JPH02230727A - Dry etching method - Google Patents

Abstract

PURPOSE:To remove an oxide film on a surface and to make it possible to keep a high selecting ratio for silicon oxide by etching the oxide film which is formed on the surface of silicon or poly/crystalline silicon as a pretreatment of dry etching under the conditions wherein the flow rate of etching gas is increased in comparison with intrinsic etching. CONSTITUTION:When SiO2 is etched as a pretreatment, the etching speed of the SiO2 becomes quick with the increase in flow rate of HBr gas which is used as etching gas. When the flow rate of HBr gas is set at, e.g. 200sccm and RIE is conducted, the etching speed of the SiO2 becomes about 40Angstrom /min. Therefore, a surface oxide film 15 which is formed by oxidizing the surface of silicon or polycrystalline silicon 13 can be removed in a short time. When the flow rate of the HBr gas is increased, however, the etching speed of the SiO2 becomes quick, and a selecting ratio for the SiO2 is lowered. When the polycrystalline silicon 13 is continuously etched, the flow rate of the HBr gas is decreased to the quantity of 100sccm. Then the etching rate of the SiO2 is deceased at this flow rate. Therefore, the dry etching having the high specific selectivity can be achieved.

Description

[Detailed Description of the Invention] [Summary] Regarding a method of dry etching silicon or polycrystalline silicon using bromine (Brz) or hydrogen bromide (HBr), the surface oxide film of silicon or polycrystalline silicon can be easily removed, The purpose is to provide a dry etching method that simplifies the process and can maintain a high selectivity to silicon oxide. In the etching method, as a pre-treatment for dry etching, an oxide film formed on the silicon or polycrystalline silicon surface of the portion to be etched is removed by using the same flow rate of bromine gas or hydrogen bromide gas to etch the silicon or polycrystalline silicon. The method includes a dry etching method characterized in that etching is performed under conditions increased compared to the dry etching method.

[Industrial Field of Application] The present invention relates to a dry etching method, particularly a method for dry etching silicon or polycrystalline silicon using bromine (Brz) or hydrogen bromide (lIBr).

? [Prior art] In recent years, with the miniaturization of semiconductor devices, insulating oxide films on silicon substrates have become thinner, and silicon oxide (SiO
(2) There is a need for etching technology for silicon, such as polycrystalline silicon, that has a fairly high selectivity to films. For this purpose, a dry etching method using Brz or HBr as an etching gas is effective. However,
Silicon or? When the surface of crystalline silicon is oxidized naturally or in a certain step during the wafer process and a SiO film is formed, this SiO film cannot be removed due to its high selectivity to Sin2, and the silicon Alternatively, there has been a problem that etching of polycrystalline silicon does not start. Therefore, when performing etching with Brz or HBr, it is necessary to remove in advance the Sin2 film formed by oxidizing these surfaces.

Conventionally, the present applicant filed a patent application for the technology developed as a pretreatment method for dry etching of silicon or polycrystalline silicon using Brz or HBr (Japanese Patent Application No. 16228/1982).

This method is a method of selectively dry etching single-crystal silicon or polycrystalline silicon, and after dry-etching the natural oxide film formed on the silicon surface of the part to be etched with fluorine-based gas or chlorine-based gas, This method is characterized in that the single crystal or polycrystalline silicon is selectively etched by reactive ion etching using gas. This method removes the natural oxide film on the silicon surface before performing reactive ion etching of silicon using bromine gas, so anisotropic etching can be performed to form holes with good reproducibility without roughening of the bottom of the hole or variations in hole depth. This method can also be applied to etching for forming trenches for element isolation and selective etching of single crystal silicon or polycrystalline silicon.

? Therefore, the influence of the pretreatment gas remains, which causes the next B
It has also been found that etching with rz or I{Br increases the etching rate of SiO■ and reduces the selectivity to SiO■.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a dry etching method that facilitates the removal of the surface oxide film of silicon or polycrystalline silicon, simplifies the process, and maintains a high selectivity to silicon oxide. .

? [Problems to be Solved by the Invention] In the conventional pretreatment method described above, in order to remove the SiO film on the surface uniformly within the wafer, if the pretreatment time is prolonged, silicon or polycrystalline silicon is 《The amount of this film reduction is uncertain due to etching, and the next Br
! Another problem is that reproducibility deteriorates when etching silicon or polycrystalline silicon using HBr.

In addition, in this gas switching method, residual gas components and components adsorbed and deposited on the chamber wall and wafer surface during preprocessing [Means for solving the problem] In a method of dry etching silicon or polycrystalline silicon using gas, as a pretreatment for dry etching, an oxide film formed on the silicon or polycrystalline silicon surface of the portion to be etched is removed using the same bromine gas or hydrogen bromide. This is achieved by a dry etching method characterized by etching with a gas flow rate increased compared to the etching of silicon or polycrystalline silicon.

? Effect] In the present invention, as shown in FIG. 3, for example, polycrystalline silicon (polysilicon) and Sin
．． This method takes advantage of the fact that as the flow rate of llBr gas increases, the etching rate of SiO2 increases linearly, whereas the increase in the etching rate of polycrystalline silicon gradually decreases. In Fig. 3, the horizontal axis represents the flow rate of HBr (sccm:
The left vertical axis shows the etching rate of polysilicon in [in/min), and the right vertical axis shows the etching rate of silicon oxide (SiOz) in [in/min]. The scale of the vertical axis is larger than the scale of the left vertical axis. That is, as a pretreatment, SiO■
When etching Si02, the etching rate of Si02 increases as the flow rate of IBr gas used as the etching gas increases. For example, the flow rate of HBr gas is
Is it 200sccm? When using IE, what is the etching rate of SiO■? 40 people/min. Therefore, a surface oxide film formed by oxidizing the surface of silicon or polycrystalline silicon in a short time can be removed in a short time. However, as the flow rate of tlBr gas increases, the etching rate of SiOz increases and the selectivity to SiO■ decreases, so when subsequently etching polycrystalline silicon, H
When the flow rate of Br gas is reduced to 100 sccm or less, the etching rate of SiO2 is reduced at this flow rate, so dry etching with a high selectivity can be achieved.

Further, during the pretreatment, that is, after etching SiOz and before etching polysilicon, a vacuum is maintained and the surface of the silicon or polycrystalline silicon is not exposed to the atmosphere to prevent reoxidation. Therefore, when removing an oxide film formed by oxidizing the surface of silicon or polycrystalline silicon, perform RIE L at an HBr flow rate of 200 sccm, and then perform RIE at a HBr flow rate of 100 sccm or less to achieve high speed and high selectivity. It can be used as a dry etching method with a high ratio.

? Example] Hereinafter, the present invention will be specifically described with reference to an illustrated example.

FIG. 1 is a sectional view of a sample used in an example of the present invention. In the figure, on a silicon substrate 11, an SiO2 film 12 with a thickness of about 1,000 layers is formed as an insulating oxide film.
On top of that is a polycrystalline silicon layer 13 with a thickness of about 4,000 layers.
is formed, and on top of that, a film with a line width of 1 μm and a film thickness of 20 μm is formed.
About 0.00 SiO2 mask patterns 14 are formed. As described above, the oxide film 15 is present where the surface of the polycrystalline silicon 13 should be exposed.

Although the oxide film on the surface of a silicon substrate is not shown, this corresponds to the case where the polycrystalline silicon layer 13 and underlying oxide film 12 in FIG. 1 are removed.

Figure 2 shows the parallel plate type R used to carry out the method of the present invention.
FIG. 2 is a schematic cross-sectional view of the IE device. In the figure, 21 is an etching chamber, 22 is a wafer as a sample, 23 is a lower electrode, 24 is a counter electrode, 25 is an insulator, 26 is a high frequency power source,
27 is a gas supply port, 28 is a gas exhaust port, 29 is a cooling water,
30 is a grounding point. Using HBr as an etching gas,
HBr gas is introduced into the etching chamber 21 from the gas inlet 27 and exhausted from the exhaust port 28.
2 within 0. The pressure was maintained at ITorr. Then, the power of frequency 13.56Mtlz is 30% per board.
Polycrystalline silicon was etched by applying 0W.

When performing the pretreatment reaction chamber and the etching reaction chamber separately, two of these RIE apparatuses may be lined up and the sample may be transported between them in a vacuum.

Below, the results of experiments conducted under various conditions will be explained.

[Example 1] Using the sample shown in Fig. 1 and the RIE apparatus shown in Fig. 2, removal of the silicon oxide film formed on the surface of polycrystalline silicon by RIH using HBr gas as a pretreatment, and Performed silicon etching.

The etching conditions used for the pretreatment to remove the surface oxide film of polycrystalline silicon were as follows: IIBr gas flow rate was 50 scc.
m, RF power is 300-, pressure is 0. ITorr
The temperature of the cooling water was 35°C, and the etching time was 3 minutes.

Thereafter, an attempt was made to etch polycrystalline silicon by changing the flow rate of HBr gas to 100 sccm among the conditions used in the pretreatment, but etching was not possible.

This was due to the fact that the oxide film present on the polycrystalline silicon surface could not be removed.

[Example 2] The sample shown in Fig. 1 was used, the RIE apparatus shown in Fig. 2 was used, and HBr gas was used as a pretreatment. The silicon oxide film formed on the surface of the polycrystalline silicon was removed by fE, and the polycrystalline silicon was etched.

The etching conditions used for removing the surface oxide film of polycrystalline silicon as pre-treatment were as follows: HBr gas flow rate was 100scc.
m, RF power is 300W, pressure is Q. Torr
The temperature of the cooling water was 35° C., and the etching time was 3 minutes.

After this, an attempt was made to etch the polycrystalline silicon under the same conditions as used in the pretreatment, but it was not possible to etch the polycrystalline silicon. This was because the oxide film present on the surface of polycrystalline silicon could not be removed.

[Example 3] Using the sample shown in Fig. 1 and the RIE apparatus shown in Fig. 2, removal of the silicon oxide film formed on the polycrystalline silicon surface by RIE using HBr gas as a pretreatment, and Performed silicon etching.

The etching conditions used for the pretreatment to remove the surface oxide film of polycrystalline silicon were as follows: HBr gas flow rate was 130scc.
m, RF power is 300W, pressure is 0.1Torr
The temperature of the cooling water was 35° C., and the etching time was 2 minutes.

Thereafter, an attempt was made to etch the polycrystalline silicon by changing the flow rate of tlBr gas to 100 sccm among the conditions used in the pretreatment, but it was not possible to etch the polycrystalline silicon.

This was because the oxide film present on the surface of polycrystalline silicon could not be removed.

[Example 4] Using the sample shown in Fig. 1 and the RIE apparatus shown in Fig. 2, the silicon oxide film formed on the polycrystalline silicon surface was removed by RIE using HBr gas as a pretreatment, and the polycrystalline silicon oxide film was removed. Performed silicon etching.

The etching conditions used for the pretreatment to remove the surface oxide film of polycrystalline silicon were as follows: HBr gas flow rate was 13? scc
m, RF power is 300W, pressure is 0. ITorr
The temperature of the cooling water was 35° C., and the etching time was 3 minutes.

Thereafter, among the conditions used in the pretreatment, an attempt was made to etch the polycrystalline silicon by changing the flow rate of HBr gas to 100 sccm, but in some cases the etching was successful and in others it was not. This is due to whether the oxide film present on the polycrystalline silicon surface was removed or not. After etching, the cross-sectional shape of the product was vertical, but a considerable amount of etching residue (polycrystalline silicon residue) was left on the underlying insulating oxide film (SiO2 film). Even if the pretreatment etching time was 5 minutes, this etching residue remained.

[Example 5] Using the sample shown in Fig. 1, the RIIl! shown in Fig. 2 was used. Using a device, the silicon oxide film formed on the polycrystalline silicon surface is removed by RIB using lBr gas as a pretreatment;
Polycrystalline silicon was etched.

The etching conditions used for removing the surface oxide film of polycrystalline silicon as pre-treatment were as follows: HBr gas flow rate was 150scc.
m, RF power is 300mm, pressure is 0. ITorr
The temperature of the cooling water was 35° C., and the etching time was 3 minutes.

Thereafter, among the conditions used in the pretreatment, the flow rate of HBr gas was changed to 100 sccm, and polycrystalline silicon was etched. Etching started immediately and a good vertical profile was obtained. A slight etching residue (polycrystalline silicon residue) was observed on the underlying insulating oxide film (SiO2 film). At this time, the selection ratio of polycrystalline silicon to the underlying layer Sin2 was 100 or more.

[Example 6] Using the sample shown in FIG. 1 and the [E apparatus shown in FIG. Etching of crystalline silicon was performed.

The etching conditions used for the pretreatment to remove the surface oxide film of polycrystalline silicon were that the flow rate of tlBr gas was 200 sc.
cm, RF power is 300W, pressure is . 0.1To
rr, cooling water temperature is 35°C, etching time is 2
It was set as 1 minute.

After this, among the conditions used in the pretreatment, the flow rate of IIBr gas was set to 100 sccm, and the etching time was set to 3 minutes.
Instead, polycrystalline silicon was etched.

Etching started immediately and a good vertical profile was obtained. No etching residue (polycrystalline silicon residue) was found on the underlying insulating oxide film (SiO2 film). At this time, the selection ratio of polycrystalline silicon to the underlying SiO■ is 100.
That was it.

[Example 7] Using the sample shown in Fig. 1 and the RIE apparatus shown in Fig. 2, the silicon oxide film formed on the polycrystalline silicon surface was removed by RIB using HBr gas as a pretreatment, and the polycrystalline Performed silicon etching.

The etching conditions used for removing the surface oxide film of polycrystalline silicon as pre-treatment were as follows: HBr gas flow rate was 200scc.
m, RF power is 300W, pressure is 0.1Torr
The temperature of the cooling water was 35° C., and the etching time was 1 minute.

Thereafter, among the conditions used in the pretreatment, an attempt was made to etch polycrystalline silicon by changing the flow rate of 11Br gas to 100 sccm and the etching time to 3 minutes, but some etching was successful and some were not.

Is this an oxide film on the surface of polycrystalline silicon? The reason is whether they were able to leave or not. After etching, the cross-sectional shape was vertical, but
Etching residue (polycrystalline silicon residue) was found on the underlying insulating oxide film (SiOz film).

[Example 8] Using the sample shown in Fig. 1 and the RIB apparatus shown in Fig. 2, the silicon oxide film formed on the polycrystalline silicon surface was removed by RIE using HBr gas as a pretreatment, and the polycrystalline silicon oxide film was removed. Performed silicon etching.

The etching conditions used for removing the surface oxide film of polycrystalline silicon as pre-treatment were as follows: HBr gas flow rate was 300scc.
m, RF power is 300W, pressure is 0. ITorr
The temperature of the cooling water was 35° C., and the etching time was 2 minutes.

Thereafter, polycrystalline silicon was etched under the conditions used in the pretreatment, with the HBr gas flow rate changed to 100 sccm and the etching time changed to 3 minutes.

Etching started immediately and a good vertical profile was obtained. Are there any etching residues (polycrystalline silicon residues) found on the underlying insulating oxide film (SiO■ film)? . At this time, the selection ratio of polycrystalline silicon to the underlying SiO■ is 100.
That was it. Similar results were obtained even when the pretreatment etching time was shortened to 80 seconds.

Table 1 shows the etching conditions and results of the pretreatment in Examples 1 to 8 above. In addition, in this table, in the column of surface oxide film removal, the distinction between possible and impossible is when the surface oxide film can be completely removed within 2 minutes of pretreatment time (subsequent RIE with HBr). In the case where no etching residue was formed afterwards), it was made possible, and in the case where it took longer than that (in case there was etching residue), it was made impossible. If it is both possible and impossible, it means that the etching of polycrystalline silicon by HBr has started in some cases, and in other cases it has not started. made it impossible. This is possible only if etching has started and no etching residue is found.

(Left below) Table I? Examples and conventional examples under other conditions will be described below as comparative examples.

[Example 9] Same as Example 8, but the flow rate of HBr gas was 200 sccm.
Etching was performed continuously for 5 minutes in one step.

At this time as well, a good vertical shape was obtained and no etching residue was observed, but the selectivity of polycrystalline silicon to the underlying SiO2 was as small as about 40.

[Comparative example] Similarly, CF4 gas was used as pretreatment at a flow rate of 50 scc.
m, RF power is 300W, pressure is Q. Torr
The temperature of the cooling water was 35° C., and the etching time was 40 seconds. Then, switch to HBr gas and increase the flow rate to 10
When etching was carried out at 0 sccm and other conditions were kept the same, etching started immediately, a good vertical shape was obtained, and there was no etching residue. However, the base material Sin2
The selectivity ratio of polycrystalline silicon to polycrystalline silicon was as small as about 20.

Figures 4 (a) to (C) show cross-sectional shapes etched using a normal parallel plate type RIE device without any pretreatment. It is a schematic diagram created based on the SEM photograph shown.

The mask uses a SiO film, and the etching conditions are RF'
Power is 300, pressure is 0. ITorr, the temperature of the cooling water was 35°C, and the flow rate of HBr gas was varied.

In the same figure (a), the flow rate of HBr gas was increased to 1 without pretreatment.
This is the cross-sectional shape after etching at 30 sccm. It has already been confirmed that the smaller the IBr flow rate, the slower the etching rate of Sin2. For this reason, it takes time to remove the natural oxide film formed on the polycrystalline silicon surface, and the removal time also varies, resulting in etching residues as shown by the sandy area in the figure. At this time, the selectivity ratio of polycrystalline silicon to SiO■ is 84
Met. In order to remove this etching residue, additional over-etching time is required. Therefore, the total etching time takes a considerable amount of time, resulting in a reduction in throughput.

Figures (b) and (C) show that the flow rates of tlBr gas were 150 sccm and 200 sccm, respectively, without pretreatment.
This is the cross-sectional shape after etching. See it in the picture? The result was that the amount of etching residue was reduced. In other words, although there is an etching residue shown as a sandy area in FIG. 5(b), there is almost no etching residue in the state shown in FIG. 2(c). However, when the flow rate of HBr gas was increased, the selectivity of polycrystalline silicon to SiO2 tended to decrease, and the selectivity was 67 and 54, respectively.

FIG. 5 is a schematic diagram created based on a SEM photograph showing the cross-sectional shape etched in the sixth embodiment.

As shown in the figure, a good vertical shape was obtained, no etching residue was observed, and a high selection ratio of polycrystalline silicon to SiO2 of 100 or more was obtained.

As described above, by performing RIB at a flow rate of HBr gas of 200 sccm or more as a pretreatment of the present invention,
It becomes possible to remove the oxide film formed on the surface of silicon or polycrystalline silicon, and then the flow rate of HBr gas is reduced to 1.
By performing RIE at 00 sccm or less, it becomes possible to easily perform etching with a selectivity to St(h of 100 or more).

Note that in the above example, HBr gas is used, but Br gas is used.
It is also possible to use z gases or mixtures with other gases.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to remove the surface oxide film of silicon or polycrystalline silicon only by changing the flow rate of HBr gas, simplifying the process, and using a gas other than tlBr as an etching gas. Since it is not affected by this, it has the effect of being able to perform etching while maintaining a high selectivity to Si02.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a sample used in an example of the present invention, Figure 2 is a schematic cross-sectional view of a parallel plate type RIIE apparatus used in an example of the present invention, and Figure 3 is a diagram showing the relationship between polycrystalline silicon and the flow rate of HBr gas. S
FIG. 3 is a diagram showing the etching rate of iO■. Figures 4 (a) to (C) are schematic diagrams based on SEM photographs showing cross-sectional shapes etched without pretreatment, and Figure 5 are schematic diagrams based on SEM photographs showing cross-sectional shapes etched in the sixth embodiment. It is a diagram. 30 indicates a grounding point. In the figure, 11 is a silicon substrate, 12 is a Sing film, 13 is a polycrystalline silicon layer, 14 is a Sing mask pattern, 15 is an oxide film, 21 is an etching chamber, 22 is a wafer, 23 is a lower electrode, 24 is a counter electrode, 25 is an insulator, 26 is a high frequency power supply, 27 is a gas supply port, 28 is a gas exhaust port, 29 is a cooling water, Patent applicant: Fujitsu Ltd. Representative Patent attorney Akito Kukimoto Yoshiyuki Osuga? Nuta δ and Yumiike Iku 112 T・F 2 test 10 sho ■■■
1st view Figure 1 HBr PL @ (sccm) Takakinunami power supply 26 Figure 3 Figure 2 Figure

Claims (3)

[Claims] (1) In a method of dry etching silicon or polycrystalline silicon using a gas containing bromine gas or hydrogen bromide gas, as a pre-treatment for dry etching, a A dry etching method characterized in that the oxide film is etched under conditions where the flow rate of the same bromine gas or hydrogen bromide gas is increased compared to the etching of silicon or polycrystalline silicon. (2) As the pretreatment, the flow rate of hydrogen bromide gas was
2. The dry etching method according to claim 1, wherein after the surface oxide film is removed by etching at a flow rate of at least 100 sccm, silicon or polycrystalline silicon is etched at a flow rate of hydrogen bromide gas at a flow rate of at most 100 sccm. (3) The reaction chamber in which the pretreatment with hydrogen bromide gas is performed and the reaction chamber in which etching is performed are the same, or the sample is transported between the reaction chambers in a vacuum. The dry etching method according to claim 1 or 2.