copper contamination of the SC-1 cleaning solution itself was reduced. Removal is important in preventing copper contamination of silicon wafers.
[0049]
In the present embodiment, the copper in the polishing slurry adhered to the surface of the silicon wafer in the chamfering step is washed away by the HF cleaning liquid that does not affect the copper contamination of the silicon wafer (see the experimental result on the left side of FIG. 5). Copper introduced into the SC-1 cleaning solution can be reduced. Moreover, the HF cleaning solution itself does not need to be replaced frequently.
[0050]
In addition, when the silicon wafer is cleaned using an SC-1 cleaning solution having a copper contamination concentration of 50 ppt or less in the solution, and the SC-1 cleaning solution itself is contaminated with copper, the copper contamination concentration in the solution is reduced to 50 ppt. Since the SC-1 cleaning solution is replaced at the stage, copper contamination of the silicon wafer by the SC-1 cleaning solution can be prevented.
[0051]
FIG. 1 shows the relationship between the copper concentration (ppt) in the SC-1 cleaning solution and the copper contamination amount (atoms / cm ² ) of the silicon wafer.
[0052]
In FIG. 1, the characteristic L1 (the point plotted with a circle) indicates that the copper that had diffused inside when the silicon wafer cleaned using the SC-1 cleaning liquid was stored for a long time (for example, three months) was on the wafer surface. The figure shows the amount of contamination (atoms / cm ² ). That is, the characteristic L1 indicates the amount of copper contamination diffused into the inside of the silicon wafer.
[0053]
Further, in FIG. 1, the characteristic L2 (the point plotted with a cross) is the amount of copper contamination (not entering the wafer) adhered to the surface of the silicon wafer immediately after cleaning with the SC-1 cleaning solution ( atoms / cm ² ).
[0054]
As shown by the characteristic L1 in FIG. 1, as the copper concentration (ppt) in the SC-1 cleaning solution increases, the amount of copper contamination (atoms / cm ² ) diffused into the inside of the silicon wafer increases. However, when the concentration of copper in the SC-1 cleaning solution is set to 50 ppt or less, the amount of copper contamination diffused into the silicon wafer can be suppressed to 10 ⁹ atoms / cm ² or less. When the concentration of copper in the SC-1 cleaning solution is set to 50 ppt or less, the amount of copper contamination adhering to the silicon wafer surface can be suppressed to 10 ¹⁰ atoms / cm ² or less. Here, the contamination amount of 10 ⁹ to 10 ¹⁰ atoms / cm ² is considered to be a threshold value of the contamination level that adversely affects the yield of the semiconductor device.
[0055]
Therefore, when a silicon wafer is cleaned using an SC-1 cleaning solution having a copper concentration of 50 ppt or less, the amount of copper contaminant that diffuses into the inside of the silicon wafer, that is, the amount of copper contaminant when it is deposited on the surface, is 10 ^9. A contamination level of atoms / cm ² or less, that is, a contamination level that does not adversely affect the yield of semiconductor devices can be suppressed.
[0056]
In the present embodiment, SC-1 cleaning is performed using an SC-1 cleaning liquid having a copper concentration of 50 ppt or less, and the SC-1 cleaning liquid is replaced in a cycle in which the copper concentration does not reach 50 ppt. As a result, copper contamination inside the silicon wafer can be suppressed to a level that does not adversely affect the device yield.
[0057]
In the embodiment, copper is not brought into the SC-1 cleaning solution by HF cleaning, but the following process may be performed instead of the HF cleaning process as a reference example.
[0058]
(Ultrasonic cleaning process)
In this ultrasonic cleaning step, after chamfering, the surface of the silicon wafer is cleaned by ultrasonic waves to remove copper from the wafer surface.
[0059]
The ultrasonic cleaning step may be performed in combination with the HF cleaning step.
[0060]
Although the embodiment has been described on the assumption that the SC-1 cleaning solution is used, the cleaning is performed using an SC-2 cleaning solution obtained by mixing hydrochloric acid, hydrogen peroxide solution, and water instead of the SC-1 cleaning solution as a reference example. It may be performed.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the concentration (ppt) of copper (Cu) in an SC-1 cleaning solution and the amount of copper contamination (atoms / cm ² ) on the wafer surface.
FIG. 2 is a diagram showing the relationship between the number of batches (1 batch, 24 batches) and the copper concentration in the HF cleaning solution.
FIG. 3 is a diagram showing the relationship between the number of batches (1 batch, 24 batches) and the copper concentration in the SC-1 cleaning solution.
FIG. 4 is a diagram showing a relationship between the number of batches and the amount of copper contamination of a silicon wafer.
FIG. 5 is a diagram showing a relationship between the number of batches and the amount of copper contamination of a silicon wafer.

Claims (4)

A polishing step of polishing a semiconductor wafer using a polishing slurry, and a semiconductor wafer manufacturing method including a step of cleaning the polished semiconductor wafer using a cleaning liquid,
After the polishing step,
An HF cleaning step of HF cleaning the semiconductor wafer;
And a SC-1 cleaning step of SC-1 cleaning the semiconductor wafer. A polishing step of polishing a semiconductor wafer using a polishing slurry, and a semiconductor wafer manufacturing method including a step of cleaning the polished semiconductor wafer using a cleaning liquid,
After the polishing step,
An HF cleaning step of HF cleaning the semiconductor wafer;
An SC-1 cleaning step of cleaning the semiconductor wafer with an SC-1 cleaning solution having a contaminant metal concentration of 50 ppt or less. 3. The method according to claim 2, wherein the SC-1 cleaning liquid is replaced in a cycle in which the concentration of the contaminant metal does not reach 50 ppt. In a method for manufacturing a semiconductor wafer including a step of cleaning the semiconductor wafer using an SC-1 cleaning solution,
The semiconductor wafer is cleaned using an SC-1 cleaning liquid having a concentration of the contaminant metal of 50 ppt or less so that the contaminant metal inside the semiconductor wafer is deposited at a surface of 10 ⁹ atoms / cm ² or less when deposited on the surface. Semiconductor wafer manufacturing method.

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