JPH0917779A - Formation method of oxide film for element isolation of semiconductor device - Google Patents

Abstract

PURPOSE: To obtain a formation method in which respective elements are electrically insulated and isolated surely even when an element isolation region is made fine by a method wherein an ion implantation process in which oxygen ions are implanted into the formation position of an element isolation oxide film is executed before the formation process of the element isolation oxide film. CONSTITUTION: With a resist pattern 6 left, O2 ions 15 are implanted into the inside of a silicon substrate 1 from an opening part 7 for element isolation. Then, while about the 1800Å depth from the surface of the silicon substrate 1 is used as a reference position, an O2 ion implantation layer is formed about 600Å wide in the upper part and the lower part. Then, a resist 6 is stripped from a siliconitride film 5. After that, the silicon substrate 1 is thermally oxidized in a diffusion furnace. Thereby, the silicon substrate 1 is oxidized selectively. An oxide film (LOCOS) 8 for element isolation is formed by the thermal oxidation of the silicon substrate in the opening part 7 in an oxidation-resistant film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an oxide film for element isolation of a semiconductor device. More specifically, the present invention relates to a method for forming an element isolation oxide film in a semiconductor device in which an element isolation region on a substrate is selectively thermally oxidized to form an element isolation oxide film.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, a LOCOS method is used as one of element isolation methods for electrically isolating elements such as a plurality of transistors formed in parallel on a silicon substrate. . In this LOCOS forming method, first, an oxidation resistant film such as a silicon oxide film (SiO2 film) is formed on a silicon substrate (wafer), and the oxidation resistant film is etched to form an opening in an element isolation region. Then, the silicon substrate is thermally oxidized to oxidize the silicon in the open element isolation region, and a LOCOS made of a bulky thick silicon oxide film is formed in the element isolation region of the silicon substrate. With the recent trend toward miniaturization and high density of semiconductor devices and miniaturization of design rules for each element formed on a wafer, such LOCOS
It has become necessary to miniaturize the element isolation region due to.

[0003]

However, in the conventional LOCOS forming method, the processing time is limited in order to suppress the lateral spread of the LOCOS due to the thermal oxidation at the time of forming the LOCOS, and the LOCOS having a sufficient thickness can be obtained. I couldn't do it. That is, the processing time of thermal oxidation is shortened and L
When an oxide film having a narrow OCOS width was formed, the film thickness was reduced as the LOCOS film width was reduced. for that reason,
There is a risk that punch-through may occur due to a decrease in the element isolation capability due to the insufficient depth of LOCOS embedded in the silicon substrate. This problem will be explained further below.

FIG. 7 shows L formed on a conventional silicon substrate.
It is a principal part sectional drawing of OCOS. N region 5 of an element to be separated on P region 51 formed on N silicon substrate 50
4, 55 are formed. A LOCOS oxide film 52 is formed between these N regions 54 and 55 to separate the respective elements.
A polysilicon wiring layer 53 is formed on the LOCOS oxide film 52 as needed to form an IC circuit. in this case,
The structure composed of the polysilicon wiring layer 53, the LOCOS 52, and the N silicon substrate 50 constitutes a parasitic transistor using the LOCOS 52 as a gate oxide film. For this reason, when a voltage higher than a certain value is applied to the wiring, the parasitic transistor is turned on and the elements on both sides are electrically conducted to break the element isolation. Then, a problem of causing a punch through phenomenon occurs. To deal with this, LOCOS
When the thermal oxidation treatment time is increased to increase the film thickness of 52, the embedded depth in the substrate increases and the LOC
The amount of protrusion of the OS 52 from the surface of the silicon substrate becomes large, and the level difference with the surface of the substrate increases, resulting in poor flatness. Further, in this case, there is a problem that the element formation region is reduced by expanding the LOCOS width by expanding in the lateral direction.

The present invention has been made in view of the above-mentioned problems of the prior art. Even if the element isolation region is miniaturized due to the miniaturization of the design rule of the semiconductor device, the electrical connection between the respective elements can be ensured. It is an object of the present invention to provide a method for forming an oxide film for element isolation of a semiconductor device having a high element isolation ability of insulating isolation.

[0006]

In order to achieve the above object, in the present invention, an oxidation resistant film forming step of forming an oxidation resistant film on a substrate, and a resist coating for forming a resist pattern on the surface of the oxidation resistant film. Step, an opening forming step of forming an element isolation opening by etching the oxidation resistant film using the resist as a mask, a resist removing step of removing the resist, and an element by thermal oxidation treatment on the opening. An element isolation oxide film forming method for a semiconductor device, comprising: an element isolation oxide film forming step of forming an isolation oxide film; and an oxidation resistant film removing step of etching and removing the oxidation resistant film. A method for forming an oxide film for element isolation of a semiconductor device is characterized in that an ion implantation step of implanting oxygen ions is provided at the formation position of the element isolation oxide film before the formation step. To. In a preferred embodiment, the ion implantation step is performed after the opening forming step and before the resist stripping step.

In another preferred embodiment, the ion implantation step is performed before the oxidation resistant film forming step.

In yet another preferred embodiment, the ion implantation step is performed during the oxidation resistant film forming step.

In yet another preferred embodiment, the ion implantation step is performed after the resist coating step and before the opening forming step.

In still another preferred embodiment, the ion implantation step is performed in a state where resist patterning for implanting oxygen ions into a predetermined region within the element isolation region has been performed.

[0011]

Before the element isolation oxide film forming step, oxygen ions are implanted into the formation position of the element isolation oxide film to form an oxygen ion implantation layer. After that, a thermal oxidation process is performed to form an element isolation oxide film. As a result, an oxide layer formed by oxidation of the oxygen ion-implanted layer implanted inside the substrate is added to the element isolation oxide film, and an element isolation oxide film (LOCOS) having a thicker layer in the depth direction is formed.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing a manufacturing process of an element isolation oxide film forming method for a semiconductor device according to an embodiment of the present invention, and FIGS. 2 to 4 are LOCOS forming processes of a semiconductor device corresponding to respective steps of this manufacturing process. FIG. 3 is a cross-sectional view of main parts showing in sequence. First, in step S1, an oxidation resistant film is formed on a silicon substrate. This oxidation-resistant film is the LO
This is for preventing a region other than LOCOS on the substrate from being oxidized during COS thermal oxidation. In the step of forming the oxidation resistant film, first, as shown in FIG. 2A, the surface of the silicon substrate 1 is oxidized to form a silicon oxide film (S
i02) 2 is formed to a thickness of about 50 Angstroms. Next, as shown in FIG. 2B, a polysilicon film 3 having a thickness of about 480 Å is formed on the silicon oxide film 2 by CVD, and the surface of the polysilicon film 3 is oxidized to form the silicon oxide film 4. Form to a thickness of about 80 Å. Further, a silicon nitride film (SiN) 5 is formed on the silicon oxide film 4 by CVD to a thickness of about 1000 angstroms.

Subsequently, in step S2, a resist is applied on the entire surface of the silicon nitride film 5 to form a resist pattern 6 having openings for element isolation regions (see FIG. 2C). Next, in step S3, using the patterned resist pattern 6 as a mask, the silicon nitride film 5, the silicon oxide film 4, and the polysilicon film 3 are removed by etching leaving about 300 angstroms from the surface of the silicon substrate 1 for element isolation. The opening 7 is formed (see FIG. 2D).

Subsequently, as shown in FIG. 3E, with the resist pattern 6 left, O 2 ions 15 are implanted into the silicon substrate 1 through the element isolation opening 7 as shown by an arrow II ( Step S4).

An example of the ion implantation conditions at this time is as follows.

Ion species: O2 ion energy: about 90 keV O2 ions 15 are implanted into the silicon substrate 1 under the above implantation conditions, and a depth of about 1800 angstroms from the surface of the silicon substrate 1 is set as a reference position (the ion concentration is highest. As an implantation target position), an O2 ion-implanted layer is formed to have a width of about 600 angstroms above and below that. In addition, the depth of this 1800 angstrom is
This is the depth of LOCOS depending on the thermal oxidation conditions when LOCOS was formed only by conventional thermal oxidation.

Then, in step S5, the resist 6 is peeled off from the silicon nitride film 5 (FIG. 3 (F)).
reference). Then, in step S6, the silicon substrate 1 is thermally oxidized in the diffusion furnace. As a result, the silicon substrate 1
Are selectively oxidized.

The thermal oxidation conditions at this time are exemplified as follows.

Gas: H 2 + O 2 Temperature: 950 ° C. Time: 115 min By thermally oxidizing the silicon substrate in the opening 7 of the oxidation resistant film under the above-mentioned thermal oxidation conditions, an oxide film for element isolation (LOCOS).
8 is formed. This thermal oxidation condition is a condition that LOCOS is formed from the reference surface to a depth of 1800 angstroms in the case of the conventional LOCO formation method by only thermal oxidation without ion implantation as described above.

The LOC of this embodiment formed in this way
OS 8 is shown in FIG. The depth of this LOCOS 8 is formed from the surface of the substrate 1 to 1800 angstroms (the position of the dotted line) by the thermal oxidation effect as in the conventional case. Since this portion is oxidized, the depth of LOCOS 8 is about 240 from the surface of the substrate 1.
It becomes 0 angstrom, which is deeper than before. on the other hand,
The height of the LOCOS 8 protruding on the upper surface of the substrate 1 is about 220.
It is 0 angstrom, which is the same as the conventional method using only thermal oxidation and does not deteriorate the flatness. Further, an oxide film (SiO2 film) 9 is formed on the surface of the silicon nitride film 5 by this thermal oxidation.

Then, in step S7, the oxidation resistant film (a laminate of 2, 3, 4, 5 and 9) is etched and removed. At this time, the upper surface of the LOCOS 8 is also etched and the film thickness is reduced, so that the protrusion amount from the substrate surface becomes about 900 angstroms. In this way, the LOC
S8 is formed (see FIG. 4 (H)). This LOCOS
Width and multiple LOCOS in parallel LOCOS8
The line width (spacing) between them is about 0.6 μm. After that, MO is applied to both sides of each LOCOS 8 according to a normal process.
A transistor element such as S is formed.

FIG. 4 (I) shows the LOCOS 8 of this embodiment.
FIG. 6 is a cross-sectional view of an element region separated by. This figure corresponds to the above-mentioned conventional sectional view of FIG. Similar to the case of FIG. 7, N regions 19 and 20 of the element to be separated are formed on the P region 17 formed on the N silicon substrate 16. The LOCOS 8 of the above-described embodiment is formed between these N regions 19 and 20 to separate the respective elements. This LO
A polysilicon wiring layer 18 is formed on the COS 8 as needed to form an IC circuit. In this embodiment, the LOC
Since the OS 8 is formed deeper in the substrate than in the conventional example (FIG. 7) described above, the elements are reliably separated from each other, and the problem of punch-through due to leakage unlike the conventional example does not occur. In addition, the projection height above the substrate does not increase, and the required flatness is secured.

Next, another embodiment of the present invention will be described. 5 (A), (B), and (C) are the second to third aspects of the present invention, respectively.
FIG. 9 is a main-portion cross-sectional view of the semiconductor device showing the timing of O 2 ion implantation into the silicon substrate according to the fourth example.

FIG. 5A shows a second embodiment of the present invention.
In the first embodiment described above, the implantation of O2 ions is performed between step S3 and step S5 in the flowchart of FIG. 1, that is, after forming the opening in the oxidation resistant film and before peeling the resist 6. O in the second embodiment
2 Ion implantation is performed before step S1, that is, silicon substrate 1
This is performed before forming the oxidation resistant film on the top. In this case, the silicon substrate 1 is covered with a resist 10 having an element isolation region as an opening, and O 2 ions are implanted into the silicon substrate 1 using the resist 10 as a mask.

FIG. 5B shows a third embodiment of the present invention.
In the third embodiment, the implantation of O2 ions is performed during the step S1 which is the oxidation resistant film forming step, that is, after the polysilicon film 3 is formed by CVD and before the silicon oxide film 4 is formed. In this case, the polysilicon film 3
A resist 11 having an element isolation region as an opening is coated thereon, and O 2 ions are implanted into the silicon substrate 1 through the silicon oxide film 2 and the polysilicon film 3 using the resist 11 as a mask.

FIG. 5C shows a fourth embodiment of the present invention.
In the fourth embodiment, the O2 ion implantation is performed between step 2 of forming a resist pattern on the oxidation resistant film and step 3 of etching the oxidation resistant film. That is, after the resist pattern 6 having the element isolation region as the opening is formed, the resist pattern 6 is used as a mask to perform ion implantation before the oxidation resistant film 2 is etched.

FIG. 6 shows a fifth embodiment of the present invention. FIG.
FIG. 7A is a sectional view of a semiconductor device according to the fifth embodiment, which is covered with a resist pattern 13 for defining an implantation region of O 2 ions into a silicon substrate. FIG. 6B is a sectional view of the LOCOS 8 formed according to the fifth embodiment. In the above-mentioned respective embodiments, the O2 ion implantation is carried out in the entire element isolation region of the silicon substrate 1, but in the fifth embodiment, as shown in FIG. 6 (A), an opening is made only in a predetermined region in the element isolation region. A resist pattern 13 is formed in the opening, and with this resist pattern 13 used as a mask, O2 ions 15 are implanted into this predetermined region. Thus, L
As shown in FIG. 6B, the OCOS 8 is locally formed deep inside the substrate 1, and the LOCOS 22 having the protrusion 21 is formed toward the inside of the substrate.

In each of the above embodiments, the resist is used to pattern the O2 ion-implanted region. However, if the oxidation resistant film is open, this oxidation resistant film itself is used instead of the resist pattern. May be.

[0029]

As described above, in the method of forming an oxide film for element isolation of a semiconductor device according to the present invention, oxygen ions are implanted into the inside of the substrate before the element isolation oxide film forming step by thermal oxidation. Since thermal oxidation is performed with the oxygen ion implantation layer formed, if formed under the same thermal oxidation conditions as before, the element isolation oxide film will be formed deeper in the substrate by the amount of the oxygen ion implantation layer, improving element isolation performance. To be Also,
Since the element isolation oxide film can be formed in the depth direction with respect to the film width, the amount of protrusion from the substrate can be suppressed even if the element isolation region is miniaturized due to the miniaturization of the design rule of the semiconductor device. Therefore, it is possible to secure the required film thickness in the depth direction while maintaining the flatness, and to achieve reliable element separation. Furthermore, since the heat treatment time for forming the element isolation oxide film having a predetermined film thickness required in the depth direction can be shortened, the yield of semiconductor devices can be improved. Further, in this case, as the heat treatment time is shortened, the amount of the oxide film protruding from the substrate is reduced, the flatness is improved, the coverage is improved, and a semiconductor element having excellent characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a flow chart showing a manufacturing process of an element isolation oxide film forming method for a semiconductor device according to a first exemplary embodiment of the present invention.

FIG. 2 is a cross-sectional view of main parts showing in sequence a LOCOS forming process of a semiconductor device corresponding to each step of the manufacturing process of the element isolation oxide film forming method of the semiconductor device according to the example.

3A and 3B are cross-sectional views of main parts sequentially showing the LOCOS formation process of the semiconductor device following FIG.

FIG. 4 is a cross-sectional view of the essential part showing the process of forming LOCOS of the semiconductor device in order, following FIG. 3;

5A, 5B, and 5C are cross-sectional views of the essential part of the semiconductor device showing the oxygen ion implantation timing according to the second, third, and fourth embodiments of the present invention, respectively.

FIG. 6 is a cross-sectional view of essential parts of a semiconductor device showing a case where an oxygen ion implantation region is narrowed in a semiconductor device element isolation oxide film forming method according to a fifth embodiment of the present invention.

FIG. 7 is a cross-sectional view of essential parts for explaining LOCOS formed on a silicon substrate by a conventional method for forming an oxide film for element isolation of a semiconductor device.

[Explanation of symbols]

1: Silicon substrate, 2: Silicon oxide film, 3: Polysilicon film, 4: Silicon oxide film, 5: Silicon nitride film, 6: Resist pattern, 7: Opening, 8: LOC
OS, 9: oxide film, 10: resist, 11: resist,
13: resist pattern, 15: O2 ion.

Claims (6)

[Claims] 1. An oxidation resistant film forming step of forming an oxidation resistant film on a substrate, a resist coating step of forming a resist pattern on the surface of the oxidation resistant film, and etching the oxidation resistant film using the resist as a mask. An opening forming step for forming an element separating opening, a resist removing step for removing the resist, an element separating oxide film forming step for forming an element separating oxide film in the opening by a thermal oxidation treatment, In a method for forming an oxide film for element isolation of a semiconductor device, which comprises a step of removing an oxidation resistant film by etching and removing the oxidation resistant film, in the formation position of the element isolation oxide film before the element isolation oxide film forming step. A method for forming an oxide film for element isolation of a semiconductor device, comprising an ion implantation step of implanting oxygen ions. 2. The method for forming an element isolation acid film of a semiconductor device according to claim 1, wherein the ion implantation step is performed after the opening formation step and before the resist stripping step. 3. The method for forming an oxide film for element isolation of a semiconductor device according to claim 1, wherein the ion implantation step is performed before the oxidation resistant film forming step. 4. The method for forming an oxide film for element isolation of a semiconductor device according to claim 1, wherein the ion implantation step is performed during the oxidation resistant film forming step. 5. The method for forming an oxide film for element isolation of a semiconductor device according to claim 1, wherein the ion implantation step is performed after the resist coating step and before the opening forming step. 6. The element isolation of a semiconductor device according to claim 1, wherein the ion implantation step is performed in a state where a resist patterning for implanting oxygen ions is applied to a predetermined region in the element isolation region. For forming oxide film for automobile.