# Patent

## Title
Semiconductor device and method of manufacturing the same

## Abstract

In one embodiment, a method of manufacturing a semiconductor device includes forming first patterns on a workpiece layer, and forming second patterns containing a first metal on side faces of the first patterns. The method further includes removing the first patterns after forming the second patterns, and forming third patterns on side faces of the second patterns by a chemical change of the first metal after removing the first patterns. The method further includes removing the second patterns after forming the third patterns, and processing the workpiece layer by using the third patterns as a mask after removing the second patterns.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority from the prior U.S. Provisional Patent Application No. 62/213,821 filed on Sep. 3, 2015, the entire contents of which are incorporated herein by reference.


FIELD
Embodiments described herein relate to a semiconductor device and a method of manufacturing the same.
BACKGROUND
Fine patterns of a semiconductor device are often formed by a sidewall transfer technique. In this case, the fine patterns having a desired dimension are formed by repeating formation, processing and slimming of plural layers. Therefore, many steps are required to form the fine patterns, which increase a manufacturing cost of the semiconductor device.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A to 3C are cross-sectional views illustrating a method of manufacturing a semiconductor device of a first embodiment;
FIGS. 4A to 5 are cross-sectional views illustrating a method of manufacturing a semiconductor device of a second embodiment; and
FIG. 6 is a cross-sectional view illustrating a method of manufacturing a semiconductor device of a modification of the second embodiment.



DETAILED DESCRIPTION
Embodiments will now be explained with reference to the accompanying drawings.
In one embodiment, a method of manufacturing a semiconductor device includes forming first patterns on a workpiece layer, and forming second patterns containing a first metal on side faces of the first patterns. The method further includes removing the first patterns after forming the second patterns, and forming third patterns on side faces of the second patterns by a chemical change of the first metal after removing the first patterns. The method further includes removing the second patterns after forming the third patterns, and processing the workpiece layer by using the third patterns as a mask after removing the second patterns.
First Embodiment
FIGS. 1A to 3C are cross-sectional views illustrating a method of manufacturing a semiconductor device of a first embodiment.
First, an underlying layer 2, a workpiece layer 3 and a core material layer 4 are formed on a substrate 1 (FIG. 1A).
An example of the substrate 1 is a semiconductor substrate such as a silicon substrate. FIG. 1A shows an X direction and a Y direction parallel to a surface of the substrate 1 and perpendicular to each other, and a Z direction perpendicular to the surface of the substrate 1. In the present specification, a +Z direction is treated as an upper direction, and a −Z direction is treated as a lower direction. The −Z direction in the present embodiment may or may not correspond to the gravity direction.
Examples of the underlying layer 2 and the workpiece layer are various conductive layers, semiconductor layers and insulating layers. The workpiece layer 3 may be formed on the substrate 1 via the underlying layer 2 as shown in FIG. 1A, or may be formed directly on the substrate 1. Although the workpiece layer 3 is a layer different from the substrate 1 in FIG. 1A, the substrate 1 itself may be used as the workpiece layer 3 instead. Examples of the core material layer 4 are a resist layer and a hard mask layer.
The core material layer 4 is then processed into core material patterns 4a and 4b by etching (FIG. 1B). The core material patterns 4a and 4b are an example of first patterns.
A metal layer 5 is then formed on the entire surface of the substrate 1 and is processed by etching (FIG. 1C). As a result, sidewall patterns 5a to 5d made of the metal layer 5 are formed on side faces of the core material patterns 4a and 4b. The sidewall patterns 5a to 5d are an example of second patterns. A metal contained in the metal layer 5 is, for example, tungsten (W), aluminum (Al) or copper (Cu). The metal contained in the metal layer 5 is an example of a first metal. The metal layer 5 in the present embodiment is an elemental metal layer such as a W layer, an Al layer or a Cu layer.
After the sidewall patterns 5a to 5d is formed, the core material patterns 4a and 4b are removed (FIG. 2A).
After the core material patterns 4a and 4b are removed, the metal in the metal layer 5 is oxidized (FIG. 2B). As a result, oxide film patterns 6a to 6d made of a metal oxide film 6 are formed on side faces and upper faces of the sidewall patterns 5a to 5d. The oxidation of the metal in the metal layer 5 is an example of a chemical change of the first metal. The oxide film patterns 6a to 6d are examples of third patterns. In the present embodiment, the metal layer 5 is a tungsten layer, and the metal oxide film 6 is a tungsten oxide film.
The metal in the metal layer 5 is oxidized by ashing with an oxygen (O2) gas. This makes it possible to form the metal oxide film 6 having a sufficient thickness. The thickness of the metal oxide film 6 can be controlled by adjusting the amount of oxidation of the metal layer 5. The ashing in the present embodiment may be performed with the oxygen gas and a nitrogen (N2) gas. The nitrogen gas is used to raise an oxidation rate of the metal layer 5. The ashing in the present embodiment is performed in a dry etching apparatus, for example. In this case, the etching in FIG. 1C, the removal of the core material in FIG. 2A, and the ashing in FIG. 2B may be performed in the same dry etching apparatus.
FIG. 2B illustrates a first side face S1 of each oxide film pattern 6a to 6d and a second side face S2 of each oxide film pattern 6a to 6d, the second side face S2 being more inclined than the first side face S1. In the present embodiment, the oxide film patterns 6a to 6d are formed to form first gaps G1 between the first side faces S1 of the oxide film patterns 6a to 6d and to form second gaps G2 between the second side faces S2 of the oxide film patterns 6a to 6d. 
FIG. 2B also illustrates a width W of bottom faces of the sidewall patterns 5a to 5d, a width W1 of bottom faces of the first gaps G1, and a width W2 of bottom faces of the second gaps G2. In the present embodiment, the width W1 and the width W2 are set to values close to a value of the width W, and are specifically set to be 0.5 to 1.5 times of the width W (0.5 W≦W1≦1.5 W, 0.5 W≦W2≦1.5 W).
Next, a sacrificial film 7 is formed on the entire surface of the substrate 1 (FIG. 2C). As a result, the sidewall patterns 5a to 5d and the oxide film patterns 6a to 6d are covered with the sacrificial film 7. The sacrificial film 7 is an example of a first film. The sacrificial film 7 is a silicon oxide film or a silicon nitride film, for example. The sacrificial film 7 may be a polysilicon layer or a metal layer.
A surface of the sacrificial film 7 is then planarized by etch back (FIG. 3A). As a result, the oxide film patterns 6a to 6d are exposed from the sacrificial film 7. Furthermore, the sidewall patterns 5a to 5d are exposed from the oxide film patterns 6a to 6d. At this time, since the oxide film pattern 6a is removed from the upper face of the sidewall pattern 5a, the oxide film pattern 6a provided on the sidewall pattern 5a is divided into two. The same is true of the other oxide film patterns 6b to 6d. 
The exposed sidewall patterns 5a to 5d and the sacrificial film 7 are then removed (FIG. 3B). Since the widths W1 and W2 of the present embodiment is set to the values close to the value of the width W (refer to FIG. 2B), distances between the oxide film patterns 6a to 6d are close values to each other.
Next, the workpiece layer 3 is processed by etching using the oxide film patterns 6a to 6d as a mask (FIG. 3C). As a result, the oxide film patterns 6a to 6d are transferred to the workpiece layer 3, and desired fine patterns 3a to 3d are formed of the workpiece layer 3.
Thereafter, various interconnect layers, plug layers and inter layer dielectrics are formed on the substrate 1. In this manner, the semiconductor device of the present embodiment is manufactured.
As described above, in the present embodiment, the sidewall patterns 5a to 5d are formed of the metal layer 5, the oxide film patterns 6a to 6d are formed by oxidation of the metal layer 5, and the oxide film patterns 6a to 6d are used as a mask to process the workpiece layer 3.
Accordingly, the present embodiment makes it possible to form the fine patterns 3a to 3d only with a single layer (metal oxide film 6) by a sidewall transfer technique without forming core material patterns and sidewall patterns plural times. The reason is that the process of forming the core material patterns plural times and the process of forming the sidewall patterns plural times can be replaced with the process of forming the oxide film patterns 6a to 6d. In the present embodiment, the fine patterns 3a to 3d can be formed while the number of times of forming the core material patterns 4a and 4b is decreased to one, and the number of times of forming the sidewall patterns 5a to 5d is decreased to one.
As described above, the present embodiment makes it possible to form the desired patterns 3a to 3d by the sidewall transfer technique easily.
Second Embodiment
FIGS. 4A to 5 are cross-sectional views illustrating a method of manufacturing a semiconductor device of a second embodiment.
First, the steps in FIGS. 1A to 2B are performed.
Next, a metal layer 8 is formed on the entire surface of the substrate 1 (FIG. 4A). As a result, the sidewall patterns 5a to 5d and the oxide film patterns 6a to 6d are covered with the metal layer 8. The metal layer 8 is an example of the first film.
A metal contained in the metal layer 8 is, for example, tungsten (W), aluminum (Al) or copper (Cu). The metal contained in the metal layer 8 is an example of a second metal. The metal layer 8 in the present embodiment is an elemental metal layer such as a W layer, an Al layer or a Cu layer. The metal layer 8 may contain a metal same as or different from the metal in the metal layer 5. For example, the metal layers 5 and 8 may both be W layers or may respectively be a W layer and an Al layer.
A surface of the metal layer 8 is then planarized by etch back (FIG. 4B). As a result, the oxide film patterns 6a to 6d are exposed from the metal layer 8, and the sidewall patterns 5a to 5d are exposed from the oxide film patterns 6a to 6d. At this time, since the oxide film pattern 6a is removed from the upper face of the sidewall pattern 5a, the oxide film pattern 6a provided on the sidewall pattern 5a is divided into two. The same is true of the other oxide film patterns 6b to 6d. Furthermore, buried patterns 8a to 8e formed of the metal layer 8 are formed between the oxide film patterns 6a to 6d. The buried patterns 8a to 8e are examples of fourth patterns.
The exposed oxide film patterns 6a to 6d are then removed (FIG. 4C). Since the widths W1 and W2 of the present embodiment is set the values close to the value of the width W (refer to FIG. 2B), distances between the sidewall patterns 5a to 5d and the buried patterns 8a to 8e are close values to each other.
Next, the workpiece layer 3 is processed by etching using the sidewall patterns 5a to 5d and the buried patterns 8a to 8e as a mask (FIG. 5). As a result, the sidewall patterns 5a to 5d and the buried patterns 8a to 8e are transferred to the workpiece layer 3, and desired fine patterns 3a to 3d and 3A to 3E are formed of the workpiece layer 3. The fine patterns 3a to 3d correspond to the sidewall patterns 5a to 5d, and the fine patterns 3A to 3E correspond to the buried patterns 8a to 8e. 
Thereafter, various interconnect layers, plug layers and inter layer dielectrics are formed on the substrate 1. In this manner, the semiconductor device of the present embodiment is manufactured.
As described above, in the present embodiment, the sidewall patterns 5a to 5d are formed of the metal layer 5, the oxide film patterns 6a to 6d are formed by oxidation of the metal layer 5, the buried patterns 8a to 8e are formed between the oxide film patterns 6a to 6d, and the sidewall patterns 5a to 5d and the buried patterns 8a to 8e are used as a mask to process the workpiece layer 3.
Similarly to the first embodiment, the present embodiment makes it possible to form the desired patterns 3a to 3d and 3A to 3E by the sidewall transfer technique easily. Also, the present embodiment makes it possible, by using the metal layers 5 and 8 as a mask, to improve etching resistance of the mask and to perform etching of the workpiece layer 3 easily.
Modification of Second Embodiment
FIG. 6 is a cross-sectional view illustrating a method of manufacturing a semiconductor device of a modification of the second embodiment.
In the present modification, the sidewall patterns 5a to 5d and the buried patterns 8a to 8e are used as interconnects, not as a mask. Accordingly, after the step in FIG. 4C, the sidewall patterns 5a to 5d and the buried patterns 8a to 8e are covered with an inter layer dielectric 9 (FIG. 6). Examples of the inter layer dielectric 9 is a silicon oxide film and a silicon nitride film. Thereafter, contact plugs that reach the sidewall patterns 5a to 5d and the buried patterns 8a to 8e are formed in the inter layer dielectric 9.
The sidewall patterns 5a to 5d and the buried patterns 8a to 8e in the present modification are formed alternately on the underlying layer 2. The sidewall patterns 5a to 5d are an example of first interconnect patterns. The buried patterns 8a to 8e are an example of second interconnect patterns.
FIG. 6 illustrates widths A1 and B1 of an upper face and a lower face of each sidewall pattern 5a to 5d, and widths A2 and B2 of an upper face and a lower face of each buried pattern 8a to 8e. FIG. 6 illustrates shapes of the sidewall patterns 5a to 5d and the buried patterns 8a to 8e further in detail than FIG. 4C. Specifically, the width A1 is approximately equal to the width B1, and the width A2 is longer than the width B2. This results from shapes of the oxide film patterns 6a to 6d. 
Accordingly, in the present modification, a second value C2 derived by subtracting the width B2 from the width A2 of the buried patterns 8a to 8e is a positive value and is higher than a first value C1 derived by subtracting the width B1 from the width A1 of the sidewall patterns 5a to 5d. That is, C2>0 and C2>C1 are established. It is noted that the first value C1 may be a positive value, a negative value or zero.
A sign F represents an upper face of the underlying layer 2. The sidewall patterns 5a to 5d and the buried patterns 8a to 8e contact the upper face F of the underlying layer 2. The underlying layer 2 is an example of a first layer, and the upper face F is an example of a first upper face. In a case where the sidewall patterns 5a to 5d and the buried patterns 8a to 8e are formed directly on the substrate 1, an upper face of the substrate 1 is an example of the first upper face. The upper face F of the underlying layer 2 is classified into upper faces F1 under the sidewall patterns 5a to 5d, upper faces F2 under the buried patterns 8a to 8e, and upper faces F3 between the sidewall patterns 5a to 5d and the buried patterns 8a to 8e. A sign E represents a width of the upper faces F3.
The sidewall patterns 5a to 5d and the buried patterns 8a to 8e in the present modification are formed in the shapes in FIG. 6 by removing the oxide film patterns 6a to 6d by etching. At this time, since the sidewall patterns 5a to 5d and the buried patterns 8a to 8e are elemental metal layers and the oxide film patterns 6a to 6d are metal oxide films, it is easy to set high selectivity of this etching. For this reason, this etching can be performed while restricting denting of the upper face F3.
Here, a difference between the upper faces F1 and F3 is expressed by ΔF1 (ΔF1=|F1−F3|), and a difference between the upper faces F2 and F3 is expressed by ΔF2 (ΔF2=|F2−F3|). In the present modification, since the denting of the upper face F3 does not exist or is small, values of the differences ΔF1, and ΔF2 are low. For example, the values of the differences ΔF1 and ΔF2 in the present modification can be lower than 0.5 times of the width E of the upper faces F3 (ΔF1<0.5E, ΔF2<0.5E). In this case, a depth of the dents of the upper faces F3 is smaller than a radius of a circle whose diameter is the width E of the upper faces F3.
In a case where the upper faces F3 are dented, the thickness of the underlying layer 2 needs to be large in consideration of the dents. However, according to the present modification, since the denting of the upper faces F3 can be restricted, the thickness of the underlying layer 2 can be small.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel devices and methods described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the devices and methods described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

## Claims

1. A method of manufacturing a semiconductor device, comprising:
forming first patterns on a workpiece layer;
forming second patterns containing a first metal on side faces of the first patterns;
removing the first patterns after forming the second patterns;
forming third patterns on side faces of the second patterns by a chemical change of the first metal after removing the first patterns;
removing the second patterns after forming the third patterns; and
processing the workpiece layer by using the third patterns as a mask after removing the second patterns.

2. The method of claim 1, wherein the chemical change of the first metal is oxidation of the first metal.

3. The method of claim 2, wherein the first metal is oxidized by ashing with an oxygen gas.

4. The method of claim 3, wherein the ashing of the first metal is performed with the oxygen gas and a nitrogen gas.

5. The method of claim 1, wherein the second patterns are formed of an elemental metal layer containing the first metal.

6. The method of claim 1, wherein the third patterns are formed to form a first gap between first side faces of the third patterns and to form a second gap between second side faces of the third patterns, the second faces being more inclined than the first side faces, a width of a bottom face of the first gap and a width of a bottom face of the second gap being 0.5 to 1.5 times of a width of bottom faces of the second patterns.

7. The method of claim 1, further comprising:
forming a first film on the third patterns after forming the third patterns,
planarizing a surface of the first film to expose the second patterns from the third patterns, and
removing the exposed second patterns and the first film.

8. A method of manufacturing a semiconductor device, comprising:
forming first patterns on a workpiece layer;
forming second patterns containing a first metal on side faces of the first patterns;
removing the first patterns after forming the second patterns;
forming third patterns on side faces of the second patterns by a chemical change of the first metal after removing the first patterns;
forming fourth patterns containing a second metal between the third patterns;
removing the third patterns after forming the fourth patterns; and
processing the workpiece layer by using the second and fourth patterns as a mask after removing the third patterns.

9. The method of claim 8, wherein the chemical change of the first metal is oxidation of the first metal.

10. The method of claim 9, wherein the first metal is oxidized by ashing with an oxygen gas.

11. The method of claim 10, wherein the ashing of the first metal is performed with the oxygen gas and a nitrogen gas.

12. The method of claim 8, wherein the second patterns are formed of an elemental metal layer containing the first metal.

13. The method of claim 8, wherein the second metal is a same metal as the first metal.

14. The method of claim 8, wherein the second metal is a different metal from the first metal.

15. The method of claim 8, wherein the third patterns are formed to form a first gap between first side faces of the third patterns and to form a second gap between second side faces of the third patterns, the second faces being more inclined than the first side faces, a width of a bottom face of the first gap and a width of a bottom face of the second gap is 0.5 to 1.5 times of a width of bottom faces of the second patterns.

16. The method of claim 8, further comprising:
forming a first film on the third patterns after forming the third patterns, and
planarizing a surface of the first film to expose the second patterns from the third patterns and to form the fourth patterns of the first film.