JPH04340741A - Ion implantation amount measuring method, forming method of silicon crystal for ion implantation amount measurement and manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a method of absolutely measuring the distribution of the number of implanted ions in the depth direction, in the submicron region of silicon crystal. CONSTITUTION:Ions are implanted in silicon crystal 2 having a silicon oxide layer 3, at a part thereof, which is formed while sandwiching an interface 4 having a plurality of step-differences in the depth direction of the silicon crystal 2, and then the silicon oxide layer 3 is eliminated. The number of traces of ion implantation formed on each step of the step-wise interface 4 of the silicon crystal 2 is measured. On the basis of the difference of traces between adjacent steps, the distribution of the number of implanted ions on the depth direction from the silicon crystal surface is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the depth distribution of the number of ions implanted into a silicon crystal. Furthermore, the present invention relates to a silicon crystal for measuring the amount of ion implantation using this method, and a method for manufacturing a semiconductor device that uses this method to determine ion implantation conditions.

With the recent miniaturization of semiconductor devices, there is a need to control ion implantation in minute regions. For this purpose, it is necessary to measure the distribution of the amount of implanted ions in the depth direction in a minute region (submicron or less). The present invention relates to measuring the amount of ion implantation in such a semiconductor device, particularly during an ion implantation process used to adjust the gate voltage of a MOS.

0003

[Prior Art] Typical conventional techniques for measuring the distribution of the number of implanted ions in the depth direction include backscattering method, nuclear reaction method,
There are three methods: activation analysis method. Table 1 summarizes the characteristics of these three technologies.

0004

[Table 1]

[0005]

Problems to be Solved by the Invention As is clear from Table 1, the resolution of the number of implanted ions in the depth direction of the prior art is 0.
However, all of these prior art methods relatively measure the number of implanted ions using a calibration curve prepared in advance using a standard sample, and are not quantitative. The discussion of gender depends largely on the quality of this calibration curve. However, in order to prepare a good calibration curve, advanced techniques are required, so these conventional methods have the disadvantage that they cannot be easily performed.

[0006] Also, as is clear from Table 1, the horizontal resolution of the conventional measuring method was at most 10 μm or more. This makes it impossible to directly measure the number of ion implantations in the submicron region.

An object of the present invention is to provide a method for absolutely measuring the distribution of the number of ions implanted in the depth direction in a submicron region of a silicon crystal.

Another object of the present invention is to provide a method for producing a silicon crystal for use in measuring ion implantation dose using the method of the present invention. It is also an object of the present invention to provide a method for manufacturing a semiconductor device that achieves a desired distribution of the number of ions implanted in the submicron region of a silicon crystal in the depth direction.

[0009]

[Means for Solving the Problems] The ion implantation amount measuring method of the present invention includes a silicon crystal that partially has a silicon oxide layer formed across an interface having a plurality of steps in the depth direction of the silicon crystal. Ions are implanted so as to reach the interface through the silicon oxide layer, then the silicon oxide layer is removed, and the number of ion implantation traces formed at each step of the stepped interface of the exposed silicon crystal is measured. This method is characterized in that the distribution of the number of ion implantations in the depth direction from the silicon crystal surface is determined based on the difference in the number of ion implantation traces in adjacent stages.

[0010] The silicon crystal used to measure the ion implantation amount by this method is formed at the position where the ion implantation amount is to be measured, with an interface having a plurality of steps in the depth direction sandwiched therebetween. It has a silicon oxide layer. As shown in FIG. 2, this silicon crystal measuring section 1 is
The silicon crystal 2 and the silicon oxide 3 have a structure in which they are in contact with each other at an interface having a plurality of steps.

Referring to FIG. 1, the method for measuring the amount of ion implantation according to the present invention will be explained. FIG. 1(a) shows ions being implanted into the measurement part 1 of the silicon crystal of the present invention illustrated in FIG. An ion implantation trace 5 is schematically shown. Further, in this figure, d1 to d5 represent the depth from the surface of each step formed in the measuring section. After the ion implantation, the silicon oxide 3 is removed by etching with a hydrofluoric acid aqueous solution or the like. The number of ion implantation traces 5 formed on the stepped interface 4 thus exposed is measured for each step by an appropriate means. FIG. 1(b) schematically shows a silicon crystal having ion implantation traces 5 at each stepped interface after removing the silicon oxide layer, with n1, n2, n3, n4 marked corresponding to each step. , n5 represents the number of measured ion implantation traces. The difference in the number of ion implantation traces between adjacent stages is then determined, ie, they correspond to the number of ions remaining, ie, implanted, between the adjacent stages. For example, between the top stage (number of ion traces n1) of the silicon crystal 2 in FIG. 1(b) and the next stage (number of ion traces n2), in other words, the silicon crystal 2
The number of ions implanted in the range between depths d1 and d2 is the difference between n1 and n2 (i.e. n1 - n2 )
is equal to In this manner, by determining the difference in the number of traces of implanted ions in adjacent stages, it is possible to measure the distribution of the number of implanted ions in the depth direction from the silicon crystal surface.

To explain more specifically, FIG. 3 is a graph created with the vertical axis representing the difference in the number of ion implantation traces between adjacent stages and the horizontal axis representing the depth from the surface. If ion implantation can be considered uniform on each stage of the silicon crystal 2, the vertical axis of the graph in FIG. 3 is the depth d from the surface of the silicon oxide.
It can be interpreted as the number of ions staying between m and dm+1. This assumption of uniformity seems to hold true in normal ion implantation as long as a region larger than submicron is targeted. Furthermore, assuming that this silicon oxide is a silicon crystal, the distribution of the number of implanted ions in the depth direction can be calculated using an appropriate conversion method, such as the well-known Monte Carlo simulation software (TRIM 90), as shown in Figure 3. It can be obtained by converting the vertical axis of the graph.

[0013] In the ion implantation amount measurement method of the present invention, at a silicon oxide-silicon crystal interface having a certain depth,
When ions are implanted into the silicon crystal of the substrate through silicon oxide, the number of ion implantation traces created at the interface between the silicon oxide and the silicon crystal, within a certain implantation condition, matches the number of implanted ions that have passed through that interface. The I.
H. Report by Wilson et al. (Phy.Rev.B.38
, 8444 (1988)). The above-mentioned implantation conditions are conditions for ion implantation energy (acceleration energy), for example, As
If ions are implanted with an implantation energy of 200 keV or less, the number of ions passing through the interface will match the number of traces left at the interface. Beyond this critical implant energy, multiple traces will be created per ion passed. Therefore, ion implantation is preferably performed within a certain critical implantation energy range as described above, which is determined depending on the ion species.

[0014] The form of the trace formed at the interface is determined by the above-mentioned Wil
As described in the report by Son et al., when the implanted ion species is arsenic, the trace is crater-like, whereas when the implanted ion species is phosphorus or boron, the trace becomes a terrace-like elevation. is expected.

[0015] Appropriate means for measuring the number of ion implantation traces formed at the interface are a scanning electron microscope (SEM) or a scanning tunneling microscope (STM). Scanning electron microscopes have sufficient horizontal resolution, but no vertical resolution. On the other hand, a scanning tunneling microscope has a spatial resolution at the atomic level, so if you use this microscope to examine ion implantation traces, as Wilson et al. ) Even small, randomly distributed traces are not overlooked. Furthermore, the scanning range of a scanning tunneling microscope is usually 1 nm.
Since it can be freely changed from a corner to a 10 μm square, this microscope can be used to count the absolute number of ion implantation traces, that is, the absolute number of implanted ions that have passed through the interface, in the submicron region. Therefore, scanning tunneling microscopy is the most suitable means for measuring the number of ion implantation traces.

[0016] The above, as mentioned earlier,
This is for a silicon oxide-silicon crystal interface having a certain depth, and it is not possible to measure the distribution of the number of ions implanted into the silicon crystal in the depth direction using this alone. In order to make this possible, a silicon crystal for measurement is first prepared that has a silicon oxide layer formed across a step-like interface having a plurality of steps in the depth direction of the silicon crystal. Such a step-shaped interface can be formed with each step having a submicron angle and a step difference of 10 nm or less according to the method of the present invention described below.

[0017] A method for producing a silicon crystal having an ion implantation amount measurement portion in which silicon oxide and silicon crystal are in contact with each other across a stepped interface, in other words, a method for producing a silicon crystal according to the present invention is to A part of the silicon crystal is oxidized to form a silicon oxide layer, an oxygen impermeable film is placed on a part of the surface of this silicon oxide layer, and then the silicon crystal is exposed to an oxygen atmosphere again so that it is covered with the oxygen impermeable film. This method is characterized by forming a silicon oxide layer across the silicon crystal with an interface having a plurality of steps in the depth direction of the silicon crystal by further oxidizing the silicon crystal in the region where the silicon crystal is not oxidized.

In addition, the silicon crystal of the present invention is obtained by placing an oxygen impermeable film on the surface of the silicon crystal in advance, leaving a part of the area, and then exposing the silicon crystal to an oxygen atmosphere and covering it with the oxygen impermeable film. oxidize the silicon crystal in the area not covered by the oxygen impermeable film, then remove a part of the oxygen impermeable film adjacent to the oxidized area of the silicon crystal, and then oxidize the silicon crystal in the area not covered by the oxygen impermeable film. By doing so, it is also possible to fabricate according to a method characterized in that a silicon oxide layer is formed between a silicon crystal and an interface having a plurality of steps in the depth direction.

The method for producing these silicon crystals will be explained in more detail in the examples below.

Furthermore, the method for manufacturing a semiconductor device according to the present invention is characterized in that the ion implantation conditions are determined based on the distribution of the number of implanted ions determined by the above-described method for measuring the amount of ion implantation according to the present invention. be.

[0021]

[Operation] In the ion implantation amount measuring method of the present invention, after ion implantation, the number of ion implantation traces formed on the stepped interface of the silicon crystal obtained by removing the upper layer silicon oxide is measured, and Find the difference in the number of ion implantation traces in matching stages. The difference in the number of ion implantation traces between adjacent steps of this step-like interface corresponds to the number of ions that remain at a certain depth from the surface of the silicon oxide, and it is the same as the number of ions that remain at a certain depth from the surface of the silicon oxide. Enables conversion into numbers using an appropriate conversion method.

In addition, in the method of manufacturing a silicon crystal for measuring the amount of ion implantation of the present invention, ions are sequentially placed on the silicon oxide layer formed on the silicon crystal surface, or are placed on the silicon crystal surface in advance. The oxygen-impermeable film, which is subsequently removed successively, prevents the silicon crystal below this film from oxidizing during the silicon crystal oxidation process, thereby creating a step-like interface with multiple steps in the depth direction of the silicon crystal. Sandwiching allows the formation of a silicon oxide layer.

[0023]

EXAMPLES Next, the present invention will be further explained by examples.

Example 1 A silicon crystal for measuring the amount of ion implantation was prepared by sequentially arranging oxygen-impermeable films. The oxygen-impermeable film is a film that can effectively prevent oxygen from passing through when oxidizing a silicon crystal, thereby preventing oxidation of the underlying silicon crystal, and can be removed later leaving only the silicon crystal. It can also be from. An example of a suitable oxygen impermeable film is silicon nitride.

As shown in FIG. 6, an upper layer of silicon oxide 3 was prepared at five locations on a silicon substrate 7 having a diameter of 12.5 cm as described below. That is, an oxygen-impermeable film (silicon nitride) with an opening corresponding to the area where the silicon oxide layer is to be provided is placed on the silicon substrate, and the silicon substrate is exposed to an oxygen atmosphere. Only the silicon crystal 2 in the opening portion was changed to silicon oxide 3 to a depth of 10 nm, as shown in FIG. Next, an oxygen impermeable film 6 with a width of 0.5 μm is placed on a part of the silicon oxide 3, and the silicon substrate is exposed to an oxygen atmosphere again to crystallize the silicon in the area not covered with the oxygen impermeable film. was further oxidized by 10 nm. Subsequently, an oxygen-impermeable film having a width of 0.5 μm was added, and the silicon crystal in the region not covered by the oxygen-impermeable film was further oxidized by another 10 nm by exposing it to an oxygen atmosphere. In this way, five steps with a step difference of 10 nm and a step width of 0.5 μm were prepared. The number of steps, the difference in steps, and the width of the steps here are merely examples, and are not limited to these. Further, after each oxidation step, it is preferable to include an annealing step at 950 to 1100° C. to flatten the interface between silicon crystal 2 and silicon oxide 3.

[0026] 60 keV was applied to the object to be measured thus prepared.
Arsenic ions were implanted at a dose of 1×10 11 cm −2 , and then only silicon oxide was removed from the silicon substrate using a hydrofluoric acid aqueous solution as an etching solution. The number of crater-like ion implantation traces in each step of the exposed step portion of the silicon crystal was counted using a scanning tunneling microscope. An example of the number of traces on each stage is 40, 90, 130, 100, and 50 from the top. From this, the depth distribution of the number of arsenic ions implanted into the silicon substrate was determined as shown in Table 2. Table 2
The results are calculated using Monte Carlo simulation software TRIM 90, assuming that silicon oxide is a silicon crystal.

[0027]

[Table 2]

The number of ion implantations determined in this way could be obtained with good reproducibility if the implanted ion species and implantation conditions were the same.

Example 2 Using a method of sequentially removing the oxygen-impermeable film, an upper layer of silicon oxide was provided in the depth direction of a silicon substrate similar to that used in Example 1, and the object to be measured was made.

As shown in FIG. 5 (in this figure, only the part for measuring the amount of ion implantation is shown), an oxygen impermeable film 6 is formed on the silicon substrate except for the part where the silicon crystal 2 is first oxidized.
was placed, and the silicon substrate was exposed to an oxygen atmosphere to change the silicon crystal in the portion not covered by the oxygen-impermeable film to silicon oxide to a depth of 10 nm. Next, the oxygen-impermeable film was removed in a width of 0.5 μm, and the silicon substrate was exposed to an oxygen atmosphere again to further oxidize the silicon crystal by 10 nm. Subsequently, the oxygen-impermeable film with a width of 0.5 μm was further removed.
In the same manner, the silicon crystal was further oxidized to a thickness of 10 nm. In this way, similarly to Example 1, five steps with a step difference of 10 nm and a step width of 0.5 μm were prepared.

[0031] For the object to be measured thus prepared, the number of implanted ions was determined using the same procedure as in Example 1.
The same results as in Example 1 were obtained.

[0032]

As explained above, if the silicon crystal for measuring the ion implantation amount of the present invention is used and the measurement is performed according to the ion implantation amount measuring method of the present invention, the number of implanted ions in the submicron region of the silicon crystal can be measured. Absolute measurement of the distribution in the depth direction can be performed, making it possible to greatly contribute to the optimization of the ion implantation process into minute semiconductor devices.

Furthermore, according to the method of manufacturing a silicon crystal for measuring ion implantation amount of the present invention, a silicon crystal is formed in the depth direction of the silicon crystal suitable for measuring the ion implantation amount by the method of measuring ion implantation amount of the present invention. It is possible to produce a silicon oxide crystal in which silicon oxide is located across a step-like interface with a desired submicron-order step and step width.

Furthermore, if the ion implantation conditions are determined based on the distribution of the number of ions implanted in the depth direction determined by the ion implantation amount measuring method of the present invention, the distribution of the number of ions implanted in the submicron region in the depth direction can be determined as desired. Semiconductor devices can be manufactured with precise control.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the ion implantation amount measuring method of the present invention, in which (a) is a diagram schematically showing ions being implanted into a silicon crystal, and (b) is a diagram showing traces of ion implantation. FIG. 2 is a diagram schematically showing a step-like interface of a certain silicon crystal.

FIG. 2 is a diagram showing a measuring section of a silicon crystal for measuring the amount of ion implantation according to the present invention, in which (a) is a top view thereof, and (b) is a cross-sectional view thereof.

FIG. 3 is a graph showing the distribution of the number of implanted ions in the depth direction.

FIG. 4 is a diagram illustrating a method of manufacturing a silicon crystal for measuring ion implantation amount according to the present invention.

FIG. 5 is a diagram illustrating another method of manufacturing a silicon crystal for measuring the amount of ion implantation according to the present invention.

FIG. 6 is a diagram illustrating a silicon substrate for measuring the amount of ion implantation according to the present invention.

[Explanation of symbols]

1...Measuring part 2...Silicon crystal 3...Silicon oxide 4...Interface 5... Traces of ion implantation 6...Oxygen impermeable membrane 7...Silicon substrate

Claims (4)

[Claims] [Claim 1] Ions are applied to a silicon crystal having a silicon oxide layer in a part thereof, which is formed between an interface having a plurality of steps in the depth direction of the silicon crystal, so as to reach the interface through the silicon oxide layer. The silicon oxide layer is then removed, the number of ion implantation traces formed at each step of the stepped interface of the exposed silicon crystal is measured, and the difference in the number of ion implantation traces between adjacent steps is calculated. A method for measuring the amount of ion implantation characterized by determining the distribution of the number of ions implanted in the depth direction from the surface of a silicon crystal. 2. A part of the surface of the silicon crystal is oxidized to form a silicon oxide layer, an oxygen-impermeable film is placed on a part of the surface of the silicon oxide layer, and then the silicon crystal is placed in an oxygen atmosphere again. The method is characterized in that a silicon oxide layer is formed in the silicon crystal across an interface having a plurality of steps in the depth direction by exposing the silicon crystal in a region not covered with the oxygen-impermeable film and further oxidizing the silicon crystal. A method for producing silicon crystal for measuring ion implantation amount. 3. An oxygen-impermeable film is placed in advance on the surface of a silicon crystal, leaving a part of the area, and the silicon crystal is exposed to an oxygen atmosphere to remove the area of the silicon crystal that is not covered with the oxygen-impermeable film. oxidizing the silicon crystal, then removing a portion of the oxygen-impermeable film adjacent to the oxidized region of the silicon crystal, and then oxidizing the silicon crystal in the region not covered with the oxygen-impermeable film. A method for producing a silicon crystal for measuring ion implantation amount, the method comprising forming a silicon oxide layer across an interface having a plurality of steps in the depth direction. 4. A method for manufacturing a semiconductor device, characterized in that ion implantation conditions are determined based on the distribution of the number of implanted ions determined by the ion implantation amount measuring method according to claim 1.