JPS59201436A - Measurement of density distribution of semiconductor carrier - Google Patents

Abstract

PURPOSE:To realize a simple, quick and highly accurate measurement by a method wherein, when a surface of a semiconductor substrate is removed in stages and the sheet resistance of the surface is measured at every stage to know the carrier density distribution along the depth direction of the substrate, the substrate and a monitor sample are put into a same processing chamber and their surfaces are subjected to dry etching at the same time and each sheet resistance is measured. CONSTITUTION:A rotary shaft 3, protruded from a driving mechanism 8, penetrates into a cylindrical processing chamber 1 and a sample table 5 is provided to the tip of the shaft 3 through an attachment member 4. On one end part of this sample table 5, a semiconductor substrate 6 to be measured and a monitor sample 7 are put side by side. The substrate 6 and the sample 7 are held between an electrode 9 and a facing electrode 10 and the gas from a plasma producing gas source 13 is introduced between two electrodes 9, 10 and the substrate 6 and a sample 7 are subjected to plasma etching simultaneously. This operation is repeated and at every operation the sample table 5 is rotated to make the substrate 6 and the sample 7 touch a probe of a resistance measuring instrument 14. The sheet resistance values are displayed by a diagram in an output equipment 17 through a processor 15 and the signal is also supplied to a memory 16 in which the concerning equations are memorized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for measuring carrier density distribution in the depth direction of a semiconductor substrate.

BACKGROUND ART AND PROBLEMS Conventionally, this type of measurement method includes a method of measuring the Hall effect, a method of measuring capacitance change of a pn junction, a method of measuring spreading resistance, and the like. However, all of these methods have drawbacks in that they are impractical due to their simplicity, accuracy, and narrow range of measurable impurity concentrations.

As a more improved measurement method, there is a method in which a microcomputer is used to automatically perform a series of steps for measuring carrier density distribution by combining anodic oxidation and chemical etching. According to this method, a thin oxide film is formed on the surface of the semiconductor substrate by anodic oxidation, then a minute amount of the substrate surface is removed together with the oxide film by chemical etching, and the p-sheet resistance ρS of the substrate surface is formed by the four-probe method. By repeating the process of measuring , the resistivity changes in the depth direction of the semiconductor substrate are sequentially determined from these measured values and the minute etching amount of the semiconductor substrate, and the carrier density distribution is determined from these resistivity changes. I try to find it by calculation.

However, in this measurement method, the actual etching amount of the semiconductor substrate is not measured, but the etching amount is obtained from a known relational expression between the oxide film removed by chemical etching and the thickness of the semiconductor substrate. Therefore, there is a drawback that the depth accuracy from the substrate surface is not sufficient. Furthermore, since this measurement method uses anodic oxidation and chemical etching, treatments such as cleaning and drying are required. Therefore,
Not only does it require equipment to perform these treatments, but it also requires a large number of steps, so it has the drawback that it takes time to measure. Furthermore, since a chemical agent such as hydronic acid is used as an etching solution, it is not preferable from the viewpoint of pollution.

Purpose of the Invention In view of the above-mentioned problems, an object of the present invention is to provide a carrier density distribution measuring method that can easily and quickly measure the carrier density distribution in the depth direction of a semiconductor substrate with high precision. It is something.

Summary of the Invention A method for measuring the carrier density distribution in the depth direction of a semiconductor substrate according to the present invention is to remove the surface of the semiconductor substrate stepwise and measure the sheet resistance of the surface of the semiconductor substrate each time. In the method of measuring the carrier density distribution in the direction, (a) the step of arranging the semiconductor substrate and the monitor sample in the same processing chamber and dry etching the semiconductor substrate surface and the monitor sample surface simultaneously; b) measuring the sheet resistance of the @2 semiconductor substrate surface and the monitor sample surface in the processing chamber; (C) determining the sheet resistance of the semiconductor substrate surface from the measured value of the sheet resistance of the monitor sample surface; Obtain the amount of etching, and calculate the carrier density of the semiconductor substrate at a depth that corresponds to the amount of etching from the surface of the semiconductor substrate from the amount of etching on the surface of the semiconductor substrate and the measured value of the sheet resistance of the surface of the semiconductor substrate. The above steps (a) to (c) are sequentially repeated. By doing this,
The carrier density distribution in the depth direction of a semiconductor substrate can be measured simply, quickly, and with high precision.

EXAMPLE Hereinafter, an example of a method for measuring the carrier density distribution in the depth direction of a semiconductor substrate according to the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a carrier density distribution measuring device for explaining this embodiment. In FIG. 1, a cylindrical processing chamber (1) is evacuated to a high vacuum by a vacuum evacuation system (2). A sample stage (5) is attached to one end of the rotating shaft (3) via a mounting member (4). On this sample stage (5) are a semiconductor substrate (6) whose carrier density distribution is to be measured and a sample for monitoring etching (7).
are placed adjacent to each other.

The sample stage (5) is connected to a drive mechanism (8) located outside the processing chamber (1).
) around the rotation axis (3). An electrode (9) and a counter electrode (10) are installed inside the processing chamber (1), and a high frequency power source t1υ is connected to the electrode (9) outside the processing chamber (1). In addition, the electrode (
9) is also connected to the temperature controller (1).The processing chamber (
1) A gas source (131) for plasma generation is connected in the vicinity of the electrode (9) and the counter electrode (lO).

A ρS measurement device (1@) using a four-probe method is installed at a location on the opposite side of the electrode (9) and counter electrode (10) with respect to the rotation axis (3) inside the processing chamber (1). The measuring device includes a computing unit ([ω
, memory and output device (17) are connected.

Next, a method for measuring the carrier density distribution in the depth direction of a semiconductor substrate according to this embodiment will be explained with reference to the carrier density distribution measuring apparatus shown in FIG. 1 configured as described above.

First, the semiconductor substrate (6) whose carrier density distribution is to be measured
After the specimens (7) for monitoring etching are placed adjacent to each other on the specimen stage (5) and placed at predetermined positions, the drive mechanism (8) rotates the rotation shaft (3) to remove the specimens. Move the stand (5) to connect the electrode (9) and the counter electrode (10).
). Next, a gas source (
13) into the processing chamber (1). Gas is introduced until the degree of vacuum in the processing chamber (1) reaches a predetermined value, and when the degree of vacuum becomes stable, the electrode (9
). At this time, the gas starts to discharge in the space between the electrode (9) and the counter electrode (uo), and active gas ions are generated. These active gas ions are located near the electrode (9) and the counter electrode (lO) at 1'1.
The generated vertical electric field is incident on the surfaces of the semiconductor substrate (6) and the monitoring sample (7), respectively. As a result, RIE progresses simultaneously in the depth direction of both the semiconductor substrate (6) and the monitoring sample (force).

After performing the above etching for a predetermined period of time, the application of high frequency to the electrode (9) is stopped. Next, the rotating shaft (3) is rotated by the drive mechanism (8) to move the sample stage (5) toward the ρS measurement apparatus side. After this, the probe of the ρS measuring device H is lowered to touch the surface of the semiconductor substrate (6) and the monitor sample (7).
) is sequentially measured.

In this case, G) is placed at a predetermined position on the sample stage (5).
A semiconductor substrate (6) and a monitoring sample (the probes were lowered to one of the surfaces to measure the ρS, and then these probes were raised once and then the probes were moved to the other surface. position and then lower the probe to the other surface to measure its ρS. Once this ρS measurement is complete, the drive mechanism (8
) to rotate the rotating shaft (3) and move the sample stage (5) again to position it between the electrode (9) and the counter electrode α0) (11). Next, electrode (9) from high frequency power source 1
The surfaces of the semiconductor substrate (6) and the monitoring sample (7) are simultaneously etched as described above by applying high frequency waves to the electrodes (9). After stopping the application of , the rotating shaft (3) is rotated by the drive mechanism (8) to move the sample stage (5) again to the ρS measuring device 0 (A) side, and then as described above. Measure the ρS of the semiconductor substrate (6) surface and the monitoring sample (force surface).Etching and ρB measurement of the semiconductor substrate (6) surface and the monitor sample (force surface) are repeated in the same manner.

The surface of the semiconductor substrate (6) measured by the ρB measuring device (a) and the ρS data of the monitoring sample (the respective ρS data of the force interface are sequentially sent to the arithmetic unit 5). Note that memory (16
), the relationship between the etching amount of the force and ρS and the relationship between the etching amount of the semiconductor substrate (6) and the monitoring sample (the force) have been experimentally determined and memorized in advance. Also, note the above! j a6) contains the relational expression ([)σ
D is also stored in advance. Therefore, the etching amount and ρ
The above relational expression for determining the carrier density from the above relationship experimentally determined for S and the measured value of ρS and the above ρ
From the data of S, the carrier density at a depth corresponding to the amount of etching of the semiconductor substrate (6) can be determined using the arithmetic algorithm ω. This measured value of carrier density may be output as a numerical value, a point on a graph, or both by the output device αη.

As described above, by repeating etching by RIK, ρS measurement, and carrier density calculation multiple times, the carrier density distribution in the depth direction of the semiconductor substrate (6) can be determined.

Next, a method for determining the carrier density distribution in the depth direction of the semiconductor substrate (6) from the redundant value of ρS on the surface of the semiconductor substrate (6) will be described in detail.

The initial surface of the semiconductor substrate (6) is set as the origin, and the positive direction of the X-axis is taken in the depth direction. Let ρsi be the measured value of ρB at a depth of xi. Here, i=1°2.3. −
and xi+1>xi.

If the average resistivity of the semiconductor substrate (6) in the region of xi≦X≦xi++ (xi → 1−xi−△xi) is ρi, then the following equation is obtained: correction−Δxi / (1/ρsi −1/ρsi+1)
I). On the other hand, the specific resistance, carrier density and mobility of the semiconductor substrate (6) are expressed as ρω, respectively as a function of X.
n (expressed as → and μ(x), ρ) = 1/qs(t)・n(2) 0. Here q is unit charge. Generally, μ(2) is also a function of n(→, but if we consider a micro region with uniform carrier density in the depth direction, the mobility will be constant, so it is the well-known Irvjn equation. From the bonds, it is possible to find the Kaida of ρ and n.Therefore, by substituting the shoulder obtained by the above equation (I) into ρ of the (Company) equation, the carrier density ni corresponding to ρi can be found. It is possible to set this ni to the carrier density in one plane, where xi≦X≦zi−+1, but there is a method of setting it to the carrier density in ()(i++−xi)/2, for example.

By sequentially determining ni as described above, the carrier density distribution in the depth direction of the semiconductor substrate (6) can be obtained.

Next, a method for purchasing and manufacturing a monitoring sample (sword) used in this example will be explained in the case where the semiconductor substrate (6) whose carrier density distribution is to be measured is a Si substrate.

Figure 2 is an enlarged partial sectional view of the monitor sample (sword cross section and groove structure). This monitor sample (7) is fabricated as follows.
2 film (2) is grown, and then a polycrystalline Si film (c) sufficiently doped with phosphorus is deposited on this 5i02 film by CVD method. Since the relationship between the film thickness of i1l123 and ρS is close to a proportional relationship, the etching depth of this film can be measured from the change in ρS of the polycrystalline Si film as etching progresses. However, in general, the above inverse proportionality relationship does not hold strictly, so it is preferable to find the relationship between the core thickness and ρS of the polygonal crystalline Si film 1.-, 3) empirically in advance. .

The amount of etching of the semiconductor substrate (6) and the monitoring sample (7) at one time can be selected as required. An example of the amount of etching for 01 times which should be large is 200A. If the amount of etching is as high as this, it is possible to obtain a fairly dense A/Seyaria distribution.

It goes without saying that the amount of enching may be different each time.

As mentioned above, the amount of enching per time is t,... If it is 20
When 0A is used, the time required for one cycle from the start of etching to obtaining the carrier density value is about 6 to 4 minutes, which is extremely short.

The embodiment described above has many advantages, including:

First, etching of the semiconductor substrate and monitoring sample and ρ
Since the S measurement is performed in the same processing chamber, the carrier density distribution can be measured easily and quickly. Second, since the semiconductor substrate and the monitoring sample are simultaneously etched and the etching amount of the semiconductor substrate is obtained from the etching amount of the monitoring sample, carrier density distribution with high depth accuracy can be easily obtained. can be obtained.

Sixth, since the semiconductor substrate and the monitoring sample are etched by RIE, there is no need for cleaning, drying, or other processes that are required for chemical etching, and therefore no equipment is required to perform these processes. becomes. Fourth, since the etching and ρS measurements of semiconductor substrates and monitor samples are performed in a processing chamber in a vacuum state, the amount of etching and ρS caused by exposure of these semiconductor substrates and monitor samples to the atmosphere can be reduced. The measurement error of ρS can be removed. Fifth, since data processing is performed using an arithmetic unit and memory, the carrier density distribution can be automatically measured.

In the above embodiments, etching is performed by RIE, but other dry etching methods may be used as long as the uniformity of the etching amount is good. Furthermore, the method for measuring ρB is not limited to the four-point probe method.

Of course, the monitor sample should be changed as necessary depending on the type of semiconductor substrate whose carrier density distribution is to be measured.

Effects of the Invention According to the method for measuring the carrier density distribution in the depth direction of a semiconductor substrate according to the present invention, the semiconductor substrate whose carrier density distribution is to be measured and the sample for monitoring thereof are placed in the same processing chamber, and the surface of these substrates is measured. The carrier density is determined by dry etching and ρS measurement, and the carrier density distribution is measured by sequentially repeating these steps. Therefore, the steps, equipment, and time required to measure the carrier density distribution can be significantly reduced, and the carrier density distribution can be measured simply and quickly.

Furthermore, since the etching amount of the semiconductor substrate is determined from the measured value of ρS on the surface of the monitoring sample, it is possible to measure the carrier density distribution with high depth accuracy.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a carrier density distribution measuring device for explaining the present invention in detail, and FIG. 2 is an enlarged partial sectional view showing the cross-sectional structure of an example of a monitoring sample used in an embodiment of the present invention. It is. In addition, in the symbols used in the drawings, (1) ・Processing chamber (5)・・Sample stage (6)・Semiconductor substrate (force・monitoring sample u4)・・ρB measuring device (15)
-... Arithmetic unit (IO memory Uη - - Output device υ... - St substrate 4 - 5102 film (2)... - Polycrystalline St film. Agent Katsutsuneaki Ueya Yoshio Toshiki Sugiura

Claims (1)

[Scope of Claims] A method for measuring the carrier density distribution in the depth direction of the semiconductor substrate by removing the semiconductor substrate surface stepwise and measuring the sheet resistance of the semiconductor substrate surface each time, comprising: (a) arranging the semiconductor substrate and the monitor sample in the same processing chamber and dry etching the semiconductor substrate surface and the monitor sample surface at the same time; (b) the semiconductor substrate surface and the monitor sample in the process chamber; (C) obtaining the amount of etching on the surface of the semiconductor substrate from the measured value of the sheet resistance on the surface of the sample for monitoring; and the step of obtaining the carrier density of the semiconductor substrate at a depth corresponding to the etching amount from the surface of the semiconductor substrate from the measured value of the sheet resistance of the surface of the semiconductor substrate, respectively, and (a) A method for measuring carrier density distribution in a semiconductor substrate, characterized in that the steps from (C) to (C) are repeated in sequence.