JP3355531B2 - Calculation method of impurity concentration in silicon substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a impurity in the silicon substrate
More specifically, the present invention relates to a method for calculating an n-type impurity concentration accurately during a manufacturing process of a silicon semiconductor device.
The present invention relates to a method for calculating an impurity concentration in a silicon substrate .

[0002]

2. Description of the Related Art In a silicon semiconductor device, the performance of a semiconductor is determined by the concentration of impurities contained in the semiconductor.
Setting the impurity concentration is an important condition in semiconductor manufacturing. For this reason, the method of determining the impurity concentration in the semiconductor by a simulation based on a calculation in consideration of the heat treatment and the formation of an oxide film in the semiconductor manufacturing process has been already implemented in addition to the method of determining the impurity concentration in the semiconductor. If it is possible to obtain an accurate impurity concentration by simulation,
Compared with the case where it is determined experimentally, not only the time is shortened, but also the cost of various materials used in the experiment is reduced, and efficiency and economy can be achieved as a whole. However, conventionally,
In the calculation of the n-type impurity concentration in the silicon semiconductor,
Since an accurate calculation method has not been proposed, the efficiency has been hindered.

[0003] This example will be described by taking as an example the case of phosphorus which is a typical n-type impurity in a silicon semiconductor.

When a silicon oxide film is formed on the surface of silicon containing phosphorus, phosphorus is distributed at the boundary between the silicon and the oxide film according to a segregation coefficient determined by the thermodynamic properties of the silicon and the silicon. It is known that a small amount segregates in a narrow region at the boundary between the oxide film and the oxide film.

[0005]

However, conventionally,
Since the fine segregation in the boundary region between the silicon and the oxide film was considered to be on the silicon side, it was assumed that the segregated impurities would not be removed in the oxide film removal process performed during the semiconductor manufacturing process. Has been implemented. Therefore, when a process including an oxide film removing process is performed, a large difference occurs between the calculated value and the experimental value.

[0006] The present invention has been made in view of the above points,
Improves the accuracy of the impurity concentration calculation results and allows the optimum concentration determined by experiment to be set efficiently in a silicon substrate
It is an object of the present invention to provide a method for calculating an impurity concentration .

[0007]

SUMMARY OF THE INVENTION In the silicon substrate of the present invention ,
The method for calculating the impurity concentration of
Introduce n-type impurities into the substrate and heat-treat
After the etching, a process step including a step of removing the oxide film is performed.
In the calculation method of impurity concentration in the recon substrate, the diffusion method
Calculate the impurity concentration distribution after heat treatment by the formula
Exponential function of impurity concentration on silicon surface calculated from distribution
Is calculated by the segregation amount calculation formula based on
Calculates the amount of impurity segregation on the film side and oxidizes the amount of impurity segregation
Average than impurity distribution in silicon substrate
In the silicon substrate after removing the oxide film
Know the impurity distribution of .

[0008]

[0009]

[0010]

According to the present invention, segregation of n-type impurities forms a silicon oxide film on the surface of the silicon substrate and segregates at the boundary. Conventionally, this segregation was thought to occur on the silicon side. However, since it was found that segregation actually occurred on the oxide film side, it was confirmed that the segregation layer of the n-type impurity was removed in the oxide film removing step. It can be introduced into the method of calculating the concentration. Thereby, the accuracy of the calculation result of the impurity concentration in the semiconductor substrate is improved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has been proposed based on a novel finding on the segregation phenomenon of n-type impurities at the interface between silicon and an oxide film. The new knowledge of the segregation phenomenon is that the segregation phenomenon occurs not on the silicon side but on the oxide film side, which will be described below.

FIG. 1 is a diagram for explaining preconditions of the present invention. In the figure, each step is shown on the left side of the graph. The figure shows that a sample in which an oxide film is formed on a silicon surface is ion-implanted with phosphorus, and heat treatment is performed with the oxide film formed. The sheet resistance of the impurity layer of the sample (b) subjected to the thermal oxidation treatment after partially removing the oxide film without performing the step was measured.

In the sample (a) heat-treated with the oxide film formed, the sheet resistance increases due to the time (15 seconds to 27 seconds) of the partial removal of the oxide film performed thereafter. On the other hand, in the sample (b) in which the oxide film was partially removed without the heat treatment, it is apparent that the sheet resistance did not change.

From this result, it can be seen that phosphorus segregation at the interface of the silicon oxide film occurs on the oxide film side. That is, since a part of the ion-implanted phosphorus is segregated to the oxide film side by the heat treatment and is removed together in the step of partially removing the oxide film, the phosphorus in the silicon from the sample (b) not subjected to the heat treatment is reduced. It is considered that the sheet resistance increased due to the decrease in the density of the sheet. However, assuming that the segregation of phosphorus is on the silicon side as conventionally thought, the concentration of phosphorus in silicon does not differ between the above samples (a) and (b), and the experimental results should be explained. Can not.

The present invention has been developed based on the above-described novel findings.
When calculating the type impurity concentration, it is proposed to introduce a step of removing a concentration corresponding to the segregation of phosphorus in the step including the oxide film removing step.

FIG. 2 shows the configuration of an apparatus for calculating the impurity concentration in a semiconductor substrate according to one embodiment of the present invention. In the figure, an n-type impurity concentration calculation device includes a concentration distribution storage unit 10, a heat treatment condition input unit 11, a concentration distribution calculation unit 12, and a segregation amount calculation unit 1.
3. It is composed of the output unit 14.

The pre-change concentration distribution storage unit 10 of the n-type impurity concentration calculator is a computer memory for storing the impurity concentration at the depth from the substrate surface in correspondence with the depth from the surface in the silicon substrate. Yes, it is stored together with the concentration distribution before the heat treatment step and the concentration distribution after the heat treatment. The information on the concentration distribution is rewritten as the process proceeds. The heat treatment condition input unit 11 inputs a heat treatment temperature, a heat treatment time, and a heat treatment parameter.

In the concentration distribution calculation section 12, starting from the impurity concentration before the heat treatment stored in the concentration distribution storage section 10, based on the condition input by the heat treatment condition input section 11,
The impurity concentration distribution after the heat treatment is calculated from the diffusion equation and stored in the concentration distribution storage unit 10 again. Further, the segregation amount is calculated from the surface impurity concentration distribution obtained by the segregation amount calculation unit 13 by the following equation. Ne = 5.7E-9 × Cs × exp (0.70 ^eu / k
T) where Ne (cm ⁻² ) indicates the amount of n-type impurity segregation toward the oxide film at the interface between the substrate and the oxide film, and Cs (cm ⁻³ ) indicates the impurity concentration on the substrate surface. T is the absolute temperature during the heat treatment.

Further, the segregation amount calculation unit 13 subtracts the segregation amount from the impurity concentration distribution in the substrate stored in the concentration distribution storage unit 10 and stores the changed impurity distribution.
That is, in order to prevent the total amount of impurities from increasing by the amount of segregation, a process of averagely subtracting the amount of segregation from the impurity distribution in the substrate is performed. Specifically, {1- (amount of segregation / total amount of impurities in the substrate after calculation of the amount of segregation)} * (impurity concentration at each depth in the substrate after calculation of the amount of segregation) was calculated, and the result was calculated. Is stored in the density distribution storage unit 10 again. Further, the output unit 14 edits the data into a format that can be visually confirmed, and puts the data into a state in which the data can be output to a printer, a CRT display, or the like.

FIG. 3 shows an algorithm of an oxide film removing step according to one embodiment of the present invention. Step 1: After the n-type impurity is introduced, a pretreatment such as a heat treatment is performed. Step 2: It is determined whether or not to perform the oxide film removing process. If not, the process proceeds to the next process. Step 3: If an oxide film removal process is performed in step 2, it is determined whether or not a heat treatment process is performed as a process before step 2, and if a heat treatment process is included in the pretreatment, oxide film and segregation layer impurities are removed. Do. Step 4: If there is no heat treatment step in the pretreatment, only the treatment for removing the oxide film is performed.

In the above algorithm, when the calculation of the n-type impurity concentration is performed because the segregation at the silicon oxide film interface occurs on the oxide film side, the step including the oxide film removing step corresponds to the segregation of phosphorus. A step of removing the concentration is introduced.

Although the above description has been given of the algorithm processing, in order to make use of the conventional simulation result calculated on the assumption that the segregation layer is on the silicon side in an actual process, the following process may be employed as a manufacturing process. That is, when an n-type impurity is introduced into silicon and then a predetermined heat treatment and an oxide film removing step are performed, the n-type impurity lost during the step corresponding to the segregation amount described above is removed. A compensating amount of ion implantation is added.

FIG. 4 shows a change in the concentration of the N well in the CMOS process according to one embodiment of the present invention. The process shown in the figure includes a dry oxidation process (950 ° C.), a phosphorus ion implantation process (100 keV, 2E13 cm ⁻² ), an annealing process (900 ° C., 30 minutes), and then an annealing process (1).
(P. 100 ° C., 360 minutes), annealing step (900 ° C., 30 minutes), and then removing the oxide film.
Dry oxidation (950 ° C, 55 minutes), annealing (1
Steps q1, q2, q3 of 100 ° C., 360 minutes) are similarly annealed (900 ° C., 30 minutes), then the oxide film is removed, and dry oxidation is performed (1000 ° C., 60 minutes).
), Oxidizing film removal treatment, dry oxidation (annealing (850 ° C, 15 minutes, 950 ° C, 390 minutes) processes s1, s2, s3, and s). 950 ° C, 55 minutes), annealing (850 ° C,
(T. 30 minutes).

FIG. 4 shows the comparison between the experimental value and the calculated value of the change in the concentration of the N-well in the CMOS process along each of the above-mentioned steps.
%.

A is an experimentally determined standardized concentration, which decreases as the process proceeds. B is a calculated value performed according to the present invention, and is in good agreement with a value obtained experimentally. However, in the conventional method shown in C, the concentration was slightly reduced, and the final step showed a large difference from the experimental value.

FIG. 5 is a conceptual diagram showing a difference in calculation of an impurity concentration in a substrate according to one embodiment of the present invention.

In the figure, the left side shows the case where the n-type impurity segregation according to the present invention is on the oxide film side, and the right side shows the conventional example where the impurity segregation is on the silicon substrate side. The horizontal line indicates the concentration level of the n-type impurity.

FIG. 2 shows a state before the process, and shows a silicon substrate containing an n-type impurity. Indicates a step of oxidation. The segregation layer is generated on the oxide film side, and is set on the silicon substrate side in the conventional case. Is an oxide film removing step. In this state, the oxide segregation layer on the oxide film side disappears, but the conventional segregation layer on the substrate side remains as it is. A further step is an oxidation step. A new segregation layer appears on the oxidation side according to the present invention, and the segregation layer remains as it is on the substrate side according to the prior art. The concentration difference occurs when the segregation layer appears on either the substrate side or the oxide film side. Therefore, when the segregation layer in the present invention is on the oxide film side and when it is on the silicon substrate side in the prior art, the calculated impurity concentration in the substrate is different, so that a concentration difference occurs.

[0029]

As described above, according to the present invention, the fact that the segregation layer of the n-type impurity present at the interface between the silicon and the oxide film is removed in the step of removing the oxide film is introduced into the method for calculating the impurity concentration. By doing so, it is possible to contribute to improving the accuracy of the calculation result. As a result, the efficiency of the optimal setting of the concentration, which has been conventionally obtained through many experiments, is improved, which can greatly contribute to higher efficiency and lower cost of semiconductor manufacturing apparatus development.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining preconditions of the present invention.

FIG. 2 is a configuration diagram of an apparatus for calculating an impurity concentration in a semiconductor substrate according to one embodiment of the present invention.

FIG. 3 is an algorithm of an oxide film removing step according to one embodiment of the present invention.

FIG. 4 is a diagram showing a change in the concentration of an N well in a CMOS process according to one embodiment of the present invention.

FIG. 5 is a conceptual diagram showing a difference in calculation of an impurity concentration in a substrate according to one embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10 Concentration distribution storage unit 11 Heat treatment condition input unit 12 Concentration distribution calculation unit 13 Segregation amount calculation unit 14 Output unit

──────────────────────────────────────────────────続 き Continued on the front page (56) References Applied Physics Letters, Vol. 24, No. 4, p. 200-202, USA, 1974 IEEE TRANSACTIONS ON ELECTRON DEVIC ES, USA, 1983, VOL. ED-30, Vol. 11, p. 1438-1453 Junichi Nishizawa, “Semiconductor Research Vol. 19, Super LSI Technology 6-Semiconductor Process Part 2”, Industrial Research Committee, Inc. (1982) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/265 H01L 21/223

Claims (1)

(57) [Claims] (1)On a silicon substrate with an oxide film formed directly on it
After introducing an n-type impurity and further performing a heat treatment,
Silicon substrate in process including process of removing oxide film
In the method of calculating the impurity concentration in Find the impurity concentration distribution after heat treatment by the diffusion equation, Impurities on the silicon surface calculated from the impurity concentration distribution
The concentration is calculated using the segregation amount calculation formula based on the exponential function.
By calculating the amount of impurity segregation on the oxide film side, The amount of impurity segregation is determined based on the silicon
By subtracting the average from the impurity distribution in the plate,
To know the impurity distribution in the silicon substrate after removing the oxide film
Characteristic method for calculating impurity concentration in a silicon substrate.