JP2000150413A - Formation of contact hole of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the aspect ratio and the verticality of shape of a contact hole by performing a first contact hole forming step using a first gas system prior to a second contact hole forming step using a second gas system. SOLUTION: A method for forming contact hole includes a first step S1 and a second step of forming a silicon oxide layer 4 on an Si substrate 3 and contact holes 1 and 2 through the layer 4. The contact hole 1 is formed so that the section of the hole 1 near the substrate 1 may be tapered off by applying CHF3/CO/Ar gas as the first gas used in the main etching step S1. Then the verticality of shape of the contact hole 2 is improved by applying C4F8/CO/ O2/Ar gas as the second gas used in the over-etching step. The first step S1 is performed prior to the second step S2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a contact hole in a semiconductor device, and more particularly, to a method for forming a contact hole in a semiconductor device having a high aspect ratio and good verticality.

[0002]

2. Description of the Related Art A contact hole is formed in a semiconductor device. The contact holes are preferably perpendicular to the layer to be formed. With the increase in integration of semiconductor devices, such contact holes are required to have a high aspect ratio. The vertical and vertical contact processing is becoming more and more difficult as the degree of integration increases.

When the etching easily proceeds at the bottom of the contact hole, the shape tends to be boring, and when the shape is vertical, the etching tends to stop at the bottom of the contact hole. The fact that the etching easily proceeds at the bottom of the contact hole is referred to as good removability. The fact that the etching is easily stopped at the bottom of the contact hole is referred to as the easy stop of the etch. The removability and the shape perpendicularity are in a trade-off relationship. It is known that it is very difficult to achieve both the removability and the shape perpendicularity.

[0004] Such difficulties are shown in comparison with FIGS. 5 and 6. The contact hole shown in FIG. 5 is formed using a CHF3 / CO / Ar-based gas. As shown in FIG. 5, the CHF3 / CO / Ar-based gas has a high release property and a high PR selectivity (the selectivity is 12
To 16), but has the property of easily forming a tapered shape. The contact hole shown in FIG. 6 is formed using a C4F8 / CO / Ar / O2 based gas. The C4F8 / CO / Ar / O2 based gas is shown in FIG.
As shown in (1), the vertical workability is good, but the PR selectivity is low (the selectivity is 4 to 8), and it has characteristics that the etch stop is easily performed.

[0005] In the known etching method for forming a contact hole, from the main etching to the over etching, only one type of process condition has been performed. CHF
Known contact hole forming methods using either a one-step process using a 3 / CO / Ar-based gas or a one-step process using a C4F8 / CO / Ar / O2-based gas are compatible as described above. Since either one of the two gas systems having no airtightness is used, it is extremely difficult to achieve both the vertical shape and the releasability. It should be noted that a two-gas system having such characteristics is known from Japanese Patent Application Laid-Open No. 9-92640.

[0006] Since the contact holes of semiconductor devices that require higher integration and finer processing are required to have a higher aspect ratio, the above-mentioned difficulty in compatibility is increasing. ing. The formation of a contact hole with a high aspect ratio and high shape perpendicularity is required.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a contact hole in a semiconductor device having a high aspect ratio and a high shape perpendicularity.
Another object of the present invention is to provide a contact hole for a semiconductor device having a high aspect ratio and a high shape perpendicularity by combining the properties of a highly evacuable gas system and a highly perpendicular gas system to draw out their respective advantages. It is to provide a forming method. Still another object of the present invention is to draw out the advantages of each by combining both properties of a high-permeability, high-selectivity, low-profile vertical gas system and a high-perpendicular, low-selection-ratio, low-release gas system. It is another object of the present invention to provide a method for forming a contact hole of a semiconductor device having a high aspect ratio and a high shape perpendicularity.

[0008]

Means for solving the problem are described as follows. In that expression,
Matching correspondence numbers and symbols are attached with parentheses ().
The corresponding correspondence numbers, symbols, and the like indicate the corresponding correspondence between the technical matter described in the claims and the technical matter of the embodiment described below, but the present invention is limited to the technical matter of the embodiment. It is not meant to be interpreted.

In the method for forming a contact hole in a semiconductor device according to the present invention, the contact hole (1) is formed by a first gas system which facilitates etching at the bottom of the contact hole but lowers the perpendicularity of the shape of the contact hole. A first step (S1), and a second step (S2) of forming the contact hole (2) with a second gas system that easily stops etching at the bottom of the contact hole but increases the perpendicularity of the shape of the contact hole. The first step (S1) temporally precedes the second step (S2).

Although the characteristics of the first gas system and the characteristics of the second gas system are in a trade-off relationship, the fact shown in FIGS. 3 and 4 is that both gas systems have the advantage of one gas system over the other gas system. Not offset, indicating that the disadvantages of each one gas system are offset by the other gas system. This means
It is presumed that this is because the first gas system and the second gas system exhibit their respective etching functions with phases shifted in time.

The first step (S1) and the second step (S1)
2) forms a group and can be formed as a set having an infinite number of steps as elements. The first step (S1) and the second step (S2) can be formed completely discretely in time. Completely temporally discrete means that the second step (S2) is executed after the execution of the first step is completely completed.

The first step and the second step can be expressed as steps S1, S2,... Sn corresponding to a time sequence. On the time axis, S2 is a second step relative to S1, but a first step for S3. Such a series of discrete steps, the first step and the second step, achieves both high-speed contact hole etching and verticalization of the shape.
1 and two steps Sn. The first step (S1) can be shifted to the second step (S2) substantially continuously in time, and the first step (S1) can be shifted in time to the second step (S2).
It is also possible to shift to 2).

[0013] The first gas and the second gas can be different. In this case, the step transition can be performed by changing the mixture ratio of the first gas and the second gas stepwise.
The first gas and the second gas may be formed as a mixed gas having the same mixed component, and the step shift may be performed by changing the mixed component ratio of the first gas to shift to the second gas.

Specifically, the first gas is CHF3 / CO /
Ar and the first gas was COF in CHF3 / CO / Ar
Changes to the second gas. The first gas is C
4F8 / CO / O2 / Ar, and the first gas is C4F8
The composition ratio of CO in / CO / O2 / Ar changes and shifts to the second gas. In this manner, the first gas and the second gas also form a group, and can relatively transition to a state corresponding to the time sequence described above. The versatility of such a step transition
The contact hole accuracy is appropriately adjusted by changing the aspect ratio, the material, and the etching gas.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the drawings, an embodiment of a contact hole forming method for a semiconductor device according to the present invention forms contact holes 1 and 2 in a silicon oxide layer 4 formed on a Si substrate 3. It has steps. As shown in FIG. 1, a photoresist layer 5 is formed on the silicon oxide layer 4, etching is performed on the photoresist layer 5, and etching is started.

FIG. 1 shows a main etching step S1. As the first gas used in the main etching step S1, CHF3 / CO / Ar is appropriate.
Such a first gas facilitates etching at the bottom of the contact hole and has a high PR selectivity, but tends to lower the perpendicularity of the shape of the contact hole. Tends to be tapered (tapered).

As shown in FIG. 1, the silicon oxide layer 4
The contact hole 1 formed at the bottom has a high aspect ratio, but the bottom portion, that is, the portion near the Si substrate 3 is tapered. In this step S1, the lower end of the contact hole 1 has almost reached the Si substrate 3, or
It has reached the Si substrate 3 completely.

FIG. 2 shows an over-etching step S2.
Is shown. As the second gas used in the over-etching step S2, C4F8 / CO / O2 / Ar gas is appropriate. Such a second gas tends to stop etching at the bottom of the contact hole and does not have a high PR selectivity as compared with the first gas, but tends to increase the perpendicularity of the shape of the contact hole. is there.

As shown in FIG. 2, the contact hole 1 formed in the first step S1 of FIG. 1 is further etched by the second gas. The etching amount of the tapered portion at the bottom of the contact hole 1 formed in the first step S1 is larger than the etching amount of the upper portion thereof, and the hole surface of the contact hole 2 formed in the second step S2 is cylindrical. High verticality. Contact hole 2 is S
Although the etching reaches the i-substrate 3, the etching speed at the bottom thereof is low and the etching is almost stopped at a position close to the Si substrate 3.

[0020]

EXAMPLE An aspect ratio of 8 and a pore size of 0.2
A contact hole of 5 μm was actually formed. Cross-sectional photographs of the contact hole are shown in FIGS. FIG.
Shows the contact hole 1 formed in the first step S1, and FIG. 4 shows the contact hole 2 formed in the second step S2. The etching apparatus used was a high-density plasma etching apparatus using surface waves (see Japanese Patent Application Laid-Open No. 8-200719).

(Main etching conditions) CHF3 / CO / Ar = 50/150 / 100scc
m, pressure = 25 mTorr Microwave power: 1100 W, bias power: 14
00W

(Over-etching condition) C4F8 / CO / O2 / Ar = 10/24/7/450
sccm pressure = 30 mTorr Microwave power: 1000 W, bias power * 14
00W

The overall PR selectivity of this embodiment is 10
And a high selectivity is realized. As described above, it has been demonstrated that by applying the present invention to a high aspect ratio contact hole, a vertical shape can be realized while maintaining a high PR selectivity.

In the above-described embodiments and examples, there are shown processes of two types and two steps of main etching and over-etching. Three types of three or more steps can be employed. It is possible to use a step that shifts from a condition with high slipperiness to a condition with high perpendicularity several times in stages. With such multi-steps, shape control can be performed with higher accuracy.

The etching can be performed by changing the gas mixture ratio as the etching proceeds, using the same process instead of the combination of different process conditions. In a process using a mixed gas of CHF3 / CO / Ar, by changing the mixing amount of CO, the releasability and the PR ratio can be improved.
You can change the selection ratio. The releasability increases as the mixing amount of CO increases, and decreases as the mixing amount of CO decreases. Therefore, from the start to the end of the etching, the etching can be performed while changing the mixed amount of CO in a plurality of steps to obtain a good vertical shape. Further, C
Even when using a 4F8 / CO / O2 / Ar mixed gas,
The mixing ratio of the mixed components can be changed.

[0026]

According to the method for forming a contact hole of a semiconductor device according to the present invention, a vertical high aspect ratio contact hole can be formed, and in particular, a combination of a condition excellent in escape property and a condition excellent in vertical workability are combined. Accordingly, an etching method capable of performing vertical processing can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first step of an embodiment of a method for forming a contact hole in a semiconductor device according to the present invention.

FIG. 2 is a cross-sectional view showing a second step.

FIG. 3 is a cross-sectional photograph of the first step of the production device.

FIG. 4 is a cross-sectional photograph of the second step.

FIG. 5 is a cross-sectional view of a known semiconductor device.

FIG. 6 is a cross-sectional view of another known semiconductor device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1st contact hole 2 ... 2nd contact hole S1 ... 1st step S2 ... 2nd step

Claims (8)

[Claims] 1. A first step of forming a contact hole by a first gas system that facilitates etching at the bottom of the contact hole but lowers the perpendicularity of the shape of the contact hole, and performs etching at the bottom of the contact hole. A second step of forming the contact hole by a second gas system that is easy to stop but enhances the perpendicularity of the shape of the contact hole, wherein the first step is a semiconductor that temporally precedes the second step. A method for forming a contact hole in a device. 2. The method according to claim 1, wherein the first step and the second step are completely discrete in time. 3. The method according to claim 2, wherein the first step shifts to the second step substantially continuously in time. 4. The method according to claim 2, wherein the first step shifts to the second step stepwise in time. 5. The semiconductor device according to claim 4, wherein the first gas and the second gas are different gases, and a mixture ratio of the first gas and the second gas changes stepwise. Contact hole forming method. 6. The method according to claim 4, wherein the first gas and the second gas are a mixed gas having the same mixed component, and the mixed gas ratio of the first gas changes to shift to the second gas. A method for forming a contact hole in a semiconductor device, comprising: 7. The method according to claim 6, wherein the first gas is CHF3 / CO / Ar.
A method for forming a contact hole in a semiconductor device, wherein a gas changes a component ratio of CO in CHF3 / CO / Ar and shifts to a second gas. 8. The method according to claim 6, wherein the first gas is C4F.
8 / CO / O2 / Ar, and the first gas is C4
A method for forming a contact hole in a semiconductor device, wherein the composition ratio of CO in F8 / CO / O2 / Ar changes to transfer to the second gas.