Method for fabricating semiconductor device

Abstract

A method for fabricating a semiconductor device is provided, the method including forming a SiGe epitaxial layer pattern and a first Si epitaxial layer pattern on a semiconductor substrate, forming a second Si epitaxial layer on the entire surface, etching the second Si epitaxial layer and a predetermined thickness of the semiconductor substrate to form a trench defining an active region, removing the SiGe epitaxial layer pattern through a sidewall of the trench to form a space under the first Si epitaxial layer, forming a gap-filling insulating film to at least fill up the space and the trench, forming a gate oxide film on the second Si epitaxial layer, and depositing and patterning a gate conductive layer and a hard mask layer on the entire surface to form a gate in the gate region.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a method for fabricating a semiconductor device, and more specifically to a method for fabricating a semiconductor device wherein a gate is formed on a stepped Si epitaxial layer in order to increase an effective length of a gate channel, and an oxide film is only formed at the interface of the Si epitaxial layer under a bit line contact and the semiconductor substrate, thereby improving a characteristic of a leakage current for a storage node junction.

2. Description of the Related Art

FIG. 1 is a layout illustrating a conventional method for fabricating a semiconductor device, wherein reference numerals 1000a, 1, 2 and 3 denote a cell region, an active region, a first gate region and a second gate region, respectively.

FIGS. 2a through 2f are cross-sectional views illustrating a conventional method for fabricating a semiconductor device, wherein FIGS. 2a(i) through 2f(i) are cross-sectional views taken along the line I-I′ in FIG. 1, and FIGS. 2a(ii) through 2f(ii) are cross-sectional views in a core/peripheral circuit region 1000b.

Referring to FIG. 2a, a stacked structure of a SiGe epitaxial layer (not shown), a first Si epitaxial layer (not shown), a first oxide film (not shown) and a first nitride film (not shown) is formed on a semiconductor substrate 10 having a cell region 1000a and a core/peripheral circuit region 1000b defined therein.

Next, a first photoresist film (not shown) is deposited on the entire surface of the first nitride film (not shown) in the cell region 1000a and the core/peripheral circuit region 1000b.

Thereafter, the first photoresist film (not shown) is exposed and developed to form a first photoresist film pattern (not shown) exposing the first gate region 2 of FIG. 1 and cover the entire core/peripheral circuit region 1000b.

After that, the stacked structure is etched using the first photoresist film pattern as an etching mask to expose the semiconductor substrate 10 of the first gate region 2 and the entire core/peripheral circuit region 1000b.

The first photoresist film pattern is then removed.

Referring FIG. 2b, a first nitride film pattern 19 and a first oxide film pattern 17 in the cell region 1000a are removed via a wet etching method.

Next, a second Si expitaxial layer 25 is formed on the entire surface of the cell region 1000a and the core/peripheral circuit region 1000b.

Referring to FIG. 2c, a second oxide film 30 and a second nitride film 35 are formed on the second Si epitaxial layer 25 in the cell region 1000a and the core/peripheral circuit region 1000b.

Next, a second photoresist film (not shown) is deposited on the entire surface of the second nitride film 35. The second photoresist film is then exposed and developed to form a second photoresist film pattern (not shown) defining the active region 1 of FIG. 1 in the cell region 1000a, and also an active region in the core/peripheral circuit region 1000b.

Thereafter, the second nitride film 35, the second oxide film 30, the second Si epitaxial layer 25, the first Si epitaxial layer pattern 15, the SiGe epitaxial layer pattern 13 and a predetermined thickness of the semiconductor substrate 10 are etched using the second photoresist film pattern as an etching mask to form a trench 40 in the cell region 1000a and the core/peripheral circuit region 1000b.

After that, the second photoresist film pattern (not shown) is removed. The SiGe epitaxial layer pattern 13 is then etched through a sidewall of the trench 40 via a wet etching method to form a space 27 under the first Si epitaxial layer pattern 15.

Referring to FIG. 2d, a gap-filling insulating film 45 is formed on the entire surface to fill up the space 27 and the trench 40 in the cell region 1000a and to fill up the trench 40 in the core/peripheral circuit region 1000b.

Next, the gap-filling insulating film 45 is polished until the second nitride film 35 is exposed. The gap-filling insulating film 45 serves as a device isolation film.

Thereafter, a predetermined thickness of the gap-filling insulating film 45 in the trench 40 is etched. The second nitride film 35 is then removed via a wet etching method.

After that, a well implant process and a channel implant process are performed so as to adjust impurity concentrations in the cell region 1000a and the core/peripheral circuit region 1000b.

Referring to FIG. 2e, the second oxide film 30 in the cell region 1000a and the core/peripheral circuit region 1000b is removed via a wet etching method to expose the second Si epitaxial layer 25. A gate oxide film 50 is then formed on the exposed second Si epitaxial layer 25.

Next, gate conductive layers 60 and 70, and a hard mask insulating film 80 are formed on the gate oxide film 50 and the gap-filling insulating film 45 in the cell region 1000a and the core/peripheral circuit region 1000b.

Referring to FIG. 2f, a third photoresist film (not shown) is deposited on the hard mask insulating film 80 in the cell region 1000a and the core/peripheral circuit region 1000b.

Thereafter, the third photoresist film (not shown) is exposed and developed to form a third photoresist film pattern defining the second gate region 3 of FIG. 1 and a gate region (not shown) in the core/peripheral circuit region 1000b. Specifically, the third photoresist film pattern exposes a bit line contact region and storage node contact regions in the cell region 1000a and covers a region where a gate is to be formed in the core/peripheral circuit region 1000b.

Next, the hard mask insulating film 80 and the gate conductive layers 70 and 60 are etched using the third photoresist film pattern as an etching mask to respectively form a gate 90 in the cell region 1000a and the core/peripheral circuit region 1000b.

However, in accordance with the above-described conventional method, the gate 90 of the active region is formed on a plane second Si epitaxial layer. As a result, a gate channel length is decreased as a design rule of the semiconductor device is reduced.

Moreover, an oxide film is formed at the interface of the Si epitaxial layer under a storage node contact and the semiconductor substrate. Accordingly, the leakage current for a storage node junction is highly depended upon an interface characteristic between the Si epitaxial layer and an oxide film.

In addition, the SiGe epitaxial layer under the storage node contact is removed for forming a device isolation film. As a result, Ge in the SiGe epitaxial layer is diffused into the first Si epitaxial layer, the second Si epitaxial layer and the semiconductor substrate due to heat treatment processes prior to the formation of the device isolation film. Accordingly, there is a problem such as increase in the leakage current for the storage node junction.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method for fabricating a semiconductor device wherein a gate is formed on a stepped Si epitaxial layer to increase an effective length of a gate channel, and an oxide film is only formed at the interface of the Si epitaxial layer under a bit line contact and the semiconductor substrate, thereby improving a characteristic of a leakage current for a storage node junction.

In order to achieve the object of the present invention, there is provided a method for fabricating a semiconductor device comprising the steps:

(a) forming a SiGe epitaxial layer, a first Si epitaxial layer and an insulating film on a semiconductor substrate, (b) etching a predetermined region of the insulating film, the first Si epitaxial layer and the SiGe epitaxial layer to expose the semiconductor substrate, wherein the predetermined region includes a storage node contact region and a portion of a gate region adjacent thereto, (c) removing the insulating film, (d) forming a second Si epitaxial layer on the entire surface including the exposed semiconductor substrate, (e) etching the second Si epitaxial layer, the first Si epitaxial layer, the SiGe epitaxial layer and a predetermined thickness of the semiconductor substrate to form a trench defining an active region, (f) removing the SiGe epitaxial layer through a sidewall of the trench to form a space under the first Si epitaxial layer, (g) forming a gap-filling insulating film to at least fill up the space and the trench, (h) forming a gate oxide film on the second Si epitaxial layer, and (i) depositing and patterning a gate conductive layer and a hard mask layer on the entire surface to form a gate in the gate region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a layout illustrating a conventional method for fabricating a semiconductor device.

FIGS. 2a through 2f are cross-sectional views illustrating a conventional method for fabricating a semiconductor device.

FIG. 3 is a layout illustrating a method for fabricating a semiconductor device in accordance with a preferred embodiment of the present invention.

FIGS. 4a through 4f and FIG. 5 are cross-sectional views illustrating a method for fabricating a semiconductor device according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Reference will now be made in detail to exemplary embodiments of the present invention. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

FIG. 3 is a layout illustrating a method for fabricating a semiconductor device in accordance with a preferred embodiment of the present invention, wherein reference numerals 2000a, 101, 102 and 103 denote a cell region, an active region, a contact region and a gate region, respectively.

FIGS. 4a through 4f illustrate a method for fabricating a semiconductor device according to a preferred embodiment of the present invention, wherein FIGS. 4a(i) through 4f(i) are cross-sectional views taken along the line II-II′ of FIG. 3, and FIGS. 4a(ii) through 4f(ii) are cross-sectional views in a core/peripheral circuit region 2000b.

Referring to FIG. 4a, a stacked structure of a SiGe epitaxial layer (not shown), a first Si epitaxial layer (not shown) and an insulating film (not shown) is formed on a semiconductor substrate 110 having a cell region 2000a and a core/peripheral circuit region 2000b defined therein. Preferably, the insulating film comprises an oxide film or a stacked structure of an oxide film and a nitride film.

Next, a first photoresist film (not shown) is deposited on the entire surface of the insulating film in the cell region 2000a and the core/peripheral circuit region 2000b.

Thereafter, the first photoresist film (not shown) is exposed and developed to form a first photoresist film pattern (not shown) exposing the contact region 102 of FIG. 3 and cover the entire core/peripheral circuit region 2000b. The contact region 102 includes a storage node contact region and a portion of the gate region 103 adjacent thereto. Preferably, the portion of the gate region 103 has a line width of M ranging from ⅓F to F, where F is a gate line width.

After that, the stacked structure is etched using the first photoresist film pattern as an etching mask to expose the semiconductor substrate 110 of the contact region 102 and the entire core/peripheral circuit region 2000b.

The first photoresist film pattern is then removed.

Referring to FIG. 4b, an insulating film pattern 120 in the cell region 2000a is removed. Preferably, the removal process for the insulating film pattern 120 is performed via a wet etching method.

Next, a second Si epitaxial layer 125 is formed on the entire surface of the cell region 2000a and the core/peripheral circuit region 2000b. Preferably, a thickness of the second Si epitaxial layer 125 ranges from 10 nm to 100 nm.

The second epitaxial layer 125 in the cell region 2000a may have a step difference due to the first Si epitaxial layer pattern 115 and the SiGe epitaxial layer pattern 113.

Referring to FIG. 4c, a second oxide film 130 and a second nitride film 135 are formed on the second Si epitaxial layer 125 in the cell region 2000a and the core/peripheral circuit region 2000b.

Next, a second photoresist film (not shown) is deposited on the entire surface of the second nitride film 135. The photoresist film is then exposed and developed to form a second photoresist film pattern (not shown) defining the active region 101 of FIG. 3 in the cell region 2000a and also an active region in the core/peripheral circuit region 2000b.

Thereafter, the second nitride film 135, the second oxide film 130, the second Si epitaxial layer 125, the first Si epitaxial layer pattern 115, the SiGe epitaxial layer pattern 113 and a predetermined thickness of the semiconductor substrate 110 are etched using the second photoresist film pattern as an etching mask to form a trench 140 in the cell region 2000a and the core/peripheral circuit region 2000b.

After that, the second photoresist film pattern (not shown) is removed. The SiGe epitaxial layer pattern 113 is then etched through a sidewall of the trench 140 to form a space 127 under the first Si epitaxial layer pattern 115.

FIG. 5 is a cross-sectional view taken along the line III-III′ of FIG. 3 illustrating the structure of FIG. 4c(i) including the space 127 having a undercut structure.

Preferably, the removal process for the SiGe epitaxial layer pattern 113 is preformed via a wet etching method utilizing a mixed etchant containing HF, H₂O₂ and CH₃CHOOH, a plasma etching method utilizing a mixed gas containing (CF₃ or CH₂F₂), N₂ and O₂, or combinations thereof. Moreover, a volume ratio of HF, H₂O₂ and CH₃COOH in the mixed etchant is preferably 1:2:3.

Referring to FIG. 4d, a gap-filling insulating film 145 is formed on the entire surface to at least fill up the space 127 and the trench 140 in the cell region 2000a and to fill up the trench 140 in the core/peripheral circuit region 2000b.

Preferably, the formation process of the gap-filling insulating film 145 may include forming a thermal oxide film filling up the space 127 and forming an oxide film for a device isolation film filling up the trench 140. A nitride film may be further formed at an interface of the thermal oxide film and the oxide film for the device isolation film.

Moreover, the formation process of the gap-filling insulating film 145 may include forming a thermal oxide film to fill up a portion of the space 127, forming a nitride film to fill up the remaining portion of the space 127, and forming an oxide film for the device isolation film to fill up the trench 140.

Next, the gap-filling insulating film 145 is polished until the second nitride film 135 is exposed. The gap-filling insulating film 145 in the trench 140 serves as a device isolation film.

Thereafter, a predetermined thickness of the gap-filling insulating film 145 in the trench 140 is etched. The second nitride film 135 is then removed. Preferably, the etching process for the gap-fill insulating film 145 is performed via a wet etching method. The removal process for the second nitride film 135 is preferably preformed via a wet etching method.

After that, well implant processes and channel implant processes are performed so as to respectively adjust impurity concentrations in the cell region 2000a and the core/peripheral circuit region 2000b.

Referring to FIG. 4e, the second oxide film 130 in the cell region 2000a and the core/peripheral circuit region 2000b is removed to expose the second Si epitaxial layer 125. A gate oxide film 150 is then formed on the exposed second Si epitaxial layer 125. Preferably, the removal process for the second oxide film 130 is performed via a wet etching method.

Next, a stacked structure of a gate conductive layer 175 and a hard mask layer 180 is formed on the gate oxide film 150 and the gap-filling insulating film 145 in the cell region 2000a and the core/peripheral circuit region 2000b. Preferably, the gate conductive layer 175 comprises a lower conductive layer 160 and an upper conductive layer 170.

Referring to FIG. 4f, a third photoresist film (not shown) is deposited on the hard mask layer 180 in the cell region 2000a and the core/peripheral circuit region 2000b.

Thereafter, the third photoresist film (not shown) is exposed and developed to form a third photoresist film pattern defining the gate region 103 of FIG. 3 and a gate region (not shown) in the core/peripheral circuit region 2000b. Specifically, the third photoresist film pattern exposes a bit line contact region and storage node contact regions in the cell region 2000a and covers a region where a gate is to be formed in the core/peripheral circuit region 2000b.

Next, the stacked structure is patterned using the third photoresist film pattern as an etching mask to respectively form a gate 190 in the cell region 2000a and the core/peripheral circuit region 2000b.

In addition, subsequent processes such as an ion-implant process for forming source/drain regions in the active regions, a process for forming a spacer on a sidewall of the gate 190, a process for forming a landing plug, a process for forming a bit line contact and a bit line, a process for forming a capacitor and a process for forming an interconnect may be done.

As described above, the method for fabricating a semiconductor device in accordance with the present invention provides exposing the contact region including the storage node contact region and a portion of the gate region adjacent thereto and only forming an oxide film at the interface of the Si epitaxial layer under both a bit line contact and the semiconductor substrate. Accordingly, capacitance for a bit line contact and a short-channel effect of a cell transistor are improved.

As shown in FIG. 4f, the gate 190 in the cell region 2000a is formed on a structure having a step difference instead of over a plane structure to increase an effective length of the gate channel, and the storage node contact is formed on the Si epitaxial layer without the oxide film to minimize the leakage current of the storage node junction. Accordingly, a refresh characteristic of a DRAM can be improved.

The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated.

Claims

1. A method for fabricating a semiconductor device, comprising the steps of:

(a) forming a SiGe epitaxial layer, a first Si epitaxial layer and an insulating film on a semiconductor substrate;

(b) etching a predetermined region of the insulating film, the first Si epitaxial layer and the SiGe epitaxial layer to expose the semiconductor substrate, wherein the predetermined region includes a storage node contact region and a portion of a gate region adjacent thereto;

(c) removing the insulating film;

(d) forming a second Si epitaxial layer on the entire surface including the exposed semiconductor substrate;

(e) etching the second Si epitaxial layer, the first Si epitaxial layer, the SiGe epitaxial layer and a predetermined thickness of the semiconductor substrate to form a trench defining an active region;

(f) removing the SiGe epitaxial layer through a sidewall of the trench to form a space under the first Si epitaxial layer;

(g) forming a gap-filling insulating film to at least fill up the space and the trench;

(h) forming a gate oxide film on the second Si epitaxial layer; and

(i) depositing and patterning a gate conductive layer and a hard mask layer on the entire surface to form a gate in the gate region.

2. The method according to claim 1, wherein the step (b) comprises:

forming a photoresist film on the entire surface of the semiconductor substrate;

forming a photoresist film pattern exposing the predetermined region by exposing and developing the photoresist film, wherein the portion of the gate region of the predetermined region has a line width of M; and

etching the insulating film, the Si epitaxial layer and the SiGe epitaxial layer using the photoresist film pattern as an etching mask.

3. The method according to claim 2, wherein the M ranges from ⅓F to F, wherein F is a gate line width.

4. The method according to claim 1, wherein the insulating film comprises an oxide film.

5. The method according to claim 1, wherein the insulating film comprises a stacked structure of an oxide film and a nitride film.

6. The method according to claim 1, wherein the removal process for the insulating film in the step (e) is performed via a wet etching method.

7. The method according to claim 1, wherein a thickness of the second Si epitaxial layer ranges from 10 to 100 nm.

8. The method according to claim 1, wherein the removal process for the SiGe epitaxial layer in the step (f) is performed via one method selected from the group consisting of a wet etching method utilizing a mixed etchant containing HF, H2O2 and CH3COOH, a plasma etching method utilizing a mixed gas containing (CF4 or CH2F2), N2 and O2, and combinations thereof.

9. The method according to claim 8, wherein a volume ratio of HF, H2O2 and CH3COOH in the mixed etchant is 1:2:3.

10. The method according to claim 1, wherein the step (g) comprises:

forming a thermal oxide film filling up the space; and

forming an oxide film for a device isolation film to fill up the trench.

11. The method according to claim 10, further comprising

forming a nitride film at the interface of the thermal oxide film and the oxide film for the device isolation film.

12. The method according to claim 1, wherein the step (g) comprises:

forming a thermal oxide film to fill a portion of the space;

forming a nitride film to fill up a remaining portion of the space; and

forming an oxide film for the device isolation film to fill up the trench.