JPH0798288A - Sample for secondary ion mass spectrometry, manufacture thereof and mass spectrometry using the sample - Google Patents

Abstract

PURPOSE:To provide the sample for SIMS analysis, which can accurately measure the concentration distribution of impuritied in a submicron region narrower than a raster region in the SIMS analysis. CONSTITUTION:In a sample 1 for SIMS analysis, a columnar region to be measured 2 having the constant cross-sectional area is formed on a semiconductor substrate 1A. A polysilicon layer is formed around the region 2 at the same hight as the region to be measured 2. The area ratio between the lighting region of the primary ion beam of the SIMS and the region to be measured 2 can be computed beforehand. Therefore, the impurity concentration in the region to be measured 2 can be measured based on this ratio and the computed value of the impurity concentration in the raster reion. When this sample is used, the impurity concentration of the region of 1mumX1mum or less can be measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for measuring the concentration distribution of impurities in a semiconductor layer, and more particularly to a technique which is particularly effective when applied to the concentration measurement of impurities by secondary ion mass spectrometry. The present invention relates to a technique useful for measuring concentration.

[0002]

2. Description of the Related Art Secondary ion mass spectrometry (hereinafter referred to as "SIMS
A technique for measuring the concentration distribution of impurities introduced into the semiconductor layer is known. This SIM
When S analysis is performed, the area irradiated with the primary ion beam (hereinafter simply referred to as “raster area”) is 1
A rectangular area having sides of about 50 to 100 μm is required.
This is because the focusing area of the primary ion beam is limited.

[0003]

However, the present inventors have clarified that the above-mentioned technique has the following problems. That is, in a recent semiconductor integrated circuit device whose submicron size has been achieved, the element region (measurement region) for measuring the impurity concentration distribution becomes small,
When this minute area becomes smaller than the raster area required for SIMS analysis (submicron area), the primary ion beam is also applied to an area other than the area to be measured, and the concentration information of the area is converted to secondary ions. They are picked up and the impurity concentration cannot be measured accurately. In order to know the concentration of such a minute region, it is conceivable to separately form a region (raster region) into which impurities are introduced under the same manufacturing conditions as this and measure the concentration of this region. However, even if the manufacturing conditions are the same, the concentration distributions do not always match and accurate concentration measurement cannot be performed.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a sample for SIMS analysis capable of accurately measuring the concentration distribution of impurities in a submicron region narrower than the raster region in SIMS analysis. Its main purpose. The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0005]

The typical ones of the inventions disclosed in the present application will be outlined below. That is, according to the present invention, a semiconductor region processed into a columnar shape having a constant cross-sectional area is formed on a substrate, and impurities are not introduced into the periphery of this semiconductor region, or impurities are introduced at a predetermined concentration. A semiconductor layer formed at the same height is used as a sample for SIMS analysis.

[0006]

In the SIMS analysis sample described above, the area of the first semiconductor layer and the area of the raster region irradiated with the primary ion beam are set to a predetermined area. The impurity concentration of the first semiconductor layer can be calculated based on the area ratio and the impurity concentration in the raster region.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an explanatory view showing how SIMS analysis is performed using the SIMS analysis sample of the present embodiment, and FIG. 2 is a plan view of the SIMS analysis sample. As shown in these drawings, the SIMS analysis sample 1 has a measured region 2 that is narrower than a region (raster region) 10 irradiated with the primary ion beam. In FIG. 1, reference numeral 1A
Indicates a semiconductor substrate which is a sample base. At the time of SIMS analysis, a primary ion beam is irradiated from a primary ion source to a predetermined range (raster area) on the sample 1 via a focusing unit (both not shown). Then, the secondary ion signal generated from the irradiation point on the analysis sample 1 is measured by the mass spectrometer 12. The impurity concentration measurement value obtained at this time represents the impurity concentration of the raster region 10. In this case, the area P of the measured region, the area S of the raster region, and the impurity concentration other than the measured region (in this embodiment, the concentration is 0 [c
If m ⁻³ ]) is known in advance, the impurity concentration of the measured region 2 can be calculated based on the impurity concentration of the raster region 10.

Next, the measured region 2 has a constant area (P).
A procedure of forming the sample 1 so that the above will be described with reference to FIGS. Of these, FIG. 3 is a flowchart showing the procedure up to the SIMS analysis. SIM
In performing the S analysis, first, the minute area 2A on the semiconductor substrate is specified (step 1), and a mask corresponding to the shape of the specified minute area 2A is manufactured (step 2).
According to a manufacturing process to be described later, a columnar measured region 2 having an upper surface area substantially equal to that of the minute region 2A is formed, and the periphery thereof is filled with a semiconductor layer of the same quality as the semiconductor substrate, which is not mixed with impurities, and SIMS analysis is performed. Sample 1 for use is manufactured (step 3). Then, using this sample 1, SIMS
Perform analysis (step 4).

FIG. 4 is a flow chart showing a mask manufacturing process for forming the measured region 2 which is substantially equal to the minute region 2A formed on the semiconductor substrate 1A. still,
In the LSI in which the SIMS analysis of the present embodiment is performed, the pattern formation is performed based on the electron beam drawing file. Therefore, in forming the mask pattern for specifying the measured region 2, An electron beam drawing file is used.

In this electron beam drawing file, each drawing pattern is represented by a four-vertex coordinate system, and these drawing patterns are aligned with reference to the origin coordinates, so that the electron beam drawing data is stored as a whole. I'm building. Therefore,
The mask pattern corresponding to the minute area 2A (measurement area) can also be specified by the alignment order from the origin coordinates and its size (step 11). Then, by leaving only the specific mask pattern corresponding to the minute area 2A and erasing all other drawing data, the remaining data can be used as it is as a mask pattern (step 12). A mask is actually drawn by including a margin in consideration of mask misalignment in the mask pattern obtained in step 12 (step 1
3). If the margin for misalignment is set in this way, the measured region 2 will not protrude beyond the minute region 2A, and the accuracy of impurity concentration measurement can be improved.

Next, using the above mask pattern, SI
5 to 1 for the procedure for forming the MS analysis sample 1.
This will be described with reference to FIG. In this example, a case will be described in which a SIMS analysis sample for measuring the impurity concentration of a predetermined impurity introduction layer in a device structure formed on a semiconductor substrate is actually formed according to a semiconductor manufacturing process.

FIG. 5 is a cross-sectional view showing a device structure manufactured according to the above manufacturing process, in which all structures (oxide film, wiring layer, passivation film) formed on a semiconductor substrate are removed. That is, in this example, the structure is such that the impurity diffusion layer (minute region 2A) for measuring the impurity concentration is exposed on the surface of the semiconductor substrate 1A. Then, the impurity concentration distribution in the depth direction of the impurity diffusion layer 2A formed on the substrate 1A is measured by the SIMS analysis method. The minute area can be an area (submicron area) smaller than 1 μm × 1 μm.

In forming the SIMS analysis sample 1, a resist film 3 is formed on a semiconductor substrate (base material) 1A,
This is exposed to a predetermined shape using the mask 4 (FIG. 6).
A negative resist is used to form the resist film 3. The resist film 3 is developed to leave the resist 6 having a desired shape on the minute region 2A, and this is used as a mask.
Anisotropic etching is performed in the direction of the arrow (FIG. 7). This anisotropic etching is performed according to the depth d at which the concentration distribution is performed. The structure obtained by this etching is shown in FIG. At this time, the measured region 2 having a columnar shape whose upper surface is substantially the same as the minute region 2A is formed. When the etching is finished, the resist 6 on the measured region 2 is removed (FIG. 9), and then polysilicon 8 is deposited on the entire surface (FIG. 10). Then, the polysilicon 8 is polished until the upper surface of the measured region 2 is exposed to obtain the SIMS analysis sample 1 having the structure shown in FIG. No impurities are mixed in the deposited polysilicon.

In the SIMS analysis sample 1 thus obtained, the area P of the upper surface of the measured region 2 is determined by the mask pattern, and the polysilicon 8 surrounding the measured region 2 is determined. No impurities have been introduced into.
Therefore, 1 is set for the raster area S shown in FIGS.
The concentration of the measured region 2 can be calculated based on the concentration when the secondary ion beam is irradiated and the SIMS analysis is performed. That is, the raster area 10 is aligned with the SIMS analysis sample 1 so as to surround the measured area 2 (FIG. 2), and the raster area 10 is
SIMS analysis is performed by irradiating with a primary ion beam.
In this case, the area P of the measured region 2 can be calculated based on the data of the mask pattern. On the other hand, the area S of the irradiation area (raster area) 10 of the primary ion beam is predetermined. Therefore, the impurity concentration (y) of the measured region 2 is calculated by multiplying the measured value (x) of the impurity concentration by SIMS analysis performed on the raster region 10 by the area ratio (S / P). it can. y = x × S / P

Similarly, a large number of regions to be measured are set on the semiconductor substrate, samples for concentration detection are manufactured, and the respective measurement results are combined.
It can also be measured dimensionally.

As described above, the SIMS of this embodiment
For the analysis sample, the area ratio (S / P) between the raster region and the measurement region is calculated in advance, and the measurement target is calculated based on this ratio and the calculated impurity concentration value (x) of the raster region. It becomes possible to measure the impurity concentration (y) in the region. When the sample of this example is used, the measurement target area can be defined by the minimum area that can be formed by the mask pattern, and therefore the area where the impurity concentration can be measured also depends on the minimum area. Will be decided. Incidentally, according to the sample of this example, it was possible to measure the impurity concentration in the submicron (1 μm × 1 μm or less) region.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say. For example, in the above embodiment, the SI for the submicron region on the substrate is
Although the MS analysis has been described, the impurity concentration can be detected in any size of area that is narrower than the raster area. Further, in the above-described embodiment, an example in which the measured region 2 is surrounded by polysilicon containing no impurities is shown. However, a semiconductor layer whose impurity concentration is known in advance is deposited, and the analysis sample is prepared. It may be formed.

[0018]

The effects obtained by the representative one of the inventions disclosed in the present application will be briefly described as follows. That is, the impurity concentration distribution in the submicron region, which is narrower than the raster region in SIMS analysis, can be accurately measured.

[Brief description of drawings]

FIG. 1 shows SIM using a sample for SIMS analysis of this example.
It is explanatory drawing which shows a mode that S analysis is performed.

FIG. 2 is a plan view of the SIMS analysis sample.

FIG. 3 is a flowchart showing a procedure up to performing SIMS analysis.

FIG. 4 is a flowchart showing a manufacturing process of a mask for forming a measured region 2.

FIG. 5 is a cross-sectional view showing a substrate structure from which a device structure formed on a semiconductor substrate has been removed.

FIG. 6 is a cross-sectional view showing a step of exposing a resist on a minute region to light.

FIG. 7 is a cross-sectional view showing a step of performing etching using the resist left on the minute region.

FIG. 8 is a cross-sectional view showing a measured region formed by etching.

FIG. 9 is a cross-sectional view showing a state in which the mask on the measurement region is removed.

FIG. 10 is a cross-sectional view showing a state in which polysilicon is deposited on the measured region.

FIG. 11: S formed by etching polysilicon
It is sectional drawing which shows the structure of an IMS sample.

[Explanation of symbols]

 1 SIMS Analysis Sample 1A Semiconductor Substrate 2 Measurement Area (Semiconductor Area) 2A Micro Area 8 Polysilicon S Area of Raster Area P Area of Measurement Area

Claims (3)

[Claims] 1. A semiconductor layer, which has a columnar shape with a constant cross-sectional area, is formed on a semiconductor substrate, and in which a semiconductor region doped with impurities is formed, and is not doped with impurities around the semiconductor region and which has the same height as the semiconductor region. 2 is formed
Sample for secondary ion mass spectrometry. 2. An impurity introduction layer of a semiconductor substrate is provided with a measured region having a constant area, and the semiconductor substrate other than the measured region is etched to a predetermined depth to form the semiconductor region,
The method for producing a sample for secondary ion mass spectrometry according to claim 1, wherein an intrinsic semiconductor layer is deposited thereon and the top surface of the semiconductor region is exposed by etching this. 3. The ratio of the cross-sectional area of the semiconductor region to the area of the irradiation region irradiated with the primary ion beam is obtained, and the impurity concentration in the irradiation region is measured by secondary ion mass spectrometry. The secondary ion mass spectrometry method using the sample for analysis according to claim 1 or 2, wherein the impurity concentration of the semiconductor region is calculated based on the measurement result and the ratio of the area.