JP2744022B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a method of manufacturing a semiconductor device for forming a gettering site for removing heavy metal contamination and the like, and particularly relates to a method for manufacturing a gettering site on a substrate. And a method of manufacturing a semiconductor device formed on the main surface side of the semiconductor device.

(Prior Art) Heavy metal contamination introduced during the manufacturing process of semiconductor devices
It forms a center for trapping and emitting free electrons (holes) and causes leakage of a pn junction, thereby deteriorating the electrical characteristics of a semiconductor device. For example, in a MOS semiconductor device, a leak current due to heavy metal causes a decrease in mutual conductance and the like, which is a major cause of a decrease in yield. On the other hand, the recent increase in the number of elements of a semiconductor integrated circuit and the accompanying decrease in the dimensions of the semiconductor integrated circuit mean that a minute amount of contamination affects the element characteristics and the yield of the integrated circuit.

Conventionally, as a method of gettering such contamination, a method of mechanically damaging the back surface of the semiconductor substrate or introducing a high-concentration impurity and absorbing the contaminated heavy metal into the impurity has been used. However, since such a back surface treatment is performed in the early stage of the manufacturing process, there are disadvantages such as requiring an extra step to prevent contamination from the front surface and halving the effect after going through a number of heat treatment steps. there were.

Further, in manufacturing an integrated circuit, there is a problem that stress is applied to an element isolation region by a thick field oxide film, impurities such as heavy metals gather, and a leak current is easily generated.

(Problems to be Solved by the Invention) As described above, conventionally, in the method of forming the gettering site on the back surface side of the semiconductor substrate, an extra step must be performed to prevent contamination from the front surface, and the initial stage of the element process is required. However, there has been a problem that the gettering ability is reduced during a large number of heat treatments for forming a gettering site.

The present invention has been made in view of the above circumstances, and an object thereof is to form a gettering site that does not require an extra step and does not reduce its effect even after a number of heating steps. It is an object of the present invention to provide a method of manufacturing a semiconductor device, which can contribute to improvement in the manufacturing yield of semiconductor elements and the like.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is a pn of an element formed on a semiconductor substrate.
It is to form a gettering site on the main surface side of the substrate by performing ion implantation in a region deeper than the junction and optimizing the initial heat treatment conditions that follow.

That is, according to the present invention, in a method of manufacturing a semiconductor device having a gettering site, after forming a field oxide film for element isolation on a main surface of a semiconductor substrate, ion implantation is performed on the substrate through the oxide film to remove crystal defects. Nucleation followed by a first heat treatment at 900-1100 ° C. for 15
This is a method in which an inversion layer is formed immediately below the oxide film and oxygen is precipitated at the nucleus of the crystal defect.

(Operation) According to the present invention, gettering sites are formed on the main surface side of the semiconductor substrate, and contaminant heavy metals in the element formation region can be absorbed by the gettering sites, thereby improving the production yield of the element. It is possible to measure. Also, unlike the method of forming a gettering site on the back surface side of the substrate, there is no inconvenience that the gettering effect is reduced by half during the heat treatment step.

(Example) First, before describing an example, a basic principle of the present invention will be described.

The present inventors formed nuclei of crystal defects in a region several μm from the substrate surface by high-energy ion implantation of several MeV or more, and then performed heat treatment under various temperature conditions. As a result, the sample heat-treated at 900 to 1100 ° C is determined by ion implantation conditions when measured with a transmission electron microscope.
A dislocation loop was observed at the position of Rp (ion penetration depth). Further, when measurement was performed by secondary ion mass spectrometry, an oxygen peak was observed at the same position as that observed by the electron microscope, and it was confirmed that oxygen precipitation occurred at this position.

At a heat treatment temperature lower than 900 ° C. or higher than 1100 ° C., the dislocation loop was observed to decrease, and
In the case of heat treatment at 800 ° C. and 800 ° C., such precipitation of oxygen was hardly observed. The heat treatment time has little effect, but if it is too short, the precipitation of oxygen is insufficient even at a temperature of 900 to 1100 ° C. According to experiments by the present inventors, it has been confirmed that a heat treatment time of 15 minutes or more is sufficient.

In the sample in which such a precipitate is formed, no dislocation is observed in other regions. Therefore, by performing a heat treatment at a temperature of 900 to 1100 ° C. for 15 minutes or more after ion implantation as in the present invention, an oxygen precipitate layer can be formed on the main surface side of the substrate, and this gettering It can be used as a site.

Hereinafter, details of the present invention will be described with reference to the illustrated embodiments.

FIG. 1 is a sectional view showing a manufacturing process of a semiconductor device according to one embodiment of the present invention. First, as shown in FIG. 1A, 1 × 10 ¹⁵ cm ⁻² of phosphorus as an impurity 12 was implanted into a silicon substrate 11 at an acceleration voltage of 1.5 MeV. Five such substrates were prepared. This ion implantation was performed at room temperature. Next, as shown in FIG.
In a non-oxidizing atmosphere and a nitrogen atmosphere at 800, respectively.
Heat treatment was performed at 900, 1000, 1100, and 1200 ° C. for 20 minutes.
By this heat treatment, an oxygen deposition layer 13 was formed on the substrate surface side as shown in FIG. 1 (c).

When the cross-sectional structure of the sample was examined by a transmission electron microscope after the heat treatment, the substrate heat-treated at 900, 1000, and 1100 ° C. was about 1.1 from the substrate surface 10 corresponding to Rp as shown in FIG.
It was confirmed that oxygen was precipitated at a position of 7 μm.
Further, when each substrate was examined by secondary ion mass spectrometry, as shown in FIG. 3, the substrate heat-treated at 900, 1000 and 1100 ° C. had a peak of oxygen and a peak of oxygen near a depth of 1.7 μm at a depth of 1.7 μm. It was confirmed that. However, in FIG. 3, (a) is 800 ° C., (b) is 900 ° C., (c) is 1000 ° C.,
(D) shows the case where the heat treatment was performed at 1100 ° C, and (e) shows the case where the heat treatment was performed at 1200 ° C. It was also confirmed that the oxygen precipitate effectively functions as a gettering site in the subsequent device forming process. Note that the depth of 1.7 μm is sufficiently deeper than the element formation region in forming an ordinary element, and this gettering site does not cause any inconvenience in element formation.

As described above, in the method of the present embodiment, since the entire surface is ion-implanted at the initial stage of the formation of the semiconductor element, the gettering site can be formed in two steps of ion implantation and heat treatment at a predetermined temperature. Further, since the formed gettering site is a precipitate of oxygen, the number of gettering sites is larger than that of the conventional phosphorus gettering, and there is no problem such as outward diffusion. In the element formation process following this process, 900
In a high-temperature process at a temperature of not less than ° C, gettering ability is always added because oxygen is precipitated during the process and a new gettering site is formed. Therefore, the substrate crystallizing process can be easily and reliably performed by greatly simplifying the process, thereby contributing to an improvement in device manufacturing yield and the like.

 Next, another embodiment of the present invention will be described.

FIG. 4 is a sectional view for explaining a method of another embodiment of the present invention, which is an example applied to element isolation between MOSFETs of the present invention.

In this embodiment, field ion implantation is performed at high energy as in the previous embodiment, and a heat treatment similar to that in the previous embodiment is performed, so that a portion for gettering heavy metals or the like is formed immediately below the field. . FIG. 4 (a)
As shown in FIG. 7, after a field oxide film 42 was formed on a silicon substrate 41, field ion implantation 43 was performed at a high energy, and the same heat treatment as in the previous embodiment was performed. As a result, the inversion layer 44 was formed immediately below the field oxide film 42, and the oxygen precipitation layer 45 was formed in a region therebelow. That is, field ion implantation and gettering layer formation can be performed simultaneously.

Here, if the position of the oxygen precipitation layer 45 is too close to the field oxide film 42, there is a possibility that a leak may be given to element isolation. Further, the impurity concentration of the inversion layer 44 requires a certain amount or more for element isolation. Therefore, the ion implantation conditions are:
The dose is adjusted so that the dopant concentration directly below the field oxide film is sufficient for device isolation, and the implantation energy is used to reduce the oxygen precipitates formed around the projected range (Rp) of the implanted dopant for device isolation. It should be selected so that it is deep enough not to give a leak.

The conditions were selected in this manner, ions were implanted through the field oxide film, and then the same processing as in the previous embodiment was performed. As a result, there is almost no re-diffusion of the dopant even after the heat treatment step, and the device is isolated under the field oxide film, and at the same time, the device is leaked with a gettering site for removing the influence of impurities caused by the conventional stress. It could be formed in a sufficiently deep region to the extent that it was not. At this time
FIG. 5 shows the SIMS analysis results (results measured by secondary ion mass spectrometry). As described above, it is possible to further form a gettering site in substantially the same number of steps as in the conventional device isolation ion implantation.

After the step shown in FIG. 4A, a gate electrode 47 is formed via a gate oxide film 46 as shown in FIG. 4B, and the source / drain regions 48a and 48a are formed using the gate electrode 47 as a mask. By performing ion implantation for forming 48b, two MOs separated by the field oxide film 42 are removed.
The SFET will be completed. Note that the ion implantation for forming the gettering site can be performed after the element is formed.

Thus, according to the method of the present embodiment, an oxygen precipitate layer can be formed on the substrate surface side, particularly immediately below the field oxide film, and this oxygen precipitate layer can be used as a gettering site. Therefore, the device manufacturing yield can be improved as in the previous embodiment. In addition, since the oxygen precipitation layer can be formed simultaneously with the field ion implantation, the manufacturing process can be simplified.

Note that the present invention is not limited to the above-described embodiments. For example, the heat treatment condition is not limited to 900 to 1100 ° C., but may be any temperature at which an oxygen deposition layer is formed on the substrate surface side. In our experiments, 900-110
It has been found that an oxygen precipitation layer is surely formed in the range of 0 ° C. Further, the heat treatment time is not limited to 20 minutes at all, and can be appropriately changed depending on conditions such as the ion implantation amount and the implantation depth. Generally, a processing time of about 15 minutes or more is sufficient. Further, the impurity to be ion-implanted is not limited to phosphorus, and an impurity that acts as a gettering site may be appropriately selected. In addition, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described above in detail, according to the present invention, ions are implanted into a region deeper than a pn junction of an element formed on a semiconductor substrate, and the subsequent initial heat treatment conditions are optimized. In addition, a gettering site whose effect is not reduced even after a number of heating steps can be formed, and it is possible to contribute to an improvement in the production yield of semiconductor elements.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a manufacturing process of a semiconductor device according to one embodiment of the present invention, FIG. 2 is a schematic diagram showing a cross-sectional structure of a sample after the above-described process, and FIG. FIG. 4 is a characteristic diagram showing the results of analysis by secondary ion mass spectrometry, FIG. 4 is a sectional view of a process for explaining another embodiment of the present invention, and FIG. It is a characteristic view showing the analysis result by the following ion mass spectrometry. 11,41: silicon substrate, 12,43: phosphorus (implanted impurity),
13,45 …… Oxygen precipitate layer, 42 …… Field oxide film, 44…
... Inversion layer, 46 ... Gate oxide film, 47 ... Gate electrode, 48
a, 48b: Source / drain regions.

Continuation of the front page (56) References JP-A-61-51930 (JP, A) JP-A-60-42840 (JP, A) JP-A-56-18430 (JP, A) JP-A-59-188925 (JP) , A) JP-A-60-84813 (JP, A)

Claims (2)

(57) [Claims] A step of forming a field oxide film for element isolation on a main surface of a semiconductor substrate; and a step of ion-implanting the substrate through the oxide film to form nuclei of crystal defects. The first heat treatment following 900-1
Forming a reversal layer immediately below the oxide film and depositing oxygen in the nuclei of the crystal defects at 100 ° C. 2. The conditions for the ion implantation are such that the dopant concentration under the oxide film is necessary and sufficient for element isolation, and the projected range (Rp) of the implanted dopant is set to a depth that does not give a leak current to the element isolation. 2. The method according to claim 1, wherein
The manufacturing method of the semiconductor device described in the above.