JPS59970B2 - How to use the handbook - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention detects junctions (or boundaries) of P-N-N+ or N-P-P+ structures in semiconductors based on changes in induced current that occur when semiconductors are irradiated with light or electron beams. Concerning how to quickly determine location.

In particular, the present invention relates to a method suitable for measuring junction (or boundary) positions of the same conductivity type but different impurity concentrations. In semiconductor devices such as silicon, germanium, ■-V group, ■-■ group intermetallic compounds, p-p+
Alternatively, a structure such as N-N+, which has the same conductivity type but differs only in impurity concentration, is often used.

For example, in a power transistor, the collector layer is p-
Formed with p+ or N-N+ double structure, collector,
Efforts are being made to improve emitter saturation voltage characteristics (VcE(sat)) characteristics, etc. In this case, it is a well-known fact that the thickness of the low-concentration P or N layer has a large effect on the characteristics of the device. Conventionally, the method used to measure this type of concentration change boundary is to diagonally polish the measurement sample, then set an electrode needle on the polished surface and record the spreading resistance as a function of position. It took a long time to prepare and measure, and it was always necessary to correct the polishing angle of the measurement sample, so the measurement accuracy was not high. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a new method for determining a bonding position in a semiconductor substrate, which is easy to operate, takes a short measurement time, and has extremely high measurement accuracy.

The present invention focuses on the change in induced current that occurs when a semiconductor is irradiated with light or electron beams, and from this change in induced current, it is possible to directly, easily and quickly identify the junction position between multiple regions with different impurity concentrations in a semiconductor substrate. This method is characterized by the following.

That is, in the present invention, the junction formed between a plurality of regions having different impurity concentrations reaches the surface of the semiconductor substrate, and the surface of the substrate is covered with a thin insulating film by irradiating electrons or light onto the semiconductor substrate. This is a bonding position measuring method in which a charge inversion layer or an accumulation layer is formed on the surface of a semiconductor substrate, and then an electron beam or a light beam is scanned across the substrate surface across the bond that reaches the substrate surface. In the present invention, the cause of the formation of a charge inversion layer or an accumulation layer on the surface of a semiconductor substrate by irradiation with an electron beam or a light beam is determined by the surface states that are generally known to exist on the surface of a semiconductor substrate. , the occupancy rate of the diagonal surface states in the thin oxide film (insulating film) that normally exists naturally or the thin insulating film that has been actively provided changes, resulting in the formation of an inversion layer or an accumulation layer in the irradiated area. to cause.

The formation of this inversion layer or accumulation layer is greatly influenced by the impurity concentration of the semiconductor region, and the formation of the inversion layer or accumulation layer is more likely on the surface with a lower impurity concentration. An accumulation layer is formed, as a result of which the induced current is large, and the junction position between the regions can be determined by the difference in the induced current value. In this way, the method of the present invention, which takes advantage of the fact that the degree of formation of an inversion layer or accumulation layer on the surface depends on the impurity concentration in that area, is far superior to conventional measurements of this type. It becomes possible to easily identify the boundaries of multiple regions with different concentrations in the semiconductor. Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

Reference numeral 1 denotes an electron beam irradiated onto a sample in a scanning electron microscope; 2 a semiconductor substrate; 3 and 4 both semiconductor substrates having a conductivity type different from 2 and differing from each other only in concentration.

5 and 6 abrade the joint surfaces of the above regions.

The end faces of the bonding surfaces 5 and 6 each reach the surface of the semiconductor substrate. Reference numeral 7 indicates an amplifier for amplifying the induced current generated when the bonding surface of a semiconductor substrate having a PN junction such as 2, 3, or 4 is irradiated with an electron beam.

When the electron beam 1 is scanned across the end face of the PN junction as shown in Fig. 1, and the electromotive force induced at both ends of the PN junction is expressed as a function of the position X, the PN as shown in Fig. 2A is obtained. It has been well known that a curve having a maximum at the joining position can be obtained.

However, with such standard measurement methods, 3.
Two regions of the same conductivity type but different only in concentration cannot be distinguished, as in No. 4.

However, in the present invention, before measuring the surface of the sample to be measured under standard measurement conditions such as the upper surface, distribution measurement is performed in advance and the entire surface to be measured is irradiated with an electron beam having a large current value. After calculating this, if we perform the same observation as we obtained curve 8, we will obtain a curve 9 as shown in Figure 2B,
Not only the position 6 of the PN junction but also the position of the boundary 7 between two regions of the same conductivity type and different concentrations can be determined at the same time. In this embodiment, a three-layer structure such as P-N-N+ or N-P-P+ is used as the sample, but it goes without saying that samples having a structure of three or more layers can be identified in the same way.

Note that in the above embodiments, the measurement was performed using the electron beam of a scanning electron microscope. By changing visible or ultraviolet light, P by light
An inversion layer or an accumulation layer (formed to a depth of about 50 to 100 A from the surface) is formed on the surface where distribution measurement is to be performed, including the N junction, to increase the photovoltaic force at that time. Similar results can be obtained by performing similar measurements using this as an input to the instrument 7.

Also, as shown in Figure 3, a light beam of 10
After forming an inversion layer or accumulation layer on the surface by irradiating it with visible or ultraviolet light, the surface is scanned with an electron beam under normal standard conditions, and the induced current generated at that time is measured. Displaying the distribution as a function of position also provides similar results to the above embodiment. In addition, in the above embodiments, electric charges are accumulated on the semiconductor surface in the levels of the acid I that naturally exists on the semiconductor surface. Although we have shown an example of forming an inversion layer or an accumulation layer on the surface of a semiconductor substrate, it is also possible to intentionally form a thermal oxidation layer, an insulating layer formed by thermal decomposition, etc. on the surface of a semiconductor substrate. It is possible to give similar results.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the state of one embodiment of the present invention, and FIG.
The figure is a distribution diagram of the induced current given when the sample shown in Figure 2C is measured using the conventional method, and Figure 2B is a distribution diagram of the induced current given when similarly measured using the method of the present invention. FIG. 2C is a model diagram of a sample used in one embodiment of the present invention, and FIG. 3 is a schematic diagram showing the state of another embodiment of the present invention. The same reference numerals in the figures indicate the same or corresponding parts, 1 is an electron beam, 2 is a semiconductor substrate, 3 and 4 are semiconductor regions, 5 and 6
is a junction, 7 is an amplifier, and 10 is visible or ultraviolet light.

Claims (1)

[Claims] 1. A semiconductor substrate in which junctions formed in multiple regions with different impurity concentrations reach the surface of the semiconductor substrate, and the surface of the substrate is covered with a thin insulating film is irradiated with electrons or light, and the semiconductor substrate is A charge inversion layer or an accumulation layer is formed on the surface, and then an electron beam or a light beam is scanned across the surface of the substrate across the junction reaching the surface of the semiconductor substrate, and the induced current generated between the semiconductor substrates is detected. In a semiconductor substrate, the entire surface to be measured is irradiated with an electron beam having a large current value in advance when measuring the junction position between a plurality of regions having different impurity concentrations in the substrate. A method for measuring the joint position.