JP2008288378A - Monitor wafer manufacturing method and monitor wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a monitor wafer, capable of obtaining the measuring result of stabilized sheet resistance value in a short period of time, and a monitor wafer. <P>SOLUTION: An oxide film (SiO<SB>2</SB>) is formed on the monitor wafer. The implantation of p-type impurity is effected onto the monitor wafer, on which the oxide film is formed, to form p-well in the oxide film. Next, the p-type impurity is diffused inside by effecting heat treatment to activate the p-well. Wet treatment, employing a chemical solution obtained by mixing ammonia (NH<SB>3</SB>) water, hydrogen peroxide (H<SB>2</SB>O<SB>2</SB>) water and water, is applied immediately after removing the oxide film to form the oxide film forcibly. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a monitor wafer manufacturing method for measuring a sheet resistance value, and a monitor wafer.

  A semiconductor device is manufactured through a process of adding impurities to a silicon wafer (hereinafter simply referred to as “wafer”) by ion implantation. In the manufacturing process of a semiconductor device, the sheet resistance value of the wafer surface after the addition of impurities is measured for the purpose of quality control such as examining the concentration of the added impurities.

  The four-probe method is generally used for measuring the sheet resistance value. In addition, since the wafer surface is scratched by the contact of the probe during measurement, a monitor wafer having the same specifications is prepared separately from the product wafer, and the sheet resistance value of the monitor wafer is measured.

  Conventionally, when measuring the sheet resistance value, there has been a problem that the measurement value is changed with time and a stable measurement result cannot be obtained. The change over time of the measured value is caused by a natural oxide film formed on the wafer surface after ion implantation. That is, as the natural oxide film grows with time, the contact resistance between the probe and the wafer surface increases, and the measured value also increases.

In order to solve the above problems, various proposals have been made (see Patent Documents 1 and 2). In the method described in Patent Document 1, the natural oxide film on the wafer surface is removed immediately before starting the measurement of the sheet resistance value, and the measurement is performed in a measurement chamber into which an inert gas is introduced. In the method described in Patent Document 2, drive-in oxidation is performed on the wafer surface after 40 hours or more have elapsed since ion implantation, and measurement is performed.
Japanese Patent Laid-Open No. 07-106388 JP 2003-017424 A

  In the method described in Patent Document 1, it is necessary to strictly manage the measurement chamber so that oxygen does not enter, and there is a problem that the manufacturing cost increases. Moreover, even if strict management is performed, the invasion of oxygen is inevitable, and it is difficult to say that this is a fundamental problem solving method. In the method described in Patent Document 2, it is necessary to wait for 40 hours or more, which hinders shortening of the manufacturing time.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a monitor wafer manufacturing method and a monitor wafer capable of obtaining a stable sheet resistance measurement result in a short time.

  In order to achieve the above object, a monitor wafer manufacturing method of the present invention is a monitor wafer manufacturing method for measuring a sheet resistance value, immediately after removing an oxide film for ion implantation or ion implantation. After the removal of the oxide film, a step of forming an oxide film on the surface of the monitor wafer with a predetermined chemical solution during the growth period of the natural oxide film is provided.

  Note that the chemical solution is preferably a mixed solution of ammonia, hydrogen peroxide, and water, or a mixed solution of choline, hydrogen peroxide, and water.

  Further, it is preferable that the thickness of the oxide film be 0.5 nm or more and 1 nm or less.

  The monitor wafer of the present invention is a monitor wafer for measuring a sheet resistance value, and is characterized in that an oxide film is formed on the surface of the monitor wafer by a predetermined chemical solution before the measurement of the sheet resistance value.

  According to the method for manufacturing a monitor wafer and the monitor wafer of the present invention, an oxide film is formed on the surface of the monitor wafer by a predetermined chemical before measuring the sheet resistance value. The result can be obtained.

Hereinafter, an embodiment of the present invention will be described with reference to the flowchart of FIG. 1 and FIG. As shown in FIG. 2A, an oxide film (SiO ₂ ) 12 is formed on the surface of a monitor wafer (for example, an n-type bare silicon single crystal wafer) 11 (S1). Then, p-type impurity ions are implanted into the monitor wafer 11 on which the oxide film 12 is formed, thereby forming a p-well 13 inside the oxide film 12 as shown in FIG. 2B (S2). . Next, heat treatment is performed to diffuse the p-type impurity therein, and the p-well 13 is activated (S3).

Then, in order to measure the sheet resistance value R _s [Ω / □] of the monitor wafer 11, the oxide film 12 is removed as shown in FIG. 2C (S4). The oxide film 12 is removed using, for example, diluted hydrofluoric acid. Then, a wet process is performed immediately after the removal of the oxide film 12, and the oxide film 14 is forcibly formed as shown in FIG. 2D (S5). The sheet resistance value R _s is a value representing the resistance of a thin film having a substantially uniform thickness, and the resistance value R [Ω] of the thin film can be represented by R = R _s × L × W. . However, L shows the length of a thin film and W shows the width | variety of a thin film.

In the wet treatment, the monitor wafer 11 after removal of the oxide film 12 is immersed in a chemical solution in which ammonia (NH ₃ ) water, hydrogen peroxide (H ₂ O ₂ ) water, and water (H ₂ O) are mixed. This means that the oxide film 14 is formed on the surface of the monitor wafer 11. The thickness of the oxide film 14 is preferably not less than 0.5 nm and not more than 1 nm, which is the same as the thickness of the natural oxide film formed when the wet treatment is not performed.

  Thereafter, the sheet resistance value of the monitor wafer 11 on which the oxide film 14 is formed is measured by a four-probe method (S6). From the measurement result of the sheet resistance value, the implantation amount of the p-type impurity is converted to evaluate whether or not the ion implantation is performed correctly. A stable sheet resistance value can be obtained by measuring after forcibly forming the oxide film 14.

  In this case, the measurement result of the sheet resistance value is slightly higher because the oxide film 14 is interposed than when the surface resistance of the bare silicon single crystal wafer is measured. As you can see, the difference is so small that it does not affect the evaluation, so it can be ignored. Further, as a method for converting the implantation amount of the p-type impurity from the measurement result of the sheet resistance value, the relationship between the implantation amount of the p-type impurity and the sheet resistance value is obtained in advance by experiment, and the implantation amount is based on this data. Can be derived.

  In the above-described embodiment, the case where ion implantation of p-type impurities is described as an example. However, the present invention is not limited to this, and n-type impurities may be added instead of p-type or together with p-type.

In the above embodiments, aqueous ammonia, and hydrogen peroxide, although the case of using water and was mixed chemical solution has been described as an example, rather than being limited thereto, for example, choline ((CH _{3) 3} N ⁺ CH ₂ CH ₂ OHX ⁻ ), hydrogen peroxide solution, and water may be used. Choline is a quaternary saturated amine and is trimethylaminoethanol.

[Example]
Hereinafter, the present invention will be specifically described with reference to examples. First, the monitor wafer 11 was heat-treated to form an oxide film having a thickness of 10 nm (S1). Then, a p-type impurity is added to the monitor wafer 11 on which the oxide film 12 is formed at an energy of 40 keV (6.408 × 10 ⁻¹⁸ J) from a direction with a twist angle of 90 ° and a tilt angle of 7 ° (S2). ). The twist angle is a counterclockwise angle in the circumferential direction from a notch (not shown) formed on the peripheral edge of the monitor wafer 11. The tilt angle is an inclination angle with respect to the vertical direction with respect to the surface of the monitor wafer 11.

  Next, heat treatment was performed at 950 ° C. for 60 minutes (S3). Then, after removing the oxide film 12 (S4), ammonia water having a mass concentration of 28 to 30%, hydrogen peroxide water having a mass concentration of 34.5 to 36.0%, and water have a mass ratio of 1. : Wet treatment was performed using the chemical mixed at 4:20 (S5). The temperature of the chemical solution was 55 ° C., and the treatment time was 5.5 minutes.

[Comparative example]
Under the same conditions as in the example, formation of the oxide film 12 (S1), ion implantation (S2), heat treatment (S3), and removal of the oxide film 12 (S4) were performed. However, the wet process (S5) was not performed, and a natural oxide film was formed on the monitor wafer 11.

In the example and the comparative example, the sheet resistance value of the monitor wafer 11 was measured. As shown in FIG. 3, in the comparative example was not performed wet process (S5), the natural oxide film with the lapse of time from the removal of the oxide film 12 is grown, the sheet resistance value R _s is oxide film 12 immediately after removal Changed from about 957 Ω / □ to about 974 Ω / □, an increase of about 1.78% after about 300 minutes, and became substantially constant thereafter. In the embodiment was subjected to wet processing (S5) In contrast, the sheet resistance value R _s regardless of the passage of time was about 976Ω / □ and approximately constant. The value of the example was an error of only about 0.2% compared to the value after the change in the comparative example. Incidentally, the period from removal of the oxide film 12 to a sheet resistance value R _s is substantially constant, and the growth period of the natural oxide film.

  From the results of the above examples and comparative examples, it was confirmed that by performing the wet treatment (S5), a stable sheet resistance value can be measured regardless of the passage of time.

  In addition, when performing a wet process using the chemical | medical solution with which choline, hydrogen peroxide water, and water were mixed, it is preferable that the temperature of a chemical | medical solution is 70 degreeC and processing time shall be about 9 to 10 minutes. . The chemical solution at this time is preferably a mixture of choline, a hydrogen peroxide solution having a mass concentration of 34.5 to 36.0%, and water in a mass ratio of 1: 24: 36.6.

It is a flowchart which shows the flow of the manufacturing process of a monitor wafer. It is sectional drawing of the monitor wafer explaining a manufacturing process. It is a graph which shows the relationship between the elapsed time after removing an oxide film, and a measurement result.

Explanation of symbols

11 Monitor wafer 12 Oxide film 13 P well 14 Oxide film

Claims (6)

In the manufacturing method of the monitor wafer for measuring the sheet resistance value,
A method for manufacturing a monitor wafer, comprising a step of forming an oxide film on the surface of the monitor wafer with a predetermined chemical immediately after removing the oxide film for ion implantation.   2. The method for producing a monitor wafer according to claim 1, wherein the chemical solution is a mixed solution of ammonia, hydrogen peroxide, and water.   2. The method for producing a monitor wafer according to claim 1, wherein the chemical solution is a mixed solution of choline, hydrogen peroxide, and water.   4. The method for manufacturing a monitor wafer according to claim 1, wherein the oxide film has a thickness of 0.5 nm to 1 nm. In the manufacturing method of the monitor wafer for measuring the sheet resistance value,
A method of manufacturing a monitor wafer, comprising: forming an oxide film on a surface of the monitor wafer with a predetermined chemical solution during a growth period of the natural oxide film after removing the oxide film for ion implantation. In the monitor wafer for measuring the sheet resistance value,
Before the measurement of the sheet resistance value, an oxide film is formed on the surface of the monitor wafer by a predetermined chemical solution.

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