JPH0756881B2 - Method of forming buried oxide film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a buried oxide film in which oxygen ions are ion-implanted into a silicon substrate to form a silicon oxide film in the substrate.

[Conventional technology]

FIG. 9 is a cross-sectional view showing a step in a conventional method for forming a buried oxide film. First, as shown in FIG. 9A, oxygen ions O ⁺ are ion-implanted into the silicon substrate 1 to form an O ⁺ ion-implanted layer 2. Figure 10 shows this O ⁺ ion implantation layer 2
² shows the concentration distribution of oxygen ions O ⁺ in the inside. The horizontal axis represents the concentration N (pieces / cm ³ ), and the vertical axis represents the depth x (μm) from the surface of the silicon substrate 1 in the downward direction. Also, the alternate long and short dash line in the figure
The projection range corresponding to the peak position of the density distribution is shown. This projective range is 0.5μ at an injection energy of 200 KeV.
It will be about m.

Next, heat treatment is performed at a high temperature of 1100 ° C. (in some cases, about 1300 ° C.) to react the ion-implanted oxygen ions O ⁺ with the silicon atoms Si in the silicon substrate 1 to produce a gas as shown in FIG. 9 (B). As shown, a SiO ₂ film 3 which is a buried oxide film is formed. In order to form a SiO ₂ film by reaction, oxygen ions O ⁺ are 10 ²¹
Pieces / cm ³ order is required, for example to form a SiO ₂ film of thickness 0.4μm requires a ion dose of about 3 × 10 ¹⁸ ions / cm ^2. In the region where the number of oxygen ions O ⁺ is 10 ²¹ / cm ³ or less, the SiO ₂ film is not formed even after the heat treatment. Therefore, as shown in FIG.
The membrane 4 remains. A semiconductor device such as a diode, a bipolar transistor, a MOSFET, and an integrated circuit including them is formed in the Si film 4.

[Problems to be Solved by the Invention]

However, in the above-described ion implantation method, as shown in the enlarged view of FIG. 11, dislocations 10 extending from the SiO ₂ film 3-Si film 4 interface into the Si film 4 and excess oxygen impurity precipitation 11 in the Si film 4 are caused. Patching-out dislocations 12, or stacking crystal defects 13 that reach the surface of the Si film 4 from the interface of the SiO ₂ film 3-Si film 4 are generated,
There is a problem in that the semiconductor device cannot have sufficient characteristics.

Further, N-type and P-type impurities are ion-implanted into the silicon substrate 1 in advance, an N-type and P-type Si film 4 (for example, a well layer) is formed on the SiO ₂ film 3, and a semiconductor device is formed therein. In the case of making it, it is necessary to implant the N-type impurities such as AS ⁺ (Hiso), Sb ⁺ (Antimony), and P ⁺ (Phosphorus), and B.
There is also a problem that the thickness of the Si film 4 finally obtained is different from the implantation region of P-type impurities such as ⁺ (boron). This will be described below with reference to FIGS. 12 and 13.

First, as shown in FIG. 12 (A) and FIG. 13 (A),
As P-type impurities such as As ⁺ , Sb ⁺ , P ⁺ as N-type impurities
B ⁺ or the like is ion-implanted into the silicon substrate 1 to form the impurity ion-implanted layers 5a and 5b. Next, as shown in FIG. 12 (B) and FIG. 13 (B), O ⁺ ion-implanted layers 2a, 2b are formed by ion implantation of oxygen ions O ⁺ . And
By performing the heat treatment, SiO ₂ films 3a and 3b are formed as shown in FIGS. 12 (C) and 13 (C). At this time, the impurity ion-implanted layer 5a of the silicon substrate 1 becomes amorphous by the ion implantation of a large-mass impurity such as As ⁺ or Sb ⁺ , whereas the impurity ion-implanted layer 5a of the silicon substrate 1 becomes amorphous with a small-mass impurity such as B ⁺ or P ^+. The ion-implanted layer 5b hardly becomes amorphous.
Therefore, the formation of the SiO ₂ film 3a when As ⁺ or Sb ⁺ is ion-implanted is suppressed, and the N-type Si film 4a is smaller than the P-type Si film 4b when B ⁺ or P ⁺ is ion-implanted. It is formed thick. For example, "SEMICONDUCTOR SILICON 1986, PROCEEDING OF THE FIF
TH INTERNATIONAL SYMPOSIUM ON SILICON MATERIALS SC
IENCE AND TECHNOLOGY, ELECTRONICS AND DIELECTRICS A
ND INSULATION DIVISIONS, Proceedings Volume 86-4, TH
E ELECTROCHEMICAL SOCIETY, INC., Pp. 642-651, SJ Krause et al. Reported that SiO ₂ film 3b was not formed on B ⁺ and P ^+.
It grows 30% larger and the P-type Si film 4b is less than the N-type Si film 4a.
It is about 1 μm thinner. Thus, the Si film 4a,
A different thickness of 4b affects the characteristics of the semiconductor device formed therein, such as the subthreshold current in MOSFET, which is not preferable.

The present invention has been made to solve the above problems, and it is possible to form a Si film on a SiO ₂ film, which has good crystallinity and whose thickness does not vary depending on the added impurities. It is an object to obtain a method for forming a buried oxide film.

[Means for Solving the Problems]

According to the method for forming a buried oxide film according to the present invention, the concentration is 10 ²¹ pieces / cm ³ or more between the first depth position of the silicon substrate and the second depth position deeper than the first depth position. And a method of forming a silicon oxide film in the substrate by implanting oxygen ions into the substrate so that the concentration at the first depth position is 10 ¹⁸ / cm ³ or more. After pre-implanting silicon ions into the substrate,
The oxygen ions are ion-implanted into the substrate, and then heat treatment is performed to form a silicon oxide film in the substrate.

In addition, following the ion implantation of the silicon ions, boron, phosphorus, hiso or antimony is ion-implanted into the substrate, and boron and phosphorus are ion-implanted at a predetermined ion implantation amount, and when boron or phosphorus is ion-implanted. 5 x 10
The ion implantation may be performed at ¹⁴ ions / cm ² or less.

Furthermore, before and after the ion implantation of the silicon ions,
Silicon ions may be ion-implanted into the surface of the substrate so that the concentration in the vicinity of the surface of the substrate is 10 ¹⁸ ions / cm ³ or more.

[Action]

In the present invention, since the silicon ion Si ⁺ ion implantation is performed prior to the oxygen ion O ⁺ ion implantation,
The silicon ion-implanted layer becomes amorphous and channeling development in the subsequent oxygen ion implantation is prevented, so that the concentration distribution of the ion-implanted oxygen ions becomes equal to the theoretical distribution. Further, the vacancies in the silicon substrate at the silicon oxide film interface are eliminated by the excess silicon, resulting in a nearly ideal silicon oxide film interface. Further, in the silicon film obtained on the silicon oxide film, the nucleus of the crystal defect induced by excess oxygen is eliminated by the excess silicon.

In addition, an N-type or P-type silicon film is obtained by ion implantation of boron, phosphorus, histories or antimony.

Furthermore, if silicon ions are superposed and ion-implanted on the surface portion of the substrate, it is possible to supplement the silicon atoms released from the substrate surface by high temperature heat treatment and prevent surface deterioration.

〔Example〕

FIG. 1 is a sectional view showing a process according to an embodiment of a method for forming a buried oxide film according to the present invention. First, Fig. 1 (A)
As shown in FIG. 3, silicon ions Si ⁺ are ion-implanted into the silicon substrate 1 to form a Si ⁺ ion-implanted layer 6. Second
The figure shows the concentration distribution of silicon ions Si ⁺ in the Si ⁺ ion implantation layer 6. As shown by the alternate long and short dash line in FIG.
In the ion implantation of silicon ions Si ⁺ , there is a projection range at the depth position of the silicon substrate (the shallower one of the two) where the concentration value of oxygen ions O ⁺ to be ion-implanted is about 10 ²¹ / cm ^3. Is done like. In this embodiment, the peak value of the concentration of silicon ions Si ⁺ is set to about 10 ²¹ / cm ³ , but the ion implantation amount can be reduced to a minimum of 10 ¹⁸ / cm ³ as described later. .

Next, oxygen ions O ⁺ are ion-implanted through the Si ⁺ ion-implanted layer 6 as in the conventional case, and as shown in FIG. 1 (B).
Si ⁺ and O ⁺ ion implantation layer 6c together with O ⁺ ion implantation layer 2c
To form. The concentration distribution of oxygen ions O ⁺ at this time is the second
It is set as shown in the figure. Then, by performing heat treatment at a high temperature, as shown in FIG. 1C, a SiO ₂ film 3c which is a buried oxide film is formed. Si ⁺ and O ⁺ ion implantation layer 6
c becomes the Si film 4c, and the semiconductor device is formed in the Si film 4c.

In this embodiment, since the silicon ion Si ⁺ is ion-implanted prior to the oxygen ion O ⁺ ion-implantation, there are the following advantages. First of all, the injection volume is 10 ¹⁸
Since the Si ⁺ ion-implanted layers 6 of not less than / cm ³ are completely amorphized, in the next step of implanting oxygen ions O ⁺ ,
The channeling phenomenon is prevented. Therefore, the concentration distribution of the implanted oxygen ions O ⁺ becomes equal to the theoretical distribution. As a result, the tail of the oxygen ion O ⁺ concentration distribution at a deep position of the silicon substrate 1 is widened by channeling,
It can be prevented that a sufficient SiO ₂ film is not formed.

Secondly, the vacancies of the silicon substrate 1 at the interface of the SiO ₂ film 3c-Si film 4c are eliminated by the excess silicon (interstitial silicon), and the SiO ₂ film 3c-Si film 4c interface becomes closer to the ideal. Therefore,
It is possible to prevent dislocations, stacking crystal defects and the like generated from this interface.

Third, it is possible to prevent precipitation due to excess oxygen impurities,
Helps prevent crystal defects in 4c. This is because the vacancies are aggregated with excess oxygen as nuclei to form fine crystal defects and further laminated crystal defects, but the nuclei of these crystal defects can be eliminated by the excess silicon.

In order to effectively realize the above advantages, the SiO ₂ film 3c-Si film 4
c interface (in other words, the concentration value of oxygen ion O ⁺ is 10 ²¹ / c
The concentration value of silicon ions Si ⁺ at the shallower of the two depth positions of the silicon substrate 1 which is around m ³ is about 10 ¹⁸ / c
Must be at least m ³ . Because, if the value is less than this value, the Si ⁺ ion-implanted layer 6 is not sufficiently amorphized, and the holes originally included in the silicon substrate 1 (the number is about 10 ¹⁸ / cm ³ ) Is not sufficiently eliminated at the SiO ₂ film 3c-Si film 4c interface. The position of the projection range of the silicon ion Si ⁺ is not necessarily limited to the above-mentioned embodiment.

According to the above-described embodiment, the Si film 4c having extremely good crystallinity can be obtained for the above reason. Therefore, the characteristics of the semiconductor device formed in the Si film 4c are comparable to the characteristics of the semiconductor device formed in the silicon substrate itself. By the way, when the Si film 4 having poor crystallinity obtained by the conventional method of FIG. 9 is used, the junction leakage of the diode is large, the carrier mobility is deteriorated, and the amplification characteristics of the MOSFET and the bipolar transistor are deteriorated. Was there. Thus, the crystallinity obtained by the method of the present invention is good.
The characteristics of the semiconductor device formed in the Si film 4c are significantly improved as compared with the conventional one, and can be sufficiently evaluated as an integrated circuit device.

FIG. 3 is a sectional view showing a process according to another embodiment of the method for forming a buried oxide film according to the present invention. In this embodiment, an N-type or P-type impurity is ion-implanted into the silicon substrate 1 in advance, so that the N-type or P-type Si is formed.
A film is obtained, and in particular, in the case of ion implantation with P ⁺ or B ⁺ which is difficult to amorphize the ion implantation region, or with As ⁺ or Sb ^{+, the} implantation amount is 5 ×
This is effective when the ion implantation region is not amorphized, which is as small as 10 ¹⁴ / cm ² or less.

First, as shown in FIG. 3 (A), silicon ions Si ⁺ are ion-implanted into the silicon substrate 1 to form the Si ⁺ ion-implanted layer 6 as in the previous embodiment. Next, as shown in FIG. 3 (B), N-type or P-type impurities As ⁺ , Sb ⁺ , B ⁺ or P ⁺ are ion-implanted into the Si ⁺ ion-implanted layer 6 to form the impurity ion-implanted layer 7 To form. At this time, the fourth
As shown in the figure, it is set so that the ion-implanted impurities are distributed within the projection range of the silicon ion Si that has been ion-implanted first. Then, as before, oxygen ions
O ⁺ ion implantation with O ⁺ ion-implanted layer 2d of forming step (FIG. 3 (C)) and, through the process of forming the SiO ₂ film 3d by the heat treatment (FIG. 3 (D)), on the SiO ₂ film 3d N type or P
A Si film 4d having a shape is obtained. In this example, silicon ions
Si ⁺ is the surface area of the silicon substrate 1 which is ion-implanted Si ⁺
The ion-implanted layer 6 is sufficiently amorphized. Therefore,
Regardless of the type of impurities ion-implanted after that,
Furthermore, the concentration distribution of oxygen ions O ⁺ ion-implanted thereafter is always equal to the theoretical distribution, and the thickness of the obtained SiO ₂ film 3d, that is, the Si film 4d is always the theoretical value. In other words, if the ion implantation region is not amorphized because the ion implantation is performed by impurities of As ⁺ or Sb ⁺ with a relatively large mass and the implantation amount is as small as 5 × 10 ¹⁴ / cm ² or less, Even if the ion-implanted region is not amorphized due to the ion implantation with B ⁺ or P ⁺ impurities having a small value, the thickness of the obtained Si film 4d does not change as the theoretical value.

FIG. 5 is a sectional view showing a process according to still another embodiment of the method for forming a buried oxide film according to the present invention. In this embodiment, an N-type silicon substrate 1a is prepared as a silicon substrate. Then, as shown in FIG. 5A, silicon ions Si ⁺ are implanted into the N-type silicon substrate 1a to form a Si ⁺ ion implantation layer 6. Then, as shown in FIG. 5B, for example, boron ions B ⁺ are ion-implanted into the Si ⁺ ion-implanted layer 6 using the patterned resist film 8 as a mask to selectively form the P-type region 9. . After that, the resist film 8 is removed, and thereafter, as in the conventional case, the step of forming the O ⁺ ion-implanted layer 2e by ion implantation of oxygen ions O ⁺ (FIG. 5C) and the SiO ₂ film 3e by heat treatment. Then, the N-type Si film 4e and the P-type Si film 9a having the same thickness as the N-type Si film 4e are formed on the SiO ₂ film 3e. An integrated circuit such as a CMOS IC can be formed in the N-type and P-type Si films 4e and 9a thus obtained.

FIG. 6 is a sectional view showing a process according to still another embodiment of the method for forming a buried oxide film according to the present invention. In this embodiment, ion implantation of silicon ions Si ⁺ is performed twice. That is, first, as shown in FIG. 6A, the first Si.sup. ⁺ Ion implantation is performed to form a relatively thick first ion implantation on the silicon substrate 1.
After the Si ⁺ ion-implanted layer 6a is formed, a second Si ⁺ ion-implantation is performed as shown in FIG. 6 (B) to form a relatively thin second Si ⁺ on the first Si ⁺ ion-implanted layer 6a. The ion implantation layer 6b is formed. FIG. 7 is a graph showing the concentration distribution of silicon ions Si ⁺ in the Si ⁺ ion-implanted layers 6a and 6b at this time, where Si ⁺ (1) and Si ⁺ (2) are the first and the second, respectively.
It corresponds to the Si ⁺ ion-implanted layers 6a and 6b. As shown in the figure, the second Si ⁺ ion implantation is performed on the surface region to the extent that impurity implantation is performed. The peak values of Si ⁺ (1) and Si ⁺ (2) are set to 10 ¹⁹ pieces / cm ³ or more and 10 ¹⁸ pieces / cm ³ or more, respectively. Then, as in the conventional case, a step of forming an O ⁺ ion-implanted layer 2f by ion implantation of oxygen ions O ⁺ (FIG. 6C) and a step of forming a SiO ₂ film 3f by heat treatment (FIG. 6D). ), A Si film 4f is formed on the SiO ₂ film 3f. In this embodiment, the silicon substrate 1 is heat-treated at a high temperature.
Even if the silicon atoms are released from the surface of Si, the silicon ions Si ^{+ of} the second Si ⁺ ion-implanted layer 6b compensate for this, so that the deterioration of the surface of the silicon substrate 1 due to the high temperature heat treatment is effectively prevented. Therefore, the Si film 4f having better crystallinity than that of the Si film 4c shown in FIG. 1 can be obtained.

Further, as an application example of the embodiment of FIG. 6, as shown in FIG. 8, the epitaxial layer 10 may be formed on the Si film 4g having excellent crystallinity obtained by performing Si ⁺ ion implantation twice. it can. In this case, using the method shown in the embodiment of FIG.
By using the film 4g as a high-concentration impurity layer and the epitaxial layer 10 as a low-concentration impurity layer, the Si film 4g can be used as a collector buried layer of a bipolar element. Then, if the collector layer composed of the Si film 4g and the epitaxial layer 10 formed on the SiO ₂ film 3g is insulated in the depth direction by, for example, trench isolation, a completely insulated bipolar IC can be easily formed. .

In addition, the SiO ₂ film formed in each of the above-mentioned examples is used as a capacitor having a silicon substrate and a Si film as both electrodes,
It is also possible to enhance the function of the semiconductor device.

Furthermore, in each of the above-described embodiments, the case where the SiO ₂ film is formed in the silicon substrate has been described, but the present invention can be applied to the case where an epitaxial layer or the like is used as a silicon substrate and the SiO ₂ film is formed in the substrate. Of course.

〔The invention's effect〕

As described above, according to the invention of claim 1,
Prior to ion implantation of oxygen ions O ⁺ , silicon ions Si
^{Since +} is ion-implanted, the silicon ion-implanted layer becomes amorphous and the oxygen ion concentration becomes equal to the theoretical distribution, and the vacancies in the silicon substrate at the silicon oxide film interface disappear due to excess silicon. As a result, a near-ideal silicon oxide film interface is obtained, and nuclei of crystal defects induced by excess oxygen are eliminated by excess silicon. Therefore, there is an effect that a Si film having good crystallinity and a thickness that does not vary depending on the added impurities can be obtained on the SiO ₂ film.

Further, according to the second aspect of the invention, since boron, phosphorus, hisso or antimony is ion-implanted after the silicon ion is ion-implanted, an N-type or P-type silicon film can be obtained.

Further, according to the invention of claim 3, before and after the ion implantation of the silicon ions, the silicon ions are superposed and ion-implanted on the surface portion of the substrate. The deterioration of the surface can be prevented by supplementing the generated silicon atoms.

[Brief description of drawings]

FIG. 1 is a sectional view showing a process according to an embodiment of the method for forming a buried oxide film according to the present invention, FIG. 2 is a view showing a concentration distribution of silicon ions Si ^{+ in} the embodiment, and FIG. 3 is according to the present invention. FIG. 4 is a sectional view showing a process according to another embodiment of the method for forming a buried oxide film, FIG. 4 is a view showing the concentration distribution of silicon ions Si ⁺ and impurity ions in that embodiment, and FIGS. FIG. 7 is a cross-sectional view showing a process according to still another embodiment of the method for forming a buried oxide film according to the present invention, FIG. 7 is a view showing a concentration distribution of silicon ions Si ^{+ after} two ion implantations in the embodiment of FIG. 8
6 is a cross-sectional view showing an application example of the embodiment of FIG. 6, FIG. 9 is a cross-sectional view showing steps of a conventional method for forming a buried oxide film,
FIG. 10 is a diagram showing the concentration distribution of oxygen ions O ⁺ in that process, FIG. 11 is a diagram showing crystal defects in the Si film, and FIGS. 12 and 13 are the formation of other conventional buried oxide films, respectively. It is sectional drawing which shows the process by a method. In the figure, 1 is a silicon substrate, 2c, 2d, 2e and 2f are O ⁺
Ion-implanted layer, 3c, 3d, 3e, 3f and 3g are SiO ₂ films, 4c, 4d, 4
e, 4f and 4g are Si films, and 6,6a and 6b are Si ⁺ ion implantation layers. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] 1. A silicon substrate having a first depth position and a second depth position deeper than the first depth position so that the concentration becomes 10 ²¹ pieces / cm ³ or more. A method of implanting oxygen ions to form a silicon oxide film in the substrate, wherein the concentration at the first depth position is 10 ¹⁸
After pre-implanting silicon ions into the substrate so that the number of particles / cm ³ or more is obtained, the oxygen ions are ion-implanted into the substrate, and then heat treatment is performed to form a silicon oxide film in the substrate. A method for forming a buried oxide film having a feature. 2. Subsequent to the ion implantation of silicon ions, boron, phosphorus, hiso or antimony is ion-implanted into the substrate. Is 5 ×
The method for forming a buried oxide film according to claim 1, wherein the ion implantation amount is 10 ¹⁴ / cm ² or less. 3. Before or after the ion implantation of the silicon ions, the silicon ions are implanted into the surface portion of the substrate so that the concentration in the vicinity of the surface of the substrate is 10 ¹⁸ / cm ³ or more. The method for forming a buried oxide film according to claim 1, wherein the buried oxide film is formed.