JPH11125509A - Confocal laser scanning type microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make localizable three dimensional crystal defects non-destructively on semiconductor structure by using a microscope objective mirror strongly localizing multiphoton and having a high numerical aperture in spacial coordinates in the case where a material inspection is conducted by using a short wavelength laser pulse for multiphoton excitation. SOLUTION: By combining the confocal laser scanning microscope and a system for multiphoton excitation, a short pulse laser 1 and another laser 2 are installed in the same housing in advance, which are connected as the scanning head of the laser scanning microscope to a scanning unit with an optical fiber. The laser light of the laser 1 and 2 passes through a light path divider 4, a dichroic light path divider 5, a two-dimensional bias unit 6, a light path divider 9, an objective mirror lens 10 and to a sample 11. The reflection light from the objective lens 10 after passing through the light path divider 9 reaches a pre-filter 13 or directly a detector 12 with a focusing optical system 14 so that the sample light never comes in through the scanning light path at this moment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is based on multi-photon laser scanning microscopy, which uses non-optical detection techniques such as OBIC (light induced current) or LIVA (light induced voltage alternation). In material inspection, in particular, it relates to a method of performing an inspection technique on a structured silicon wafer, for example, OBIC or LIVA.

[0002]

2. Description of the Related Art In two-photon excitation (multi-photon excitation as a special case), coupling of a gas, a liquid or a solid (for example, an electronic, vibration-rotation junction or microstructure) in an excitation structure (Termschma) is performed. Is handled by performing two-photon quasi-simultaneous absorption at long wavelengths λ1 and λ2 (where λ1 and λ2 may be the same or different wavelengths), but otherwise, at shorter wavelengths (λ1 + λ
2) 4/4 single photons are needed. Two-photons at "long wavelength" (e.g., red) can excite, for example, ultraviolet absorption coupling, but in the normal case (i.e., conventional one-photon excitation) "short wavelength". (Eg, blue) (FIGS. 1a and b).

To excite one two-photon coupling,
Since each requires two photons, the coupling rate for a given coupling will be the square of the excitation intensity. In order to perform two-photon excitation, it is therefore generally necessary to use a laser source with a particularly strong pulse, and with a shorter but more powerful light pulse, a certain average With light output, the probability of two-photon coupling increases.

According to the first experimental observations of two-photon absorption by Kaiser and Garrett in 1961, the excitation of Eu ²⁺ -doped CaF ₂ crystals in the optical domain occurred after the development of high-performance monochromatic ruby lasers. It was possible for the first time. The possibility of two-photon absorption or two-photon simultaneous emission has already been theoretically described in 1931 by Maria Geppär-Meier. The introduction of two-photon technology to laser scanning microscopy was proposed by Denk, Strickler and Webb (1990).

[0005] WO 91/07651 discloses a two-photon laser scanning microscope which can be excited by a laser pulse in the subpicosecond range with an excitation wavelength in the red or infrared region. EP 666473A1, WO95 / 30166, DE 441494
0 A1 describes the excitation in the picosecond range using a pulsed or continuous light beam. The method of optically exciting a sample by two-photon excitation is as described in DE C2 4331570. DE 29
The applicant of 609850 describes coupling the light of a short-pulse laser in a microscope optical path using an optical fiber.

[0006]

In the detection of lattice defects, probers such as OBIC and LIVA are generally used today.
rober technology is applied. OBIC (light induced current)
A laser beam, or photon, with sufficient energy to generate electron-hole pairs can skip the bandwidth of the test semiconductor (ie, the energy of the illuminated photon is greater than the band gap energy EG of the semiconductor). Large figure 2).

In this manner, the charge carrier current having local characteristics generated from the scanning laser beam can be used to localize the location of the lattice defect in the crystal. When the wafer to be inspected is contacted (prober station) or when the wafer is packaged,
The present technology is applied to a manufactured and integrated circuit. After the charge carrier current is amplified, the scan position (non-optical detection signal)
In some cases, a "video signal" is generated.

[0008] In this method, the generation of electron-hole pairs is determined by z
The disadvantage is that no choice is made. To complete the preparation of the z information, the localization of the defect location, according to the two-dimensional technique, the wafer has to be painstakingly polished from layer to layer, and each polished layer has to be polished using an electron microscope. Therefore, inspection must be performed to localize the defect also in the z-axis. LIVA (Lightwave Induced Voltage Alternation) is a technique similar to OBIC technology, but a constant voltage is applied to the prober electrode (or IC pin), and the voltage change must be detected by the scanning laser beam.

[0009]

SUMMARY OF THE INVENTION For silicon wafer inspection by one-photon laser scanning microscopy, scanning near-infrared laser light (eg, Nd at 1064 nm; YAG laser) is typically doped. It is well penetrated into the silicon wafer and penetrates deeply into the silicon wafer. Using a laser beam, a metal film on the IC surface that cannot be penetrated optically penetrates the entire silicon substrate (several millimeters thick) optically from behind (backside imaging or backside OBIC), and reaches around the structural surface. Can be reached.

The present invention utilizes multi-photon laser scanning microscopy to enable the use of non-optical detection techniques such as OBIC (Light Induced Current) or LIVA (Light Induced Voltage Alternation) in material inspection. In particular, a method of performing an inspection technique on a structured silicon wafer, for example, OBIC or LIVA. Strongly localizing multiphotons, using microscope objectives with high numerical aperture in all three spatial coordinates, thereby enabling non-destructive localization of crystal defects in three dimensions on semiconductor structures .

By making full use of this technique, it is possible to detect a lattice defect using a two-dimensional technique (for example, laser scanning microscopy, a detection method using a non-confocal or non-optical detection signal), and The subsequent need for continuous mechanical crystal structure delamination can be combined with electron microscopy to avoid the possibility of three-dimensionally detecting defect locations.

In many cases, spatial (xyz) resolution in three dimensions in the silicon structure to be inspected will be of interest. With excitation light in the near-infrared (λ> 1100 nm), ie, reaching the opposite side of the silicon band edge, light with a slight absorption is transmitted through the normally thick doped silicon structure. In general,
Sufficiently high intensity is obtained only at the location of the focal point formed by the microscope objective with a high numerical aperture, and electron-hole pairs can be created by a nonlinear multiphoton excitation process. Electron-hole pairs can be induced by strong z-sorting with light within the wavelength range of the "optical window" of silicon with the help of two-photon microscopy.

[0013]

FIG. 3 shows an embodiment combining a confocal laser scanning microscope with a system for multiphoton excitation. Here, the short pulse laser 1 and another laser 2 are pre-mounted in the same housing, and are used as a scanning head of a laser scanning microscope or as another unit by a known method (US Ser. No.
08 / 826,906, DE-U -29609850) It is connected to the scanning unit through an optical fiber.

The laser beams of the lasers 1 and 2 are transmitted to an optical path splitter 4.
Via the dichroic optical path splitter (DB
S) 5 to a two-dimensional deflection unit 6, from which a scanning lens (SL) 7 and a tube lens (TL) 8, an optical path splitter (DBS) 9 and an objective lens (OL) 10 The sample 11 is reached. It can at least be sharply adjusted in the vertical direction. The light coming from the objective lens 10 reaches the pre-filter 13 and the direct detector (PMT) 12 with the imaging optical system 14 via the beam splitter 9 without passing the sample light through the scanning optical path. . This is advantageous from the viewpoint of using multiphotons.

Through the path splitter 9, the LSM standard detection light path is further reduced in the direction of the preceding pinhole 17 and the associated detector 15 of the filter 16. Further, as shown in FIG. 2, the non-optical detection 18 can be synchronized to perform laser scanning (Lit.). If the optical path of the microscope is performed directly without the imaging optical path with the sample, it can be additionally grasped by another detector 19 or an image capturing unit.

[0016]

According to the present invention, in the case of the conventional one-photon excitation, the excitation occurs along the spread of the entire laser light. Light coming from the focus can be sorted out. In the case of two-photon excitation, the excitation is the highest intensity part,
That is, it occurs at the focus of the laser beam. Therefore, according to the present technology, it is possible to perform deep selection without a confocal stop.

If the band gap energy EG is smaller than the photon energy E of the incident light, electron-hole pairs (1) occur in the semiconductor. In a homogeneous semiconductor, electron-hole pairs generally recombine very quickly. When this occurs near the barrier pn transition, a separation of holes and electrons occurs. (2) The electrons from the p-doped region are diffused into the n-doped region, and the induced current detected by the amplifier 3 flows. At each point of contact, this current is recorded in relation to the location, i.e. in synchronization with the scanning of the scanning laser spot,
Available to form electronic images

[Brief description of the drawings]

FIG. 1 shows the propagation of focused laser light by a microscope objective lens with a high numerical aperture

Fig. 2 shows the case where the energy E of the irradiated photon is larger than the band gap energy EG

Fig. 3 shows confocal laser scanning microscopy and multiphoton excitation combined into one instrument system

[Explanation of symbols]

 1, 2 laser 4 optical path splitter 5 dichroic optical path splitter (DBS) 6 two-dimensional deflection unit 7 scanning lens (SL) 8 tube lens (TL) 9 optical path splitter (DBS) 10 objective mirror lens (OL) 11 sample 12 Direct detector (PMT) 13 Pre-filter 14 Imaging optical system 15 Detector 16 Filter 17 Pinhole 18 Non-optical detection 19 Detector

Continued on the front page (72) Inventor Ulrich Simon (Name in original language) Ulrich Simon Germany D-07751 Rotenstein Burgstrasse 35 (Address or residence in original language) Burgstr. 35, D-7551 Rothenstein, Germany (72) Inventor Ralph Woleschensky (Name in original language) Ralf Wolleschen sky Germany D-99510 Shetten and der Promenade 3 (Address or address in original language) Ander Perme D-99510 Schoeten, Germany (72) Inventor Rainer Danz (inscription in the original language) Ra iner Danz Germany D-07768 Carla Richard Denna Stresse 4 (inscription in the original address or address) Richard-Denner-Str. 4, D-007768 Ka hla, Germany

Claims (18)

[Claims] 1. A confocal laser scanning microscope for non-optically detecting a defect when performing a material inspection using a short-wavelength laser pulse for multiphoton excitation. 2. The confocal laser scanning microscope according to claim 1, which is applicable to semiconductor inspection by OBIC or LIVA. 3. A confocal laser scanning microscope according to one of the preceding claims, which is applicable for structural inspection of silicon wafers. 4. A confocal laser scanning microscope according to claim 1, for non-destructively and three-dimensionally confirming a defect position of a crystal. 5. A confocal laser scanning microscope according to claim 1, for detecting a current synchronized with an inspection scan. 6. A confocal laser scanning microscope according to claim 1, having a laser pulse length of picoseconds or less. 7. A microscope device combining a laser scanning microscope and a confocal scanning microscope according to at least one of the preceding claims for optical detection. 8. A confocal laser scanning microscope according to at least one of the preceding claims, wherein, in addition to the short-wavelength pulsed laser, at least another laser is coupled to the scanning optical path. 9. A microscope apparatus having means for optically detecting a light beam coming from a sample in a confocal laser scanning microscope according to at least one of the above claims. 10. A confocal laser scanning microscope according to at least one of the preceding claims, wherein the additional optical detection means for detecting the light beam coming from the sample directly, ie before the return light path through the scanning means, is not provided. The combined microscope equipment. 11. A confocal laser scanning microscope according to at least one of the preceding claims, wherein a plurality of optical detection means are added to the microscope for detecting light rays coming from the sample. 12. A microscope apparatus comprising a combination of a laser scanning microscope and an infrared microscope or a radiation microscope according to at least one of the above claims. 13. A material inspection method using a multiphoton laser scanning microscope. 14. A confocal laser scanning microscope according to at least one of the preceding claims, comprising: an OBIC or LIC.
A microscope apparatus for inspecting the structure of a silicon wafer by means using a non-optical detection technique such as a VA method. 15. A microscope device for confocal laser scanning according to at least one of the preceding claims, wherein the defect position of the crystal is confirmed nondestructively and three-dimensionally. 16. Light rays penetrate through a generally thick (generally doped) silicon substrate with low absorption and reach a sufficient intensity only at the focal point generally formed by the objective lens of a high-aperture microscope, so that , Low infrared (NIR) (wavelength> 1000 n) such that multiple electron hole pairs are generated by a nonlinear multiphoton excitation process.
m), ie a confocal laser scanning microscope according to at least one of the preceding claims, which uses excitation light on the side beyond the band edge (band gap energy) of silicon. 17. A combination of a multiphoton laser scanning microscope and a confocal laser scanning microscope, mainly for optically inspecting the topology of a material or detecting an optical reflection signal in an apparatus system. A microscope device for measuring the surface structure by doing. 18. A combination of a multiphoton laser scanning microscope and a confocal laser scanning microscope, or a confocal laser scanning microscope, mainly for optically examining the topology of a material or for optically reflecting signals. A microscope device for measuring the surface structure by detecting and / or by detecting with an infrared microscope and / or an emission microscope (EMIC) in certain device systems.