JPH10339691A - Method for measuring surface impurities - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extract contamination up to an arbitrary depth from the surface of an object while preventing contamination due to operation or a jig by dripping ultrapure water onto the surface of the object exposed to vapor of dissolution liquid thereby covering the entire surface with ultrapure water. SOLUTION: After being exposed to vapor of dissolution liquid, an object 1 is held horizontally while directing the surface upward and ultrapure water 6 is dripped thereon thus covering the entire surface with ultrapure water. If the surface of the object 1 is planar, the ultrapure water is settled o the surface through surface tension. When the liquid is sampled by means of a messpipette, the liquid droplet on the surface can be sample by substantially 100% regardless of hydrophobicity or hydrophilicity. When a sample stage 5 having a rotary mechanism is employed, the dissolution liquid touches only the object 1 and the messpipette 7 and contamination due to operation or a jig can be prevented. Furthermore, impurities can be extracted up to an arbitrary depth in a film while controlling the etching amount of the object 1 when HF and HNO3 or H2 O2 are employed as the dissolution liquid and the exposing time is varied respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for etching a material surface, particularly a semiconductor wafer from a surface to an arbitrary depth, and a measuring method for extracting, qualitatively and quantitatively, impurities on the surface.

[0002]

2. Description of the Related Art In recent years, as the integration of semiconductors progresses,
The degree of cleanliness required for the manufacturing process has become severe. In particular, heavy metals such as Fe, Ni, and Cr form levels in the band gap of Si and greatly affect the characteristics of the semiconductor. Alkali metals such as Na and K exist as ion carriers on the semiconductor surface. It is said that electrical leakage is caused, and it is important to suppress such metal contamination in order not to deteriorate the electrical characteristics of the semiconductor element. Therefore, a technique for accurately qualifying and quantifying wafer surface contamination is required.

Conventionally, a sampling method for extracting contamination in order to analyze a wafer surface for such a purpose (Japanese Patent Laid-Open No.
No. -28533), a solution is dropped on a wafer with respect to a hydrophobic surface, and the wafer is uniformly scanned while tilting the wafer in various directions or applying a rotating motion.
A method of collecting contamination from the whole wafer was used. For hydrophilic surfaces, an oxide film formed on the surface is dissolved in advance by exposing the surface to hydrofluoric acid vapor, and the surface is rendered hydrophobic. A method of collecting contamination by performing the same operation has been adopted. However, with the conventional method, it is difficult to control the amount of etching from the surface, and it is not possible to extract contamination to an arbitrary depth from the surface.

In the case where contamination is extracted from a thick oxide film which cannot be dissolved only by exposure to acid vapor,
Conventionally, a method of holding ultra-high-purity HF + HNO ₃ or HF + H ₂ O ₂ using a container such as Teflon or a jig as shown in FIG. 5 and dissolving the wafer surface coating has been adopted. The method had a problem of contamination from containers and jigs.

[0005]

SUMMARY OF THE INVENTION The present invention relates to an environment, a reagent,
It is an object of the present invention to provide a surface impurity measuring method for performing etching from a surface of an object to be measured to an arbitrary depth while preventing contamination from instruments and operations, and extracting contamination from the surface.

[0006]

The present invention has the following features to attain the above object. That is,
(1) After continuously exposing the surface of the device under test to HF vapor and HNO ₃ vapor or H ₂ O ₂ vapor to condense the vapor, ultrapure water is dropped on the surface of the device under test. After covering the entire surface of the object to be measured by dissolving the droplets condensed on the surface of the object to be measured in ultrapure water to form a sample solution, the sample solution is sampled from the surface of the object to be measured, and the sample solution is removed from the surface of the object to be measured. A surface impurity measuring method characterized by performing qualitative analysis and quantitative analysis of impurities contained in a film up to a depth, and (2) ultra-high-purity HF + HNO ₃ or HF + H ₂ O _{2 on the} surface of an object to be measured.
To cover the entire surface of the object to be measured, dissolve the surface coating of the object to be measured to form a sample solution, collect the sample solution, put it in a sample container, and put the sample container in a container having a suction and exhaust port,
A clean gas is sent from the inlet of the container, and the vapor is exhausted from the exhaust port to prevent contamination from outside while removing and concentrating the solvent of the sample solution, from the surface of the object to an arbitrary depth. And a qualitative analysis and a quantitative analysis of impurities contained in the film.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, an object to be measured is first exposed in a clean room to vapor generated by heating a surface solution as shown in FIG. After the steam exposure, a fixed amount of ultrapure water is dropped while keeping the object to be measured horizontal with the surface of the object facing up as shown in FIG. 2 so that the surface is completely covered with the ultrapure water. At this time, the ultrapure water dropped by the surface tension remains on the surface of the measured object if the surface is flat. When this liquid is collected using a device such as a pipette and clean compressed air as shown in FIG. 3, almost 100% of the surface droplets can be collected regardless of hydrophobicity or hydrophilicity. In the past, it was difficult to collect dew droplets from a hydrophilic surface, and it was necessary to first make the hydrophilic surface hydrophobic. Sample can be collected by the same method.

Further, in the present invention, when dropping ultrapure water and when collecting a sample solution, the workability is improved by using a sample holding table having a rotating mechanism as shown in FIG. Can be avoided.
In addition, it is characterized in that the sample can be collected without the dissolving solution coming into contact with the object to be measured and anything other than the pipette-shaped instrument and the sample container. By collecting the sample after completely covering the surface, contamination from the jig can be avoided.

Next, the operation of the solution will be described. At this time, if the object is silicon, the surface is oxidized by HNO ₃ or H ₂ O ₂ , and the oxide is dissolved by HF. In the case of silicon oxide, it is dissolved by HF. In any case, HNO ₃ or H ₂ O ₂ alone does not dissolve the surface. When only HNO ₃ is used as the solution, only the contamination adhering to the surface of the object to be measured is extracted. Table 1 summarizes the effect of each lysis solution on each surface.

[0010]

[Table 1]

After extracting impurities adhering to the surface of the object to be measured by using HNO ₃ as a dissolving solution, H
Impurities are extracted again using F and HNO ₃ or H ₂ O _2, and qualitative and quantitative determinations of the impurities are separately carried out, whereby impurities adhering to the surface of the object and the surface film of the object are measured. Qualitative and quantitative determinations can be made by separating impurities from the inside.

According to the present invention, HF, HN
O ₃ or H ₂ O ₂ is used singly or separately continuously, impurities are extracted while controlling the etching amount of the object by changing the respective exposure times, and arbitrary impurities are extracted from the surface of the object. The qualitative and quantitative determination of impurities in the coating up to the depth can be performed. When the object to be measured is a silicon oxide film, it is first exposed to HF vapor and then HNO ₃ or H
_In the method of exposing for ₂ hours to ₂ O ₂ vapor, the amount of etching can be controlled by the time of exposing to HF vapor. When the object to be measured is a silicon wafer, the surface is oxidized by exposure to HNO ₃ or H ₂ O ₂ vapor, and then HF is applied.
The amount of etching can be controlled by the exposure time of HF vapor by dissolving the oxide film by exposure to vapor.

Next, when extracting contamination from a thick oxide film which cannot be dissolved only by exposure to an acid vapor, conventionally, a container or a jig such as Teflon is used to extract ultra-high purity HF + HNO.
₃ or HF + H ₂ O ₂ is held, and a method of dissolving the film on the surface of the wafer is adopted here, and there has been a problem of contamination from containers and jigs. In the present invention, ultra-high purity HF + HN
A certain amount of O ₃ or HF + H ₂ O ₂ is dropped on the surface of the wafer to cover the surface of the object to be measured and dissolve the surface coating, and this is used as a sample solution. By extracting the surface contamination of the object to be measured into the sample solution, Contamination from a container such as Teflon or a jig can be prevented. Further, the sample container containing the collected sample solution is placed in a container having an intake / exhaust port, a clean gas is fed from the intake port of the container, and the vapor is exhausted from the exhaust port to prevent contamination from the outside. The solvent of the sample solution can be removed and concentrated. Here, as a container used when concentrating the sample solution, a glass container is suitable.

For example, when a sample solution is dropped directly into a graphite furnace to atomize impurities and analyzed by an atomic absorption apparatus, or a nebulizer for a micro sample (MCN: micro concentric nebule).
When analyzing with a sector type high-resolution inductively coupled plasma mass spectrometer (ICP-MS) using a sampler, a sample volume of about 50 to 100 microliters is sufficient. can do. In addition, a nebulizer for micro samples (MCN: micro co
When measuring with a sector-type, high-resolution inductively coupled plasma mass spectrometer (ICP-MS) without using an ncentric nebulizer, the concentrated sample is diluted with ultrapure water and measured, so that the acid Matrix effects can be avoided. Here, the matrix effect means that the background level increases.

[0015]

【Example】

Example 1 A sample 1 in which a TEOS film, which is a kind of an interlayer insulating film, was formed on a silicon wafer by a plasma CVD apparatus was held with vacuum tweezers 2 with the surface facing down as shown in FIG. It is exposed to the vapor of the first solution 4 (hydrofluoric acid) heated in the Teflon container 3 for the time shown in Table 2.

Immediately after this, the sample is exposed to the vapor of the second dissolving solution (nitric acid) heated in a Teflon container for 30 seconds while the sample is held with vacuum tweezers face down. Thereafter, the wafer is horizontally held with its surface facing upward on a Teflon sample holder 5 having a rotation mechanism as shown in FIG. 2, and 10 ml of ultrapure water 6 is dropped by a micropipette 7 here. To completely cover the surface.

Thereafter, an air gun 8 for supplying clean compressed air as shown in FIG. 3 was appropriately used, and the sample solution 10 whose surface was covered with the micropipette 9 again was collected while appropriately rotating the holding table. The weight change was measured before the exposure to the acid vapor and after the series of operations, and the relationship between the exposure to the hydrofluoric acid vapor and the time was examined. Table 2 shows the results.

[0018]

[Table 2]

As described above, the amount of etching can be controlled by controlling the hydrofluoric acid vapor exposure time. Further, when the Ca concentration of each of these sample solutions was measured by ICP-MS, the hydrofluoric acid vapor exposure time was 5 hours.
Seconds were measurable, but for 10 seconds and 30 seconds, the mass peak of SiO eluted from the measured object hindered, and the Ca peak of mass number 44 could not be measured. . From the above, the exposure time of hydrofluoric acid is optimally 5 seconds,
It turned out that 10 seconds and 30 seconds were too long. This embodiment corresponds to claim 1.

[Embodiment 2] TE which is a kind of interlayer insulating film
An OS film is formed on a silicon wafer by a plasma CVD apparatus, polished by a CMP process, and the cleaned sample 1 is held with vacuum tweezers 2 as shown in FIG. Is exposed for 30 seconds to the vapor of the dissolving solution 4 (nitric acid) heated in the container 3 made of acetic acid.
Next, the wafer is held horizontally with its surface facing upward on a Teflon sample holder 5 having a rotating mechanism as shown in FIG. 2, and 10 ml of ultrapure water 6 is dropped with a micropipette 7 here. Completely covered the surface.

Thereafter, an air gun 8 for supplying clean compressed air as shown in FIG. 3 is appropriately used, and the sample solution 10 whose surface is covered by a micropipette is again collected while rotating the holding table appropriately, and the first time. An impurity extract was used.

Next, the silicon wafer sample was directly used and exposed to a heated hydrofluoric acid vapor in another Teflon container for 7 seconds, followed by exposure to the nitric acid vapor for 30 seconds. Thereafter, the same operation of dropping and collecting ultrapure water as described above was repeated to obtain a second impurity extract. ICP was applied to these first and second impurity extracts, respectively.
Each concentration of Na, Al, K, Ca, and Fe was measured by -MS. The results were compared between the first time and the second time.
Shown in

[0023]

[Table 3]

On the other hand, the weight of the sample was measured before and after the impurity extraction operation, and the amount of etching by the operation was determined.
In the first impurity extraction operation, the etching amount was 0 mg,
In the second operation, it was 1.5 mg. Accordingly, in the first impurity extraction and quantification operation, the impurities attached to the surface of the object to be measured were determined, and in the second operation, the impurities to a depth of about 38 nm from the surface of the object to be measured were quantified. Can be separated and quantified, and N
It was found that impurities of a, Al and K were attached, but the inside of the surface coating was not contaminated.

On the other hand, as a comparative example, the first impurity extraction operation was performed on the same object as described above in the same manner as described above, and then the object was converted into hydrofluoric acid vapor in the second extraction operation. After the exposure for 30 seconds, the extraction operation was performed by exposing to a nitric acid vapor for 30 seconds, and the etching amount was 6.5 mg.
When the peak of mass number 44Ca was measured by ICP-MS, the TEOS film was etched and eluted and interfered with the peak of SiO.
Could not be measured. This embodiment corresponds to claim 1.

Example 3 A silicon wafer on which an oxide film having a thickness of 4000 angstroms was formed by plasma CVD was placed horizontally on a sample holder 5 having a rotating mechanism as shown in FIG. And use a clean pipette-like instrument 7 to apply 0.5 ml of ultra-high-purity hydrofluoric acid to the surface.
Then, a mixed acid of 4.5 ml of nitric acid and nitric acid was dropped, and the surface of the wafer was completely covered with the dropped liquid while appropriately using an air gun 8 for supplying clean compressed air as shown in FIG. Completely dissolved.

Next, while using the air gun 8 as appropriate and rotating the sample holder 5 appropriately, a dissolving solution 10 is collected using a pipette-like instrument 9 to obtain a sample solution, which is placed in a quartz beaker. And put the beaker in a heat-resistant glass container 14 having an inlet 11, an outlet 12, and a lid 13 as shown in FIG. 4, place the glass container on an infrared hot plate 15, and pass through a filter 17 with a compressor 16. By sending clean air from the air inlet, evaporation to dryness was performed while preventing intrusion of fine particles from the outside. 10 ml of ultrapure water and 30 microliters of ultrapure nitric acid were added to the beaker 18 to dissolve contaminant metals collected from wafers remaining in the beaker,
This was measured by ICP-MS.

As a comparative example, a solution 20 (ultra-high-purity nitric acid + hydrofluoric acid) was placed in a Teflon jig 19 as shown in FIG. It was dissolved, adjusted in the same manner as above, and quantified. Table 4 shows the results. As can be seen from the table, the influence of contamination due to the operation is smaller when measured by the method of the present invention than by the conventional method. This embodiment corresponds to claim 2.

[0029]

[Table 4]

[0030]

According to the present invention, it is possible to extract and qualitatively and quantitatively determine the contamination from the surface of the object to be measured to an arbitrary depth. Further, it is possible to extract and qualitatively and quantitatively contaminate a thick film that cannot be decomposed by steam alone.

[Brief description of the drawings]

FIG. 1A is a schematic view showing a step of exposing an object to be measured to vapor of a solution. (B) Drawing showing the surface of the measured object.

FIG. 2 is a schematic view showing a step of covering a surface of an object to be measured with a recovery liquid and incorporating impurities on the surface of the object into the recovery liquid to prepare a sample solution.

FIG. 3 is a schematic view showing a step of collecting a sample solution.

FIG. 4 is a schematic view showing a step of removing a solvent from a sample solution.

FIG. 5 (a) is a perspective view showing a Teflon jig conventionally used. (B) Sectional drawing of the same figure.

[Description of Signs] 1,21: DUT 2: Vacuum tweezers 3: Teflon container with heater 4,20: Dissolution solution 5: Sample holder with rotating mechanism 6: Ultrapure water 7,9: Female pipette 8 : Air gun 10: Sample solution covering the surface 11: Intake port 12: Exhaust port 13: Lid 14: Heat resistant glass container 15: Infrared hot plate 16: Compressor 17: Filter 18: Quartz beaker 19: Teflon jig

Claims (2)

[Claims] 1. The surface of an object to be measured is made of HF vapor and HNO ₃
After being individually and continuously exposed to vapor or H ₂ O ₂ vapor to condense the vapor, ultrapure water is dropped onto the surface of the object to be measured to cover the entire surface of the object to be measured, and After dew condensation is dissolved in ultrapure water to make a sample solution, the sample solution is collected from the surface of the object to be measured, and qualitative and quantitative analysis of impurities contained in the film from the surface of the object to an arbitrary depth A method for measuring surface impurities. 2. An ultra-high-purity HF + HNO is formed on the surface of an object to be measured.
₃ or HF + H ₂ O ₂ is dropped to cover the entire surface of the object to be measured, the surface coating of the object to be measured is dissolved to make a sample solution, the sample solution is collected and put into a sample container, and the sample container is suctioned and exhausted. After removing the solvent from the sample solution and concentrating it while preventing the contamination from the outside by putting clean gas into the container and sending out the vapor from the inlet of the container and exhausting the vapor from the exhaust port, the DUT A method for measuring surface impurities, comprising performing qualitative analysis and quantitative analysis of impurities contained in a film from a surface to an arbitrary depth.