JPH05175166A - Method for measuring etched amount of semiconductor crystal - Google Patents

Abstract

PURPOSE:To provide a method by which the finely etched amount of a semiconductor crystal, in which a carrier concentration varies along its depth direction can be measured. CONSTITUTION:A carrier concentration profile in a crystal along its depth direction is found by a capacity-voltage (C-V) measuring method using a Schottky electrode before and after the surface of the crystal is etched and the etched amount of the crystal is found from the difference in film thickness of the crystal before and after the etching appearing in the carrier concentration profile. When this method is used, the finely etched amount of the semiconductor crystal can be measured in the order of 1nm. Therefore, this method can be effectively applied to the manufacturing process of a semiconductor device and evaluation of crystal growth which requires an accurate etched amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the etching amount of a semiconductor crystal, and more particularly to a method for accurately measuring the etching amount of a crystal whose carrier concentration changes from the surface to the depth direction.

[0002]

2. Description of the Related Art The etching amount of a semiconductor crystal is generally measured by a step measuring method. For example, as shown in FIG. 3, a photoresist 2 is applied to a part of the surface of the semiconductor crystal sample 1 and etched with an etching solution for a certain period of time. After the etching, the photoresist 2 is removed, and the step difference on the surface of the sample 1 caused by the etching is measured by a stylus type step meter or the like. This step is the required etching amount.

[0003]

The conventional etching amount measurement by the step measuring method has the following problems. That is, when the etching amount is larger than about 50 nm, the etching amount could be relatively accurately obtained by the step measuring method. However, in the case of etching shallower than about 50 nm, the resolution of the step measuring device itself is insufficient, and the unevenness of the surface of the etched sample becomes not negligible with respect to the etching depth. Therefore, the etching amount could not be accurately measured by the step measuring method. The present invention solves the above problems,
An object of the present invention is to provide a method for accurately measuring a minute etching amount of a crystal whose carrier concentration changes from the surface to the depth direction.

[0004]

In order to achieve the above object, the measuring method of the present invention uses a capacitance-voltage (C-
V) The carrier concentration profile in the depth direction of the crystal is obtained by the measurement method, and the etching amount is obtained from the difference in the film thickness of the crystal before and after the etching that appears in the carrier concentration profile.

[0005]

The conventional etching amount measurement has been caused by the mechanical measuring method such as a step difference meter, which causes the above-mentioned problems, whereas the method of the present invention is electrically measured by the CV measuring method. In addition, the carrier concentration profile before and after etching is obtained, and the etching amount is obtained from the difference in film thickness that appears in the profile. Therefore, it is possible to accurately obtain the etching amount with a resolution and accuracy of about 1 nm.

[0006]

[Example 1] An n-type GaAs epitaxial wafer formed on a semi-insulating GaAs substrate was 3 mm x
A sample was cut into a size of 20 mm. These eight-piece samples were etched with H ₃ PO ₄ : H ₂ O ₂ : H ₂ O = 3: 1: 50 etching solution for 10 to 120 seconds, respectively. The CV measurement was performed on the unetched sample and the above-described eight pieces of the etched sample by depositing gold on the surface to form a Schottky junction. C-
The carrier concentration profile in the depth direction of each sample obtained by V measurement was as shown in FIG.

From the sample surface, the carrier concentration is 5 × 10 ¹⁶
Table 1 shows the results obtained by defining the depth up to the point of cm ⁻³ as the film thickness of the epitaxial layer and obtaining the film thickness of each sample from the carrier concentration profile. Table 1 shows the film thickness D after etching of each sample from the etching time of 0 seconds to 120 seconds.
a is a list of film thickness differences De ′ between adjacent samples, and cumulative film thickness difference De. By this measuring method, the etching amount within a fixed time was obtained to the order of 1 nm.

[0008]

[Table 1]

Although the phosphoric acid type etching solution is used in the first embodiment, the method of the present invention is also applicable to the case of using another etching solution used for GaAs, such as sulfuric acid type or ammonia type etching solution. Needless to say, it can be applied. Further, the measuring method of the present invention can be applied to the case where the film thickness is reduced by polishing instead of etching. This is because the feature of the present invention is to accurately obtain the difference in film thickness from the comparison of carrier concentration profiles before and after the film thickness changes.

[Embodiment 2] The accuracy of the set etching amount (etching step) in the electrolytic CV method, which is a simple nondestructive measurement method for the carrier concentration and film thickness of a semiconductor crystal, was confirmed by using the method of the present invention. It was calibrated. The electrolytic CV method is
A certain etching step is set in advance, the semiconductor crystal is brought into contact with an electrolytic solution such as Tyrone solution, and the semiconductor crystal is etched by irradiating it with light or applying a voltage, and the boundary between the semiconductor crystal and the electrolytic solution. By utilizing the Schottky junction state of the surface, the relationship of capacitance (C) -voltage (V) is measured, and the carrier concentration at each etching step is obtained. The setting of the etching step is determined by the flowing current and the time for electrolysis (that is, the amount of charge).

The same GaAs epitaxial wafer as in Example 1 was measured by the electrolytic CV method. First, the n-type GaAs epitaxial layer having a thickness of 270 nm was removed by etching from the surface to a depth of 100 nm. Here, the carrier concentration profile of the sample was obtained by the CV method. Subsequently, the etching step by electrolytic etching was set to 5 nm, and the carrier concentration profile was obtained by CV measurement every time 20 nm or 10 nm was etched in 5 nm steps.

The obtained carrier concentration profile is shown in FIG.
Shown in. The film thickness for each etching is obtained from this profile, and the actual etching amount is obtained from the difference in film thickness between adjacent profiles. The results are shown in Table 2. The film thickness is represented by Da, the set etching amount is represented by Ds, and the film thickness difference between adjacent profiles is represented by De '. The total etching amount set value Ds was 160 nm, whereas the actual etching amount, that is, the total film thickness difference De ′ was 154 nm. It was confirmed that the actual etching amount was about 4% less than the set value.

[0013]

[Table 2]

The same electrolytic CV measurement as above was performed with the etching step set to 2 nm. The results are shown in Table 3. The total set etching amount Ds was 70 nm, while the actual etching amount was 86 nm. The actual etching amount is about 20% larger than the set value. As a result, in the electrolytic C-V measurement, it was clarified that an error was large when the etching step was 2 nm, but accurate etching could be performed almost as set when the etching step was 5 nm.

[0015]

[Table 3]

[0016]

According to the present invention, the minute etching amount of a semiconductor crystal can be accurately measured to the order of 1 nm. Therefore, it is effective when used for evaluation of semiconductor device manufacturing process and crystal growth, which requires an accurate etching amount. The method of the present invention is also an effective means for confirming the accuracy of the set etching amount in the electrolytic CV measurement and for calibrating the measuring device.

[Brief description of drawings]

FIG. 1 is a carrier concentration profile in a depth direction of each sample obtained in Example 1 of the present invention.

FIG. 2 is a carrier concentration profile in the depth direction of each sample obtained in Example 2 of the present invention.

FIG. 3 is a diagram showing a state of a sample when an etching amount is measured by a conventional method.

[Explanation of symbols]

 1: GaAs measurement sample 2: photoresist

Claims (1)

[Claims] 1. A carrier concentration profile in the depth direction of the crystal is obtained by a capacitance-voltage (CV) measurement method using a Schottky electrode before and after the etching of the semiconductor crystal surface, and before and after the etching that appears in the carrier concentration profile. A method for measuring an etching amount of a semiconductor crystal, wherein the etching amount is obtained from the difference in film thickness of the crystal.