JPH11287775A - Method and device for evaluating crystal defect - Google Patents

Abstract

PROBLEM TO BE SOLVED: To predict where defects exist and how many defects exist by applying laser beams to a sample by scanning and measuring the amount of current flowing to the solution between the sample and an electrode. SOLUTION: In a device, a solution 6 is poured into a cell 5 and an electrode 7 is provided. Then, laser beams 3 are applied to a sample (a semiconductor substrate) 8 from a laser light source 1 by scanning, thus measuring the value of current flowing to the solution 6 between a sample 8 and the electrode 7. More specifically, when the laser beams 3 are applied to the sample 8 and if there are many defects in the crystal of the sample 8, heat conduction is prevented 1, the surface of the sample 8 is deformed due to inflation caused by the temperature increase in an application region, and the amount of deformation depends on the defect density. On the contrary, when there are less defects, heat conduction is not prevented, so that the temperature increase in the application region of the laser beams 3 is small and hence the amount of deformation is small. The difference in the amount of deformation is captured as the change in the amount of current flowing among the electrode 7, the solution 6, and the sample 8, is measured by the current-measuring device of a workstation 10, and is displayed as the two-dimensional distribution of the defect density by an image-displaying device 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for analyzing a semiconductor device, and more particularly to a method and apparatus for evaluating a crystal defect.

[0002]

2. Description of the Related Art There is an ion implantation technique as a technique used in a semiconductor device manufacturing technique. The ion implantation technique is a technique of introducing a necessary impurity into a semiconductor substrate at a desired implantation amount and acceleration energy by ionizing an introduced impurity element, selecting the impurity element by a mass analyzer, and accelerating the element by electric field energy. After the ion implantation, a heat treatment is performed at a predetermined temperature and for a predetermined time to form an impurity distribution having a desired conductivity type and conductivity in the semiconductor device manufacturing technology. Defects (crystal defects) formed by the ion implantation and the subsequent heat treatment cause a serious problem of poor junction leakage of the semiconductor device. Therefore, it is necessary to evaluate the density and electrical characteristics of the defects caused by the ion implantation. is there.

[0003] Conventionally, as a method of evaluating the density of defects, usually, a light Jenkins etching, a Siltle etching, a seco (Se) are used.
cco) By using a wet etching method known as etching, defects are revealed as unevenness information on the sample surface, and the size and distribution (defect density) are measured.

Further, as a method of evaluating the implantation defect itself generated in the ion implantation layer, there is a transmission electron microscope. With this transmission electron microscopy, it is not possible to know where and how large an ion implantation defect exists. That is, when observing ion implantation defects by transmission electron microscopy, it is necessary to know in advance where and how many implantation defects exist. As a method therefor, when a semiconductor device is formed, it can be known from the electrical evaluation result.

[0005]

However, depending on the circuit configuration of the semiconductor device, it may not be possible to identify where the defect exists. In the case of a uniform sample surface on which no semiconductor device is formed, it is necessary to specify an ion implantation defect by some method. In this case, when the above-mentioned wet etching method is used, the defect is destroyed due to the appearance of the defect. In addition, the technique of revealing defects by wet etching may not be stable depending on the temperature of the etchant at the time of revealing and the brightness of the surroundings. In addition, due to the progress of miniaturization of semiconductor devices in recent years, defects are buried in the surface roughness of the wet etching in the wet etching, which makes it difficult to observe the defects.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide a method for knowing in advance where and how many defects, particularly ion implantation defects formed in a semiconductor manufacturing process, exist.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a crystal defect evaluation method for measuring the amount of current flowing in an aqueous solution between a sample and an electrode. This is a crystal defect evaluation method to be measured.

In the present invention, it is preferable to measure the amount of current while irradiating the sample with ultraviolet light. In the present invention, it is preferable to measure the amount of current while adjusting the temperature of the aqueous solution.

In the present invention, the current flowing between the sample and the electrode is preferably an alternating current.

In the present invention, the sample forms an anodic oxide film,
It is preferable that it has been removed.

[0011] The present invention is also a crystal defect evaluation apparatus for measuring the amount of current flowing in an aqueous solution between a sample and an electrode,
A cell in which an aqueous solution is placed, an electrode is installed, a power supply and a current measuring device connected to the electrode, a means for irradiating a sample with laser light while scanning, and a current value measured by the current measuring device are displayed. Means for evaluating a crystal defect.

In the present invention, it is preferable to have an ultraviolet light source. Further, in the present invention, it is preferable to have a means for adjusting the temperature of the aqueous solution.

The present invention is a crystal defect evaluation method and a crystal defect evaluation device as described above. H on the semiconductor substrate (sample)
Irradiation with e-Ne laser light increases the temperature of the semiconductor substrate surface. Therefore, the semiconductor substrate expands, and the surface of the semiconductor substrate deforms. The amount of deformation depends on the density of defects introduced into the semiconductor substrate. The reason for this is that if there are many defects in the crystal, heat conduction is hindered, and the temperature of the region irradiated with the laser light locally rises, so that the amount of deformation (increase in the thickness direction of the semiconductor substrate) is large. It is because it becomes. On the other hand, when the number of defects in the crystal is small, heat conduction is not hindered, so that the temperature of the region irradiated with the laser light is small, and the amount of deformation (increase in the length of the semiconductor substrate in the thickness direction) is small. The difference between these displacements is determined by the
It is captured as a change in the current flowing between the samples.

At this time, by scanning the laser beam, synchronizing it, and displaying the measured current value, the density can be displayed as a two-dimensional distribution. Further, depending on the type of defect, the electric resistance may be low only by irradiating the laser beam, and the measured current value may be displayed as a two-dimensional distribution of the density in the same manner.

Further, by irradiating the entire surface of the sample with a specific wavelength, for example, ultraviolet light, a change in the current value can be reduced by optically exciting crystal defects that cannot cause a change in current value only by scanning with laser light. And the distribution of crystal defects can be detected as a change in current value.

Further, by providing the cell temperature adjusting means, a crystal defect which cannot be caused to change its current value only by scanning with a laser beam can be caused to change its current value by performing appropriate temperature adjustment. The distribution of crystal defects can be detected as a change in current value.

Further, by performing a process in which the step of forming the anodic oxide film on the sample and the step of removing the anodic oxide film are combined, the crystallographically damaged aqueous solution and the crystal defect can be completely prevented. Existing samples can be scraped off. Thereafter, by performing measurement, even finer crystal defects can be detected. The anodic oxidation method described here is a method of forming a high-quality anodic oxide film at room temperature in an aqueous solution, and can form an oxide film without thermally affecting a sample.

Further, the dielectric characteristics of a defect can be measured by measuring the impedance of the defect using an alternating current.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A crystal defect evaluation apparatus according to a first embodiment of the present invention will be described.

In FIG. 1, 1 is a laser light source, 2 is a mirror, 3 is a laser beam, 4 is a sample holder, 5 is a cell (aqueous solution container), 6 is an aqueous solution, 7 is an electrode, 8 is a sample, and 9 is a sample stage. Reference numeral 10 denotes a workstation, and 11 denotes an image display device. Here, a silicon substrate (p-Si (100) 10 to 15 Ω · c on which a thermal oxide film having a thickness of 100 nm is formed is used.
m) P (phosphorus) ion implantation from above (acceleration energy: 1
50 keV, injection amount: 3 × 10 ¹⁵ cm ⁻² ), and 95
A sample subjected to a short-time heat treatment at 0 ° C. for 10 seconds was used. Here, the workstation 10 includes a power supply and a current measuring device.

The fact that a crystal defect can be detected according to the first embodiment of the present invention will be described with reference to FIGS. In FIG. 2, 21 is a laser beam, 22 is an upper electrode, 23
Denotes an upper wiring, 24 denotes a sample, 25 denotes a lower wiring, 26 denotes an auxiliary line for explaining a current flow, 27 denotes a current measuring device, and 28 denotes a current source. FIG. 2 is a diagram illustrating that a current flows along an auxiliary line 26 indicating a current flow to a current source 28, an upper wiring 23, an upper electrode 22, an aqueous solution, a sample 24, a lower wiring 25, and a current measuring device 27. It is.

In FIG. 2, from the aqueous solution to the sample 24,
This indicates that a current flows through a point irradiated with the laser light 21. Although there is a current flow from a portion not irradiated with the laser, here, the specified current flow from a point specified by the laser light is indicated. As shown in FIG. 2, when no crystal defect was contained, even when the current was measured while scanning the laser beam over the entire surface of the sample, the current value did not change and was almost constant at 10 ⁻¹¹ A.

The aqueous solution used here is a 0.1% acetic acid solution that slightly generates electric conductivity, but any other aqueous solution may be used as long as it has electric conductivity.

In FIG. 3, 31 is a laser beam, 32 is an upper electrode, 33 is an upper wiring, 34 is a sample, 35 is a lower wiring, 36 is an auxiliary line for explaining a current flow, 37 is a current measuring device, and 38 is a current measuring device. A current source, 39 indicates a defect, and 40 indicates a current flow to the displacement of the sample surface caused by irradiating the laser beam. FIG. 3 shows that an electric current flows from the aqueous solution to the sample 34 via a point irradiated with the laser beam 31. In the case where a defect is included as shown in FIG. 3, when the defect 39 is irradiated with a laser beam, the temperature near the defect becomes higher than when there is no crystal defect due to poor heat conduction near the defect, The volume expansion near the defect increases, causing displacement. As a result, the electric resistance increases and the current value decreases.

FIG. 4 shows an example of the result of measuring the crystal defect distribution by the crystal defect evaluation apparatus according to the first embodiment of the present invention. As described above, the current decreases in the primary implanted defect (defect formed immediately after ion implantation) composed of minute point defects. In addition, an implanted secondary defect (a relatively large defect formed by further performing a heat treatment after performing ion implantation) simply has a low electric resistance when the implanted secondary defect is pointed by a laser beam. The current will increase. Therefore, FIG.
In the figure, primary implanted defects are distributed on the order of 10 ^-12 , and secondary implanted defects are distributed on the order of 10 ^-9 . In addition, the distribution of the injected secondary defects is displayed on the image display device 11 in FIG.
FIG. 4 shows a result of processing the distribution of the injected secondary defects. As described above, according to the present invention, it is possible to display the scale and the number of defects (ion implantation defects).

A description will be given of a crystal defect evaluation apparatus according to a second embodiment of the present invention. In FIG. 5, 41 is a laser light source, 42 is a mirror, 43 is a laser beam, 44 is a sample holder, 45 is a cell (aqueous solution container), 46 is an aqueous solution,
47 is an electrode, 48 is a sample, 49 is a sample stage, 50 is a workstation, 51 is an image display device, and 52 is an ultraviolet light source (high-pressure mercury lamp / wavelength 365 nm). Sample 48
Used was the same as in the first embodiment. The reason why a crystal defect can be detected by the second embodiment of the present invention is substantially the same as that described with reference to FIGS. 2 and 3 in the first embodiment of the present invention.

FIG. 6 shows an example of the result of measuring the crystal defect distribution by the crystal defect evaluation apparatus according to the second embodiment of the present invention. In the second embodiment of the present invention, since the implantation secondary defect where a relatively large current is flowing is measured while irradiating with an ultraviolet light source (high-pressure mercury lamp / wavelength 365 nm) 52, the first The defect can be detected with higher sensitivity than in the embodiment.

A description will be given of a crystal defect evaluation apparatus according to a third embodiment of the present invention. In FIG. 7, 61 is a laser light source, 62 is a mirror, 63 is a laser beam, 64 is a sample holder, 65 is a cell (aqueous solution container), 66 is an aqueous solution,
67 is an electrode, 68 is a sample, 69 is a sample stage, 70 is a work station, 71 is an image display device, and 72 is a temperature control device. A sample 68 similar to that of the first embodiment was used. The reason why a crystal defect can be detected by the third embodiment of the present invention is almost the same as that described with reference to FIGS. 2 and 3 in the first embodiment of the present invention.

FIG. 8 shows an example in which the crystal defect distribution is measured by the crystal defect evaluation apparatus according to the third embodiment of the present invention. In the third embodiment of the present invention, since the implantation secondary defect where a relatively large current is flowing is measured while maintaining the sample temperature at 60 ° C. by the temperature controller 72,
Defects can be detected with higher sensitivity than in the first embodiment.

FIG. 9 is a schematic structural view of a reaction cell used for forming an anodic oxide film in the fourth embodiment of the present invention. In FIG. 9, 81 is a cell (container), 82 is an electrolytic solution, 83 is an anode (sample), 84 is a cathode (platinum), 85 is an ammeter, 86 is a voltmeter, and 87 is a constant voltage constant current source.
As shown in FIG. 9, the sample to be the anode 83 was placed in the electrolytic solution 82. Electrolyte 82 used was N- methylacetamide _{(CH 3 CONHCH 3 / 300cc)} + potassium nitrate (KNO ₃ /0.6g)+ water (H ₂ O / 2cc) from consisting mixture. Anodization was performed under a constant current condition of a current density of 7 mA / cm ² . Cathode-anode voltage rise 200V
In this case, an anodic oxide film having a thickness of about 100 nm was formed.
The anodic oxide film was coated with an HF / NH ₄ F mixed solution (HF / NH ₄ F =
1:10). At this time, the thickness is about 50n
The m silicon substrate receded. This step will be described with reference to FIG. Reference numeral 91 in FIG. 10 indicates a defect existing in the cross section of the semiconductor device. Reference numeral 92 denotes an anodic oxide film formed by using the apparatus shown in FIG. Numeral 93 indicates that the silicon substrate surface receded by removing the anodic oxide film 92. As the silicon substrate recedes, a defective portion comes out on the surface of the sample, so that a defect inside the silicon substrate forming the semiconductor device is detected with high sensitivity.

FIG. 11 shows an example of the result of measuring the crystal defect distribution by the crystal defect evaluation apparatus according to the fourth embodiment of the present invention. In the fourth embodiment of the present invention, since the silicon layer between the defect and the sample surface is removed, more defects can be detected with higher sensitivity than in the first embodiment.

FIG. 12 shows a fifth embodiment of the present invention. Further, a cell having a cathode and an anode, an aqueous solution filled in the cell, an alternating current is applied using a power supply and a current measuring device connected between the cathode and the anode, and the impedance is measured. This allows the dielectric properties of the defect to be measured.

A description will be given of a crystal defect evaluation apparatus according to a fifth embodiment of the present invention. 12, 101 is a laser light source, 102 is a mirror, 103 is a laser beam,
104 is a sample holder, 105 is a cell (aqueous solution container), 1
Reference numeral 06 denotes an aqueous solution, 107 denotes an electrode, 108 denotes a sample, 109 denotes a sample stage, 110 denotes a work station, and 111 denotes an image display device. The sample 108 used was the same as that used in the first embodiment. Here, workstation 1
10 includes an AC power supply and an AC current measuring device. In addition, here, the laser beam having a radius of 1 mm
The current flowing from the tinged portion has a frequency f = 200
In the case of kHz, it is 2.6 (nA).

I = 2πfc · V = 2πf · 4πε _r ε
₀ (s / d) · V = 2.6 (nA) f = 200 kHz, ε _r = 11.9 (silicon), ε ₀ =
8.854 × 10 ⁻¹² (F / m), s = π (1 × 1
0 ⁻⁶ ) ² (m ² ), d = 1 × 10 ⁻⁶ (m) As described above, in the order of nA, the first to fourth values are used.
The defect can be detected as in the embodiment. Book 5
In the embodiment, the AC frequency is set to 200 kHz, but by changing the frequency, other additional information about the defect can be obtained.

Although the present invention has been described as an ion implantation defect as a whole, it goes without saying that a crystal defect caused by metal contamination, volume film stress and a heat treatment step can be detected.

In the present invention, the case where laser light is used has been described. However, not only laser light but also light of a confocal optical system can be used.

[0037]

As described above, according to the present invention, a crystal defect can be detected with a simpler method with higher sensitivity than ever before, which leads to evaluation and improvement of a semiconductor manufacturing process.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a crystal defect evaluation apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the principle of the crystal defect evaluation method of the present invention (when there is a defect).

FIG. 3 is a diagram showing the principle of the crystal defect evaluation method of the present invention (when there is no defect).

FIG. 4 is a diagram showing a measurement result obtained by the crystal defect evaluation device according to the first embodiment of the present invention.

FIG. 5 is a structural diagram of a crystal defect evaluation apparatus according to a second embodiment of the present invention.

FIG. 6 is a diagram showing measurement results obtained by a crystal defect evaluation device according to a second embodiment of the present invention.

FIG. 7 is a structural diagram of a crystal defect evaluation apparatus according to a third embodiment of the present invention.

FIG. 8 is a diagram showing measurement results obtained by a crystal defect evaluation device according to a third embodiment of the present invention.

FIG. 9 is a structural diagram of an anodic oxide film forming apparatus according to a fourth embodiment of the present invention.

FIG. 10 is an explanatory view of a process of forming and removing an anodic oxide film according to a fourth embodiment of the present invention.

FIG. 11 is a diagram showing measurement results obtained by a crystal defect evaluation device according to a fourth embodiment of the present invention.

FIG. 12 is a structural diagram of a crystal defect evaluation apparatus according to a fifth embodiment of the present invention.

FIG. 13 is a diagram showing measurement results obtained by a crystal defect evaluation device according to a fifth embodiment of the present invention.

[Explanation of symbols]

 1, 41, 61, 101 Laser light source 3, 21, 31, 43, 63, 103 Laser light 4, 44, 64, 104 Sample holder 5, 45, 65, 105 Cell (aqueous solution container) 6, 46, 66, 106 Aqueous solution 7, 47, 67, 107 Electrode 8, 24, 34, 48, 68, 108 Sample 10, 50, 70, 110 Workstation 11, 51, 71 Image display device 27, 37, 111 Current measurement device 28, 38 Current Source 39 Defect 52 UV light source 72 Temperature controller

Claims (8)

[Claims] 1. A crystal defect evaluation method for measuring an amount of current flowing in an aqueous solution between a sample and an electrode, the method comprising irradiating the sample with a laser beam while scanning the same to measure the amount of current. . 2. The method according to claim 1, wherein the amount of current is measured while irradiating the sample with ultraviolet light. 3. The crystal defect evaluation method according to claim 1, wherein the amount of current is measured while adjusting the temperature of the aqueous solution. 4. The method according to claim 1, wherein the current flowing between the sample and the electrode is an alternating current. 5. The crystal defect evaluation method according to claim 1, wherein the sample has an anodic oxide film formed and removed. 6. A crystal defect evaluation apparatus for measuring an amount of current flowing in an aqueous solution between a sample and an electrode, comprising: a cell in which the aqueous solution is contained, an electrode is provided; a power supply connected to the electrode; An apparatus for evaluating a crystal defect, comprising: an apparatus; means for irradiating a sample with laser light while scanning; and means for displaying a current value measured by the current measuring apparatus. 7. The crystal defect evaluation apparatus according to claim 6, further comprising an ultraviolet light source. 8. The crystal defect evaluation apparatus according to claim 6, further comprising a temperature adjusting unit for the aqueous solution.