JP2003109991A - Monitor for measuring film thickness and method for reproducing the monitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reproducing a monitor for film thickness measurement and a monitor for measuring film thickness that can be more effectively used for reproduction. SOLUTION: A silicon epitaxial layer E1 is formed on the main surface of a substrate S under the same condition as a product to make a monitor Ma. A diffusion layer D1 where impurities are diffused at such a concentration that an infrared light used for FTIR method is reflected, is formed on the entire surface of the monitor Ma, and it is reused as a monitor Mb for measuring film thickness. The monitor is made larger in thickness through a plurality of reuses, and its upper layer on the main surface side is removed and a silicon epitaxial layer is formed, then impurities are diffused over the main surface thereof to be reused for film thickness measurement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film thickness monitor used for measuring the film thickness of a silicon epitaxial layer when a silicon epitaxial layer is formed on the main surface of a silicon single crystal substrate, and a monitor reproduction. Regarding the method.

[0002]

2. Description of the Related Art Conventionally, when a silicon epitaxial layer (hereinafter simply referred to as an epitaxial layer) is formed on a main surface of a silicon single crystal substrate (hereinafter simply referred to as a substrate) by vapor phase epitaxy, For example, FTIR (Fourie
The thickness (film thickness) of the epitaxial layer is measured by the r Transform Infrared method or the like. The FTIR method is, for example, as shown in FIG. 3A, irradiating the main surface of a wafer (hereinafter referred to as an epitaxial wafer EPW) having an epitaxial layer E formed on a substrate S with infrared light L1.
Reflected light L2 reflected on the surface of the epitaxial layer E,
This is a method in which the reflected light L3 reflected at the interface between the epitaxial layer E and the substrate S is incident on a detector (not shown) and the optical path difference between them is measured to calculate the film thickness of the epitaxial layer E.

In this FTIR method, it is necessary to reflect light rays at the interface between the substrate S and the epitaxial layer E, so that
Usually, the substrate S is doped with impurities at a high concentration of 5 × 10 ¹⁸ atoms / cm ³ or more. However, when the impurity concentration of the substrate S is a low concentration of, for example, 2 × 10 ¹⁵ atoms / cm ³ or less, it becomes difficult to measure the film thickness by the FTIR method. Therefore,
FT in the epitaxial wafer EPW used as a product
If it is difficult to measure the film thickness by the IR method, separately from the product,
A substrate S doped with a high concentration of impurities is used as a monitor, silicon epitaxial growth is performed under the same conditions as the product substrate, and the film thickness of this monitor is measured to evaluate the product.

[0004]

By the way, the substrate S used for the monitor can be reused as a monitor if the epitaxial layer E formed on the main surface is removed by grinding after the film thickness measurement. It is possible. In that case, since the epitaxial layer E once formed on the main surface of the substrate S needs to be completely removed, the upper portion of the main surface of the epitaxial wafer EPW is as shown in FIGS. 3B and 3C. , Is removed thicker than the formed epitaxial layer E. Therefore, the reused substrate Sa is
It becomes thinner than the original substrate S.

The reused substrate Sa is reused as a monitor by removing the epitaxial layer again after forming the epitaxial layer and measuring the film thickness again. However, each time it is reused, this monitor substrate becomes thin, and eventually becomes a thickness that cannot be used as a monitor (FIG. 3D, substrate Sb). Therefore, the number of times the substrate S can be reused as a monitor is limited.

An object of the present invention is to provide a film thickness measuring monitor reproducing method and a film thickness measuring monitor that can be recycled more.

[0007]

The first means of the present invention for solving the above problems is, for example, as shown in FIG. 1, the entire main surface of a film thickness measuring monitor having a silicon epitaxial layer formed thereon. In addition, the method for reproducing a monitor for film thickness measurement is characterized by diffusing impurities having a concentration that reflects infrared light used in the FTIR method.

Here, to diffuse an impurity having a concentration capable of reflecting infrared light means that the entire main surface of the epitaxial layer (for example, the first epitaxial layer E1) is diffused (for example, the diffusion layer D1). Further, an epitaxial layer (for example, a second epitaxial layer) is formed,
Then, when the film thickness of the second epitaxial layer is measured by the FTIR method, it is possible to reflect the infrared light incident by the FTIR measuring device at the interface between the impurity diffusion layer and the second epitaxial layer. That is, the impurities are diffused to a certain concentration. If the diffused impurity concentration is lower than the concentration at which infrared light can be reflected, the infrared light is not reflected at the interface between the impurity diffusion layer and the second epitaxial layer, and thus the film of the second epitaxial layer is formed. This is because the thickness cannot be measured. The impurities may be diffused by any method such as a vapor phase diffusion method, a spin coating method, or an ion implantation method, and the diffused impurities may be any of boron, phosphorus, antimony, and the like. However, it is preferable to use antimony, which has a relatively small diffusion coefficient.

According to the first means, the impurity having a concentration for reflecting infrared light used in the FTIR method is diffused over the entire main surface of the film thickness measuring monitor on which the silicon epitaxial layer is formed. The film thickness measuring monitor having the impurity diffusion layer formed thereon can be reused as a monitor for forming an epitaxial layer on the main surface to measure the film thickness. Therefore, a silicon single crystal substrate that was once used as a film thickness measurement monitor can be regenerated as a film thickness measurement monitor without removing the epitaxial layer formed thereon, and can be reused. Becomes

A second means of the present invention is a method of reproducing the film thickness measuring monitor according to the first means, which comprises a step of forming a silicon epitaxial layer and diffusing impurities into the silicon epitaxial layer. After removing the upper layer portion on the main surface side of the film thickness measuring monitor that has been subjected to a plurality of steps, a silicon epitaxial layer is formed on the entire main surface of the film thickness measuring monitor, and impurities are further diffused. Characterize. The removal of the upper layer portion on the main surface side of the silicon single crystal substrate is not particularly limited, but is performed, for example, by grinding (further polishing if necessary).

For example, when a process of forming an epitaxial layer and measuring a film thickness on a silicon single crystal substrate, and further performing a plurality of steps of regenerating by diffusion of impurities and reusing as a monitor, the monitor is gradually thickened. If the thickness of the monitor exceeds a certain level, for example, there will be a large difference in thickness from the product substrate, and in an epitaxial growth apparatus, the height from the bottom of the counterbore of the susceptor on which the silicon substrate is mounted to the main surface of the monitor will increase. Due to a change (becomes larger) or the like, there is a possibility that an inconvenience such as an epitaxial layer having substantially the same film thickness as that of the product is not formed favorably or the epitaxial layer is not uniformly formed.
Therefore, as in the invention of the second means, the upper layer on the main surface side of the film thickness measurement monitor (thickness measurement monitor with an increased thickness to some extent) reused as the monitor multiple times is used for film thickness measurement. It is possible to reuse it suitably as a monitor by removing impurities so as to have a proper thickness and then diffusing impurities into the main surface. And
Further, when the monitor is repeatedly reused and the monitor becomes thick again, it is possible to suitably reuse it as a monitor by removing the main surface side upper layer portion again. Therefore, according to the second means, the silicon single crystal substrate can be suitably reused as a monitor a very large number of times, so that the cost can be reduced in forming the silicon epitaxial layer.

According to a third means of the present invention, a silicon epitaxial layer (for example, E1) is formed on the main surface, and an upper layer portion of the silicon epitaxial layer has a concentration that reflects infrared light used in the FTIR method. The film thickness measuring monitor is characterized in that a diffusion layer (for example, D1) in which impurities are diffused is formed over the entire main surface.

The film thickness measuring monitor of the third means is
A plurality of silicon epitaxial layers (for example, E1 and E2) in which the diffusion layers (for example, D1 and D2) are formed may be formed in the upper layer portion. It should be noted that multiple silicon epitaxial layers having diffusion layers are formed means that impurities are diffused onto the main surface of the film thickness measurement monitor having the epitaxial layers to use it once for film thickness measurement. This means that the formed monitor was regenerated as a film thickness measuring monitor, and the formation of the epitaxial layer and the diffusion of impurities were performed once or more.

According to the invention described in the third means, the upper layer portion of the silicon epitaxial layer formed on the main surface of the monitor for measuring the film thickness has a concentration that reflects infrared light used in the FTIR method. Since the diffusion layer in which the impurities are diffused is formed on the entire main surface, it can be suitably used as a monitor for film thickness measurement.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view showing a state in which a silicon single crystal substrate (hereinafter referred to as a substrate S) used for film thickness measurement is reproduced as a film thickness measurement monitor M by the monitor reproduction method of the present invention. is there.

The substrate S used for the monitor M is C
From a p-type or n-type silicon single crystal ingot manufactured by the Z method (Czochralski method) or the like, a chamfering step, a slicing step, a lapping step, an etching step,
A silicon single crystal wafer for vapor phase growth, which is manufactured through a silicon oxide film growth step by a CVD method, a mirror-polishing step, and the like and has a silicon oxide film formed on its main back surface, is used. The impurity doped into the silicon single crystal wafer may be any of phosphorus, boron, antimony, etc., but since the diffusion coefficient of antimony is relatively small and the interface between the substrate S and the epitaxial layer E hardly moves,
It is preferable to use a monitor M doped with antimony. The impurity concentration is FTIR.
The density used in the method is to reflect the infrared light, and is approximately 5 × 10 ¹⁸ ato
ms / cm ³ or higher is desirable.

When a silicon epitaxial layer is formed on the main surface of a product silicon substrate (hereinafter referred to as a product substrate) by vapor phase epitaxy, a substrate S for film thickness measurement is used to evaluate the film thickness of the product. The epitaxial layer is formed under the same conditions as the product substrate. This epitaxial layer is formed by a single-wafer vapor phase growth apparatus that processes silicon substrates one by one, or a batch type (eg, cylinder type or pancake type) that processes multiple silicon substrates at once. Any vapor phase growth apparatus may be used. In the present embodiment, the epitaxial layer is formed by a batch type vapor phase growth apparatus.

In the vapor phase growth, the substrate S as the monitor M is placed on the susceptor of the vapor phase growth apparatus together with the product substrate,
Monitor M by heating means provided in the vapor phase growth apparatus
The silicon source gas and the dopant gas containing impurities are circulated for a predetermined time together with a carrier gas such as hydrogen while the above heating is performed. The conditions such as the heating temperature, the gas flow rate (flow velocity), the gas composition, and the time are appropriately set in order to form a desired epitaxial layer. In the film thickness measurement by the FTIR method, the impurity concentration of the epitaxial layer to be measured is 1 × 10 ¹⁷ atoms / c
If it is m ³ or less, infrared light is favorably reflected at the interface between the substrate S and the epitaxial layer E. Therefore, even in the film thickness measurement performed in this embodiment, the impurity concentration is 1 × 1.
It is preferably applied when forming an epitaxial layer of not more than ¹⁷ atoms / cm ³ .

After the vapor phase growth, the film thickness of the epitaxial layer E formed on the substrate S is measured by the FTIR method.
The measurement result is used for evaluation of the epitaxial wafer manufactured in the same batch as the monitor M. 1 for film thickness measurement
The monitor Ma used once is shown in FIG. E1
Is a first epitaxial layer formed on the substrate S.

A method of regenerating a monitor (monitor having the epitaxial layer E1 formed on the main surface) Ma once used to a monitor Mb usable again for film thickness measurement will be described. Impurities are diffused on the main surface of the monitor Ma (FIG. 1B). As impurities, for example, boron,
Any of antimony, phosphorus, arsenic, etc. may be used. Further, the diffusion method may be any method such as a vapor phase diffusion method, a spin coating method, an ion implantation method (in the case of ion implantation, further annealing heat treatment is preferably performed). Diffusion layer D1, an impurity is diffused to the infrared light used in the FTIR method is the concentration of reflecting, preferably equal to about 5 × 10 ¹⁸ atoms / cm ³ or more. In the present embodiment, antimony is diffused on the main surface of the monitor Ma by vapor phase diffusion using antimony trioxide as a diffusion source to form the antimony diffusion layer D1. By thus diffusing the impurities, the monitor Ma that has been used once is reproduced on the monitor (reproduction monitor) Mb that can be used for film thickness measurement (FIG. 1C).

After the epitaxial layer formation and the film thickness measurement were performed again on the reproduction monitor Mb (FIG. 1 (d),
Monitor Mc), similar to the playback method described above, monitor M
c When impurities are diffused on the main surface, it is reproduced as a monitor Md (FIG. 1E) that can be used for film thickness measurement. In this way, by performing impurity diffusion on the main surface of the monitor once the epitaxial layer is formed,
The used monitor is regenerated as a monitor for repeated film thickness measurement. This reproduction can be performed any number of times.

When the reproduction of the monitor M is repeated,
The thickness of the monitor M gradually increases as the epitaxial layer is repeatedly formed on the main surface thereof. When the thickness of the monitor M exceeds a certain level, for example, the difference in thickness from the product substrate becomes large, and in the epitaxial growth apparatus, the monitor is mounted on the spot of the susceptor on which the silicon substrate is mounted. When you do so, the height from the bottom of the spot facing to the monitor surface becomes large. as a result,
There is a possibility that the monitor may not be able to form an epitaxial layer having substantially the same thickness as the product substrate, or that the epitaxial layer may not be formed uniformly. Therefore, the upper layer on the main surface side of the monitor M, which has been reused multiple times to increase the thickness, is removed, and the monitor M is removed.
To an appropriate thickness. Then, by forming an epitaxial layer on the entire main surface and further performing impurity diffusion,
Play as a monitor. The removal of the upper layer portion on the main surface side of the monitor M is performed by grinding with a diamond grindstone or the like, and further polishing is performed if necessary.

After removing the upper layer portion, the monitor M has a smooth main surface and a uniform height (the monitor M has a uniform thickness) so that the formation of the epitaxial layer and the film thickness measurement can be performed appropriately. ) Is desirable. Further, the thickness of the monitor M after removing the upper layer portion may be a thickness within a range in which the epitaxial layer is appropriately formed, and may be, for example, about the initial thickness of the substrate S.

When the monitor M from which the upper layer has been removed as described above is reused repeatedly and becomes thicker,
The upper layer portion on the main surface side is removed again and reused as the monitor M. Such reproduction of the monitor M may be repeated any number of times.

As described above, according to the monitor reproducing method of the present invention, since the impurities can be diffused into the epitaxial layer formed on the main surface, the monitor M can be reproduced and thus the formed epitaxial layer can be reproduced. The monitor M can be reused without being removed, and the monitor M does not become thin each time it is reused. Further, when the monitor M is thickened to a certain extent due to repeated reuse, the upper layer portion of the monitor M can be removed and it can be suitably reused as the monitor M again. Therefore,
Monitor M for film thickness measurement very many times
Since it can be repeatedly played as a monitor and reused, the number of times it can be reused is increased compared to the past.
It is possible to reduce costs in film thickness measurement.

The present invention is not limited to the above embodiment. For example, the removal of the upper portion on the main surface side of the monitor M may be performed by etching. Also, the substrate S used for the monitor M has an impurity concentration of about 5 × 10 ¹⁸ ato in advance.
Although it is desirable that the silicon single crystal wafer is doped at ms / cm ³ or more, the main surface of the silicon single crystal wafer that is lightly doped with impurities may be subjected to impurity diffusion and used as a monitor. In addition, the monitor substrate may be formed by dividing a silicon single crystal wafer.

[0027]

EXAMPLE The substrate used for film thickness measurement is regenerated as a monitor by the monitor reproduction method of the present invention, an epitaxial layer is formed on the main surface thereof, and the film thickness is measured by the FTIR method. In this example, as a substrate for film thickness measurement, antimony was produced on the main surface with a mirror-finished diameter of 125 mm, a crystal orientation of <100>, manufactured by the CZ method.
Resistivity of about 0.01 doped at a concentration of 5 × 10 ¹⁸ atoms / cm ³
An n-type silicon single crystal wafer of Ω · cm is used. An n-type epitaxial layer having a thickness of 10 μm and a resistivity of about 5 Ω · cm (1 × 10 ¹⁵ atoms / cm ³ ) was formed on the entire main surface of this substrate by a batch-type vapor deposition apparatus, and then antimony trioxide was used. 5 × 10 ¹⁸ ato of antimony by vapor phase diffusion using
Diffuse over the main surface to a concentration of ms / cm ³ . Using the substrate on which the epitaxial layer has been formed and antimony has been diffused as a reproduction monitor, the following epitaxial layer formation and film thickness measurement are performed.

First, ten reproduction monitors ((1) to (1
0)), silicon epitaxial layers having different film thicknesses are formed by vapor phase epitaxy. For the vapor phase growth, a batch type vapor phase growth apparatus is used, a heating temperature of 1130 ° C., trichlorosilane as a source gas, phosphine (PH ₃ ) as a dopant gas, and hydrogen as a carrier gas are passed over the substrate for a predetermined time. Let At this time, the unused substrates ((11) to (20)) for film thickness measurement are placed one by one in the same batch. For each of the 10 playback monitors,
Epitaxial layers are formed by vapor phase growth to form various epitaxial layers.

The film thicknesses of the epitaxial layers formed on the reproduction monitors (1) to (10) were measured by the FTIR method, and were (1) 4.5, (2) 8.8, (3) 9.
6, (4) 10.0, (5) 10.1, (6) 10.5, (7) 12.6, (8) 12.9,
(9) 13.2, (10) 13.3 μm.

Similarly, when the film thicknesses formed on the unused substrates (11) to (20) were measured, the film thicknesses were (11) 4.5, (12) 8.9, (13) 9.7, (14) 10.2, (15) 10.
3, (16) 10.9, (17) 12.8, (18) 13.1, (19) 13.4, (20) 13.
It was 6 μm.

The film thickness on the reproduction monitors (1) to (10),
A graph for comparing the film thicknesses on the unused substrates (11) to (20) is shown in FIG. In Figure 2, the vertical axis is the playback monitor
The measured film thickness of the epitaxial layer formed in (1) to (10), and the horizontal axis is the measured film thickness of the epitaxial layer formed in the unused substrates (11) to (20).

As shown in FIG. 2, the film thickness of the epitaxial layer formed under the same conditions on the reproduction monitor and the unused substrate was measured by the FTIR method. Shows almost a straight line (the regression line is Y =
0.9733X + 0.0825). By comparing the reproduction monitor with the unused substrate, even when the epitaxial layer was formed on the reproduction monitor and the film thickness was measured by the FTIR method, the epitaxial layer was formed on the unused substrate as a monitor and the film thickness was measured. It can be seen that almost the same results are obtained as in the case. Therefore, there is no problem in reusing the monitor in which the epitaxial layer is formed with the impurities diffused as the monitor, and the monitor regenerated by the method of the present invention can be suitably reused for film thickness measurement. .

[0033]

According to the invention of the first means, a film thickness measuring monitor which has already been used for film thickness measurement can be regenerated as a substrate for monitoring without removing the epitaxial layer once formed. You can

According to the invention of the second means, the silicon single crystal substrate can be suitably reused as a monitor a very large number of times, so that the cost can be reduced in forming the silicon epitaxial layer. Become.

According to the third aspect of the invention, the upper layer portion of the silicon epitaxial layer formed on the main surface of the film thickness measuring monitor contains impurities having a concentration for reflecting infrared light used in the FTIR method. Since the diffused layer is formed over the entire main surface, it can be suitably used as a monitor for film thickness measurement.

[Brief description of drawings]

FIG. 1 is a side sectional view showing how a substrate used for film thickness measurement is regenerated as a monitor by a monitor regeneration method of the present invention. FIG. 1A shows a state in which an epitaxial layer is formed on a substrate, (b) is a state in which impurities are diffused on the main surface of the epitaxial layer, (c) is a reproduction monitor in which the impurity layer is formed, (d) is a state in which an epitaxial layer is further formed in the reproduction monitor, and (e) is the second time. It is a reproduction monitor on which the reproduction processing of is performed.

FIG. 2 is a graph showing a correlation when an epitaxial layer is formed on a main surface of a substrate not used for film thickness measurement and a reproduction monitor reproduced by the reproduction method of the present invention, and film thickness is measured. Is.

FIG. 3 is a diagram showing a method of reusing a conventional monitor.

[Explanation of symbols]

Ma Used monitor (monitor for film thickness measurement) Mb, Mc Regenerated monitor (monitor for film thickness measurement) S substrate (silicon single crystal substrate) E epitaxial layer (silicon epitaxial layer) E1 first epitaxial layer (silicon) Epitaxial layer) E2 Second epitaxial layer (silicon epitaxial layer) D1, D2 Diffusion layer

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2F065 AA30 BB22 CC32 FF41 HH03                       HH12 JJ08                 4M106 AA01 AA10 CA48 DH03 DH13                       DJ32                 5F045 AB02 AF03 AF19 GB09 GH09                       HA20

Claims (4)

[Claims] 1. A film thickness measuring monitor characterized by diffusing impurities having a concentration for reflecting infrared light used in the FTIR method, over the entire main surface of the film thickness measuring monitor having a silicon epitaxial layer formed thereon. How to play. 2. A film for measuring film thickness, wherein a step of forming a silicon epitaxial layer and a step of diffusing impurities into the silicon epitaxial layer are carried out a plurality of times, and then the upper layer portion on the main surface side is removed, and then the film is removed. The method for reproducing a film thickness measuring monitor according to claim 1, wherein a silicon epitaxial layer is formed on the entire main surface of the thickness measuring monitor, and impurities are diffused. 3. A silicon epitaxial layer is formed on the main surface, and an F layer is formed on the silicon epitaxial layer.
A monitor for film thickness measurement, characterized in that a diffusion layer is formed in which an impurity having a concentration for reflecting infrared light used in the TIR method is diffused over the entire main surface. 4. The film thickness measuring monitor according to claim 3, wherein a plurality of silicon epitaxial layers having the diffusion layer formed thereon are formed in an upper layer portion.