JPH06338549A - Detecting method for defect of insulating film buried in semiconductor board - Google Patents

Abstract

PURPOSE:To accurately locate defects in a short time by a method wherein a semiconductor board is irradiated with an electron beam to generate carriers, and carriers are led out and checked in quantity change. CONSTITUTION:If no pipe defect 4 is present in a buried oxide film 2 irradiated with an electron beam 7, only carriers 8 generated inside a surface silicon layer 1 are able to reach a space-charge layer 6 by scattering. On the other hard, if a pipe defect 4 is located in a buried oxide film 2 irradiated with an electron beam 7, not only carriers 8 generated in the surface silicon layer 1 but also carriers generated even in a board 3 region are able to reach the space-charge layer 6 and led out as external signals. Therefore, a part of the oxide film 2 where carriers are relatively high in yield is detected as a spot, where a pipe defect 4 is located. The contrast signal of a scanning electron microscope is modulated with this carrier yield, whereby a pipe defect 4 can be easily defined as a microscopic image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to evaluation of a semiconductor substrate obtained by a method of forming a buried insulating film by ion implantation.

[0002]

2. Description of the Related Art A method of forming a buried insulating film in a semiconductor substrate by doping the semiconductor substrate with a high concentration of an element that reacts with an element of the semiconductor substrate to form an insulator, For example, in a semiconductor substrate formed by a method of implanting oxygen into a silicon substrate to form a buried oxide film (hereinafter referred to as SIMOX method), a part of the buried insulating film becomes discontinuous, and the buried buried film is originally buried. A defect (hereinafter, this defect is referred to as a pipe defect) may occur in the embedded insulating film in which the surface silicon layer electrically separated by the embedded insulating film is electrically connected to the substrate silicon.

For example, when an electronic device is formed on a semiconductor substrate (hereinafter referred to as SIMOX wafer) formed by the SIMOX method, such a pipe defect of the buried insulating film causes a malfunction of the device. Therefore, it is important to suppress the occurrence of pipe defects as much as possible in the formation of the buried insulating film in the semiconductor substrate, and development of a method for detecting this pipe defect is required.

Since the pipe defect, which is a problem here, exists in the buried insulating film inside the semiconductor substrate, an etch pit obtained by chemically etching the substrate surface as in the case of a normal semiconductor substrate is observed. In some cases it is difficult to detect.

As a pipe defect evaluation method, for example, P.I. P. Roitman et al.
There is a report of observing pipe defects by etching off the surface silicon layer of the IMOX wafer and further etching the substrate silicon through the pipe defects to form pits that can be observed with an optical microscope (1990 IEEE inter
national SOI / SOS conference proceedings P. 154).

Furthermore, Kei. K. Jovner et al. Formed a number of electrically isolated silicon islands on the surface silicon layer of a SIMOX wafer by lithography and etching techniques and observed these silicon islands by scanning electron microscopy. . At this time, the presence or absence of pipe defects was confirmed by the difference in the contrast of the scanning electron microscope images of the silicon islands with pipe defects in the buried oxide film under the silicon islands (1991 IEEE international SOI conference pr
oceedings P. 64).

[0007]

However, for example, P.I. The method of observing the etch pits by etching KOH solution by Reuttman et al. Is to detect when the pipe defects are three-dimensionally arranged in the buried insulating film or when they have a crevasse shape along the grain boundaries. Is difficult,
In addition, it is difficult to know the size and shape of the pipe defect itself. See you again. The method of Jovener et al. Is complicated because it requires a process such as lithography and etching to form a silicon island to be measured, and the turn-around-time (turn arou-
nd time) becomes longer. Although this method can know whether or not there are pipe defects within the area of the separated island, it is not possible to detect the position and shape of each pipe defect.

The present invention has been made in view of such problems in the conventional method, and an object thereof is to detect a place where a defect exists and its shape in a short turn-around-time.

[0009]

In order to achieve the above object, the present invention is directed to a semiconductor substrate having a buried insulating film formed inside the semiconductor substrate by ion implantation, wherein both upper and lower semiconductor layers sandwiching the buried insulating film are provided. A metal electrode is formed on the surface or one side surface, a carrier is generated inside the semiconductor substrate by scanning the semiconductor substrate with a particle beam or a light beam, the carrier is taken out through the electrode, and the amount of the carrier is Characterized by investigating changes, more preferably sandwiching a buried insulating film 2
One of the semiconductor regions is made of a conductor different from the other.

[0010]

By scanning the semiconductor substrate with a particle beam or a light beam, carriers are generated inside the semiconductor substrate and taken out to the outside through the electrodes. At this time, the yield of carriers that can be taken out depends on the presence or absence of a pipe defect. Is different. That is, when there is no pipe defect and the surface silicon layer 1 and the substrate 3 are completely insulated, the carriers that can reach the electrode are only the carriers generated in the surface silicon layer 1, and the carriers below the buried oxide film 2 The carriers generated on the substrate 3 undergo a recombination reaction during diffusion and are mostly eliminated. On the other hand, when there is a pipe defect, the carriers are generated not only on the surface silicon layer 1 but also in the region of the substrate 3 through the pipe defect. This is because the generated carrier 8 can also be taken out as an external signal. The distribution of pipe defects is identified by the scanning signal and the external signal based on the carrier.

[0011]

【Example】

Example 1 When a buried oxide film is formed in a silicon substrate by the SIMOX method, oxygen ions with a dose amount of 0.3 × 10 ¹⁸ cm ⁻² are implanted with an implantation energy of 180 keV, and then at 1300 ° C. in an Ar atmosphere. When a buried oxide film is formed in a silicon substrate by heat treatment for 6 hours, the buried oxide film 2 becomes discontinuous as shown in FIG. 1 due to the presence of particles on the surface of the substrate during implantation and the surface silicon layer 1 and the substrate. A pipe defect 4 is generated which is electrically connected to the silicon 3. A metal is vapor-deposited on the surface of this substrate as shown in FIG. 2 to form an electrode 5, from which a current can be taken out as an external signal. This metal is such that it creates a Schottky junction to the silicon substrate. For example, in this case, if an Au electrode is formed on the surface of the N-type silicon substrate under appropriate conditions, a Schottky junction is formed at the N-type silicon / Au interface, and as a result, the space charge layer 6 is formed near the silicon surface. When the electron beam 7 is irradiated here, a large number of carriers 8 are generated when they pass through silicon (FIG. 3a). A part of the generated carriers 8 diffuse and reach the space charge layer 6 near the surface layer, and the carriers 8 reaching the space charge layer 6 are carried to the metal electrode 5 by the electric field in the space charge layer 6 and then wired to the electrodes. Meter 1 through the lead wire 9
At 0 the quantity is measured. If there is no pipe defect in the buried oxide film where the electron beam 7 is irradiated and the surface silicon layer 1 and the substrate 3 are completely insulated, it is possible to diffuse and reach the space charge layer 6. Only the carriers generated in the surface silicon layer 1 and the carriers generated in the substrate 3 under the buried oxide film 2 undergo recombination reaction during diffusion and most of them disappear. On the other hand, when the electron beam is applied to the buried oxide film 2 where the pipe defect 4 exists, not only the surface silicon layer 1 but also the region of the substrate 3 below the buried oxide film 2 through the pipe defect 4. The carriers 8 generated in 1 also reach the space charge layer 6 and are taken out as an external signal. That is, as a result of two-dimensionally scanning the substrate with an electron beam or a light beam, a portion having a relatively high carrier yield can be detected as the location of the pipe defect (FIG. 3).
b). If the carrier yield is modulated into the contrast signal of the scanning microscope, the location of the pipe defect 4 can be easily specified as a microscope image. Furthermore, the presence of electrically active defects in the surface silicon 1 can also be detected by this method.

Example 2 Similar measurement can be performed by using a space charge layer formed by a PN junction of a semiconductor instead of the Schottky coupling at the semiconductor / metal interface as described above. That is, N-type SIMOX
For the wafer, the surface silicon layer 1 is made to have an opposite conductivity type, that is, P
Make a mold. Further, an electrode 12 having ohmic contact is formed on the surface so that a current can be taken out as an external signal from the electrode 12. At this time, due to the presence of the pipe defect 4, the PN junction is formed only in the portion where the surface silicon layer 1 and the substrate 3 are in contact with each other, and the space charge layer 13 is generated. The electron beam or the light beam 7 is applied to the same as above. Here, where the surface silicon layer 1 and the substrate 3 are insulated from each other by the buried oxide film 2, most of the carriers 8 generated inside the substrate 3 recombine and disappear during the diffusion. On the other hand, when a PN junction is formed at the location of the pipe defect 4 and an electron beam or a light beam is applied to the location where the space charge layer 13 exists, the generated carriers are generated on the surface by the electric field of the space charge layer 13. It reaches the formed electrode 12 and is taken out as an external signal. By two-dimensionally scanning the surface of the substrate with an electron beam or a light beam as described above, a portion having a relatively large signal current can be detected as the presence of a pipe defect. Further, by controlling the addition of impurities in the surface silicon layer to electrically degenerate the surface silicon layer 1, it is possible to suppress the influence of carriers generated due to surface defects and improve the detection sensitivity of the pipe defect 4. it can.

[0013]

As described above, in the defect observation of the insulating film embedded in the semiconductor substrate, the present invention can accurately detect the location of the defect in a short period of time.

[Brief description of drawings]

FIG. 1 SI in which a pipe defect exists in the buried oxide film.
Sectional view showing MOX wafer,

FIG. 2 is a cross-sectional view showing that a Schottky junction is formed by depositing a metal on the surface of the SIMOX wafer of FIG.

FIG. 3A is a schematic diagram showing the detection method in Example 1, and FIG. 3B is a diagram showing the results.

FIG. 4 is a schematic diagram showing a detection method in Example 2.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Surface silicon layer 2 ... Buried oxide film 3 ... Substrate silicon 4 ... Pipe defect 5 ... Electrode 6 ... Space charge layer by Schottky junction 7 ... Electron beam 8 ... Carrier 9 ... Conducting wire 10 ... Meter 11 ... Carrier yield distribution 12 ... Electrode with ohmic contact 13 ... Space charge layer by PN junction

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenji Kajiyama 5-10-1 Fuchinobe, Sagamihara-shi, Kanagawa Inside the Electronics Research Laboratory, Nippon Steel Corporation

Claims (2)

[Claims] 1. A semiconductor substrate in which a buried insulating film is formed inside a semiconductor substrate by ion implantation, wherein metal electrodes are formed on both surfaces or one surface of upper and lower semiconductor layers sandwiching the buried insulating film. By generating a carrier inside the semiconductor substrate by scanning with a particle beam or a light beam, taking out the carrier to the outside through the electrode, and examining the change in the amount of the carrier embedded in the semiconductor substrate. Insulating film defect detection method. 2. The insulating film embedded in the semiconductor substrate according to claim 1, wherein one of the two semiconductor regions sandwiching the embedded insulating film is a conductor different from the other in the semiconductor substrate. Defect detection method.