JPS5921169B2 - Failure analysis method for semiconductor devices - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a failure analysis method for semiconductor devices, and particularly to a method for analyzing the quality of bonding in a PN junction region.

As is well known, a semiconductor element basically consists of a PN junction region containing at least two types of impurities having different conductivity types in a semiconductor. One of the important electrical characteristics imposed on this PN junction region is reverse direction characteristics. This is the relationship between the reverse voltage and reverse current when a reverse voltage is applied to the PN junction, but if the reverse current exceeds the specified current value, it will become a PN junction leak current, which will cause the semiconductor device to malfunction. becomes. Leakage currents that cause defects in semiconductor devices include, in addition to PN junction leakage currents, leakage currents caused by pinholes in insulating films. Therefore, when examining a semiconductor element as a black box, it is difficult to distinguish whether the leakage current is due to a PN junction leakage current or a leakage current due to a pinhole in an insulating film. Therefore, the insulating film etc. are finally removed and the PN
It may become necessary to analyze only the joint area. In this final P
Conventionally, methods for analyzing only the N-junction region include forming a metal electrode in the PN-junction region and examining the reverse characteristics between this and the semiconductor substrate, or irradiating the PN-junction region with an electron beam to analyze the PN-junction region or its surroundings. A well-known method is to extract and examine the electron beam induced current from a metal electrode formed nearby. However, all of these conventional analysis methods have drawbacks. That is, these conventional methods require the formation of a metal electrode at or near the PN junction region and the need for probe contact thereto. BACKGROUND ART In semiconductor devices, especially highly integrated and highly dense semiconductor devices such as integrated circuits, tens of thousands of PN junction regions with fine pattern dimensions are built into the semiconductor device. Forming a metal electrode in the PN junction region of such a fine pattern area, for example, a pattern area several μm square, is
Regardless of the manufacturing process of semiconductor/conductor elements, the sample to be analyzed for failure usually has a package, etc., making it extremely difficult to apply known photolithography techniques. Furthermore, contacting the probe to obtain electrical connection to the microelectrode is difficult, as is often the case with wafer probers. Furthermore, conventionally, as an analysis method designed to eliminate the above-mentioned drawbacks, there has been a method described in Japanese Patent Application Laid-open No. 134379/1983.

In this method, a liquid crystal layer and a glass plate were provided on the PN junction area, and polarized light was continuously projected onto the PN junction area through these layers, allowing the birefringence changes in the liquid crystal layer to be visually observed. It was hot. However, in the above conventional method, the PN junction leakage current adversely affects other electric circuits,
Therefore, it had the disadvantage that accurate analysis and inspection could not be done, and the electric field effect of the liquid crystal weakened, making inspection and analysis difficult.

The present invention was made in order to eliminate the drawbacks of the above-mentioned conventional method, and a field-effect liquid crystal film and a glass plate are provided on the PN junction region, and the polarized light and the polarized light are transmitted through these to the PN junction region. To provide a failure analysis method for semiconductor devices that does not have an adverse effect on other electric circuits and does not weaken the electric field effect of a liquid crystal film by simultaneously and overlappingly and intermittently projecting light that is The purpose is

The analysis method according to the present invention will be described below with reference to the drawings. FIG. 1 is a process-by-step cross-sectional view for explaining the analysis method according to the present invention, and shows only the PN junction region 1, which is the subject of analysis, and the insulating film, metallization, etc. are not removed. There is.

By analyzing the PN junction region 1 from which the insulating film, metallization, etc. have been removed, it can be determined whether the leakage current is truly due to a defect in the PN junction. FIG. 1a shows a state in which the PN junction region 1 is exposed on the semiconductor substrate 2. In FIG.
In the analysis method according to the present invention, the exposed main surface 2a of the semiconductor substrate 2 in the PN junction region 1 is covered with a field effect crystal film 3 (FIG. 1b), and then the glass plate 4 is It is placed on the field effect type liquid crystal film 3. The coverage area of the field-effect liquid crystal film 3 and the shape and size of the glass plate 4 are set to a shape and size that can sufficiently cover the PN junction region 1 that is the object of analysis (FIG. 1c). Subsequently, as shown in FIG. 2, the sample 100 provided with the field effect liquid crystal film 3 and the glass plate 4 is placed under an optical system 200. The optical system 200 is for projecting light 7, which is obtained by polarizing light from the light source 5 using a polarizer 6, onto the PN junction region 1. Either the unpolarized normal light 7' from the light source 5'' is also projected onto the PN junction region 1, or this normal light 7'', unlike the optical path of the polarized light 7, is directly obliquely incident on the surface of the sample 100. P
The N-junction region 1 is irradiated, and the beam is uniformly reflected by the surface of the sample 100 and emitted. Therefore, the normal light 7'' does not pass through the eyepiece 11. On the other hand, the polarized light 7 passes through the prism 8.
, passes through the objective lens 9, the glass plate 4, and the field effect type liquid crystal film 3, reaches the PN junction region 1, and is reflected there. Then, the reflected light passes through the field effect liquid crystal film 3, the glass plate 4, and the objective lens 9 again and reaches the prism 8. The prism 8 is a semi-transparent mirror, and the reflected polarized light 7 travels straight, passes through an analyzer 10 and an eyepiece 11, and is observed by the human eye or a television camera. Objective lens 9, eyepiece lens 11
is provided to enlarge the minute PN junction region 1 for detailed observation. If the relative relationship between the polarizer 6 and the analyzer 10 in terms of the polarization plane is such that the analyzer 10 blocks the reflected polarized light 7, etc., then the field of view seen by the human eye or a television camera is If the analyzer 10 is in a completely dark state and the relative relationship of the analyzer 10 is such that it allows reflected polarized light 7, etc. to pass through, the field of view seen by the human eye or a television camera is a completely bright field.

Here, if a certain part of the field-effect liquid crystal film 3 has birefringence, the polarized light 7 etc. that passes through the part of the field-effect liquid crystal film 3 that has birefringence will be polarized. Rotation occurs in the wavefront, and in the field of view observed through the analyzer 10,
A bright field appears in a dark state, or a dark area appears within a bright field. By the way, it is well known that there is a phenomenon in which a photovoltaic force is generated when a PN junction is irradiated with light.

Therefore, even when the PN junction region 1 is irradiated with polarized light 7 or the like, a photovoltaic force is generated between the PN junction region 1 and the semiconductor substrate 2. If a photovoltaic force is induced, P
PN appearing on the main surface 2a of the semiconductor substrate in the N junction region 1
An electric field is also formed across the bonding line 1a. This electric field causes electric lines of force to pass through the field effect liquid crystal film 3, and the field effect liquid crystal film 3 causes birefringence due to this electric field. As described above, this birefringence rotates the plane of polarization of the polarized light 7, etc., and can be confirmed by the human eye or a television camera through the analyzer 10. However, if the PN junction characteristics of the PN junction region 1 are poor and cause a reverse leakage current, the photoelectromotive force induced by the polarized light 7 decreases, and the field effect liquid crystal film 3
The electric field weakens, and the brightness of the bright field in the dark state or the darkness of the dark part in the bright field observed through the analyzer 10 changes. In the past, it was possible to determine whether the PN junction characteristics were good or bad by comparing and observing a PN junction region with excellent PN junction characteristics and a PN junction region with poor PN junction characteristics. Although not shown in FIG. 1, many PN junction regions are formed in a semiconductor device such as an integrated circuit, so there are always several other PN junction regions around the PN junction region that requires pass/fail determination. Since the PN junction region group that is not subject to quality determination can be compared with the PN junction region that is subject to quality determination, it is possible to determine the quality of the PN junction characteristics. In addition, normal light was irradiated from a path other than the optical path of the polarized light 7 toward the PN junction region 1 to be analyzed caused by the PN junction leakage current. This results in a completely dark state or a completely bright field, which causes the PN junction leakage current to adversely affect other electrical circuits.

In other words, it is possible to prevent a defective portion from turning a normal portion into an abnormal one, and it is possible to accurately determine the quality of the PN junction. Depending on the type of field-effect liquid crystal, the degree of birefringence may be alleviated by light irradiation for a relatively long period of time, and the optical properties of the field-effect liquid crystal film 3 may not show electric field dependence. However, in this example, in this case, the polarized light 7
And since the light that is not polarized like normal light is used as intermittent light, the electric field effect of the liquid crystal is not weakened, and a clear P
N-junction quality determination can be performed.

The field effect liquid crystal film 3 is made of, for example, MBBA (P-Meth).
Oxybenzylidene-P-Butylani
A nematic liquid crystal such as LINE) is used.

The insulation resistance of a liquid crystal such as MBBA is 1010 Ω or more, and the leakage current caused by the liquid crystal is very small even if it is applied linearly onto the PN junction region. As described in detail above, the failure analysis method according to the present invention that can determine the quality of the PN junction characteristics of the PN junction region is such that a field effect liquid crystal film and a glass plate are provided on the PN junction region, and the PN junction region is connected to the PN junction region through these. Since polarized light and unpolarized light are simultaneously projected overlappingly and intermittently, the PN junction region of a fine pattern can be analyzed based on simple operations without forming any metal electrodes in the PN junction region. In this case, the PN junction leakage current does not adversely affect other electric circuits, and the electrolytic effect of the liquid crystal is not weakened.

If a local dark area or bright spot is found in the PN junction region, it is possible not only to simply determine the quality of the PN junction region itself, but also to discover defective locations.

Application of the failure analysis method of the present invention to integrated circuits, etc., which are becoming increasingly highly integrated and finely patterned, will provide clues and improvements to the formation of better PN junctions, and will further promote progress in semiconductor device manufacturing technology. It is.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of each step to explain a sample processing method when applying the failure analysis method for semiconductor devices according to the present invention, and FIG. 2 is an optical diagram for applying the failure analysis method according to the present invention. A schematic diagram of the system is shown. 1 is a PN junction region, 2 is a semiconductor substrate, 3 is a field effect liquid crystal film, 4 is a glass plate, 6 is a polarizer, 7 is polarized light,
8 is a prism, 9 is an objective lens, 10 is an analyzer, 11 is an eyepiece, 100 is a sample, and 200 is an optical system.

Claims (1)

[Claims] 1. In a method for analyzing failure of PN junction in a PN junction region in which impurities of a conductivity type opposite to that of the semiconductor substrate are diffused into the main surface of a semiconductor substrate, a field effect liquid crystal film sufficiently covering the PN junction region is formed in the PN junction region. A glass plate is formed on the bonding region and further covers the PN junction region sufficiently, and is placed on the field effect liquid crystal film to simultaneously emit polarized light and unpolarized light in an overlapping and intermittent manner. irradiating the PN junction region through the glass plate and the field effect liquid crystal film, and observing the light reflected from the PN junction region and the field effect liquid crystal with an analyzer. Failure analysis method.