# Patent

## Title
Semiconductor device having improved contact area

## Abstract

A semiconductor device forms a salicide layer to surround an upper surface and a circumference of a lateral surface of a pillar. A contact area between the pillar and a lower electrode may be increased to reduce a contact resistance.

## Background
CROSS-REFERENCES TO RELATED APPLICATION
This application is a division of U.S. patent application Ser. No. 14/044,475 filed on Oct. 2, 2013, which claims priority under 35 U.S.C. 119(a) to Korean application number 10-2013-0068347, filed on Jun. 14, 2013, in the Korean Patent Office. The disclosure of each of the foregoing application is incorporated by reference in its entirety.


BACKGROUND OF THE INVENTION
1. Technical Field
Various embodiments of the inventive concept relate to a semiconductor device and a method for manufacturing the same, and more particularly, to a semiconductor device having a vertical transistor and a method for manufacturing the same.
2. Related Art
With increase in a degree of integration of semiconductor devices, a channel length of a transistor is reduced increasingly. The reduction in the channel length causes drain induced barrier lowering (BIDL), a hot carrier effect, and a short channel effect, such as punch-through.
To alleviate these concerns, various methods, such as a method of reducing a length of a junction region, a method of increasing a channel length by forming a recess in a channel region of the transistor, and the like are suggested.
However, as the degree of integration of semiconductor devices is approaching Giga bytes, it may be difficult to satisfy a required device area using a planar transistor structure in which junction regions are formed at both sides of gates even when the channel length is scaled down. Therefore, to alleviate this concern, vertical transistor technology is suggested.
A semiconductor device having a vertical transistor in the related art will be described with reference to FIG. 3.
The semiconductor device in the related art includes a plurality of pillars 115 extending to a vertical direction from a semiconductor substrate 110, and a gate insulating layer 130 surrounding a lateral surface of each of the pillars 115, and a gate electrode 140 surrounding each of the pillars surrounded with the gate insulating layer 130 to a predetermined height. A silicide layer 160 is formed on an upper surface of each of the pillars, and a lower electrode 170 is formed on the silicide layer 160.
A level of difficulty in a process is considerably increasing according to decrease in the size of semiconductor device having the vertical channel transistor, specifically, a phase-change random access memory (PRAM). In particular, an ON current may be reduced due to increase in a contact resistance according to decrease in size of a 20 nm-graded or less device.
Therefore, there is a need for a method for increasing an ON current due to reduction in a contact resistance in a recent semiconductor device.
SUMMARY
One or more exemplary embodiments of the present invention are directed to a semiconductor device that may increase an ON current due to reduction in a contact resistance when manufacturing the semiconductor device and a method for manufacturing the same.
According to an aspect of an exemplary embodiment of the present invention, a semiconductor device may include a semiconductor substrate, a plurality of pillars formed to extend substantially perpendicular from the semiconductor substrate, a gate electrode formed to surround a circumference of a lower portion of a lateral surface of each of the pillars and to have an upper surface having a height lower than a height of an upper surface of each of the pillars, a salicide layer formed to surround the upper surface of each of the pillars and a circumference of an upper portion of a lateral surface of each of the pillars, a lower electrode formed to surround an upper surface and a lateral surface of the salicide layer, and a first spacer formed to surround a portion of the lateral surface of each of the pillars, between the upper surface of the gate electrode and the salicide layer.
According to an aspect of another exemplary embodiment of the present invention, a method for manufacturing a semiconductor device may include forming a plurality of pillars by etching a semiconductor substrate using a hard mask pattern, gap-filling a conductive material between the pillars, and etching back the conductive material so that an upper surface of the etching backed conductive material has a height lower than that of an upper surface of each of the pillars, forming a first spacer on a lateral surface of the hard mask pattern and on an upper portion of a lateral surface of each of pillars, which is uncovered with the etching backed conductive material, the first spacer formed of the same material as that of the hard mask pattern, removing the hard mask pattern and an upper portion of the first spacer to expose the upper surface of each of the pillars and a portion of the upper portion of the lateral surface of each of the pillars, forming a salicide layer to surround the exposed upper surface of each of the pillars and the exposed portion of the upper portion of the lateral surface of each of the pillars, and forming a lower electrode to surround the salicide layer.
These and other features, aspects, and embodiments are described below in the section entitled “DETAILED DESCRIPTION”.



BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, features and other advantages of the subject matter of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a cross-sectional view illustrating a semiconductor device according to an embodiment of the inventive concept;
FIGS. 2A to 2I are cross-sectional views illustrating a method for manufacturing a semiconductor device according to an embodiment of the inventive concept; and
FIG. 3 is a cross-sectional view illustrating a semiconductor device in the related art.



DETAILED DESCRIPTION
Hereinafter, exemplary embodiments will be described in greater detail with reference to the accompanying drawings.
Exemplary embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of exemplary embodiments (and intermediate structures). As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, exemplary embodiments should not be construed as limited to the particular shapes of regions illustrated herein but may be to include deviations in shapes that result, for example, from manufacturing. In the drawings, lengths and sizes of layers and regions may be exaggerated for clarity. Like reference numerals in the drawings denote like elements. It is also understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other or substrate, or intervening layers may also be present. In addition, a singular form may include a plural form as long as it is not specifically mentioned in a sentence.
Hereinafter, a semiconductor device according to an embodiment of the inventive concept will be described using a phase-change random access memory (PRAM). However, it would have been obvious to the person having ordinary skill in the art that the inventive concept may be applied to any nonvolatile memory device using a resistor, such as a resistive RAM (RRAM) or a ferroelectric RAM (FRAM).
Referring to FIG. 1, a semiconductor device (a PRAM) according to an embodiment of the inventive concept may include a vertical transistor structure.
The vertical transistor structure may include a plurality of pillars 15 extending to a vertical direction from a semiconductor substrate 10, a gate insulating layer 30 formed on a surface of the semiconductor substrate 10 and surrounding a lateral surface of each of the pillars 15, and a gate electrode 40 surrounding each of the pillars 15 surrounded with the gate insulating layer 30 to a predetermined height.
An upper surface of the gate electrode 40 is lower than upper surfaces of the gate insulating layer 30 and the pillars 15.
As illustrated in FIG. 1, a self-aligned silicide (salicide) layer 80 is formed on an upper portion of the vertical transistor structure, that is, on an upper portion of each of the pillars 15 on which the gate electrode 40 is not formed.
The salicide layer 80 is formed to surround an upper surface of each of the pillars 15 and a circumference of a lateral surface of the upper portion of each of the pillars 15. As compared with a silicide layer only formed on an upper surface of each of the pillars in the related art, it may be seen that a substantial surface area of the salicide layer 80 is increased.
A lower electrode 90 is formed to surround an upper surface and a lateral surface of the salicide layer 28.
Spacers 50 and 60 are formed on an upper portion of the vertical transistor structure, that is, the lateral surface of the upper portion of each pillar 15 on which the gate electrode 40 is not formed as illustrated in FIG. 1. The spacers may include a first spacer 50 formed to surround a space between the gate electrode 40 and the lower electrode 90 on the lateral surface of each of the pillars 15, and a second spacer 60 formed to surround lateral surfaces of the first spacer 50 and the lower electrode 90. At this time, the first spacer 50 may include a material having the same etch selectivity as or a similar etch selectivity to that of a hard mask pattern (see 20 of FIG. 2A) for the formation of the pillars 15.
That is, in an embodiment of the inventive concept, a contact area of the salicide layer 80 with the pillar 15 is increased by a circumferential area in the lateral surface of the upper portion of the pillar 15, and thus a contact resistance of the salicide layer 80 with the lower electrode 90 is reduced. An ON current is increased according to reduction in the contact resistance of the salicide layer 80 with the lower electrode 90.
A method for manufacturing a semiconductor device according to an embodiment will be described below.
As illustrated in FIG. 2A, a hard mask layer (not shown) is formed on a semiconductor substrate 10. The hard mask layer may be formed of a material having an etch selectivity different from the semiconductor substrate 10, for example, silicon oxide. A photoresist pattern (not shown) is formed on the hard mask layer through a general process, and the hard mask layer is etched using the photoresist pattern as a mask to form a hard mask pattern 20.
As illustrated in FIG. 2B, a semiconductor substrate 10 is etched to a predetermined depth using a hard mask pattern 20 as a mask to form a plurality of pillars 15 in the semiconductor substrate 10. The pillars 15 are formed to a direction extending substantially perpendicular from the semiconductor substrate 10.
A gate insulating layer 30 is formed on the semiconductor substrate 10 including the pillars 15, that is, an exposed lateral surface of each of the pillars 15 and on a surface of the semiconductor substrate 10 between the pillars 15. For example, the gate insulating layer 30 may include a silicon oxide (SiO2) layer, a hafnium oxide (HFO2) layer, a tantalum oxide (Ta2O5) layer, or an oxide/nitride/oxide (ONO) layer.
After the pillars 15 and the gate insulating layer 30 are formed, impurities are doped into the semiconductor substrate 10 to form a source region (not shown).
As illustrated in FIG. 2C, a conductive material 40a is gap-filled in the semiconductor substrate including the gate insulating layer 30 illustrated in FIG. 2B, and then etched back so that the gap-filled conductive material 40a has a predetermined height.
As illustrated in FIG. 2D, a spacer surrounding a lateral surface of each of the pillars 15 is located on the conductive material 40a and a lateral surface of the hard mask pattern 20. The spacer includes a first spacer 50 and a second spacer 60 located in an outer side of the first spacer 50.
The first spacer 50 may be formed by depositing a material for the first spacer, for example, an oxide having the same etch selectivity as or a similar etch selectivity to that of the hard mask pattern 20, along a surface of the semiconductor substrate including the conductive material 40a illustrated in FIG. 2C, and spacer-etching the material for the first spacer.
The second spacer 60 is located in the outer side of the first spacer 50 as described above. The second spacer 60 may be formed by depositing a material for the second spacer, for example, a nitride along a step of the surface of the semiconductor substrate including the first spacer 50, and spacer-etching the material for the second spacer.
The conductive material (see 40a of FIG. 2B) is etched to form a gate electrode 40. The gate electrode 40 may surround a lateral surface of a lower portion of each of the pillars 15 to a predetermined height. That is, the gate electrode 40 may be formed to have an upper surface having a height lower than that of an upper surface of each of the pillars 15.
As illustrated in FIG. 2E, a gap-fill insulating material is formed on the semiconductor substrate including the gate electrode 40 illustrated in FIG. 2D, and then planarized until an upper surface of the second spacer 60 is exposed to form an inter-cell insulating layer 70.
As illustrated in FIG. 2F, the hard mask pattern 20 and a portion of the first spacer 50 having the same etch selectivity as that of the hard mask pattern 20 are removed through a dipping out process. Therefore, in the embodiment of inventive concept, a space 25 exposing the upper surface and a lateral surface of an upper portion of each of the pillars 15 is formed.
Into the upper portion of each of the pillars 15 exposed by removing the hard mask pattern 20 and the portion of the first spacer 50 in the removing process, impurities are doped to form a drain region (not shown).
As illustrated in FIG. 2G, a self-aligned silicide (salicide) layer 80 is formed along the upper surface and a circumference of the lateral surface of the upper portion of each of the pillars 15 exposed through the above-process.
Specifically, a salicide formation material is deposited in the space 25 formed by removing the hard mask pattern 20 and the portion of the first spacer 50 among a resultant structure of FIG. 2F. The salicide formation material may include a transition metal, such as cobalt (Co), titanium (Ti), nickel (Ni), or tungsten (W).
The pillars 15 may react with the salicide formation material through a heat treatment. The salicide formation material reacts with each of the pillars at a direct contact portion thereof to form a salicide layer 80 through a selective reaction of silicon and metal.
A non-reacted portion of the salicide formation material may be removed through a general process. In other words, the salicide layer 80 is formed to surround the upper surface and the circumference of the lateral surface of the upper portion of each of the pillars 15.
As illustrated in FIG. 2H, a lower electrode 90 is formed on each of the pillars 15 on which the salicide layer 80 is formed. The lower electrode 90 may be formed by depositing a conductive material on the semiconductor substrate including the salicide layer 80 illustrated in FIG. 2G and then planarized through an etch back process.
The conductive material for the lower electrode 90 may include a material such as titanium nitride (TiN), tantalum nitride (TaN), tungsten nitride (WN), niobium nitride (NbN), titanium silicon nitride (TiSiN), titanium aluminum nitride (TiAlN), titanium boron nitride (TiBN), zirconium silicon nitride (ZrSiN), tungsten silicon nitride (WSiN), tungsten boron nitride (WBN), zirconium aluminum nitride (ZrAlN), molybdenum aluminum nitride (MoAlN), tantalum silicon nitride (TaSiN), tantalum aluminum nitride (TaAlN), titanium (Ti), tungsten (W), molybdenum (Mo), tantalum (Ta), titanium silicide (TiSi), tantalum silicide (TaSi), titanium oxynitride (TiON), titanium aluminum oxynitride (TiAlON), tungsten oxynitride (WON), or tantalum oxynitride (TaON).
A phase-change layer (not shown) and an upper electrode (not shown) may be formed on the lower electrode 90 to complete the PRAM.
Therefore, in the semiconductor device manufactured through the manufacturing method, as the salicide layer formed between the pillar and the lower electrode is formed along the upper surface and the circumference of the lateral surface of the upper portion of the pillar, a substantial surface area of the salicide layer may be increased compared to the related art. Thus, a contact area of the salicide layer according to an embodiment of the inventive concept with the lower electrode may be increased, and thus a contact resistance of the salicide layer with the lower electrode may be reduced.
The above embodiment of the present invention is illustrative and not limitative. Various alternatives and equivalents are possible. The invention is not limited by the embodiment described herein. Nor is the invention limited to any specific type of semiconductor device. Other additions, subtractions, or modifications are obvious in view of the present disclosure and are intended to fall within the scope of the appended claims.

## Claims

1. A semiconductor device, comprising:
a semiconductor substrate;
a plurality of pillars formed to extend substantially perpendicular from the semiconductor substrate;
a gate electrode formed to surround a circumference of a lower portion of each of the pillars and to have an upper surface having a height lower than a height of an upper surface of each of the pillars;
a salicide layer formed to surround the upper surface of each of the pillars and a lateral surface of each of the pillars, wherein the salicide layer does not contact the upper surface of the gate electrode;
a lower electrode formed along a whole surface of the silicide layer with covering the upper surface and the lateral surface of each of the pillars; and
a first spacer formed at the lateral surface of each of the pillars and between the upper surface of the gate electrode and the salicide layer.

2. The semiconductor device of claim 1, further comprising a second spacer formed to surround a lateral surface of the first spacer and a lateral surface of the lower electrode.

3. The semiconductor device of claim 2, wherein a gate insulating layer is further formed between each of the pillars and the gate electrode and between each of the pillars and the first spacer.

4. A semiconductor device, comprising:
a semiconductor substrate;
a pillar formed to extend substantially perpendicular from a surface of the semiconductor substrate;
a gate electrode formed to surround a circumference of a lower portion of the pillar;
a lower electrode covers a top surface and a lateral surface of the pillar,
a first spacer formed at the lateral surface of the pillar and between the lower electrode and the gate electrode; and
a second spacer formed to surround a circumference of the first spacer
wherein a sum of widths of the first and second spacers is substantially the same as a width of the gate electrode.

5. The semiconductor device of claim 4, wherein the lower electrode includes a top portion formed on the top surface of the pillar, and a lateral portion extended from an edge of the top portion along the lateral surface of the pillar.

6. The semiconductor device of claim 5, wherein the lateral portion of the lower electrode is separated from the gate electrode and insulated from the gate electrode.

7. The semiconductor device of claim 5, wherein the second spacer is formed to surround the lateral portion of the lower electrode.

8. The semiconductor device of claim 4, wherein the first and second spacers are formed on the gate electrode.

9. The semiconductor device of claim 4, further comprising a salicide layer formed between the lower electrode and the pillar,
wherein the salicide layer is formed on the top surface and the lateral surface of the pillar.

10. The semiconductor device of claim 4, further comprising a gate insulating layer formed between the gate electrode and the pillar.