JPH027510B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a secondary ion mass spectrometer that can measure and display the etching depth of a sample to be inspected at the same time as the mass analysis of the measured element in measuring the depth distribution of impurity concentration. It is something.

In general, secondary ion mass spectrometers irradiate a sample with primary ions such as argon or oxygen, and mass analyze the secondary ions generated from the sample to be inspected. It performs measurements, and its detection sensitivity is the highest among surface analysis instruments, and it has the excellent feature of being applicable to all elements, including hydrogen. In particular, it is a very effective analytical instrument for compositional analysis in the depth direction, as it detects secondary ions emitted from the surface layer while etching the sample to be inspected with secondary ions. It is effectively used for evaluating impurity concentration profiles and epitaxial layer interfaces.

Measuring the etching depth is essential for analysis in the depth direction, and it is particularly desirable to know the depth at the time of measurement at the same time as elemental analysis. However, none of the conventional secondary ion mass spectrometers can meet this requirement. Usually, after the analysis is completed, the etching depth is measured using an optical interferometer or surface depth meter (Talysurf), and the etching rate is calculated from the etching time. However, when evaluating multilayer epitaxial crystals of different materials or interfaces between semiconductors and metals or oxides, the etching rate of each layer is naturally different, so even if the overall etching depth is measured, the thickness of each layer is Currently, it is impossible to evaluate the thickness of each layer, and the thickness of each layer is estimated separately by diagonal polishing. This is a major obstacle to obtaining rapid measurement results.

The present invention has improved the above-mentioned drawbacks, and its purpose is to measure the continuously changing etching depth of a sample to be inspected using an optical interferometer installed in the sample chamber of a secondary ion mass spectrometer. The purpose is to measure the depth of the surface on the spot by displaying the signal with an external recorder and analyzing it with a mass spectrometer. Particularly in the depth direction analysis mode, the etching depth is displayed along with the detected count number of each element.

A detailed explanation will be given below based on examples.

FIG. 1 shows an optical etching depth measuring system according to an embodiment of the present invention. 1 is a primary ion generating section;
Duoplasmatron, electrostatic condenser lens,
It consists of an electrostatic deflector, etc., and is of the same type as a normal primary ion generation mechanism. 2 is a sample to be inspected. The primary ions generated by the Duoplasmatron are condensed to a beam diameter of about 10 cyclones by an electrostatic condenser lens, and then electrically scanned by an electrostatic deflator and irradiated onto the sample 2. Sample 2
will be etched into a rectangle of arbitrary size. The primary ion beam is obliquely incident on the sample 2 at a predetermined angle, and the generated secondary ions are taken out perpendicularly to the etching surface. Reference numeral 3 denotes an electrode to which an accelerating electric field is applied to extract secondary ions, which are guided to a mass spectrometry system 4 by an accelerating electric field of about 10 KV. The mass spectrometry system 4 has a conventional configuration including a fan-shaped electromagnetic field, a scintillation counter, and the like.

The optical system for measuring the etching depth uses a Michelson interferometer. The light source uses a semiconductor laser, which is an ultra-compact laser that can generate coherent light. In the case of this device, the wavelength is approximately 7500Å.
A GaAs/GaAlAs double hetero laser was used.
The beam from a semiconductor laser is emitted after being spread out due to diffraction, but this problem does not occur if a circular self-occurring lens is used that has been adjusted in advance to become a parallel beam. The light source 5 is arranged and attached to the side wall of the electrode 3 so that the laser beam is extracted in the direction shown in the figure. The semiconductor laser light source 5 is
It is used in CW operation, and its power is supplied externally through a lead wire 6. 7 is a small semi-transparent mirror, and the beam from the light source 5 is divided into two directions via the semi-transparent mirror 7, one of which is reflected as a reference beam 13 by a reflecting mirror 9 provided on the right side wall 8 of the sample chamber; Pass through the semitransparent mirror 7 again, pass through the slit 11 fixed to the left side wall 10 of the sample chamber, and pass through the left side wall 10 of the sample chamber.
The light converges on the light receiving surface of the photodetector 12 fixed to.
The optical path through which the reference light 13 passes is indicated by a dotted line in the figure. On the other hand, the distance measuring light 14 travels straight through the semi-transparent mirror 7, is reflected by the sample etching surface 2, is reflected again by the semi-transparent mirror 7, passes through the slit 11 fixed to the left side wall 10 of the sample chamber, and is detected. It converges on the light receiving surface of the device 12. The optical path through which the ranging light 14 passes is shown by a solid line in the figure. Therefore, bright and dark interference fringes are generated on the light receiving surface of the photodetector 12 every time the optical path difference between the distance measuring light 14 and the reference light 13 becomes an integral multiple of the wavelength of the laser light. Here, as the sample surface 2 is scratched by ion etching, the optical path length for the distance measuring light 14 becomes longer and changes from time to time. For example, when the sample surface 2 is etched by half the wavelength of the light source, the optical path length changes by one wavelength, so if bright fringes were observed before the etching started, as the etching progresses, dark fringes are observed and then bright fringes are observed again. It will be done. When using a GaAs/GaAlAs double hetero laser as in this device, the above change is observed when etching is approximately 3750 Å. This level is sufficient for practical use in samples that are normally subjected to secondary ion mass spectrometry. Incidentally, the reflecting mirror 9 provided on the right side wall 8 of the sample chamber is variable in position, and can be adjusted from the outside so that the maximum bright or maximum dark fringes can be obtained before the start of etching. In the case of this device, the photodetector 12 uses a semiconductor photodiode, for example, a silicon photodiode, for the purpose of miniaturization, and is led to an external recorder 16 by a lead wire 15 for recording. In this case, there is no need to use an avalanche photodiode because a fast optical response speed is not required. What is important in the arrangement of the optical measurement system described above is that it does not interfere with the ion beam system. Therefore, the arrangement shown in FIG. 1 is adopted so that the straight line connecting the reflector 9 of the optical measurement system and the photodetector 12 is not parallel to the plane connecting the primary ion generating section 1 sample surface 2 extraction electrode 3. ing.

Figure 2 shows an example of measurement using this device.
The sample was boron ion implanted into silicon at 100KV. In addition to the depthwise distribution of impurity boron 17 and host silicon 18, intensity changes 19 of interference fringes are recorded at the bottom of the graph, and serve as a scale of etching depth. Incidentally, not only such an analog display but also a digital display as a numerical value can be easily achieved by using an appropriate electric circuit.

The method of the present invention can be applied not only to the above-mentioned mass spectrometers, but also to devices that have a mechanism for physically etching surfaces with ions (e.g., electron microscope sample preparation devices, audio electron spectroscopy devices, etc.). Needless to say, this method is very useful since the etching depth of the sample can be observed on the spot.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing one embodiment of the present invention. Second
The figure shows an example of the results of measuring the impurity depth distribution and etching depth in boron-implanted silicon using the present invention. In the figure, 1...Primary ion generation part, 2... Cross-sectional view of the sample to be inspected, 3... Secondary ion extraction electrode, 4
...Mass spectrometry system, 5...Semiconductor laser light source, 6...Semiconductor laser lead wire, 7...Semi-transparent mirror, 8...Right side wall of sample chamber, 9...Reflector, 10...Left side wall of sample chamber, 1
DESCRIPTION OF SYMBOLS 1...Slit, 12...Semiconductor photodetector, 13...Reference light optical path, 14...Distance measuring light optical path, 15...Semiconductor photodetector lead wire, 16...Recorder, 17...Boron profile, 18...Silicon profile, 19...
Interference fringe intensity change.

Claims (1)

[Claims] 1. A mass spectrometer is equipped with an optical distance meter that uses a semiconductor laser as a light source and a photodiode as a light receiver in the measurement sample chamber, and simultaneously measures and records the etching depth of the measurement sample at the same time as the mass analysis of the measurement sample. A secondary ion mass spectrometer configured to display information.