CN103811409B

CN103811409B - Method for enhancing etching selectivity of low dielectric material to TiN hard mask

Info

Publication number: CN103811409B
Application number: CN201210449657.7A
Authority: CN
Inventors: 杜若昕; 王兆祥; 刘志强
Original assignee: Advanced Micro Fabrication Equipment Inc Shanghai
Current assignee: Medium And Micro Semiconductor Equipment (shanghai) Co Ltd
Priority date: 2012-11-12
Filing date: 2012-11-12
Publication date: 2016-04-20
Anticipated expiration: 2032-11-12
Also published as: TW201419417A; TWI495012B; CN103811409A

Abstract

The invention provides a method capable of effectively enhancing the etching selectivity of a low dielectric material to a TiN hard mask, which divides the operation of stripping photoresist into two steps, wherein O is utilized in the first step₂/CO/CO₂The plasma is used for etching until the surface of the TiN hard mask is close to the position where the surface can not be exposed, and in the second step, nitrogen-containing (oxygen-free) plasma is used for over-etching to completely remove the residual part of the photoresist and the like, so that the surface of the TiN hard mask can not be oxidized, and the nitrogen content of the surface of the TiN hard mask is ensured. Therefore, when a channel is formed by plasma etching of fluorocarbon, stable channel can be obtained compared with the prior method using O₂/CO/CO₂The etching speed of the plasma is relatively slow, so that the selectivity of the low dielectric material to the TiN hard mask is improved, and the effect of channel etching is improved.

Description

Method for enhancing etching selectivity of low dielectric material to TiN hard mask

Technical Field

The invention relates to the field of semiconductor manufacturing, in particular to a method capable of enhancing the etching selectivity of a low dielectric material to a TiN hard mask in a process of realizing one-step molding of a channel and a through hole in a semiconductor device.

Background

As shown in fig. 1 to 4, the flow of a conventional one-step forming (alline) process for a Trench (Trench) and a Via (Via) in a semiconductor device is schematically illustrated.

As shown in fig. 1, a metal layer (e.g., copper) is formed on a silicon substrate, and a barrier layer (e.g., nitrogen-doped carbide (NDC)), a dielectric layer of low dielectric constant (low-k) material, an intermediate layer, a hard mask of TiN (titanium nitride), a bottom anti-reflection layer (BARC), and a Photoresist (PR) are sequentially formed on the surfaces of the substrate and the metal layer. Wherein, the TiN hard mask is provided with an opening which is needed for etching a channel in the semiconductor structure subsequently, and the bottom anti-reflection layer BARC not only covers the top surface of the TiN hard mask, but also is filled in the opening; the photoresist PR has also been formed with a pattern required for the subsequent etching of a via hole.

As shown in fig. 2, etching is performed according to the pattern on the photoresist PR to penetrate the depth positions of the bottom anti-reflection layer BARC, the intermediate layer and the dielectric layer in sequence and etch a part of the barrier layer from the top surface downwards but not penetrate the barrier layer, thereby forming most of the through hole of the semiconductor structure in the depth direction. And the bottom anti-reflection layer BARC in the opening of the TiN hard mask is etched in particular while penetrating the position corresponding to the depth of the TiN hard mask.

As shown in fig. 3, the photoresist is stripped, i.e. the photoresist PR and the bottom anti-reflective layer BARC are all removed, so that the opening on the TiN hard mask defining the channel shape is exposed.

As shown in fig. 4, the trench in the semiconductor structure is formed by etching down the opening of the TiN hard mask, sequentially through the intermediate layer, and etching a portion of the dielectric layer from the top surface down, but not extending the full depth of the dielectric layer. And continuing the etching of the through hole, namely etching the rest part of the barrier layer downwards until the barrier layer is penetrated, and etching a part of the copper metal layer downwards from the top surface so as to expose the copper metal layer in the through hole. The subsequent processing of the semiconductor structure can now continue.

For the above-mentioned prior art method, in the step shown in fig. 3, the conventional photoresist stripping process requires 100% over-etching ratio (OE%), i.e. the over-etching needs to be continued downwards to ensure the effect of photoresist stripping except for completely removing the photoresist PR and the bottom anti-reflection layer BARC, and during this over-etching time, the surface of the TiN hard mask is completely exposed to the plasma of photoresist stripping.

However, due to oneGenerally, O is used₂(oxygen), CO (carbon monoxide) and/or CO₂(carbon dioxide) plasma to achieve the photoresist stripping process described above. Then, during the over-etching process, the O (oxygen) in the plasma will chemically react with the surface of the TiN hard mask to change the N nitrogen content of the surface of the TiN hard mask, i.e. equivalent to forming a modified layer containing oxygen on the surface of the TiN hard mask.

In the step shown in fig. 4, a fluorocarbon plasma is used to etch the channel, and the etching rate is related to the N nitrogen content in the TiN titanium nitride, and the higher the N nitrogen content, the lower the etching rate. Therefore, if the oxygen-containing modified layer is previously formed on the surface of the TiN hard mask, the chemical reaction speed of etching is increased because the bonding energy between Ti-O is smaller than that between Ti-N on the surface. That is, the higher the oxygen content or the thicker the modification layer, the higher the etching rate of the hard mask, and the lower the selectivity of the low dielectric constant to the hard mask, which undesirably affects the stability of etching to form the channel.

Disclosure of Invention

The invention aims to provide a method for enhancing the etching selectivity of a low dielectric material to a TiN hard mask, wherein photoresist is stripped into two steps, after etching is carried out in the first step to be close to the surface of the TiN hard mask, the second step is carried out by using nitrogen-containing gas plasma to carry out over-etching on the photoresist, and when part of the surface of the TiN hard mask is etched in the second step, the surface of the TiN hard mask is not oxidized, so that the etching rate of subsequent etching to form a channel can be effectively ensured.

In order to achieve the above object, the technical solution of the present invention is to provide a method for enhancing the etching selectivity of a low dielectric material to a TiN hard mask, the method being used in a process of one-step forming a channel and a through hole in a semiconductor structure, the semiconductor structure comprising a metal layer formed on a substrate, and a barrier layer, a dielectric layer of a low dielectric constant material, an intermediate layer, a TiN hard mask, a bottom anti-reflection layer and a photoresist sequentially formed on the substrate and the surface of the metal layer upwards; the method comprises the following steps:

etching the bottom anti-reflection layer, the middle layer and the dielectric layer downwards in sequence according to a pattern formed on the photoresist to form the through hole in the semiconductor structure;

after the through hole is formed, sequentially carrying out two steps of photoresist stripping:

in the first step, using plasma of a first reaction gas to etch and remove all the photoresist, and etching and removing most parts of the bottom anti-reflection layer in the depth direction;

in the second step, the plasma of the second reaction gas is used for over-etching to etch and remove the residual part of the bottom anti-reflection layer so as to expose the surface of the TiN hard mask; the second reactive gas is a nitrogen-containing but oxygen-free gas;

and after the photoresist is stripped, sequentially etching the intermediate layer and the dielectric layer downwards according to the opening formed on the TiN hard mask so as to form the channel in the semiconductor structure.

In a preferred embodiment, in the first step of the photoresist stripping, the first reaction gas for generating plasma is oxygen gas, carbon monoxide gas or carbon dioxide gas, or a mixed gas of any two or three of them.

In a preferred embodiment, in the second step of the photoresist stripping, the second reaction gas for generating plasma is nitrogen gas, or ammonia gas, or a mixed gas of nitrogen gas and hydrogen gas.

In a preferred embodiment, in the two steps of photoresist stripping, the etch rate of the second step is less than the etch rate of the first step.

In a preferred embodiment, in the first step of photoresist stripping, the gas pressure of the first reactive gas is below 100mT and the plasma for etching is formed by applying a radio frequency power of 60MHz or 13 MHz.

In a preferred embodiment, in the second step of photoresist stripping, the pressure of the second reactive gas is lower than 100mT or higher than 180mT, and a plasma for over-etching is formed by applying a radio frequency power of 60MHz/13MHz, or 60MHz/2 MHz.

In a preferred embodiment, after the first step of photoresist stripping, the thickness a of the remaining portion of the bottom anti-reflective layer is small enough to keep the underlying surface of the TiN hard mask from being exposed.

When etching the channel in the semiconductor structure by using fluorocarbon plasma, the higher the nitrogen content in the TiN hard mask, the lower the etching rate of the channel, and the higher the selectivity of the dielectric layer of the low dielectric constant material to the TiN hard mask.

After the channel is formed by etching, the channel penetrates through the intermediate layer and extends downwards to a set depth b of the dielectric layer;

the through hole is arranged to extend downwards from the position of the set depth b of the dielectric layer, penetrate the dielectric layer and the barrier layer and expose the surface of the metal layer in the through hole.

In a preferred embodiment, the process of forming the through hole in the semiconductor structure by etching includes:

before the two steps of photoresist stripping, the photoresist sequentially penetrates downwards through the positions, corresponding to the depths of the bottom anti-reflection layer, the TiN hard mask, the middle layer and the dielectric layer, in the semiconductor structure, and a part of the barrier layer, which is downward from the top surface, is etched, but the barrier layer is not penetrated;

and after the channel is formed by etching, continuously etching the rest part of the barrier layer and a part of the metal layer from the top surface to the bottom so as to expose the surface of the metal layer in the through hole.

In another preferred embodiment, the process of forming the through hole in the semiconductor structure by etching includes:

before the two steps of photoresist stripping, etching downwards to reach the position corresponding to the depth of the bottom anti-reflection layer, the middle layer and etching and staying in the dielectric layer;

and after the channel is formed by etching, continuously etching the residual part of the dielectric layer, the barrier layer and a part of the metal layer from the top surface to the bottom so as to expose the surface of the metal layer in the through hole.

In a preferred embodiment, before the two steps of photoresist stripping, an opening defining the shape of the channel is formed on the TiN hard mask, and the bottom anti-reflection layer not only covers the top surface of the TiN hard mask, but also is filled in the opening; the TiN hard mask is penetrated in the depth direction by etching the bottom anti-reflection layer within the opening of the TiN hard mask in the process of forming the via hole by etching.

Compared with the prior art, the operation of stripping the photoresist is divided into two steps in the invention, and O is utilized in the first step₂/CO/CO₂The plasma is used for etching until the surface of the TiN hard mask is close to the position where the surface can not be exposed, and in the second step, nitrogen-containing (oxygen-free) plasma is used for over-etching to completely remove the residual part of the photoresist and the like, so that the surface of the TiN hard mask can not be oxidized, and the nitrogen content of the surface of the TiN hard mask is ensured. Therefore, when a channel is formed by plasma etching of fluorocarbon, stable channel can be obtained compared with the prior method using O₂/CO/CO₂The etching speed of the plasma is relatively slow, so that the method for effectively enhancing the etching selectivity of the low dielectric material to the TiN hard mask is provided, and the effect of channel etching is improved.

Drawings

FIGS. 1 to 4 are schematic views illustrating a conventional process for forming a trench and a via in a semiconductor device in one step; wherein,

FIG. 1 is a schematic diagram of a semiconductor structure prior to etching;

FIG. 2 is a schematic diagram of a semiconductor structure after via etching;

FIG. 3 is a schematic view of a semiconductor structure after photoresist stripping;

fig. 4 is a schematic diagram of a semiconductor structure after a channel etch.

FIGS. 5 to 9 are schematic views illustrating a process of performing a one-step forming process on a trench and a via in a semiconductor device in the method for enhancing the etching selectivity of a low dielectric material to a TiN hard mask according to the present invention; wherein,

FIG. 5 is a schematic view of a semiconductor structure prior to etching;

FIG. 6 is a schematic diagram of a semiconductor structure after via etching;

FIG. 7 is a schematic view of the semiconductor structure after a first step of photoresist stripping;

FIG. 8 is a schematic view of the semiconductor structure after a second step of photoresist stripping;

FIG. 9 is a schematic diagram of a semiconductor structure after a channel etch.

Detailed Description

An embodiment of the present invention will be described below with reference to fig. 5 to 9.

In the steps shown in fig. 7 and 8, the process of stripping the photoresist is divided into two steps; the corresponding processing steps before the photoresist stripping as shown in fig. 5-6 and after the photoresist stripping as shown in fig. 9 are similar to those of the semiconductor structure obtained by the prior art method.

As shown in fig. 5, a metal layer 11 of copper is formed on a silicon or other substrate 10, and a barrier layer 20 (for example, nitrogen-doped carbide NDC), a dielectric layer 30 of a low dielectric constant (low-k) material, an intermediate layer 40, a hard mask 50 of TiN (titanium nitride), a bottom anti-reflection layer BARC 60, and a photoresist PR 70 are sequentially formed on the surfaces of the substrate 10 and the metal layer 11.

Wherein, the TiN hard mask 50 is already formed with an opening 51 defining the shape of the trench 90 in the semiconductor structure, and the bottom anti-reflection layer BARC 60 not only covers the top surface of the TiN hard mask 50, but also fills in the opening 51; the photoresist PR 70 has also been formed with a pattern 71 defining the shape of the via 80 in the semiconductor structure.

As shown in fig. 6, the pattern 71 on the photoresist PR 70 is etched to penetrate down to the position corresponding to the depth of the bottom anti-reflective layer BARC 60, the intermediate layer 40 and the dielectric layer 30, and to etch a portion of the barrier layer 20 from the top surface to the bottom surface, but not to penetrate the barrier layer 20, thereby forming a majority of the via 80 of the semiconductor structure in the depth direction. While penetrating the depth of the TiN hard mask 50, specifically the bottom anti-reflective layer BARC 60 within the opening 51 of the TiN hard mask 50 is etched.

In other embodiments, there is another way to etch the via (not shown in the figures): that is, the photoresist PR · 70 is etched according to the pattern 71, and the photoresist PR · 70 sequentially penetrates downward through the bottom anti-reflection layer BARC · 60 and the position corresponding to the depth of the intermediate layer 40, and is further etched into the dielectric layer 30 to stay at a certain depth position of the dielectric layer 30.

As shown in FIG. 7, the present invention uses, for example, O-containing in the first step of photoresist stripping₂(oxygen), CO (carbon monoxide) or CO₂(II)Carbon oxide) to remove all of the photoresist PR 70 and etch away most of the bottom anti-reflective layer BARC 60 in the depth direction. In a second step shown in FIG. 8, a nitrogen-containing (oxygen-free) gas, such as N, is used₂(Nitrogen), NH₃(ammonia gas), or N₂/H₂(mixed gas of nitrogen and hydrogen), etc., to form corresponding gas plasma to perform over-etching of the photoresist to remove the remaining portion of the anti-reflective layer barc.60, thereby exposing the surface of the TiN hard mask 50.

The thickness a of the remaining portion of the bottom anti-reflective layer barc.60 during the first step etching is controlled so that the thickness a is small enough to prevent the surface of the underlying TiN hard mask 50 from being exposed, and the specific value of the thickness a of the remaining portion can be determined through limited experiments.

In the first step, since the distance from the surface of the TiN hard mask 50 is long, a relatively high etching rate can be used to reduce the etching time; in the second step, a relatively low etching rate is used instead. The adjustment of the etch rate may be achieved by changing the flow rate, pressure of the reactant gases, the rf frequency at which the plasma is generated, or other similar process parameters, such that the etch rate of the second step is less than the etch rate of the first step.

For example, in some embodiments, in the first step, O with a pressure less than 100mT is introduced into the plasma etching apparatus₂/CO/CO₂Or a mixture of several of them, and applying a radio frequency power of 60MHz or 13MHz to form a plasma for etching. In the second step, nitrogen-containing (but oxygen-free) gas N2 or N2/H2 or NH3 is introduced at a pressure of less than 100mT or more than 180mT, and radio frequency power of 60MHz/13MHz, or 60MHz/2MHz is applied to form plasma and perform over-etching.

Referring to fig. 8, when the photoresist PR 70 and the bottom anti-reflective layer BARC 60 are all removed by the above two steps, the opening 51 of the TiN hard mask 50 defining the shape of the channel 90 is exposed. As shown in fig. 9, the trenches 90 in the semiconductor structure are formed by etching the intermediate layer 40 and the dielectric layer 30 in sequence down from the opening 51 of the TiN hard mask 50 using a fluorocarbon plasma. The etching of the via 80 is then completed, i.e. the remaining portion of the barrier layer 20 and the copper metal layer 11 are continuously etched (or, in the above-mentioned another via structure, the remaining portion of the dielectric layer 30, the barrier layer 20 and the copper metal layer 11 are etched). Then, in the semiconductor structure, the trench 90 corresponds to the opening 51 of the TiN hard mask 50, penetrates through the intermediate layer 40, and extends down to the set depth b of the dielectric layer 30; the via 80 extends from the position of the set depth b of the dielectric layer 30 downwards, penetrates the dielectric layer 30 and the underlying barrier layer 20, and exposes the copper metal layer 11 in the via 80.

At this point, the process of forming the trench 90 and the via 80 in the semiconductor structure at one time is completed, and the subsequent processing of the semiconductor structure can be continued.

In summary, in the photoresist stripping process of the present invention, especially when etching the surface close to the TiN hard mask 50 (fig. 7-8), the surface of the TiN hard mask 50 is not oxidized due to the over-etching with the plasma containing nitrogen (without oxygen), thereby ensuring the nitrogen content on the surface of the TiN hard mask 50. Thus, a stable, comparable to the previous use of O, channel 90 can be achieved when subsequent plasma etching with a fluorocarbon compound is used to form channel 90₂/CO/CO₂The relatively slow etch rate of the plasma provides a method that can effectively enhance the etch selectivity of low dielectric materials to the TiN hard mask 50.

While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.

Claims

1. A method for enhancing the etch selectivity of low-dielectric materials to TiN hard masks, the method is used in the process of forming channels and via holes in a semiconductor structure, and the semiconductor structure is included in the substrate The metal layer (11) formed on (10), the barrier layer (20) and the dielectric layer (30) of low dielectric constant material are sequentially formed upward on the surface of the substrate (10) and the metal layer (11). ), an intermediate layer (40), a TiN hard mask (50), a bottom antireflection layer (60), and a photoresist (70); it is characterized in that the method comprises the following steps:

According to the pattern (71) formed on the photoresist (70), etch the bottom anti-reflection layer (60), the intermediate layer (40) and the dielectric layer (30) downwards sequentially, so as to form the semiconductor structure said through hole (80);

After the via hole (80) is formed, two steps of photoresist stripping are performed in sequence:

In the first step, all of the photoresist (70) is etched away, and most of the bottom anti-reflective layer (60) in the depth direction is etched away using a plasma of a first reactive gas ;

In the second step, overetching is performed using plasma of a second reactive gas to etch and remove the remaining portion of the bottom anti-reflection layer (60) to expose the surface of the TiN hard mask (50); The second reaction gas is a nitrogen-containing but oxygen-free gas;

After the photoresist is stripped, according to the opening (51) formed on the TiN hard mask (50), the intermediate layer (40) and the dielectric layer (30) are sequentially etched downward to form the semiconductor structure The channel (90).

2. The method of claim 1, wherein

In the first step of photoresist stripping, the first reaction gas used to generate plasma is oxygen, or carbon monoxide gas, or carbon dioxide gas; or, the first reaction gas is any of oxygen, carbon monoxide gas, and carbon dioxide gas. A mixed gas of two gases; or, the first reaction gas is a mixed gas of oxygen, carbon monoxide gas, and carbon dioxide gas.

3. The method of claim 1, wherein,

In the second step of photoresist stripping, the second reaction gas used to generate plasma is nitrogen or ammonia; or, the second reaction gas is a mixed gas of nitrogen and hydrogen.

4. The method of claim 1 or 2, wherein,

In the two steps of photoresist stripping, the etching rate of the second step is smaller than that of the first step.

5. The method of claim 4, wherein,

In the first step of photoresist stripping, the pressure of the first reaction gas is lower than 100 mT, and the plasma for etching is formed by applying 60 MHz or 13 MHz RF power.

6. The method of claim 4, wherein,

In the second step of photoresist stripping, the pressure of the second reaction gas is lower than 100mT or higher than 180mT, and by applying 60MHz/13MHz, or 60MHz/2MHz RF power, to form a plasma for over-etching .

7. The method of claim 1, wherein,

After the first step of photoresist stripping, the thickness (a) of the remaining portion of the bottom antireflective layer (60) is small enough that the underlying surface of the TiN hard mask (50) does not exposed.

8. The method of claim 1, wherein,

When using fluorocarbon plasma to etch the channel (90) in the semiconductor structure, the higher the nitrogen content in the TiN hard mask, the faster the etching rate of the channel (90). low, the higher the selectivity of the dielectric layer (30) of the low dielectric constant material to the TiN hard mask (50).

9. The method of claim 1, wherein,

After the trench (90) is formed by etching, the trench (90) is arranged to penetrate the intermediate layer (40) and extend down to a set depth (b );

The arrangement of the through holes (80) extends downwards from the set depth (b) of the dielectric layer (30), and penetrates the dielectric layer (30) and the barrier layer (20) , and expose the surface of the metal layer (11) in the through hole (80).

10. The method of claim 9, wherein,

The process of etching and forming the through hole (80) in the semiconductor structure includes:

Before the two steps of photoresist stripping, etch downwards to reach positions corresponding to the depths of the bottom anti-reflection layer (60), intermediate layer (40) and dielectric layer (30) that can be penetrated sequentially, and etching a part of the barrier layer (20) downward from the top surface, but not penetrating the barrier layer (20);

And, after forming the channel (90) by etching, continue to etch the remaining part of the barrier layer (20) and a part of the metal layer (11) from the top surface downward, so that the metal layer The surface of ( 11 ) is exposed in this through hole ( 80 ).

11. The method of claim 9, wherein,

Before the two steps of photoresist stripping, etch down to reach the positions corresponding to the depths of the bottom anti-reflection layer (60) and the middle layer (40) in turn, etch and stay at the position In the dielectric layer (30);

And, after forming the trench (90) by etching, continue to etch the remaining part of the dielectric layer (30), the barrier layer (20), and the metal layer (11) from the top down A part of the metal layer (11) is exposed in the through hole (80).

12. The method of claim 10 or 11, wherein,

Before the two steps of photoresist stripping, an opening (51) defining the shape of the channel (90) has been formed on the TiN hard mask (50), and the bottom antireflection layer (60) not only covers The top surface of the TiN hard mask (50) is also filled in the opening (51); then in the process of etching the through hole (80), the opening of the TiN hard mask (50) is etched (51) inside the bottom anti-reflection layer (60), thereby penetrating the TiN hard mask (50) in the depth direction.