JPS62122227A - Method for evaluation of impurity doped layer - Google Patents

Abstract

PURPOSE:To make it possible to evaluate an impurity doped layer formed by use of high-energy ion implantation easily and accurately by forming a layer made of the material which enables it to selectively remove only that layer easily on a substrate of a semiconductor device. CONSTITUTION:On a substrate 12, a film 1 made of the material which can be removed selectively and easily is formed and after high-energy ion implantation into that substrate, only the upper layer is selectively removed by etching. For that, a conventional method can be applied to the evaluation of an impurity layer. In this case, the thickness of a deposited layer can be determined on the basis of the LSS theory. For example, when B (boron) is implanted is Si(silicon) with 1 MeV energy, a projection range Rp is 1.76mum and a standard deviation DELTARp is 0.136mum. A range within which an impurity concentration (CI) is seemed to be significant is + or -3DELTARp. Accordingly, it becomes enough to remove 1.35mum of Si. By converting this by an inhibition performance of the material of the deposited layer, the thickness of the deposited layer can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for evaluating impurity distribution in a semiconductor device, and particularly relates to a method suitable for evaluating an impurity doped layer formed using high-energy ion implantation. .

[Conventional technology]

Evaluation of impurity-doped layers formed using methods such as ion implantation and thermal diffusion in semiconductor devices is usually performed using the following methods. That is, 1) measurement of the carrier concentration distribution in the depth direction by repeatedly etching the surface layer by anodic oxidation etc. and measuring the layer resistance by the four-probe method;
2) Measurement of depthwise impurity concentration distribution by a combination of secondary ion mass spectrometry (SIMS) or Auger electron spectroscopy (AES) and sputter etching using an ion beam;
3) Measurement of impurity concentration distribution in the depth direction using RBS (lower backscattered light).

Among these, method 1) is the most common method in terms of measurement accuracy and simplicity.

As one area of ion implantation methods, high-energy ion implantation in which the implantation energy is on the order of M e V has been actively researched in recent years. High energy ion implantation
For example, solid state technology, 198
4, May issue, pages 211 to 216 (Solid
5tate Technology, pp211-
216, May (1984)),
This method has the advantage of allowing precise control of impurity distribution in deep regions and the creation of devices with new structures that can only be realized using this method. When ion implantation is performed, the ions are deposited in the second direction in the depth direction according to the LSS theory.
As shown in the figure, the projected range Rp and the standard deviation ΔRP are distributed. In the area of high-energy ion implantation, 1. For example, when boron (hereinafter referred to as B) is implanted into silicon (hereinafter referred to as Si) with implantation energy IMeV, Rp is 1.76 μm and ΔRp is 0.136 μm. becomes.

[Problem that the invention seeks to solve]

When evaluating an impurity-doped layer formed using high-energy ion implantation, using the conventional method described above, in methods 1) and 2), one surface layer is etched to a depth where the impurity concentration shows a significant value. Methods 2) and 3) have a problem in that the 5-distribution cannot be accurately determined because of the difficulty in measuring accuracy in deep regions.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a method that can accurately and easily evaluate an impurity-doped layer formed in a deep region by high-energy ion implantation.

[Means for solving problems]

When high-energy ion implantation is used, the impurity degree distribution at! The reason why I is difficult to determine is that impurities are distributed only in deep regions. In other words, since the impurity concentration value is not significant (WI, which is meaningless even if determined by 21t!I) is thick, 81
11, much of the information that should be determined is hidden. Therefore, if the upper layer, which is meaningless to measure, can be easily removed, the impurity distribution of the layer to be measured can be determined in the same manner as in the conventional method.

[Effect]

The present invention uses high-energy ion implantation to form a layer of a material that can be easily selectively removed using wet etching or the like on top of a substrate (e.g., Si) into which ions are to be implanted. This makes it possible to easily and accurately evaluate impurity-doped layers. Figure 1 shows its conceptual diagram. By forming a film 1 made of a material that can be easily selectively removed on top of the substrate 2, implanting high-energy ions into the substrate, and then selectively removing only the upper layer, the conventional method can be directly applied to evaluate the impurity layer. become. Here, the thickness of the deposited layer can be determined based on the LSS theory, which is an already established theory. For example, when implanting B with an energy of 1-M e V during S1, Rp is 1.76 μm.
, ΔRp is 0.136 pm, so the range in which the impurity concentration is considered significant is ±3ΔRp, so S'
i for 1.35 μm.

It would be best to remove it. If this is converted by the stopping power of the material of the deposited layer, the thickness of the deposited layer can be determined.

For example, if the deposited layer is 5 iOz, the ratio of the stopping power of Si and 5iOz for I M e V to B is 1.13, so the thickness is 1.52 μm. Appropriate thicknesses of the deposited layers can be determined using the same procedure for other combinations of substrates, deposited layers, and implanted ion species. FIG. 3 shows the relationship between the accelerating voltage and the appropriate deposited layer J5 when the substrate is Si and the deposited layer is SiO2. B,
The results are shown for three types of ion species: phosphorus (hereinafter referred to as P) and arsenic (hereinafter referred to as As). In this figure, the appropriate thickness range of the deposited layer is indicated by diagonal lines. Here, the upper limit corresponds to the case where the surface after removing the deposited layer is at the position Rp, and the lower limit corresponds to the case where the position 3ΔRP from the above surface is the position Rp. Further, this deposited layer needs to be formed with uniform film quality and film thickness in order to ensure accuracy of impurity layer evaluation.

〔Example〕

The present invention will be described in detail below using examples.

[Example 1] On an n-type, (100) plane orientation, 10Ω-marked Si substrate,
After depositing 5iOz'P and 0.7μm by low-pressure CVD, As was implanted at an energy of 2.5Mev and an implantation amount of IX 1011Icw-"T,t':/, followed by annealing at 1000°C for 30 minutes in a N2 atmosphere. HzO / HF = 20 / 1 5JOz was selectively removed using a Nox etching solution, and the active impurity distribution was determined by repeating anodization and layer resistance measurements. The results are shown in Figure 3. The concentration was 5×10”am-8, and the maximum concentration was 2×101G country-8 at a position 0.6 μm from the surface.

According to this embodiment, it is not necessary to remove the surface layer whose impurity concentration is not significant by repeated anodic oxidation, and it can be easily removed by one etching process, thereby making it possible to shorten the measurement time. The thickness of 81 layers that can be removed by one anodic oxidation is as follows: Electrolyte: KNOa supersaturated aqueous solution, 10 mA/f
f1 (current density at the sample surface) Under normal measurement conditions of constant current, oxidation for 1 minute results in approximately 20 layers m. Therefore, in this example, Si equivalent to SiO2 (deposited layer)
Approximately 50 times of anodic oxidation are required to remove the oxide film, and if the time required for the process of removing the oxide film is also considered, the measurement time can be shortened by approximately 1.5 hours by the present invention.

[Example 2] A positive photoresist 1 was placed on a Si substrate with the same specifications as in Example 1.
-AZ-III (manufactured by Silapray) was applied to a thickness of 1.7 μm, and then P ions were implanted at an implantation energy of IMeV and an implantation amount of I.times.10 "cn-". FIG. 4 shows the results of impurity concentration distribution determined using SIMS after removing the resist using a resist removal solution and a plasma oxygen asher. In addition to measurement results 3 in this example, impurity concentration distribution 4 obtained by SIMS when similar ion implantation was performed without using the method of the present invention is also shown. Here, in the measured values when the method of the present invention is not used, the position in the depth direction is a value obtained by subtracting the thickness of Si equivalent to the resist layer of this example.

When measured using the conventional method, the values are generally larger than those of this embodiment, and the distribution is more tailed. This is because when SIMS measures impurity concentrations in deep regions, it is difficult to detect true impurities due to effects such as the knock-on effect of sputtering ions and the fact that if the sputtered surface becomes dish-shaped, impurities in the surface layer are also detected at the same time. This is because it tends to be measured higher than the concentration. Therefore, in this embodiment, since these influences can be reduced, the reliability of the measurement results is significantly higher than that of the conventional method.

[Example 3] After depositing 0.3 μm of 5iaNa on an n-type, (100)-oriented GaAs substrate by low-pressure CVD, S
i is implanted, energy I M e V, implantation amount 5X1
Ion implantation at 0"■-2 and 5ia with boiling phosphoric acid.
N4 was selectively removed. FIG. 5 shows the impurity concentration distribution obtained by SIMS in Example 6 as well as in Example 2.
Similarly, the measurement using the conventional method has a large error, and the deeper the depth, the larger the measurement value 4 using the conventional method is than the measurement value 3 using the present invention.

[Embodiment 4] In the previous embodiments, measurement of the depth distribution of ion-implanted impurities has been described, but in this embodiment, the distribution of impurities within the wafer surface will be described. Conventionally, the layer resistance measurement method using the four-probe method has been used to evaluate the implantation uniformity of ion implantation layers, but it cannot be used directly to evaluate impurity-doped layers formed by high-energy ion implantation technology. do not have. The reason for this is as shown in FIG.

This is because a layer not doped with impurities is formed on the surface. According to the present invention, the film p shown in FIG.
Form a selectively removable layer of 1! Jt allows measurement of layer resistance. For example, B ion is 2 M e V
5 x 10”cm-2 implanted n-type (100)1
The layer resistance distribution on the 0Ω·− silicon wafer could be measured by setting the thickness of the selectively removable layer to 1.3 μm. The reason for the difference in film thickness from that shown in Figure 3 is as follows.
In the four-probe measurement method, the needle penetrates 0.5-1 μm into the substrate to be measured due to the needle pressure, and the lower limit of the film thickness shown in Figure 3 is 0.5 μm due to the needle pressure during measurement. -It becomes thinner by about 1 μm.

〔Effect of the invention〕

According to the present invention, when evaluating an impurity layer formed in a deep region using high-energy ion implantation, it is possible to improve measurement accuracy and shorten measurement time. In particular, one aspect of the present invention is that the above-mentioned effects can be obtained while using conventional measurement techniques as they are, rather than using a new impurity concentration measurement method.

The effects of its implementation are significant. In particular, it is an indispensable means for evaluating the implantation amount uniformity within the wafer surface.

[Brief explanation of drawings]

Figure 1 is a curve diagram for explaining the present invention in detail;
The figure is a curve diagram for explaining the conventional method. 3 to 6 are curve diagrams for explaining the present invention in detail. Fig. 1 Fig. 2 Attachment surface force 3I) +fllJM (, ayt) I
〆 Figure left city η・UQ distance (

Claims (1)

[Claims] Before the step of forming an impurity doped layer inside the semiconductor device, a step of depositing a layer of a material selectively removable by the semiconductor device on the semiconductor device, and after the step of forming the impurity doped layer, A method for evaluating an impurity-doped layer, the method comprising the step of removing a deposited layer.