JPH10214844A - Manufacturing method of semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove and getter contaminants or contamination elements from an active SOI layer by gettering the contaminants to crystal defect, and taking it in a LOCOS oxide film and/or segregating it in the interface between the LOCOS oxide film and a buried oxide film. SOLUTION: Ion implantation is performed to bring a separated SOI layer 8 into an amorphous state. Then photoresist 6 is removed, and annealing is performed in a nitrogen atmosphere for the restoration of crystallinity. As the result of this process, crystal defect 9 as the primary defect due to the ion implantation is transformed into dislocation defect 10 or polycrystalline silicon as secondary defect, and the contaminants present in an active SOI layer 7 is gettered to the dislocation defect 10. Finally, processing is performed in a dry oxygen atmosphere to form a LOCOS oxide film 11, and the separated SOI layer 8 is completely oxidized. Here, the contaminating impurities gettered to the dislocation defect 10 is taken in the LOCOS oxide film 11 or the boundary between the LOCOS oxide film 11 and a buried oxide film 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly, to an SOI having a silicon layer on an insulating layer.
The present invention relates to a method for reducing heavy metals in an active silicon layer (hereinafter, referred to as an “SOI layer”) forming a device when manufacturing a semiconductor substrate device having a structure.

[0002]

2. Description of the Related Art In today's large-scale integrated circuits, various improvements have been made in response to demands for higher operating speeds. To further increase the speed, however, it is essential to greatly reduce parasitic capacitance. . To reduce such parasitic capacitance, an SOI technique in which a silicon single crystal thin film is formed on an insulating film layer and the silicon single crystal thin film is used as an element formation region is promising.
Also, among SOI substrates, SIMOX (Separa)
Tion by Implanted Oxygen)
The substrate is considered to be one of the most promising SOI substrates because an element formation region having a large area and good crystallinity can be easily obtained.

However, in a conventional SOI substrate, since a buried oxide film is formed over the entire surface of a silicon single crystal substrate, it is difficult to apply a gettering technique for removing heavy metals and the like contaminating an element formation region. here,
Gettering means that gettering sites such as crystal defects are formed in regions other than the element formation region, and contaminant impurities are captured in these sites.
This is the technique of sticking.

Usually, this gettering site is formed on the back surface or inside the bulk of a silicon single crystal substrate. Therefore, it is necessary to diffuse the contaminant impurities attached to and taken into the substrate surface (element formation region) from the attached portion to the gettering site.

However, in the SOI substrate, since a silicon oxide film exists between the element formation region and the inside of the substrate bulk or the back surface of the substrate, diffusion of a contaminant impurity is significantly prevented. This is because the general impurity diffusion coefficient is much smaller in a silicon oxide film than in a silicon single crystal. For example, the diffusion coefficient of gold in a silicon oxide film at 900 ° C. is 10% of the diffusion coefficient in a silicon single crystal.
^-7 or less.

As described above, it is difficult to apply the gettering technique to the SOI substrate, and contaminant impurities are likely to remain in the element formation region, and the element characteristics (junction leak, breakdown voltage) are likely to be deteriorated by these contaminant impurities. .

In order to solve such a problem, Japanese Patent Application Laid-Open No. 8-45943 discloses the following technique as shown in FIG.

That is, when performing gettering of an SOI semiconductor wafer, first, as shown in FIG.
By bonding two silicon wafers 21 and 23 together,
Alternatively, a high-dose oxygen is implanted into the silicon single crystal wafer 2 by the SIMOX method, so that the SO
An I semiconductor wafer 20 is formed.

Further, as shown in FIG. 2B, an oxide film 24 is formed by heat treatment on the surface of the active layer 23 of the SOI semiconductor wafer 20 formed by the above method, and after being patterned by photolithography. Region B other than the active region A where the semiconductor device is manufactured by etching, ie, the semiconductor device isolation region B
Open the window.

Next, as shown in FIG. 2C, polycrystalline silicon 25 serving as a gettering layer is grown on the surface of the active layer 22 and the surface of the oxide film 24 which are opened by a normal low pressure CVD method. Let it.

Further, as shown in FIG. 2D, after patterning by photolithography, unnecessary polycrystalline silicon 25 on oxide film 24 is etched.
And the polycrystalline silicon 25 is left only in the semiconductor device isolation region B.

Finally, as shown in FIG. 2E, the oxide film 24 is removed by etching, and the gettering is completed. In such a gettering method, gettering of heavy metal impurities and defects mixed in the semiconductor device active region A is performed by the polycrystalline silicon 25 formed on the surface of the active layer 23 and in the semiconductor device isolation region B. Will be

[0013]

However, in the above-described process, the step of removing polycrystalline silicon (FIG. 2C)
2 (d) or the removal of the polycrystalline silicon 25 in FIG. 2 (e)), and the polycrystalline silicon (reference numeral 25 in FIG. 2 (e)) itself operates as a semiconductor. It is feared that desired device characteristics cannot be obtained.

In recent years, the processing apparatus for processing a semiconductor substrate has a very low level of heavy metal contamination and a low processing temperature. Therefore, creating gettering sites inside the bulk is important in terms of thermal diffusion of contaminants that adhere during the process.
Gettering efficiency is not good. Recently, a fully depleted transistor device utilizing the entire depth of an SOI layer is becoming the mainstream of SOI devices.
It has become impossible to form gettering sites in the I layer.

In such an SOI device, gettering of a contaminant element such as a heavy metal due to crystal production or a heavy metal from a high-dose oxygen ion implanter in SIMOX is the most important.

The present invention provides a technique for reducing the concentration of heavy metals in an active SOI layer, that is, a contaminant element originally contained in a silicon substrate due to crystal production or used in a SIMOX substrate. It is an object of the present invention to remove and getter a contamination element from an active SOI layer from an oxygen ion implanter.

[0017]

According to a first aspect of the present invention, there is provided a method of manufacturing a semiconductor substrate, comprising: forming a mask having an element isolation region on a semiconductor substrate having an SOI structure having a silicon layer on an insulating layer; Using the mask, a predetermined impurity is ion-implanted, thereby introducing a crystal defect into a silicon layer to be an element isolation region, and forming a LOCOS oxide film in the element isolation region by a LOCOS oxidation method. During the formation of the LOCOS oxide film, contaminant impurities contained in the silicon layer are gettered to the crystal defects, and then the contaminant impurities are incorporated into the LOCOS oxide film or / and embedded in the LOCOS oxide film. And a step of segregating at the interface with the oxide film.

According to a second aspect of the present invention, there is provided a method for manufacturing a semiconductor substrate, comprising: forming a mask having an element isolation region on an SOI semiconductor substrate having a silicon layer on an insulating layer; A step of introducing crystal defects into a silicon layer serving as an element isolation region by ion-implanting a predetermined impurity, and converting the crystal defects into dislocation defects by heat treatment at a predetermined temperature, thereby contaminating the silicon layer. A step of gettering impurities to the dislocation defects and forming a locos oxide film in an element isolation region by a locos oxidation method so as to be incorporated into the locos oxide film or /
And segregating at the interface between the LOCOS oxide film and the buried oxide film.

Further, according to a third aspect of the present invention, in the method of manufacturing a semiconductor substrate, the ion implantation for forming the crystal defect includes the steps of:
Group IIIb, Group IVb, Group Vb, Group VIb or VI
3. The method for manufacturing a semiconductor substrate according to claim 1, wherein an ion composed of any one of a group Ib element and a rare gas element is used.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments.

FIG. 1 is a manufacturing process diagram of a semiconductor substrate according to a first embodiment of the present invention.

The conventional gettering uses a crystal defect portion in which interstitial oxygen in the bulk is coagulated and precipitated inside the substrate. In the present invention, the introduction of the crystal defect is carried out by ion implantation and subsequent thermal treatment. Utilizes residual dislocation defects due to annealing.

In order to increase the efficiency in removing and reducing contaminants from the active SOI layer, the gettering site needs to be as close as possible to the active SOI layer. It is formed inside the isolation SOI layer between the layer regions.

According to the present invention, the crystallinity of the SOI layer is destroyed by implanting ions into the isolation SOI layer. The primary defects introduced at this time are precursor defects of crystal defects (dislocation defects) which are gettering sites. This precursor defect is converted into a secondary defect such as dislocation by a subsequent heat treatment. In the process of generating the secondary defects, gettering of the contaminant impurities occurs, and the remaining secondary defects themselves have the gettering ability. Therefore, the amount of ion implantation used here is appropriate enough to leave crystal defects after annealing, generally 10 ¹⁴ cm ^-2 or more. That is, although it cannot be said unconditionally depending on the type of the implanted ions, when the implanted amount is on the order of 10 ¹⁴ cm ⁻² , the implanted region becomes an aggregate of island-like crystal defects, and the crystallinity is not completely recovered even after annealing. . If the implantation amount is on the order of 10 ¹⁵ cm ⁻² or more, the implantation region becomes amorphous, and in the case of a bulk substrate, the crystallinity recovers and grows using the region where the crystallinity is maintained by annealing as a seed.

However, in the SOI substrate, since the amorphous SOI layer has a buried oxide film underneath, the seed at the time of the recovery of the crystallinity is only at the junction surface with the active SOI layer where the ion implantation has not been performed. Will not be. In this case, a shift in the crystal plane occurs at a position where the growth planes in which the crystal has been recovered from multiple directions cross each other, and this remains as a dislocation defect.

In the case where the area of the isolation SOI layer is large, conversion growth into polycrystalline silicon proceeds in a region far from the single crystal seed portion together with defect recovery growth. Contaminant impurities will also be captured at the crystal / polycrystalline interface.

As described above, when a crystal defect such as a dislocation is introduced into the isolation SOI layer, the defect portion having the disordered crystallinity is in a state where the Si—Si bond is broken or the bond angle is distorted. And become energetically high.
A contaminant element that thermally diffuses in the substrate is captured by the defective portion having high energy, and a gettering effect is generated in the SOI substrate.

Therefore, in the ion implantation here, it becomes a necessary condition to introduce a residual secondary defect into the isolation SOI layer, and the implantation energy without fear of deteriorating the buried oxide film, for example, the average ion range ( Projected
It is safe to select the energy so that (Range) is in the SOI layer. The element used for ion implantation is a buried oxide film or LOC by a high-temperature heat treatment by LOCOS oxidation (hereinafter referred to as “LOCOS oxidation”) in the next step.
It is necessary to use an element that does not adversely affect the electrical characteristics of the OS oxide film. From this viewpoint, B, Ga, I
C, Si of the Vb group, N, P, As of the Va group, O, S of the VIb group, F, Cl of the VIIb group, Ar of the rare gas element and the like are effective.

Next, the isolation SOI layer having the crystal defects is entirely oxidized using a selective oxidation mask such as Si ₃ N ₄ .
Convert to LOCOS oxide film. By this oxidation, contaminant impurities such as heavy metals are taken in near the interface between the LOCOS oxide film or the LOCOS oxide film and the buried oxide film, and
It will be removed from the I layer. For example, an element that easily segregates in an oxide film such as Fe is taken into the LOCOS oxide film from the separated SOI layer by this oxidation treatment. On the other hand, elements such as Ni and Cu pile up in silicon by oxidation, but the SOI layer is completely LOC
As the OS is oxidized, it is taken into the LOCOS oxide film / buried oxide film interface so as to be segregated.

According to the above operation, the primary defect introduced by the ion implantation is converted into the secondary defect by the heat treatment. Therefore, in some cases, even if the defect recovery annealing before the LOCOS oxidation is omitted, the isolation SOI Secondary defects remain in the layer, and the effect of the present invention is achieved. For example, 1
When the isolated SOI layer is made amorphous with an ion implantation amount of 0 ¹⁵ cm ⁻² or more, the OSF (O 2) in which the amorphous defect is a secondary defect is formed due to an oxidizing atmosphere at the time of LOCOS oxidation.
xidation Induced Stacking
(Fault). Then, due to the heat treatment of the LOCOS oxidation, gettering of a contaminant impurity occurs from the active SOI layer to the OSF. Here, in the bulk substrate device, the device characteristics are degraded (increase in junction leak and decrease in element isolation capability) due to the occurrence of OSF.

However, in a device formed in the SOI layer, especially in a fully depleted transistor device using a thin film SOI, the OSF once generated in the isolation SOI layer
Disappears as all the isolated SOI layers are oxidized by LOCOS oxidation. Therefore, deterioration of device characteristics due to the occurrence of OSF, which is a problem in a bulk device, cannot occur.

Further, in a device that does not use a LOCOS oxide film, even if there is no step of oxidizing the isolated SOI layer by the LOCOS oxide film, residual dislocation defects in the isolated SOI layer maintain the effect of reducing heavy metals. However, if a high temperature of 900 ° C. or more is used in the subsequent thermal process, there is a concern that the contaminant element will re-diffuse from the gettering region.

Hereinafter, a manufacturing process of a semiconductor substrate according to an embodiment of the present invention will be described with reference to FIG.

First, using a SOI substrate having a buried oxide film 2 formed on a silicon single crystal substrate 1, an SOI layer 3 is oxidized to form a 10-nm pad oxide film 4 for relieving stress during LOCOS oxidation. Subsequently, a silicon nitride film 5 is deposited to a thickness of 100 nm by LP-CVD (FIG. 1).
(A)). At this time, the thickness of the SOI film 3 is adjusted to 50 nm.

Next, a photoresist 6 is patterned on the silicon nitride film 5 by using a normal photolithography technique, and the silicon nitride film 5 is anisotropically etched by a general dry etching technique, and LOCOS oxidation is performed. The silicon nitride film 5 serving as an oxidation-resistant mask at this time was processed (FIG. 1B). Here, 7 indicates an active SOI layer, and 8 indicates an isolation SOI layer.

Next, the photoresist 6 is directly used as a mask pattern for ion implantation, and argon ions are
Ion implantation was performed at an implantation energy of eV at a dose of 1 × 10 ¹⁵ cm ⁻² , and the isolated SOI layer 8 was made amorphous (FIG. 1C). At this time, argon (Ar) ions are implanted into the separated SOI layer with a depth peak profile of about 11 nm. Here, argon, which is a rare gas element, is used as the implanted ions,
Any of a group IIb, group IVb, group Vb, group VIb, group VIIb element or a rare gas element ion may be used.
Further, the implantation energy may be changed to perform multi-stage implantation.

After the ion implantation, the photoresist 6 was removed by ordinary oxygen ashing, and annealing for recovering crystallinity was performed at 900 ° C. for 30 minutes in a nitrogen atmosphere. With respect to the annealing temperature, conditions generally employed are approximately 700 to 950 ° C. and the time is generally 10 to 60 minutes. By this processing, the crystal defect 9 which is a primary defect in the ion implantation is recovered and converted to a dislocation defect 10 which is a secondary defect or, in some cases, to polycrystalline silicon.
The contaminant impurities mixed in the dislocations are gettered by these dislocation defects 10 (FIG. 1D).

The annealing for the recovery of the crystallinity is as follows.
It is preferable to perform the method more reliably to remove contaminant impurities mixed in the active SOI layer. However, in the heat treatment in the next LOCOS oxide film forming step, gettering of the contaminant impurities can be caused, and thus may be omitted. .

Finally, this sample is treated in a dry oxygen atmosphere at 1100 ° C. to form a 120 nm LOCOS oxide film 11 using the silicon nitride film 5 as an oxidation resistant mask.
All the OI layers 8 were oxidized. Here, the contaminant impurities gettered by the dislocation defects 10 are removed by the LOCOS oxide film 11.
Internal or LOCOS oxide film 11 and buried oxide film 2
At the interface between the active SOI layer 7 and the active SOI layer 7.

That is, since the diffusion coefficient of the heavy metal in the oxide film is orders of magnitude smaller than the diffusion coefficient of the heavy metal in the silicon, the heavy metal is transferred to the active SOI layer 7 unless a process at a high temperature of 1000 ° C. or more is adopted. There is no distribution (FIG. 1 (e)). Then, the silicon nitride film 5 is removed by treatment with hot phosphoric acid, and a series of steps is completed (FIG. 1F).

In order to verify the gettering effect of the SOI substrate of the above embodiment, the amount of crystal defects generated on the surface of the active SOI layer due to the heavy metal contamination was compared.

In the step of FIG. 1A, before the pad oxide film 4 is formed, copper equivalent to 5 × 10 ¹² atoms / cm ² is applied using a copper sulfate solution, and a heat treatment at 700 ° C. is performed. Then, copper was diffused into the SOI layer. Next, in order to compare the state of occurrence of defects on the surface of the active SOI layer depending on the presence or absence of the ion implantation process (FIG. 1C), the processes of FIGS. 1B to 1F were performed. However, the pad oxide film 4 in this step
Employed a CVD oxide film. The SOI surface of these substrates, selectively etched by light etching, when measuring the surface defect density, pits and stacking faults of a number in the substrate ion implantation without due to heavy metals (10 ⁵ / cm ² order) is observed Was done. On the other hand, when using the embodiment of the present invention, reduction of the bit and stacking fault density in the active SOI layer (10 ⁴ / cm ²⁾ is observed, the closer to the vicinity of the LOCOS oxide film, the effect is large Was recognized.

[0043]

As described in detail above, by using the present invention, it becomes possible to reduce the contaminant elements mixed in the active SOI layer region forming the device. Characteristics and manufacturing yield can be improved.

Further, by using the present invention, the contaminant impurities mixed in the SOI layer can be more reliably gettered.

Further, by using the present invention, ions implanted for forming a crystal defect do not adversely affect the electrical characteristics of the buried oxide film or the LOCOS oxide film.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a manufacturing process of a semiconductor substrate according to an embodiment of the present invention.

FIG. 2 is a view showing a manufacturing process of a conventional SOI substrate.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 silicon single crystal substrate 2 buried oxide film 3 SOI layer 4 thermal oxide film 5 silicon nitride film 6 photoresist 7 active SOI layer 8 isolation SOI layer 9 ion implantation defect 10 dislocation defect 11 LOCOS oxide film

Claims (3)

[Claims] An element isolation region is formed by forming a mask having an element isolation region opened on a semiconductor substrate having an SOI structure having a silicon layer on an insulating layer, and ion-implanting a predetermined impurity using the mask. A step of introducing crystal defects into the silicon layer to be formed, and a step of forming a locos oxide film in the element isolation region by a locos oxidation method, whereby contamination contained in the silicon layer during the formation of the locos oxide film. A step of gettering impurities to the crystal defects and then incorporating the contaminating impurities into the LOCOS oxide film and / or segregating at the interface between the LOCOS oxide film and the buried oxide film. Substrate manufacturing method. 2. An element isolation region is formed by forming a mask having an element isolation region opened on a semiconductor substrate having an SOI structure having a silicon layer on an insulating layer, and ion-implanting a predetermined impurity using the mask. A step of introducing a crystal defect into a silicon layer to be formed, a step of converting the crystal defect into a dislocation defect by heat treatment at a predetermined temperature, and gettering a contaminant impurity in the silicon layer to the dislocation defect, Forming a LOCOS oxide film in the element isolation region by using the LOCOS oxide film, and / or segregating the LOCOS oxide film at the interface between the LOCOS oxide film and the buried oxide film. Manufacturing method. 3. The method according to claim 1, wherein:
Group IIIb, Group IVb, Group Vb, Group VIb or VI
3. The method for manufacturing a semiconductor substrate according to claim 1, wherein an ion composed of any one of a group Ib element and a rare gas element is used.