JP2001041931A - Laser mass spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly cut a film down to the foreign matter on a semiconductor sample up to the position of the foreign matter and remove the film on the surface of the sample, when the foreign matter in the film or at the interface of the film is to be analyzed by observing a laser spot on the sample, every time the sample surface is cut by making a laser irradiation. SOLUTION: After a semiconductor wafer sample 4 is placed on a stage, the stage is moved to move the position of foreign matter below an objective lens 17. The focal point of a laser light is focused for correction by moving a collective lens 19. A carved depth Δz of the surface of the sample is obtained from a movement distance M.Δz of the collective lens 19, every time a pulse laser light is irradiated once. The cut depth per pulse can be adjusted, by adjusting the attenuation rate of an attenuation filter 13. The intensity of the laser light is set to be minimum at first, and then increased stepwise by each pulse. The intensity of the laser light is fixed, when the cut depth per pulse becomes approximately 1/10 the depth from a sample surface to the foreign matter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a memory, an ASIC, and the like.
This is a chemical analyzer for microscopic foreign matter and contaminated parts necessary for improving the yield of semiconductor devices such as LSIs, magnetic disk devices, and liquid crystals, especially for foreign matter present in the film, at the film interface, and in the deep groove. It is.

[0002]

2. Description of the Related Art In recent years, with the improvement in the degree of integration of semiconductor products and the like, even minute foreign matters or minute amounts of contaminants have caused defects. In order to improve the yield, it is necessary to analyze the size, composition, and components of these foreign substances and contaminants. As an elemental analysis method for inorganic fine foreign substances, SEM-
Although EDX and the like have been established, as a method for analyzing the molecular structure of organic minute foreign matter, development such as laser mass spectrometry is currently in progress.

[0003] An example of the prior art of a microscopic laser mass spectrometer is described in JP-A-63-146339. FIG.
Fig. 1 shows the configuration of a conventional device. The laser light emitted from the laser light source 11 is focused and irradiated on the sample 4 by the objective lens 17. By this irradiation, molecules and fragments are desorbed and ionized from the sample 4. The generated ions are accelerated by the electric field generated by the ion extraction electrode 21 and are reflected by the ion reflector 23.
After being reflected by the light, the light enters the ion detector 24. The ion reflector 23 reduces variations in flight time due to a difference in initial velocity of ions emitted from the sample. The energy of the ions accelerated by the electric field is constant regardless of the mass of the ions. Therefore, ions having a larger mass have a lower velocity and a longer time to fly a certain distance. From this, the mass of the ions can be determined by measuring the difference between the time when the sample 4 is irradiated with the laser light and the time when the ions enter the detector 24.

[0006] Foreign matter which causes a defect in a semiconductor element adheres not only to the surface of a sample but also to a film or a film interface. In the above-mentioned conventional technology, it is necessary to remove the film on the surface in order to quickly analyze these foreign substances. For this reason, FIB has hitherto been used, but this has a problem that the sample is deteriorated and the original analysis information of the foreign matter is lost. On the other hand, in a laser mass spectrometry system, the sample surface is shaved by laser irradiation, so that foreign matter can be exposed by irradiating a laser beam with an appropriate intensity. In addition, the laser light has little deterioration of the sample such as FIB.

However, the above-mentioned prior art does not mention a method of removing a surface layer by a laser beam. Also,
In order to quickly perform such foreign substance analysis at a manufacturing site, it is necessary to automate the analysis work. However, the above-mentioned conventional technology does not mention any specific means for automation.

[0006]

In order to analyze foreign matter in the film of a semiconductor sample or at the film interface, it is necessary to remove the film on the surface and confirm that the surface has been cut to the depth of the foreign matter. Further, when trying to cut the sample surface by laser irradiation, it is necessary to irradiate a laser beam having an appropriate intensity in accordance with the depth at which a foreign substance exists. However, since the absorption rate and the boiling point of the laser light differ depending on the sample, setting the laser light intensity is not easy. Furthermore, the above-mentioned conventional apparatus does not describe automation of an analysis operation. If the analysis operation takes a long time, there are problems that the feedback of the analysis data to the manufacturing site is delayed and that an operator of the apparatus is always required.

A first object of the present invention is to establish a method for accurately removing a film on a foreign substance to the position of the foreign substance as a substitute for FIB when analyzing a foreign substance in a film or a film interface by a laser mass spectrometer. It is in.

[0008] A second object is to simplify the operation of setting the laser beam irradiation conditions optimally.

A third object is to automate the operation related to measurement in order to speed up and simplify the analysis work.

[0010]

For the above-mentioned first object, every time the surface of the sample is cut by irradiating a laser beam, the depth of the cut is confirmed by observing a laser spot on the sample. It is like that.

For the second object, a variable filter for changing the intensity of the laser light is provided, and the intensity of the laser light is increased step by step with each irradiation of the laser light pulse.
The analysis is performed when the intensity reaches a predetermined level.

For the third purpose, measurement positioning,
Focusing, laser beam intensity setting, laser beam irradiation, and data acquisition are performed according to a sequence.

That is, the operation of the present invention will be described with reference to FIG. FIG. 1A shows a cross section of a semiconductor wafer sample, where F1, F2, and F3 are films, and P is a foreign substance.
(B) shows a state in which the sample stage is moved to move a foreign substance near the laser beam. Here, L1 and L2 are two laser beams condensed by the objective lens, but at the stage (b), the focal points of both are made to coincide. (C) shows a state where the stage height is adjusted and the laser beams L1 and L2 are focused on the foreign matter. FIG. 2 shows a focusing method.
(A) and (b) are an image of a laser spot observed by a camera and a light intensity distribution obtained by image analysis in a state where the foreign matter is not focused and a state where the foreign matter is focused, respectively. The focus is determined by confirming that the peak height h is maximum or the peak width w is minimum.

FIG. 1D shows a state where the focal point of the laser beam L1 has been moved upward from the state of FIG. This operation is performed not by moving the sample stage but by moving the laser optical system. Figure 3 shows the method.
It was shown to. 12 is a continuous wave laser light source, 13 is a continuously variable attenuation filter, 19 is a condenser lens, 18 is a collimator lens, 17 is an objective lens, 4 is a sample, and F is a focal point.
The focal point F is transferred to the focal point on the sample 4 by the two lenses 17 and 18. The vertical magnification of this optical system is set to M. Sample 4
When the focal length on the side moves by Δz, the position of the focal point F on the opposite side moves by M · Δz. The moving distance of the focal point F is equal to the moving distance of the condenser lens 19. Therefore, FIG.
By measuring the moving distance of the condenser lens 19 from FIG. 1 to FIG. 1D, the film thickness Δz on the foreign matter P can be obtained.

Incidentally, to confirm that the laser light L1 is focused on the sample surface as shown in FIG. 1D, the following is performed. Light reflection occurs at the interface between the film F1 / F2 and the surface of the sample, similarly to the surface of the foreign matter. That is, the surface of the foreign matter, F1
At the three points of the / F2 interface and the sample surface, a phenomenon in which the laser spot diameter becomes extremely small as shown in FIG. 2B is observed. Therefore, when the focal point of the laser beam is scanned from the back of the sample toward the sample surface, the position where this phenomenon first appears is a foreign substance,
The position that appears last may be determined as the sample surface.

FIG. 1 (e) shows a state where the same position as the laser beam L1 is irradiated with a pulsed laser beam to cut the sample surface. FIG. 1F shows a state in which the laser beam L1 is refocused on the bottom of the laser irradiation mark. In this state, the surface of the sample is shaved by irradiating pulse laser light again. FIG. 1 (g) shows a state in which this operation is repeated and the laser irradiation mark reaches the foreign matter. The determination of this state is performed after confirming that the focal points of the laser beams L1 and L2 match. In this state, ions are generated from the foreign matter by irradiation with a pulse laser beam, and the ions are taken into a mass spectrometer to obtain a mass spectrum.

By the way, as shown in FIG. 1 (g), in order for the irradiation mark to accurately reach the foreign matter depth, it is necessary to set the depth to be cut per pulse of the pulsed laser light to an optimum value. In the present invention, refocusing of the laser light L1 is performed by moving the condenser lens 19 of FIG. Therefore, each time the pulsed laser light is irradiated once, the condenser lens 1
From the moving distance M · Δz of No. 9, the depth Δ
z was determined. Adjustment of the shaving depth per pulse can be made by adjusting the attenuation rate of the attenuation filter 13. Initially, the laser beam intensity is minimized, and the intensity is increased stepwise for each pulse.
When the shaved depth per pulse reaches about one-tenth of the depth from the sample surface to the foreign matter, the laser beam intensity may be fixed.

As described above, when mass spectrometry is performed on a foreign substance present in the film, at the film interface, or in the deep groove, the surface film can be accurately cut to the position of the foreign substance, and the accurate analysis can be performed without any problem of altering the foreign substance. Data can be obtained. If the above operation is automated, mass analysis can be performed quickly and unattended.

[0019]

(Embodiment 1) FIG. 4 shows an apparatus configuration of Embodiment 1 of the present invention. 1 is a time-of-flight mass spectrometer, 2 is a sample chamber, 3x, 3y, and 3z are moving mechanisms of the sample stage in the x, y, and z directions, respectively.
1 is a YAG laser light source, 12a and 12b are He-Ne
Laser light source, 13 is a continuously variable attenuation filter, 14 is a halogen lamp, 15a and 15b are TV cameras, 16 is a perforated mirror, 17 is an objective lens, 18a, 18b, 19a,
19b is a lens, 20 is a lens moving mechanism, 21 is an ion extraction electrode, 22 is a deflection electrode, 23 is an ion reflector,
24 is an ion detector, 25 is an ion orbit, 41 is a stage controller, 42 is a computer for acquiring a mass spectrum, 43 is a computer for controlling a measurement sequence, 51
Denotes an SEM, F1 to F4 denote polarization filters, and L1 and L2 denote laser beams.

The semiconductor wafer sample 4 is placed on the stages 3x, 3
After mounting on y and 3z, the stage is moved to move the position of the foreign matter below the objective lens 17. This position setting is performed by inputting the coordinates obtained by the foreign matter inspection device in advance to the measurement sequence control computer 43 using a magnetic disk or the like, and transmitting the coordinate data to the stage control device 41. Alternatively, the sample 4 is
The position is adjusted while the operator looks at the image obtained by the TV camera 15b after illuminating with.

Light L1 from He-Ne laser light source 12a
And light L2 from the He-Ne laser light source 12b irradiate the sample surface and the foreign matter, respectively. These two
The polarization directions of the two laser beams were set perpendicular to each other so as to be distinguished and recognized. The setting of the polarization direction was performed by the polarization filters F1 to F4. The laser spots L1 and L2 are observed by the cameras 15a and 15b. These images are taken into the measurement sequence control computer 43, and the light intensity and the spot diameter are obtained. A control signal is sent from the computer to the stage controller 41, and the laser light L2
The height of the stage 3z is adjusted so that the focal point of the stage 3 is adjusted to the foreign matter.

The computer sends a control signal to the lens moving mechanism 191 to adjust the position of the lens 19a so that the laser beam L1 is focused on the sample surface. The stage 3z can be moved in 0.1 μm steps. The magnification of the image by the objective lens 17 and the lens 18a was 100 times. In order to move the focal position of the sample 4 in 0.1 μm steps, the lens moving mechanism 1
Reference numeral 91 denotes a unit that moves in steps of 10 μm.

FIG. 5 shows a measurement sequence. In the figure, Z is the height of the z stage, and Δz is the laser beam L1.
, LAG is the intensity of the YAG laser, L1 is the reflection intensity of the laser beam L1, and L2 is the laser beam L.
2 is the reflection intensity. The focusing of the laser beam L2 is z
While scanning the stage, use the camera 1
Monitor at 5b and search for a position Z0 at which the intensity is maximum. Next, for focusing on L1, the above-described condensing lens 19a is moved to scan Δz, and a position Δz0 at which the minimum intensity of the laser beam L1 appears last is searched for.

Next, the YAG laser light source 11 is oscillated at 1 Hz. The transmittance of the variable attenuation filter 13 is gradually increased for each pulse of the YAG laser light to increase the laser light intensity. The focusing lens 19 is moved each time the pulsed laser light is irradiated, and the focal position of the He-Ne laser 12a is adjusted again to the irradiation mark. From this, the change of Δz, that is, the shaved depth of the sample is obtained. When the change in Δz per pulse became 1/10 of the depth from the surface of the sample 4 to the foreign matter, the YAG laser light intensity was kept constant.

When Δz was 0, that is, when the laser beam irradiation mark reached the foreign matter, ions generated by irradiating the sample with the light of the YAG laser 11 were taken into the time-of-flight mass spectrometer 1. The signal from the detector 24 was taken in by the spectrum processing computer 42 to obtain a mass spectrum. further,
This spectrum was stored on a magnetic disk corresponding to the coordinates of the foreign matter. As described above, when mass spectrometry is performed on a foreign substance present in the film, at the film interface, or in the deep groove, the surface film can be accurately cut to the position of the foreign substance, and there is no problem of deteriorating the foreign substance. In addition, mass spectrometry can be performed quickly and unattended.

(Embodiment 2) Embodiment 2 will be described with reference to FIG. In this apparatus, the SEM 51 is attached to the sample chamber 2.
The objective 17 of the laser mass spectrometer and the SEM 51 are 1
They were placed 80 mm apart so that their axes were parallel to each other. The movement of the sample between the laser mass spectrometer and the SEM can be performed by the stage 3x.

In the method of observing the laser spot described in the first embodiment, the upper limit of the resolution for measuring the depth of the YAG laser irradiation mark is about 0.1 μm. On the other hand, a measurement resolution of several tens of nm can be obtained by the SEM. However, observation of the laser spot does not require moving the sample,
Although hardly any time is required, the SEM observation takes about 10 s because the sample is moved.

Therefore, in the present embodiment, the film thickness on the foreign material is set to 0.
While 1 μm or more remained, the laser spot was observed and the film thickness was measured in the same manner as in Example 1, and when the film thickness was smaller than 0.1 μm, the film thickness was measured by SEM. Thus, even when the thickness of the foreign matter is thinner than 0.1 μm, the sample can be accurately cut to the position of the foreign matter.

As described above, in the same manner as in Example 1, in the film, at the film interface,
It is possible to perform mass analysis of the foreign substance present in the deep groove quickly and unmannedly.

(Embodiment 3) Embodiment 3 will be described with reference to FIG. In this embodiment, the He-Ne lasers 12a and 12b have wavelengths different from 633 nm and 535 nm, respectively, and the filters F1 and F2 are 633 nm, F3 and F3.
No. 4 selectively transmits 535 nm. Thus, the laser beams L1 and L2 can be identified and observed as in the first embodiment.

As described above, in the same manner as in Example 1, in the film, at the film interface,
It is possible to perform mass analysis of the foreign substance present in the deep groove quickly and unmannedly.

(Embodiment 4) Embodiment 4 will be described with reference to FIG. In this embodiment, the He-Ne laser 12 and the camera 15 are used.
Are simplified to only one each. In this embodiment, each time the sample is irradiated with the YAG laser 11, the stage 3
The laser beam is focused on the foreign matter and the irradiation mark alternately by raising and lowering z, and the stage height at which each is focused is read. From the difference between the two, the film thickness remaining on the foreign matter can be determined.

As described above, in the same manner as in Example 1, in the film, at the film interface,
It is possible to perform mass analysis of the foreign substance present in the deep groove quickly and unmannedly.

[0034]

As described above, according to the present invention, a mass spectrum of a foreign substance existing in a film, a film interface, and a deep groove of a semiconductor sample can be measured by a quick and simple operation. In addition, accurate analysis data can be obtained without any problem of deteriorating foreign matter before analysis.

[Brief description of the drawings]

FIG. 1 is a side sectional view for explaining the order of laser beam focusing.

FIG. 2 is a diagram showing a focused image.

FIG. 3 is a principle diagram of a focusing optical system.

FIG. 4 is a diagram illustrating a configuration of an apparatus according to the first embodiment of the present invention.

FIG. 5 is a timing chart showing a measurement sequence according to the first embodiment of the present invention.

FIG. 6 is a configuration diagram illustrating an apparatus according to a fourth embodiment of the present invention.

FIG. 7 is a configuration diagram showing a conventional device.

[Explanation of symbols]

1. Time-of-flight mass spectrometer 2. Sample chamber 3x, 3y,
3z: sample stage, 4: sample, 11: YAG laser light source, 12a, 12b: He-Ne laser light source, 13: continuous variable attenuation filter, 14: halogen lamp, 15a,
15b: TV camera, 16: Perforated mirror, 17: Objective lens, 18a, 18b, 19a, 19b: Lens, 191
... Lens moving mechanism, 21 ... Ion extraction electrode, 22 ... Deflection electrode, 23 ... Ion reflector, 24 ... Ion detector,
25: ion trajectory, 41: stage controller, 42: computer for mass spectrum acquisition, 43: computer for measurement sequence control, 51: SEM, F1 to F4 ...
Polarizing filters, L1, L2... Laser light.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Kinya Eguchi, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Hitachi, Ltd.Production Technology Laboratory (72) Inventor Yusutoshi Sugimoto 6-16, Shinmachi, Ome-shi, Tokyo (3) Inside the Device Development Center, Hitachi, Ltd. (72) Inventor: Masanori Sakimoto 5-2-1, Kamimizuhonmachi, Kodaira-shi, Tokyo F-term in the Semiconductor Group, Hitachi, Ltd. 5C038 GG07 GH06 GH10 GH10 GH17

Claims (14)

[Claims] In an analyzer for irradiating a laser beam to a foreign substance or a contaminant adhered to a minute portion of a semiconductor device sample to generate ions and measuring a mass spectrum of the ions, a semiconductor device sample film, a film interface, Alternatively, when analyzing foreign matter contained in the groove, laser mass spectrometry is characterized in that the laser light focus is moved from the sample surface to the depth of the foreign matter according to a predetermined sequence, and is moved for each pulse of the laser light. Total. 2. A laser mass spectrometer according to claim 1, wherein an optical system for irradiating the sample with a pulse laser beam for generating sample molecules or ions and a continuous wave laser beam for reference superimposed thereon, An optical system for observing the laser spot on the sample, a circuit or software for determining whether or not the laser light is focused on the analysis location from the laser spot image; and A laser mass spectrometer provided with a focusing circuit or software. 3. A method for analyzing a foreign substance contained in a film, an interface of a film, or the inside of a groove of a semiconductor device sample using the laser mass spectrometer according to claim 1 or 2, wherein a focus of a continuous wave laser beam is applied to the foreign substance. Determining the depth of the foreign matter from the sample surface from the sample position coordinates when the sample is adjusted to the sample position and the sample position coordinates when the continuous wave laser beam is focused on the sample surface. . 4. In the foreign substance analysis according to claim 1, when removing a film on the foreign substance by irradiating a pulse laser beam, each time one pulse or a plurality of pulses of the laser beam are irradiated, a request is made. Item 2. A laser mass spectrometer, which determines whether or not a laser irradiation mark has reached the depth of a foreign substance by the operation described in Item 2. 5. A method according to claim 1, wherein when removing the film on the foreign material by irradiating a pulsed laser beam, if the film thickness on the foreign material is equal to or more than a predetermined value, the method is performed. Item 3. A laser mass spectrometer characterized in that when the film thickness is smaller than a predetermined value, the depth of the foreign matter from the sample surface is measured using an SEM. 6. The laser mass spectrometer according to claim 5, wherein the SEM is provided in the same vacuum vessel as the laser mass spectrometer. 7. In the foreign substance analysis according to any one of claims 1 to 3, the intensity of the pulsed laser light is set so that the depth of the laser pulse cut from the sample surface is maintained at a predetermined value. A laser mass spectrometer characterized by comprising means. 8. A laser mass spectrometer according to claim 7, wherein said intensity setting means is an attenuation filter for changing the light intensity continuously or stepwise. 9. The intensity setting according to claim 7, wherein the intensity of the laser light is increased step by step for each laser pulse.
A laser mass spectrometer characterized by employing laser light intensity at a point in time when a depth cut per pulse reaches a predetermined value. 10. The laser mass spectrometer according to claim 1, further comprising two continuous oscillation lasers and two cameras for observing a laser spot of each of the continuous oscillation lasers, wherein the two lasers are provided in or on a film of a semiconductor device sample. A laser mass spectrometer characterized in that, when analyzing a foreign substance contained in an interface, a first continuous wave laser beam is focused on the foreign substance and a second continuous wave laser beam is focused on a sample surface. 11. The foreign matter analysis according to claim 1, wherein the operation of focusing the continuous wave laser beam on the sample surface or the foreign matter is performed by moving a lens in the laser light path. Features laser mass spectrometer. 12. A laser mass spectrometer according to claim 10, wherein the two continuous wave lasers have different wavelengths or different directions of polarization. 13. The method according to claim 3, wherein the focus of the laser light is focused on the surface of the sample or the foreign matter.
Alternatively, a laser mass spectrometer characterized by performing the measurement based on a spot diameter. 14. When a plurality of foreign substances whose positions are determined in advance by a foreign substance inspection device or the like are analyzed using the laser mass spectrometer described in each of the above claims, the foreign substance position coordinates are read from a storage medium. After moving the sample to the coordinates,
The method according to claim 4, wherein the film on the foreign matter is removed by a pulse laser beam, and after confirming that the laser irradiation mark has reached the foreign matter, a mass spectrum is measured, and the measurement result is made to correspond to the foreign matter position coordinates. A laser mass spectrometer characterized in that the operation of storing in a laser mass spectrometer is performed according to a preset sequence.