JP3755586B2 - Silicon desorption method and silicon wafer impurity analysis method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for effectively desorbing silicon from a silicon-containing solution and a method for analyzing metal impurities on the surface of a silicon wafer (hereinafter sometimes simply referred to as a wafer), and in particular, prevents a decrease in analysis accuracy due to silicon. On how to do.
[0002]
[Related technologies]
In recent years, as semiconductor integration progresses, the degree of cleanliness required for the manufacturing process has become stricter. In particular, heavy metals such as Fe, Ni, and Cr have a great influence on the characteristics of semiconductors and cause defects such as leakage of pn junctions. In order not to deteriorate the electrical characteristics of semiconductor elements, these metal contamination It is important to suppress this. Therefore, a technique for accurately qualifying and quantifying the contamination on the wafer surface is required.
[0003]
The most commonly used method for measuring metal impurities present on the surface (surface layer) of a silicon wafer is to collect the metal impurities on the surface in a solution by vapor phase decomposition (VPD) and to collect the recovered liquid in an atom. It is a method of analyzing and quantifying by absorption spectrometry (AAS) or inductively coupled plasma mass spectrometry (ICP-MS).
[0004]
For example, an oxide is formed on the wafer surface, the oxide is exposed to HF vapor and decomposed, the decomposition solution is recovered, and the recovered decomposition solution is diluted with pure water or the like to obtain a sample solution for analysis. It has been known.
[0005]
Further, there is a method (Japanese Patent Laid-Open No. 2-28533, etc.) for directly collecting and analyzing metal impurities on the wafer surface without forming an oxide film. This is because a solution (corresponding to the decomposition solution in this specification) is dropped onto the wafer, and the wafer surface is uniformly scanned while tilting the wafer in various directions or applying a rotational motion. This is a method for collecting impurities.
[0006]
Furthermore, as shown in FIG. 7, ultra-high purity HF + HNO _Three A method of analyzing a silicon decomposition product by evaporating a decomposition solution such as a wafer to decompose the wafer surface has been used. This silicon decomposition product is a silicon wafer or bulk silicon and HF + HNO. _Three The reaction product produced | generated by reacting etc. means. Silicon wafer and bulk silicon and HF + HNO _Three The reaction with HNO is generally HNO _Three It is considered as a series of reactions in which a silicon wafer or bulk silicon is oxidized by HF and then decomposed with HF. In this specification, the product of this reaction is referred to as a silicon decomposition product, HF + HNO used in this reaction. _Three The solution is referred to as a decomposition solution, and such a process is referred to as a decomposition process or simply as a decomposition.
[0007]
In the method shown in FIG. 7, after the wafer preparation (step 100), the decomposition solution (HF or HF / HNO _Three The mixed acid solution is evaporated and exposed to the wafer surface to generate a silicon decomposition product (step 102a). Next, pure water or the like (recovered solution) is dropped on the wafer surface, and the generated silicon decomposition product (impurities are included). (Step 102b), and the collected solution is analyzed after the silicon desorption treatment (Step 102m) and then analyzed (Step 104) to analyze the contamination of the bulk region of the wafer surface layer with high sensitivity. Yes. In this method, the pretreatment process (step 102) is constituted by the decomposition process (step 102a), the recovery process (step 102b), and the silicon desorption process (102m).
[0008]
In addition, the wafer and the chemical solution are sealed in a synthetic resin bag, immersed in warm water, reacted with the wafer and the chemical solution, and elemental analysis of a part of the reaction solution is performed to analyze the impurities on the wafer surface. Methods are known. As shown in FIG. 8, after wafer preparation (step 100), dilute HF / HNO _Three The wafer is put in a bag containing the mixed acid solution and the step of boiling (step 102c) is performed, a part of the boiled solution is extracted (step 102d), and the extracted solution is analyzed after silicon desorption treatment (step 102m). (Step 104). In the method of FIG. 8, the pretreatment process (step 102) is constituted by the above-described decomposition process by boiling (step 102c), recovery process by extraction (step 102d), and silicon desorption process (step 102m).
[0009]
In addition, a method for directly decomposing bulk silicon with a strong acid vapor has been developed recently for analyzing bulk silicon other than the wafer surface, and a method for recovering (solid) decomposition products with pure water has been adopted. Yes. As shown in FIG. 9, fine bulk silicon produced by cleaving a wafer or the like is prepared (step 100), and then a decomposition solution (HF / HNO _Three The mixed acid solution) is evaporated to decompose the bulk silicon to generate a silicon decomposition product (step 102e). Next, a recovered liquid (pure water or the like) is dropped onto the silicon decomposition product, and the generated silicon decomposition product is removed. This is a method of collecting (step 102f), and analyzing the collected solution after removing the silicon (step 102m) (step 104). In the method of FIG. 9, the pretreatment process (step 102) is constituted by the decomposition process (step 102e), the recovery process (102f), and the silicon desorption process (step 102m).
[0010]
Thus, even for silicon wafers or bulk silicon, HF / HNO is basically used to obtain a sample for analysis. _Three The metal impurities are evaluated by a method in which the silicon decomposition product generated by the decomposition process is recovered, the resulting silicon decomposition product is recovered, and the recovered liquid is analyzed.
[0011]
[Problems to be solved by the invention]
When the silicon surface is decomposed by the conventional method as described above and the decomposition solution containing the silicon decomposition product is recovered, the recovered solution contains a large amount of silicon in addition to the metal impurities. Yes.
[0012]
When a solution containing a large amount of silicon is introduced into an analytical instrument, a ghost peak due to a silicon complex molecule appears at the peak position where the target element should appear, particularly in ICP-MS, etc. Depending on the rise of the detection limit, depending on the device, silicon may accumulate on the backbone of the device [solution introduction system (path) or analysis system (path)), and the analysis sensitivity may decrease over time. In particular, the deposition of silicon on the backbone of the device is a major problem. Therefore, as shown in the conventional methods of FIGS. 7 to 9, the silicon desorption treatment is usually performed before analysis.
[0013]
As a method for desorbing silicon, a method in which a strong oxidizing agent is added and heated and volatilized is known. Perchloric acid and aqua regia are used as strong oxidants. However, these strong oxidants are often affected by the contamination of the oxidant itself, and there is a problem that metal impurities cannot be analyzed with high sensitivity.
[0014]
The present invention has been made in view of the above-described problems. It is easy to remove silicon from a silicon-containing solution with low contamination before being put into an analytical instrument without being affected by impurity contamination caused by operation and chemical solution itself. It is an object of the present invention to provide an impurity analysis method for a silicon wafer which can be separated, and a silicon wafer impurity analysis method which can improve analysis sensitivity and perform highly sensitive and stable analysis by applying this silicon desorption method.
[0015]
[Means for Solving the Problems]
In order to solve the above problems, the silicon desorption method of the present invention is a method for desorbing silicon from a silicon-containing solution, wherein the silicon-containing solution and the desorption solution containing hydrogen fluoride water and nitric acid are the same. The silicon in the silicon-containing solution is desorbed by placing each solution in a sealed container and heating each solution for a predetermined time.
[0016]
By comprising in this way, the silicon | silicone can be efficiently removed from a silicon containing solution, and the sample for analysis with few silicon | silicones can be prepared. This is because when both solutions are kept heated in the same sealed container, HF / HNO in the silicon-containing solution _Three It is thought that this is because the silicon vapor reacts to produce silicofluoride, and this silicofluoride evaporates or sublimates when it is kept for a long time by heating and pressurization and desorbs from the solution, resulting in the removal of silicon. It is done. In particular, when the target of silicon desorption is a solution as in the present invention, since silicon is difficult to desorb, the silicon-containing solution and hydrogen fluoride water (HF) are treated in the same sealed container, and the silicon-containing solution itself Even heating is important.
[0017]
As the desorption solution, HF concentration of 15 to 35% by weight and HNO _Three Using a mixed acid prepared so that the concentration is 70 to 30% by weight and the sum of both does not exceed 100% by weight and the balance is water, each solution is heated at 100 to 150 ° C. for 2 to 24 hours. preferable.
[0018]
By performing the silicon desorption treatment as described above, it is possible to obtain a solution that does not contain silicon while keeping the metal impurities intact. Therefore, it is possible to prevent the occurrence of ghost peaks and the contamination of the apparatus at the time of analysis. Can be done.
[0019]
The method for analyzing impurities of a silicon wafer according to the present invention is a method for analyzing impurities on the surface of a silicon wafer, wherein the silicon wafer is exposed to a vapor of a decomposition solution containing hydrogen fluoride water and nitric acid. A silicon decomposition product is generated on the surface layer, and the silicon decomposition product is recovered by a recovery solution containing hydrogen fluoride water and hydrogen peroxide water to produce a silicon decomposition product-containing recovery solution. The contained recovery solution and the desorption solution containing hydrogen fluoride water and nitric acid are placed in the same sealed container, and each solution is heated for a predetermined time to desorb and desorb silicon from the silicon decomposition product-containing recovery solution. A silicon silicon decomposition product-containing recovery solution is prepared, the siliconized silicon decomposition product-containing recovery solution is evaporated to dryness, and the resulting residue is dissolved in dilute hydrogen fluoride water to obtain a sample. To prepare a liquid, in which so as to analyze the sample solution.
[0020]
The treatment for generating the silicon decomposition product is carried out by using, as the decomposition liquid, an HF concentration of 15 to 35% by weight and HNO. _Three Using a mixed acid prepared such that the concentration is 70 to 30% by weight and the sum of both does not exceed 100% by weight and the balance is water, the decomposition liquid is heated to 100 to 150 ° C. It is preferable to generate silicon decomposition products on the surface of the silicon wafer by exposing the silicon wafer for 10 minutes to 2 hours. The processing time is adjusted according to the depth of the surface layer to be analyzed.
[0021]
By the decomposition process, the oxide film and silicon on the wafer surface layer are decomposed. Metal impurities are present in the decomposed product. Thereby, the metal impurity which exists in the area | region of 1-10 micrometers of wafer surface layers can be analyzed. As a silicon decomposition product after treatment with such a decomposition solution (NH _Four ) ₂ SiF ₆ Etc. are formed.
[0022]
In addition, the silicon decomposition product generated on the wafer is recovered by exposing the wafer surface to the diluted HF / H after exposing the vapor of the decomposition solution to the wafer. ₂ O ₂ A recovery solution made of an aqueous solution is dropped, and the surface of the wafer is uniformly scanned and recovered, and then the recovery solution is recovered. As this recovery solution, in particular, the HF concentration is about 1.5 to 3.5% by weight, H ₂ O ₂ Is a dilute HF / H of about 0.5 to 2.5% by weight ₂ O ₂ It is preferable to use an aqueous solution because silicon decomposition products can be efficiently recovered from the wafer surface. That is, the silicon decomposition product can be easily recovered as compared with the conventional recovery using pure water.
[0023]
The desorption treatment of silicon is performed using the HF concentration of 15 to 35 wt% and HNO as the desorption solution. _Three Using a mixed acid prepared such that the concentration is 70 to 30% by weight and the sum of the two does not exceed 100% by weight and the balance is water, the above-described silicon decomposition product-containing recovery solution and desorption solution are the same. It is preferable to carry out by heating at 100 to 150 ° C. for 2 to 24 hours in a sealed container. The treatment time is appropriately adjusted depending on the amount of the silicon decomposition product-containing recovery solution.
[0024]
The solution recovered in this way (silicon-containing solution) is further subjected to silicon desorption treatment to eliminate the influence of silicon on the analysis, and the nitric acid component contained in the desiliconized silicon decomposition product-containing recovery solution from which this silicon has been desorbed By evaporating to dryness, metal impurities that do not contain silicon or extra substances are obtained in the residue.
[0025]
In order to analyze the metal impurities in the residue, the residue is dissolved with a treatment solution such as a dilute hydrofluoric acid solution of about 2 to 10% by weight to prepare a sample solution, and the prepared sample solution is analyzed. As this analysis method, AAS or ICP-MS may be used.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. 1 to 6 in the accompanying drawings. However, the illustrated examples are illustrative and various modifications can be made without departing from the technical idea of the present invention. Needless to say.
[0027]
FIG. 1 is a flowchart showing a process sequence of an impurity analysis method for a silicon wafer according to the present invention, and FIGS. 2 to 4 are cross-sectional views showing an example of a wafer processing apparatus used in the impurity analysis method for a silicon wafer according to the present invention and its usage. FIG. 2 is an embodiment of a method of exposing the decomposition solution vapor to the wafer, FIG. 3 is an embodiment of dropping the recovered solution onto the surface of the wafer on which the silicon decomposition product is formed on the surface, and FIG. One mode of recovering the recovered solution dropped on the surface is shown.
[0028]
As shown in the flowchart of FIG. 1, the wafer impurity analysis method of the present invention includes a step of preparing a wafer to be analyzed (step 100), a step of pre-processing this wafer (step 102), and a pre-processing. And a step of analyzing the sample solution obtained in the step (step 104).
[0029]
In the pretreatment step (step 102), the silicon wafer is decomposed into a decomposition solution (HF / HNO). _Three A decomposition treatment step (step 102a) in which a mixed acid solution) is exposed to steam generated by heating to generate a silicon decomposition product, and a recovered solution (HF / H) ₂ O ₂ A mixed aqueous solution) is dropped on the wafer surface to recover a silicon decomposition product (102b) and a silicon desorption process (102n).
[0030]
This decomposition process (step 102a) is performed using a wafer processing apparatus 10 as shown in FIG. The wafer processing apparatus 10 includes a container 16 provided with a hot plate 12 at the bottom and provided with an opening 14 that opens upward, and the opening 14 is closed so as to be openable and closable, and a peripheral male screw portion 17 of the container 16 has a peripheral edge. And a lid 19 that is detachably screwed through a female screw portion 18.
[0031]
Inside the container 16 is provided a wafer stage 20 on which the wafer W is placed on the upper surface. Reference numeral 21 denotes a decomposition liquid container, which is a decomposition liquid (HF / HNO _Three (Mixed acid solution) 22 is accommodated. The stored decomposition solution 22 is heated by the hot plate 12 to generate decomposition solution vapor 22a. The generated decomposition liquid vapor 22a comes into contact with the surface of the wafer W to generate a silicon decomposition product S (FIG. 3).
[0032]
In FIG. 2, 24 is a PTFE (polytetrafluoroethylene) seal provided on the upper surface of the peripheral male screw portion 17 of the container 16, and the peripheral female screw portion 18 of the lid 19 is the peripheral male screw portion. When screwed to the outer peripheral portion 17, the upper surface of the peripheral male screw portion 17 and the lower surface of the peripheral female screw portion 18 of the lid 19 are sealed. A gas vent 26 is attached to the lid 19 and is used when exhausting the decomposition liquid vapor inside the container 16 to the outside as necessary.
[0033]
The recovery process (102b) for recovering the silicon decomposition product S is performed with the lid 19 of the wafer processing apparatus 10 removed as shown in FIG. After the exposure to the decomposition liquid vapor 22a, while holding the silicon decomposition product S generated on the surface of the wafer W horizontally and holding it horizontally, as shown in FIG. Is dropped on the surface of the wafer W so that a droplet of the recovered solution 28 is formed on the surface of the wafer. The recovered solution 28 dropped at this time remains on the surface due to surface tension if the surface of the object to be measured is flat.
[0034]
The droplet 28 of the recovered solution is scanned in the surface of the wafer W, and the silicon decomposition product S is contained in the recovery solution 28 to obtain a silicon decomposition product-containing recovery solution 28S (FIG. 4). As shown in FIG. 4, when the silicon decomposition product-containing recovery solution 28S is collected using a clean instrument such as the recovery pipette 32, almost 100% of the droplets 28S of the silicon decomposition product-containing recovery solution can be collected. Conventionally, it has been difficult to collect droplets from a hydrophilic surface, but using this method, a sample can be collected efficiently regardless of hydrophilicity. Thereafter, a silicon desorption process is performed to analyze the metal impurities contained in the analyzer.
[0035]
Next, the operation of the decomposition liquid 22 will be described. As shown in FIG. 2, the decomposition liquid container 21 containing the decomposition liquid 22 is heated by heating means such as a heater (hot plate 12 in the illustrated example) to generate steam. If the substance to be decomposed is silicon, the decomposition solution is HNO. _Three After the surface is oxidized by, the oxide is decomposed by HF. Moreover, if the substance to be decomposed is silicon oxide, it can be decomposed only by HF.
[0036]
This decomposition liquid (HF / HNO _Three By changing the exposure time to the vapor 22a of the mixed acid solution), impurities can be extracted while controlling the etching amount of the wafer W, and the qualitative and quantitative determination of impurities from the surface of the wafer W to an arbitrary depth can be performed. HF used for the decomposition liquid 22 is preferably EL (electronic industry) grade 50 wt% HF, and HNO. _Three Is preferably 98% by weight of fuming nitric acid. HF / HNO _Three The mixing ratio of the mixed acid solution is not particularly limited, but 50 wt% HF and 98 wt% HNO. _Three 2: 1 or 1: 1 or 1: 2 mixed acid (HF concentration 15-35 wt% and HNO _Three A range of mixed acid prepared at a concentration of 70 to 30% by weight is preferable. In particular, those prepared in a ratio of 2: 1 or 1: 1 are suitable.
[0037]
The silicon decomposition product S decomposed by the decomposition liquid 22 is held on the surface of the wafer W (FIG. 3). The silicon decomposition product S is a solid film and is present on the surface of the wafer W. As shown in FIG. 3, the recovery solution 28 is dropped by a dropping pipette 30 or the like, and the silicon decomposition product S is recovered from the surface of the wafer W.
[0038]
The recovery solution 28 is HF / H. ₂ O ₂ Mixed aqueous solutions can be used, especially thin HF / H ₂ O ₂ A mixed aqueous solution is preferred. This thin HF / H ₂ O ₂ HF concentration in the mixed aqueous solution is about 1.5 to 3.5% by weight and H ₂ O ₂ What is necessary is just to set it as the solution in which a density | concentration is about 0.5 to 2.5 weight%. Specifically, 31 wt% H for 38 wt% HF 2 ml to 4 ml ₂ O ₂ Is preferably mixed in 1 ml to 4 ml and diluted to 50 ml with pure water.
[0039]
This concentration is the most hydrophobic with respect to the silicon decomposition product, and the amount of chemical used can be reduced. High purity HF and H ₂ O ₂ By using this in a low concentration state, it is possible to reduce the influence of contamination from the recovered solution (chemical solution) itself.
[0040]
HF / H used as a recovery solution in this way ₂ O ₂ Since the mixed aqueous solution is water-repellent with respect to the silicon decomposition product S, as shown in FIG. ₂ O ₂ The mixed aqueous solution becomes droplets 28 on the wafer W and, as shown in FIG. 4, after the silicon decomposition product S is recovered, it remains in the state of the droplets 28S and can be easily recovered by the recovery pipette 32 or the like.
[0041]
HF / H ₂ O ₂ Since the mixed aqueous solution has a scanning capability by a little self-reaction with the reaction with the silicon decomposition product S, the recovery operation of the silicon decomposition product S can be performed while uniformly scanning the wafer W. Can be recovered very easily. Since the scanning and recovery operations using the recovery solution 28 are simple, the influence of external contamination can be suppressed.
[0042]
When analysis of the wafer surface layer of 2 to 3 μm is performed, about 0.15 g of silicon is decomposed in an 8-inch wafer. When this total amount is contained in about 1 ml of the recovered solution 28, the silicon concentration is about 15% by weight, and the recovered solution (silicon decomposition product-containing recovered solution 28S) is a solution containing a large amount of silicon. .
[0043]
One of the eyes of the present invention is that the influence of silicon in the analysis of silicon decomposition products is achieved by efficiently desorbing a large amount of silicon contained in the silicon decomposition product-containing recovery solution 28S from the wafer described above. In the following, the silicon desorption process will be described with reference to FIGS. 5 and 6. FIG. FIG. 5 is an explanatory view schematically showing one aspect of the silicon desorption process in the silicon desorption method of the present invention, and FIG. 6 schematically shows one aspect of the metal impurity recovery step performed after the silicon desorption process of the present invention. It is explanatory drawing shown.
[0044]
As shown in FIG. 5, the silicon desorption method of the present invention includes a step of desorbing silicon from a silicon-containing solution, for example, a silicon decomposition product recovery solution (silicon-containing recovery solution) 28S. The step of desorbing silicon from the silicon-containing solution includes a silicon-containing recovery solution 28S placed in the container 60 and a desorbing solution 64 placed in the container 62, such as HF / HNO. _Three The mixed acid solution is placed in a sealed container 66 and each solution is heated by heaters 68 and 70 for a predetermined time. 5 shows an example in which the heaters 68 and 70 are disposed inside the sealed container 66, it goes without saying that these heaters 68 and 70 may be disposed outside the sealed container 66. Absent.
[0045]
The containers 60, 62 and 66 used for this treatment are preferably PTFE containers having chemical resistance and a certain degree of heat resistance. In order to efficiently react the desorbing solution 64 with a limited amount with the silicon-containing solution 28S, it is preferable to use a highly airtight container. Although the specific reaction mechanism of the silicon desorption action is unknown, it is considered that the desorption of silicon in the solution is promoted because the vapor pressure becomes high when heated in a highly sealed container for a long time. Further, in the sealed container 66, it is considered that the temperature difference is generated between the upper part and the lower part of the container, and the action that the evaporated solution is condensed again is repeated. It is considered one of the above. In view of the desorption of silicon and the pressure resistance of the container from the above points, it is preferable to heat at a temperature of about 100 to 150 ° C.
[0046]
The HF used in the desorption solution 64 for desorbing silicon is preferably EL (electronic industry) grade 50 wt% HF, and HNO. _Three Is preferably 98% by weight of fuming nitric acid. HF / HNO _Three The mixing ratio of the mixed acid solution is not particularly limited, but 50 wt% HF and 98 wt% HNO. _Three 2: 1 or 1: 1 or 1: 2 mixed acid (HF concentration 15-35 wt% and HNO _Three A range of mixed acid prepared at a concentration of 70 to 30% by weight is preferable. Especially HNO from the HF concentration in the desorption solution _Three A higher concentration is preferred, and a mixture of 1: 1 or 1: 2 is appropriate.
[0047]
Subsequently, the silicon-desorbed silicon decomposition product-containing recovery solution 28S from which the silicon has been desorbed. _M Thus, metal impurities to be analyzed are recovered. In this metal impurity recovery step, as shown in FIG. 6, the silicon-desorbed silicon decomposition product-containing recovery solution 28S placed in a container 72 (usually using the container 60 as it is) after the silicon desorption process. _M The residue 76 obtained by evaporating to dryness is heated by a heater 74 (usually using the heater 68 as it is), and the residue 76 obtained by evaporating to dryness is treated with a treatment liquid (diluted hydrogen fluoride water of about 2 to 10% by weight) 78. It is performed by dissolving and recovering in The treatment liquid 78 in which the residue 76 is dissolved becomes a sample solution 80 containing metal impurities. By analyzing the sample solution 80, the metal impurities in the residue can be analyzed.
[0048]
Although it was not possible to clearly confirm how much silicon was desorbed in the silicon desorption treatment, the solution was evaporated to dryness with and without the silicon desorption treatment, and the amount of residue was confirmed. . As a result, when the silicon desorption treatment was performed, almost no residue was confirmed, but when the silicon desorption treatment was not performed, a large amount of residue remained. This difference in residue is considered to be the elimination of silicon.
[0049]
【Example】
The present invention will be described more specifically with reference to the following examples. However, these examples are shown by way of illustration and should not be construed as limiting.
[0050]
Example 1
An 8-inch mirror-polished wafer (object to be measured) that had undergone a general silicon wafer manufacturing process was processed in a clean room using the processing apparatus shown in FIG. Decomposed liquid (HF / HNO) heated in a PTFE container with a heater held on the wafer stage with the surface facing up _Three ) Vapor for 20 minutes. The decomposition solution is 50% by weight HF: 98% by weight HNO. _Three Of mixed acid in a ratio of 1.3: 0.7 (specifically, 98 wt% HNO with respect to 1.3 ml of 50 wt% HF) _Three In a PTFE beaker and evaporated by heating with a heater. The heating temperature for decomposition (more precisely, the heater set temperature) is 150 ° C.
[0051]
After the exposure for a predetermined time, the recovered solution (HF / H) is held while the object to be measured (sample wafer) is held on the wafer stage. ₂ O ₂ Aqueous solution) was added dropwise with a 750 μl micropipette. The wafer stage can be held with a slight inclination by a PTFE holding table having a rotation mechanism, and the recovered solution is scanned over the entire surface of the sample wafer by moving the wafer stage. The recovered solution used in this example had an HF concentration of 3.2% by weight, H ₂ O ₂ A mixed solution having a concentration of 2.5% by weight was used.
[0052]
Thereafter, a recovered solution (sample solution) whose surface was covered with a micropipette was collected. The recovered solution was in the form of droplets and could be recovered easily.
[0053]
Next, silicon desorption treatment was performed. As a desorption step of the silicon desorption treatment from the recovery solution (silicon-containing solution), first, the recovery solution (silicon-containing solution) and 10 ml of HF / HNO _Three The solution was placed in a sealed container and each solution was heated for a predetermined time. HF / HNO _Three The solution was 5% 50% HF, 98% HNO. _Three This is a mixed solution of 5 ml of (fuming nitric acid). The heating temperature at this time may be 100 ° C. to 150 ° C. (set value of the heater). In this example, the temperature was 150 ° C. When sealed at such a temperature for a long time, it is held in a pressurized state in a sealed container. The holding time is about 10 to 18 hours, and silicon is completely detached by heating. In this example, it was performed in 12 hours.
[0054]
After the heating, as the impurity recovery step, the solution after the heat treatment was evaporated to dryness at 200 ° C., and the residue obtained by evaporation to dryness was recovered with 1 ml of the treatment liquid. The treatment liquid used was 9.5 wt% HF. That is, this residue was dissolved in dilute hydrofluoric acid to prepare an analytical solution containing no silicon. Although the metal impurities originally present in the sample wafer existed in the evaporated and dried residue, the amount of silicon was very small.
[0055]
Moreover, according to the method of the present invention, it can be carried out without using strong oxidizing agents such as perchloric acid and aqua regia that are easily contaminated with metal, so that it can be carried out without worrying about external contamination.
[0056]
The solution subjected to the silicon desorption treatment was measured by ICP-MS. The sample used for analysis is 1 ml. For ICP-MS, ELEMENT made by FinniganMAT was used. Hereinafter, this apparatus is referred to as HR-ICP-MS. HR stands for High Resolution.
[0057]
Representative metals Fe, Ni, and Cu were evaluated by HR-ICP-MS. As a result, Fe: 1 × 10 ¹² atoms / cm ^Three , Ni: 0.5 × 10 ¹² atoms / cm ^Three , Cu: 0.2 × 10 ¹² atoms / cm ^Three Met. In addition, light metals and heavy metals such as Mg, Al, V, Cr, Mn, and Zn were analyzed, but they could be analyzed with high sensitivity without being influenced by silicon. Repeatability was also sufficient.
[0058]
(Comparative Example 1)
Impurities were analyzed in the same procedure as in Example 1 except that the same sample wafer as in Example 1 was used and the silicon desorption treatment was not performed. As a result, the analysis system of HR-ICP-MS was clogged and could not be analyzed. In this comparative example, about 15% of silicon is contained, so that it is considered that it was more easily clogged.
[0059]
The HR-ICP-MS used in Example 1 and Comparative Example 1 has a desolvation system, and when HF is added to the analysis solution, it is not affected by silicon of about 700 ppm, but exceeded 1000 ppm. In the same manner as in Comparative Example 1, a phenomenon that silicon was clogged in the analysis system and the introduction system of the apparatus was observed. If a sample of about 1000 ppm is frequently analyzed, the analysis accuracy will deteriorate over time if it is repeatedly used. If the silicon desorption treatment of the present invention is performed and analyzed, such a change with time can be prevented and a long-term stable evaluation can be performed.
[0060]
In Example 1 above, an example in which the vapor phase decomposition method was used for the analysis of the wafer surface layer was shown. _Three Wafer and HF / HNO in addition to the solution decomposed and recovered by gas and vapor phase decomposition _Three The silicon desorption method of the present invention is effective for a solution containing a large amount of silicon, such as a solution obtained by sealing a chemical solution such as a plastic resin bag and immersing it in warm water to react the wafer with the chemical solution. .
[0061]
Further, the solution subjected to such silicon desorption treatment may be analyzed by an apparatus other than ICP-MS, for example, an analytical apparatus such as atomic absorption spectrometry.
[0062]
【The invention's effect】
As described above, according to the present invention, silicon can be easily desorbed from a silicon-containing solution with low contamination without being affected by impurity contamination caused by operation and the chemical solution itself. By applying the separation treatment to the impurity analysis of the silicon wafer, the analysis sensitivity can be improved, and a highly sensitive and stable impurity analysis can be performed.
[0063]
In addition, the silicon decomposition products formed on the wafer surface are converted into hydrogen fluoride water (HF) and hydrogen peroxide water (H ₂ O ₂ ), The metal impurities can be efficiently recovered from the wafer surface, improving the analysis accuracy.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a process sequence of a method for analyzing impurities of a silicon wafer according to the present invention.
FIG. 2 is a schematic cross-sectional explanatory view showing an example of a wafer processing apparatus used in the silicon wafer impurity analysis method of the present invention, showing an embodiment of a method for exposing a decomposition liquid vapor to the wafer.
FIG. 3 is a schematic cross-sectional view showing an example of a wafer processing apparatus used in the silicon wafer impurity analysis method of the present invention, in which a recovered solution is dropped onto the surface of a wafer on which a silicon decomposition product is formed on the surface layer. One aspect is shown.
FIG. 4 is a schematic sectional view showing an example of a wafer processing apparatus used in the method for analyzing impurities of a silicon wafer according to the present invention, showing an embodiment for recovering a recovery solution containing a silicon decomposition product.
FIG. 5 is an explanatory view schematically showing one embodiment of the silicon desorption method of the present invention.
FIG. 6 is an explanatory view schematically showing one embodiment of recovery of metal impurities in the residue.
FIG. 7 is a flowchart showing an example of a process sequence of a conventional impurity analysis method for a silicon wafer.
FIG. 8 is a flowchart showing another example of the process sequence of the conventional impurity analysis method for a silicon wafer.
FIG. 9 is a flowchart showing an example of the order of steps in a conventional bulk silicon impurity analysis method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10: Wafer processing apparatus, 12: Hot plate, 14: Opening part, 16: Container, 17: Peripheral external thread part, 18: Peripheral internal thread part, 19: Lid body, 20: Wafer stage, 21: Decomposition liquid storage part , 22: decomposition solution, 22a: decomposition solution vapor, 28S: recovery solution containing silicon decomposition products, 28S _M : Recovery solution containing silicon desorption silicon decomposition product, 30: Pipette for dropping, 32: Pipette for recovery, 60, 62, 72: Container, 64: Desorption solution, 66: Sealed container, 68, 70, 74: Heater 76: residue, 80: sample solution, S: silicon decomposition product, W: wafer.

Claims (6)

A method for desorbing silicon from a silicon-containing solution, wherein the silicon-containing solution and a desorbing solution containing hydrogen fluoride water and nitric acid are placed in the same sealed container, and the respective solutions are heated for a predetermined time. A method for desorbing silicon, comprising desorbing silicon in a contained solution. A mixed acid prepared with an HF concentration of 15 to 35% by weight and an HNO ₃ concentration of 70 to 30% by weight is used as the desorption solution, and each solution is heated at 100 to 150 ° C. for 2 to 24 hours. The silicon desorption method according to claim 1. A method for analyzing impurities on the surface of a silicon wafer, wherein the silicon wafer is exposed to vapor of a decomposition solution containing hydrogen fluoride water and nitric acid to generate a silicon decomposition product on the surface of the silicon wafer, A silicon decomposition product is recovered by a recovery solution containing hydrogen fluoride water and hydrogen peroxide water to prepare a silicon decomposition product-containing recovery solution, and the silicon decomposition product-containing recovery solution is combined with hydrogen fluoride water and nitric acid. The contained desorption solution is placed in the same sealed container, and each solution is heated for a predetermined time to desorb silicon in the silicon decomposition product-containing recovery solution to prepare a desiliconized silicon decomposition product-containing recovery solution. Evaporating the recovered solution containing the desiliconized silicon decomposition product to dryness, dissolving the obtained residue with dilute hydrogen fluoride water to prepare a sample solution, and analyzing the sample solution Impurity analysis method of a silicon wafer to be. As the decomposition liquid, a mixed acid prepared with an HF concentration of 15 to 35% by weight and an HNO ₃ concentration of 70 to 30% by weight is used. The decomposition liquid is heated to 100 to 150 ° C. 4. The silicon wafer impurity analysis method according to claim 3, wherein a silicon decomposition product is produced on the surface layer of the silicon wafer by exposure for minutes to 2 hours. A mixed acid prepared with an HF concentration of 15 to 35% by weight and an HNO ₃ concentration of 70 to 30% by weight is used as the desorption solution, and each solution is heated at 100 to 150 ° C. for 2 to 24 hours. The method for analyzing impurities of a silicon wafer according to claim 3 or 4. 6. The method for analyzing impurities of a silicon wafer according to claim 3, wherein the method for analyzing the sample solution is AAS or ICP-MS.

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