JP2917937B2 - Method for analyzing impurity concentration distribution of semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for analyzing impurity concentration distribution in a diffusion layer of a semiconductor device.

[0002]

2. Description of the Related Art Analysis of impurity concentration distribution in a diffusion layer of a semiconductor device is extremely important in manufacturing a high-performance semiconductor device. Conventionally, secondary ion mass spectrometry has been widely used as a method for analyzing the impurity concentration in a semiconductor. However, this method has insufficient resolution in the planar direction due to the restriction of the ion beam diameter, and is not suitable for analyzing a semiconductor device having a fine structure.

As a method applicable to the analysis of a semiconductor device having a fine structure, Japanese Patent Application Laid-Open No. Sho 59-31038 and Japanese Patent Application Laid-Open No. Hei 4-111337 disclose that a cross section of a sample is chemically etched and the etching rate varies depending on the impurity concentration. An analysis method for determining an impurity concentration by utilizing the above is disclosed. This is because, as shown in FIG. 2A, after the cross section of the analysis point of the device sample is exposed by cleavage or the like,
As shown in (b), the unevenness corresponding to the concentration is formed by etching, and the unevenness is observed by STM (scanning tunnel microscope) or SEM (scanning electron microscope).

[0004]

However, the above-mentioned method has room for improvement in the following points. First, the measurement accuracy is not always sufficient. The reason is that in the conventional method, the etching rate is calculated from the unevenness and the concentration distribution is calculated from the relationship between the concentration and the etching rate, which is obtained in advance.However, the etching rate varies greatly depending on the temperature and composition of the etching solution. To do
This is because reproducibility is low and accurate concentration quantification is difficult.
The second point is that it is difficult to evaluate a specific minute area. The reason is that the conventional method exposes the cross section of the sample by cleavage or the like, so that it is difficult to accurately expose the cross section of a specific minute region.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and accurately measure the impurity concentration distribution of a minute diffusion layer of a semiconductor device.

[0006]

According to the method of analyzing the impurity concentration distribution of a semiconductor device of the present invention, a first step of producing a dummy wafer having a region with a known impurity concentration distribution is provided, and one surface of the dummy wafer is provided. A second step of forming an etching-resistant thin film on the surface of the dummy wafer, and bonding the surface of the dummy wafer on which the etching-resistant thin film is formed and the surface of the analysis sample, and then mirror-polishing the side surface to obtain an impurity concentration in the dummy wafer. A third step of forming a cross section where the distribution is known and the analysis area in the analysis sample is exposed, and a fourth step of etching the cross section by an etching solution in which the etching rate of the semiconductor changes according to the impurity concentration. Measuring the unevenness of the cross section caused by the step and the fourth step to obtain an edge in the cross section of the dummy wafer and the analysis sample. And a sixth step of analyzing the concentration distribution of the analysis region from the relationship between the impurity concentration of the dummy wafer and the etching speed and the relationship between the impurity concentration and the etching speed of the dummy wafer determined in advance. And a step of: The method may further include, between the third step and the fourth step, a step of removing a portion damaged by mirror polishing with an ion beam. In the fifth step, the unevenness of the cross section caused by the etching is measured by a scanning probe microscope.

In the present invention, an analysis sample and an impurity concentration are determined in advance, and a dummy wafer is bonded and simultaneously etched. As a result, it is possible to take into account the influence of the composition and temperature of the etching solution on the etching rate, and it is possible to perform quantitative determination with higher precision than before.

Further, in the present invention, the side surface is mirror-polished to form a cross section in which the region in the dummy wafer where the impurity concentration distribution is known and the analysis region in the analysis sample are exposed. Thus, unlike the conventional method in which the cross section of the sample is exposed by cleavage, the cross section of a specific minute region can be accurately exposed.

In the present invention, after mirror polishing,
Perform ion etching. This makes it possible to remove the damaged layer of the crystal by polishing, suppress the occurrence of local abnormalities in the etching rate due to crystal defects, and improve the measurement accuracy.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An analysis sample according to the present invention is obtained by doping a semiconductor such as silicon, gallium arsenide, and indium phosphide with impurities. The impurities in the present invention include boron, arsenic, phosphorus and the like. A dummy wafer is a wafer having a region with a known impurity concentration distribution, and is used as a reference during etching. A sample made of the same kind of semiconductor material as the analysis sample is used.

Hereinafter, the method for analyzing impurity concentration distribution according to the present invention will be described with reference to FIG. 1 or FIG. First, a dummy wafer 4 is manufactured. The dummy wafer 4 is preferably a wafer having two or more epitaxial layers having different impurity concentrations or a wafer having an impurity concentration distribution in order to improve measurement accuracy. The dummy wafer is
It can be manufactured by an epitaxial method, an ion implantation method, or the like. In the case of the epitaxial method, a high-impurity-concentration layer and a low-concentration layer are formed on a substrate under a commonly used condition to form a dummy wafer. When the ion implantation method is used, a dummy wafer is formed by performing a heat treatment after ion implantation of impurities. An etching-resistant thin film 8 is formed on the surface of the dummy wafer. The etching-resistant thin film 8 serves to partition the analysis sample and the dummy wafer and to prevent etching from a surface other than the cross section 10 during etching. The material used for the etching resistant thin film 8 varies depending on the type of the etching solution. For example, when a mixed solution of hydrofluoric acid and nitric acid is used, a film formed by polymerizing a hydrocarbon gas by plasma and depositing at a low temperature is used. It is preferably used. This film has better etching resistance than an epoxy-based adhesive.

The dummy wafer 4 thus manufactured
, The impurity concentration distribution is determined by secondary ion mass spectrometry (SIMS) or the like, and the relationship between the impurity concentration and the etching rate is determined in advance. Then dummy wafer 4
The analysis sample 1 is bonded to the analysis sample 1 with the epoxy adhesive 9 in the arrangement shown in FIG. Analysis sample 1 and dummy wafer 4
Is only a few μm apart with the adhesive 9 interposed therebetween, so that etching unevenness during etching can be suppressed. Next, the bonded wafer is mirror-polished. As described above, in the conventional method, the cross section is formed by the cleavage plane. However, in the present invention, the cross section of the measurement target is exposed by polishing, and the impurity concentration distribution of the diffusion layer in a specific minute region can be measured. . Subsequently, the mirror-polished section is subjected to ion etching. Thereby, the damaged layer of the crystal due to the polishing is removed, and the local abnormality of the etching rate due to the crystal defect can be suppressed. As an ion etching method, a method using an argon ion beam is preferably used.

After preparing the sample as described above, chemical etching is performed using an etching solution. As the etchant, an etchant whose etching rate of a semiconductor changes according to the impurity concentration is used. The relationship between the etching rate and the impurity concentration is determined in advance. As the etching solution, for example, when the wafer is silicon, a mixed solution of hydrofluoric acid and nitric acid is used. The etching amount after completion of the etching can be measured by, for example, a scanning probe microscope. Among them, the measurement by an atomic force microscope (AFM) is preferable in terms of measurement sensitivity. The relationship between the impurity concentration and the etching rate of the dummy wafer determined by this measurement is
By correcting using the relationship between the impurity concentration of the dummy wafer and the etching rate, which has been obtained in advance, it is possible to take into account the influence of the composition and temperature of the etchant on the etching rate. The correction is specifically performed as follows. First, prior to the actual analysis, the relationship between the etching rate and the impurity concentration of the dummy wafer is obtained, and the relationship as shown in FIG. 3 is grasped. Next, the relationship between the etching rate of the dummy wafer and the impurity concentration in this analysis is determined. When this deviates from the relationship in FIG. 3, the etching rate is often a constant multiple of the etching rate shown in FIG. At this time, the relationship between the etching rate and the impurity concentration at the time of this analysis is corrected by multiplying the relational expression relating to the etching rate obtained from FIG. 3 by a constant. If the number does not become a constant,
The relationship between the impurity concentration and the etching rate is determined for several points of the dummy wafer in this analysis method, and the inclination is corrected. In this way, measurement errors due to fluctuations in etching conditions can be reduced, and measurement accuracy can be improved.

[0014]

【Example】

(Embodiment 1) Next, a first embodiment of the present invention will be described in detail with reference to the drawings. First, a dummy wafer 4 was manufactured. The dummy wafer 4 is manufactured using silicon, like the analysis sample 1. A high impurity concentration layer doped with a phosphorus concentration of 1 × 10 ¹⁸ cm ⁻³ is formed to a thickness of 0.2 μm on a silicon substrate by an epitaxial growth method, and a phosphorus concentration of 2 × 10 ¹⁷ cm ⁻³ is formed thereon. The impurity low concentration layer thus formed was formed to a thickness of 0.2 μm to obtain a dummy wafer. The dummy wafer 4 thus manufactured and the analysis sample 1 were bonded with the epoxy adhesive 9. FIG. 2 shows a cross-sectional structure. The dummy wafer 4 has epitaxial layers 6 and 7 having different phosphorus concentrations, and the surface is covered with an etching-resistant thin film 8. Next, after the cross section 10 of the analysis point is mirror-polished to a specific diffusion region, it is irradiated with argon ions of energy 2 keV at an incident angle of 10 degrees by an ion milling device (model 600, manufactured by GATAN) and damaged by mirror polishing. The layer was removed. A mixed solution of hydrofluoric acid and nitric acid (HF: HNO ₃ = 1: 200) whose etching rate changes depending on the phosphorus concentration is used.
Etching was performed. The liquid temperature was 7 ± 1 ° C. When the relationship between the phosphorus concentration of the phosphorus-containing silicon and the etching rate was confirmed, it became clear that the etching rate was proportional to the logarithm of the phosphorus concentration, as shown in FIG. Using this relationship, it is possible to calculate the phosphorus concentration by determining the etching rate of the analysis sample.

In the cross section of the analysis region after the etching, as shown in FIG. 4, the region of the diffusion layer 3 is deeply etched, and a step is formed between the high impurity concentration layer 6 and the low impurity concentration layer 7 of the dummy wafer 4. Been formed. The unevenness of the cross section after the etching was measured by AFM (atomic force microscope) or the like. The step between the high impurity concentration layer 6 and the low impurity concentration layer 7 is as follows.
It is expressed by (etching rate in high impurity concentration layer 6−etching rate in low impurity concentration layer 7) × (etching time). Therefore, by using the relationship between the phosphorus concentration and the etching rate of each section of the sections 6 and 7 in the dummy wafer 4, the relationship between the phosphorus concentration and the etching rate, which is obtained in advance, can be corrected. In this manner, analysis taking into account the etching conditions became possible, and the distribution of the phosphorus concentration could be analyzed with high accuracy.

(Embodiment 2) In a second embodiment of the present invention, a dummy wafer was manufactured by impurity ion implantation and annealing. A tilt angle of 7 degrees and an energy of 200 were implanted on a (001) plane silicon substrate by ion implantation.
After implanting phosphorus ions under the conditions of keV and a dose of 5 × 10 ¹³ cm ⁻² , the ion implantation is performed at 1000 ° C. for 60 hours in a nitrogen gas atmosphere.
Heat treated for minutes. The impurity concentration distribution of the dummy wafer thus obtained was measured by secondary ion mass spectrometry. The peak phosphorus concentration was of the order of 10 ¹⁸ cm ^-3 . Thereafter, the analysis was performed in the same manner as in Example 1. The cross section of the dummy wafer after the etching was different from Example 1 in that no step was formed and the cross section was curved. Using the relationship between the impurity concentration and the etching rate in each section of the dummy wafer cross section, errors caused by fluctuations in the etching conditions could be corrected, and the distribution of the impurity concentration could be analyzed with high accuracy.

[0017]

According to the analysis method of the present invention, since the analysis sample and the dummy wafer are simultaneously etched, errors caused by fluctuations in the etching conditions can be corrected, and the impurity concentration distribution of the diffusion layer can be accurately measured. Further, in the analysis method of the present invention, since the cross section is exposed by mirror polishing and ion milling, the analysis region can be accurately exposed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a sample used in an impurity concentration distribution analysis method of the present invention.

FIG. 2 is a cross-sectional view of a sample used in the impurity concentration distribution analysis method of the present invention.

FIG. 3 is a diagram showing a relationship between an impurity concentration and an etching rate.

FIG. 4 is a cross-sectional view of a sample after chemical etching.

FIG. 5 is a process sectional view of a conventional impurity concentration distribution analyzing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Analysis sample 2 Si substrate 3 Diffusion layer 4 Dummy wafer 5 Si substrate 6 High impurity concentration layer 7 Low impurity concentration layer 8 Etching resistant thin film 9 Adhesive 10 Sample section 11 Sample cleavage section

Claims (5)

(57) [Claims] A first step of forming a dummy wafer having a region with a known impurity concentration distribution; a second step of forming an etching-resistant thin film on one surface of the dummy wafer; After bonding the surface on which the etching-resistant thin film is formed and the surface of the analysis sample, the side surface is mirror-polished and the impurity concentration distribution in the dummy wafer and the cross-section where the analysis region in the analysis sample is exposed are exposed. A third step of forming; a fourth step of etching the cross section with an etchant in which an etching rate of a semiconductor changes according to an impurity concentration; and measuring unevenness of the cross section generated in the fourth step. A fifth step of obtaining an etching rate at the cross section of the dummy wafer and the analysis sample, and the fifth step obtained by the fifth step A sixth step of analyzing the concentration distribution of the analysis region from the relationship between the impurity concentration and the etching rate of the mee wafer and the relationship between the impurity concentration and the etching rate of the dummy wafer determined in advance. A method for analyzing impurity concentration distribution of a semiconductor device. 2. The method according to claim 1, further comprising a step of removing a portion damaged by the mirror polishing with an ion beam between the third step and the fourth step.
3. The method for analyzing an impurity concentration distribution of a semiconductor device according to item 1. 3. The method for analyzing an impurity concentration distribution of a semiconductor device according to claim 1, wherein in the fifth step, unevenness generated on the cross section is measured by a scanning probe microscope. 4. A method of manufacturing the dummy wafer by forming two or more epitaxial growth layers having different impurity concentrations on a semiconductor substrate, and measuring an impurity concentration of the two or more epitaxial growth layers. The method for analyzing an impurity concentration distribution of a semiconductor device according to claim 1. 5. The method according to claim 1, further comprising the steps of: performing a heat treatment after implanting ions into the semiconductor substrate to form the dummy wafer; and measuring impurity concentrations at a plurality of points in the dummy wafer. The method for analyzing an impurity concentration distribution of a semiconductor device according to any one of claims 1 to 3.