JP3345269B2 - Element isolation method for semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element isolation method for a semiconductor device, and more particularly to a shift from an active region to an element isolation region and improvement of damage in forming an active region.

[0002]

2. Description of the Related Art In recent years, the technology for manufacturing semiconductor devices has been remarkably developed, and the degree of integration has been dramatically improved due to the progress of miniaturization. In particular, miniaturization of active elements has been promoted with the development of processing technology. However, in order to achieve high integration, it is necessary to miniaturize not only an active region for forming an active element but also an element isolation region (inactive region) for isolating the element. For this reason, the manufacturing process is complicated, and the number of processes is increasing.

FIG. 6 is a process chart showing a procedure of element isolation of a conventional semiconductor device. In FIG. 6, 101 is a silicon substrate, 102 is an oxide film (102a is an oxide film after wet etching), 103 is a photoresist (resist mask), 104 is a channel cut region, 105 is a buffer oxide film, and 106 is silicon nitride. A film (106a is a silicon nitride mask), 107 is a LOCOS oxide film, A is an active region, and B is an element isolation region.

FIG. 6A shows a procedure 1 of element isolation of a conventional semiconductor device. A thick oxide film resist mask 103 having an opening in the oxide film 102 formed on the silicon substrate 101 is formed (FIG. 6A-1). Using the resist mask 103, the oxide film 102 is removed by wet etching, exposing the substrate surface to be an active region (FIG. 6A-2). The resist mask 103 is removed to form an active region A and an element isolation region B. If necessary, ion implantation of a channel stop serving as the channel cut region 104 is performed in the element isolation region below the oxide film 102a (FIG. 6A-3).

FIG. 6B shows a procedure 2 of element isolation of a conventional semiconductor device. A thin oxide film 105 for buffering is formed on a silicon substrate 101, and a silicon nitride film 106 is formed thereon.
Is deposited, and a photoresist 103 is formed (FIG. 6).
(B-1)). Using the photoresist 103 as a mask,
After the region of the silicon nitride film 106 where the element isolation oxide film 107 is to be formed is removed by etching, the photoresist 103 is removed (FIG. 6B-2).

A LOCOS oxide film 107 (element isolation oxide film) is formed using silicon nitride film 106a as a mask (FIG. 6).
(B-3). After that, by removing the silicon nitride film 106a, an element isolation region and an active region are separately formed. If necessary, ion implantation of a channel stop serving as the channel cut region 104 is performed in the element isolation region below the oxide film 107 (FIG. 6B-4). This element isolation technique is generally called a LOCOS (Local Oxidation of Silicon) technique.

[0007] Japanese Patent Application Laid-Open No.
Japanese Unexamined Patent Publication No. -125087 describes an element isolation technique in which a channel cut region matches an element isolation region.

[0008]

However, FIG.
The problem of the element isolation method shown in FIG. 6A is that when the oxide film 102 is removed by an isotropic etching method of wet etching to open the substrate surface serving as an active region, FIG.
As shown by the arrow 2), the active region A is separated from the element isolation region B.
, Ie, side etching from the end of the mask is large, and the margin of the element isolation region becomes large, which is not suitable for miniaturization.

The problem of the LOCOS technique shown in FIG. 6B is that, as indicated by the arrow in FIG. 6B-3, the shift caused by the indentation of the LOCOS oxide film 107 during oxidation, called a bird's beak, occurs in the element isolation region. There is a problem that it is difficult to miniaturize because it is generated from B to the active region A. Further, there is a problem that complicated manufacturing steps such as deposition, processing, and removal of the silicon nitride film 106 are required, and element characteristics are deteriorated because local stress is generated by oxidation.

FIG. 6C shows a procedure 3 of element isolation of a conventional semiconductor device. As shown in FIG. 6C, when the anisotropic etching method using plasma is used, the oxide film 1 is removed.
Since the edge of 02a becomes steep, problems such as disconnection of wiring formed thereon, residual etching, and a reduction in photo margin at the time of patterning occur. Further, the anisotropic etching technique has a problem that the characteristics of the element are degraded due to various types of damage caused by plasma.

FIG. 7 is an explanatory view showing an example of etching processing on an element isolation region according to the prior art. In FIG.
101 is a silicon substrate, 102a processed oxide film (element isolation film), 108 is a gate oxide film, 109 is polysilicon (gate electrode and gate electrode wiring), 110 is etching remaining, A is an active region, B is element isolation The regions are indicated respectively. FIG. 7A shows that the polysilicon 109 to be removed by etching is deposited on the element isolation region and the active region. Since the region indicated by the arrow in FIG. 7A becomes a shadow of the element isolation film 102, etching is difficult. As shown in FIG. 7B, an etching residue 110 is easily generated at the end of the element isolation film 102 due to a shadow, which causes a short circuit. Therefore, if the wiring portion has a step as shown in FIG. 7A, the step portion obstructs the flow of current and generates heat, shortening the life of the wiring and easily causing disconnection. Further, since the orientation of the crystal also changes at the step portion, disconnection is likely to occur.

The element isolation method described in Japanese Patent Application Laid-Open No. 61-125087 discloses a method in which a conductive film serving as a gate electrode is formed on an active region and then an element isolation film is formed by selective growth. Rework of the gate electrode is required,
It is complicated and requires many steps to form the element isolation region. In addition, the edge of the oxide film becomes steep, causing problems such as disconnection of wiring, remaining etching, and a reduction in photo margin at the time of patterning.

The present invention has been made in view of the above circumstances. For example, by providing an ion implantation step before a step of wet-etching an element isolation film, it is possible to selectively etch by wet etching. Provided is an element isolation method for a semiconductor device in which damage to a semiconductor substrate is small and element isolation formation corresponding to miniaturization is obtained.

[0014]

According to the present invention, a step (i) for forming an insulating film on a semiconductor substrate and a step (i) for forming a mask having an opening on an active region on the insulating film.
i), a step (iii) of implanting ions into the insulating film using the mask, a step (iv) of removing the insulating film in the ion-implanted region by wet etching using the mask, A region that passes through the mask and the insulating film and is directly below the insulating film, and a depth that does not affect the threshold in the active region.
And a step (v) of implanting ions for forming a channel cut region in a self-aligned manner into the region and a step (v) of removing the mask. .

In the step (i), the semiconductor substrate may be a P-type well or an N-type well. Further, the semiconductor substrate may be formed with one or more N-type wells or P-type wells. The insulating film is made of SiO ₂ (silicon oxide film), P
SG, BPSG, and Si ₃ N ₄ (silicon nitride film) materials are used and formed by a CVD method. The film thickness may be set to a required film thickness (0.01 to 1 μm) according to the characteristics of the device.

In the step (ii), the mask is formed by applying a photoresist (photosensitive agent) of 0.1 to 2 μm on the insulating film, and forming an opening in the shape of an active region by using ordinary photolithography technology. Is done. In step (iii), ions are implanted into the insulating film from the opening using the mask. The ion implantation of the present invention is intended to increase the wet etching rate and enable selective etching when the insulating film is removed by wet etching using the same mask in the next step (iv). Therefore, it is preferable that the ion implantation region is also performed so as to slightly extend in the lateral direction from the opening end of the mask.

For ion implantation, ions such as boron (B), phosphorus (P), arsenic (As), and boron fluoride (BF ₂ ) are used. Thickness, shape). When the insulating film is a silicon oxide film having a thickness of, for example, 0.2 μm, for example, arsenic ions are converted to an ion energy of 50 KeV.
1.2 × 10 ¹⁵ / cm ² and ion energy 22
It is preferable to carry out implantation at a dose of 1.2 × 10 ¹⁵ / cm ² at 0 KeV.

The ion implantation into the insulating film is performed at least once by changing the ion implantation energy / injection amount according to the thickness of the insulating film, the ion depth, and the ion concentration. Actually, an implantation profile of the ion-implanted concentration region is obtained in advance by using ion energy / ion implantation amount as a parameter, each data is stored in a memory of a computer, and the ion implantation apparatus is controlled by the computer.

In the step (iv), known chemicals are used for the wet etching of the insulating film. For example, when the insulating film is an oxide film, a mixed solution of ammonium fluoride and hydrofluoric acid is used. When the insulating film is a nitride film, a mixed solution of borofluoric acid and phosphoric acid is used. When the ion-implanted insulating film is wet-etched using the mask, the type, mixture ratio, concentration, etc. of the solution are determined by the etching conditions (type of insulating film, depth of ion implantation, shape, etching rate). .

In particular, when the insulating film is an oxide film, a mixed solution of ammonium fluoride and hydrofluoric acid is often used. For example,
Using a 10: 1 (HF + NH ₄ F) hydrofluoric acid buffer solution,
Perform wet etching. At this time, the ion-implanted region has an etching rate 10 times that of the non-implanted region. The etching rate changes according to the ion concentration of the implanted ions. 0.3 μm from the surface to 0.15 μm
/ Min. Thereafter, etching is performed at a rate of 0.1 μm / min. If the oxide film reaches 0.3 μm, the etching is completed in about 1 minute. In step (v), the mask is peeled off by a known method to complete the formation of the active region and the element isolation region.

According to the element isolation method of the semiconductor device of the present invention, the wet etching rate of the insulating film (oxide film) in the ion-implanted region is increased to enable selective etching, and the lateral etching is suppressed by the wet etching. The optimum active region and the element isolation region are formed separately. Therefore, it is possible to cope with miniaturization of the active region and the element isolation region.

That is, wet etching has been used for isotropic etching, but by implanting ions into the insulating film in advance, the etching rate of the ion-implanted region changes and selective etching becomes possible. Was. That is, the etching in the vertical direction can be performed while suppressing the shift of the oxide film in the horizontal direction, so that an optimum element isolation shape can be obtained. In addition, since it can be manufactured by wet etching, damage to the silicon substrate can be prevented, and good device characteristics can be obtained.

Further, the amount of etching gradually attenuates from the vicinity of the surface due to the ions wrapping around the oxide film surface, so that a gentler taper shape than the anisotropic etching is obtained at the element isolation end. As a result, a disconnection at the edge of the wiring crossing the element isolation and a short circuit due to the remaining etching at the edge are avoided.

If it is necessary to form a channel cut region, before the step (v), an ion implantation step of forming a channel cut region in a region immediately below the insulating film through the mask and the insulating film. (Va). The ions used in this step are composed of boron, phosphorus, arsenic, and boron fluoride. In order to form a channel cut region, for example, boron is ion energy of 100 to 300 KeV and dose is 0.5 × 10 ¹³ to
It is preferable to implant at 2 × 10 ¹³ / cm ² .

That is, the channel cut region is formed on the surface of the element isolation region. In the channel region of the active region, for example, ion energy / boron is set so that boron penetrates deep into the substrate so as not to affect the threshold value of the transistor.
Control the dose. As a result, the channel cut region can be formed in a self-aligned manner, and the miniaturization of the element isolation region is facilitated without requiring an overlapping margin between the element isolation region and the channel cut region.

According to the present invention, for example, one photolithography step (resist mask forming step), one ion implantation step, one wet etching step, and one ion implantation for channel cut formation Thus, an active region and an element isolation region can be formed, so that the manufacturing process can be reduced.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. Note that the present invention is not limited by this.

FIG. 1 is a process chart showing a procedure of element isolation of a semiconductor device according to the present invention. In FIG. 1, 1 is a silicon substrate, 2 is an oxide film (insulating film), 2a and 2b, 3 is a photoresist mask, 4 is an ion implantation region, 5 is an etching region, A is an active region, and B is an element isolation region. Shown respectively.
Embodiment 1 of the present invention will be described in detail below. An oxide film 2 is formed on the silicon substrate 1 to a thickness of 200 nm (FIG. 1A). The silicon substrate 1 may be a P-type well or an N-type well. Further, one or more N-type wells or P-type wells may be formed in the silicon substrate 1. Further, an impurity for a channel cut region may be introduced at a desired position. The oxide film may have a required thickness depending on the characteristics of the element.

Next, using a photoresist mask 3 having an opening on the ion-implanted region 4 using an ordinary photolithography technique, 3 × 10 ¹⁵ / cm ^{2 of} arsenic ions at an energy of 50 KeV and 3 × 10 ¹⁵ / cm ^{2 at} an energy of 220 KeV are used.
An implantation of × 10 ¹⁵ / cm ² is performed (FIG. 1B). The ions to be implanted are boron (B), phosphorus (P), arsenic (A
s), boron fluoride (BF ₂ ) or the like depending on the implantation conditions.

FIG. 4 is an explanatory diagram showing an implantation profile of ions implanted into the ion implantation region in the present invention. In FIG. 4, the vertical axis represents the depth (μ) from the surface of oxide film 2.
m), and is formed to a thickness of 0.2 (μm).
The horizontal axis indicates the distance (μm) from the edge of the photoresist mask 3 to the surface of the silicon substrate 1. Each solid line at the upper right shows an implantation profile of a high-concentration region where ions are actually implanted using ion energy / ion implantation amount as a parameter. The dotted line shows the etched shape of the oxide film 2 opened by wet etching.

FIG. 5 is an explanatory diagram showing a concentration profile of ions implanted into the ion implantation region in the present invention. The vertical axis represents the ion concentration (log / c) implanted into the oxide film.
m ³ ), and the horizontal axis represents the depth (μm) from the surface of the oxide film 2.
Is shown. The relationship between the concentration of ions implanted into the oxide film 2 and the depth is shown.

Subsequently, the oxide film 2 is coated with a 10: 1 buffered hydrofluoric acid solution (BHF (buffered hydrofluoric acid) solution; HF + NH ₄ F).
Wet etching using. At this time, the ion-implanted region 4 has an etching rate 10 times that of the non-implanted region. Therefore, 30 nm from the surface to 150 nm.
Etched at 0 nm / min. After that, 100 nm /
And the etching is completed in about one minute (FIG. 1 (c)). The chemical used for wet etching is selected from hydrofluoric acid, buffered hydrofluoric acid and the like according to the etching conditions.

That is, by implanting ions into the oxide film in advance using a mask having an opening, the ion-implanted oxide film changes in the wet etching rate, and can be selectively etched. That is, the etching rate becomes high near the substrate surface, and vertical etching can be performed while suppressing horizontal shift (side etching). Therefore, when the wet etching is completed, the etching shape is also gentle as shown by the dotted line in FIG. 4, and the etching end is formed within 0.05 μm from the mask end.

Therefore, it is possible to cope with miniaturization of the active region and the element isolation region. In addition, since there is no damage to the silicon substrate 1 due to wet etching, good device characteristics can be obtained. Here, reduction of side etching from the active region to the element isolation region has been described, but side etching from the element isolation region to the active region can be reduced by the same method.

In the first embodiment, the thickness of the oxide film 2 for element isolation is 200 nm, but a desired ion implantation shape can be obtained by optimizing the ion implantation energy and the implantation amount for any thickness. Can be. In addition, by performing ion implantation in plural times by changing the energy and the implantation amount, the etching end can be formed in a desired shape. Next, the photoresist mask 3 is peeled off using a known technique to complete the formation of the active region and the element isolation region (FIG. 1).
(D)).

An N-channel transistor (MOSFET) according to the second embodiment will be described below by using the element isolation forming method of the present invention.
Will be described. A P-channel transistor (MOSFET) can be manufactured by using the same method.

FIG. 2 is a process chart showing a procedure for manufacturing the semiconductor device of the present invention. In FIG. 2, 1a is a silicon substrate (P-type semiconductor substrate), 2b is an oxide film (oxide film for element isolation), 3 is a photoresist (mask), 5 is an etching region, 6 is a channel cut region, 7 is a gate electrode. 8 is a gate insulating film, 9 is a source / drain diffusion region, 10 is an interlayer insulating film, 11 is a contact hole,
Reference numeral 12 denotes a metal wiring, A denotes an active region, and B denotes an element isolation region.

In the same manner as in Example 1, a 200 nm isolation oxide film 2 and a photoresist 3 are formed on a P-type semiconductor substrate 1, and after ion implantation, wet etching is performed to form an oxide film on the active region. Open (FIG. 2A). next,
Boron (B) is implanted at a dose of 120 KeV and a dose of 1.5 × 10 ¹³ / cm ² to form the channel cut region 6. Thereby, the channel cut region 6 is formed on the surface of the element isolation region B (FIG. 2B).

However, in the channel region (active region A) of the transistor, boron does not penetrate deep into the substrate, so that it does not affect the threshold value of the transistor. That is, the channel cut region can be formed in a self-aligned manner, and no overlapping margin is required between the element isolation region and the channel cut region.

Next, the photoresist 3 is peeled off by a known method, conductive polysilicon for forming a gate electrode and a gate electrode wiring 7 is deposited, and the photoresist 3 is formed by a known photolithography and dry etching technique. The polysilicon is processed to form a gate electrode and a gate electrode wiring 7 (FIG. 2C).

FIG. 3 is a cross-sectional view showing an example of etching processing on an element isolation region according to the present invention. As shown in FIG. 3, a gate electrode to be removed by etching and a gate electrode wiring 7 are deposited on the element isolation region and the active region. At this time, since the end (oxide film) of the element isolation film 2b has a gentle shape, the gate electrode and the gate electrode wiring 7 can also be formed smoothly. Therefore, the gate electrode 7
During the formation of polysilicon, disconnection of polysilicon and residual etching are less likely to occur. Here, the number of steps is small because the gate electrode and the gate electrode wiring 7 can be processed at one time.

Next, the formation of a gate oxide film 8, the formation of a gate electrode 7, the formation of a source / drain diffusion region 9, the deposition of an interlayer insulating film 10, the formation of a contact hole 11, and the formation of a metal wiring 12 are sequentially performed in a conventional manner. The transistor is completed by using the technique (FIG. 2D).

Therefore, one photolithography step (resist mask formation step), one ion implantation step (one or more ion implantations as necessary), one wet etching step, and one channel cut Since the active region and the element isolation region can be formed in the ion implantation process for formation, the manufacturing process can be shortened.

[0044]

According to the present invention, by using the ion implantation step and the wet etching step together, it is possible to change the etching rate and reduce the lateral shift from the mask, so that a region corresponding to miniaturization is formed. can do. Therefore, the active region and the element isolation region can be miniaturized with fewer steps, and furthermore, wet etching can be used in the formation process, and the active region and the element isolation region can be formed without damaging the semiconductor substrate. .

[Brief description of the drawings]

FIG. 1 is a process chart showing a procedure of element isolation of a semiconductor device of the present invention.

FIG. 2 is a process chart showing a procedure for manufacturing a semiconductor device of the present invention.

FIG. 3 is an explanatory view showing an example of etching processing on an element isolation region according to the present invention.

FIG. 4 is an explanatory diagram showing an implantation profile of ions implanted into an ion implantation region in the present invention.

FIG. 5 is an explanatory diagram showing a concentration profile of ions implanted into an ion implantation region in the present invention.

FIG. 6 is a process chart showing a procedure of element isolation of a conventional semiconductor device.

FIG. 7 is an explanatory view showing an example of an etching process on an element isolation region according to a conventional technique.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 1a silicon substrate 2 oxide film 2a oxide film 2b oxide film 3 photoresist (mask) 4 ion implantation region 5 etching region 6 channel cut region 7 gate electrode and gate electrode wiring (polysilicon) 8 gate insulating film 9 source Drain diffusion region 10 Interlayer insulating film 11 Contact hole 12 Metal wiring

Claims (4)

(57) [Claims] A step of forming an insulating film on a semiconductor substrate; a step of forming a mask having an opening on an active region on the insulating film; and a step of forming the insulating film using the mask. A step (iii) of implanting ions into the film, a step (iv) of removing the insulating film in the region where the ions are implanted by wet etching using the mask, and a step of passing the insulating film through the mask and the insulating film. The area just below the membrane and the threshold in the active area
Step of implanting ions for forming a channel cut region in a self-aligned manner with a region having a depth that does not affect the value
(va) and a step (v) of removing the mask. Wherein ions used in the step (iii) boron (B), phosphorus (P), arsenic (As), a semiconductor according to claim 1, characterized in that it consists of boron fluoride (BF ₂₎ Device isolation method. 3. The method according to claim 3, wherein the ion implantation into the insulating film performed in the step (iii) is performed at least once by changing ion implantation energy / injection amount according to the thickness of the insulating film. 3. The element isolation method for a semiconductor device according to claim 1, wherein: 4. The method according to claim 1, wherein the ion implantation into the insulating film performed in the step (iii) is performed at least once by changing ion implantation energy / implantation amount in accordance with a desired distribution state of an impurity implanted in the insulating film. 3. The method according to claim 1, wherein the semiconductor device is implanted.