JPH02166733A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To realize etching characterized by a high selecting rate and high etching rate by using the mixed gas of sulfur hexafluoride, oxygen and hydrogen bromide having a specified ratio as etching gas. CONSTITUTION:As etching gas for etching a silicon nitride film, the mixed gas of sulfur hexafluoride, oxygen and hydrogen bromide is used. The flow rate of the oxygen is made to be about 200% or less of the flow rate of the sulfur hexafluoride. The flow rate of the hydrogen bromide is made to be about 60% or less of the sulfur hexafluoride. When the adequate quantity of the oxygen is mixed with the sulfur hexafluoride, the fact that the etching rate of the sulfur hexafluoride is low is improved. When the adequate quantity of the hydrogen bromide is mixed, the decrease in selecting ratio due to the mixing of the oxygen is prevented. Thus the etching wherein both the selecting ratio and the etching rate are high can be realized.

Description

[Detailed Description of the Invention] [Summary] Provided is a method for manufacturing a semiconductor device, in particular a method for reactive ion etching of a silicon nitride film, which can achieve etching with a large selectivity and a high etching rate. For this purpose, in a semiconductor device manufacturing method that involves reactive ion etching of a silicon nitride film, a mixed gas of sulfur hexafluoride, oxygen, and hydrogen bromide is used as the etching gas, and the flow rate of oxygen is set to the same level as that of the meteor of sulfur hexafluoride. 200 qg or less, and the flow rate of bromide water is about 60 qg of sulfur hexafluoride. tl is set to 1 so that it is 6 or less.

[Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor device, and particularly to a method for reactive ion etching of a silicon nitride film.

With the recent increase in the degree of integration of semiconductor devices and the increase in 31N heat.

There is a need to efficiently form a large number of elements in a limited element area. For this purpose, it is necessary to reduce the bird's beak in LOCO8, and LOGO3 tends to become thinner. Therefore, when etching a silicon nitride film formed on a thin silicon oxide film, the etching selectivity to the silicon oxide film must be high, and at the same time, it is important to reduce the etching rate due to the relationship with the etching time. Therefore, it is required to realize etching with a large selectivity and a high etching rate.

[Prior Art] In reactive ion etching of a silicon nitride film, the etching gas determines the selectivity and the etching gray. For this reason, various etching gases have been proposed in the past.

Carbon tetrafluoride (CF) and nitrogen trifluoride (NPi) are known as etching gases for silicon nitride films, based on b'. However, these etching gases have a selectivity ratio of about 3 to the silicon oxide film, so the underlying silicon oxide film only needs to be thick. The problem with this device is that the selection ratio is too small.

Methane fluoride (CH,F) and methane difluoride (CHtF2) are used as etching gases to increase the selectivity.
has been proposed fT, Kure, Y, avrano
to, N, Hashi+noto, T, Takaict
+i, IEEE 19831EDH'10C11n, D
i(]O3t 11.757). However, methane butylene and difluoride methane have a large amount of deposited components during the etching process, the permissible pressure margin is narrow, the etching conditions are too severe, and the etching stability is poor.

When sulfur hexafluoride (SF6) is used as the etching gas, a satisfactory selection ratio of about 5 to 7 can be obtained, but there is a problem that the etching rate of silicon nitride 1 is too low and the etching time is too long.

In order to improve the etching rate, an attempt has been made to use a mixture of sulfur hexafluoride and oxygen as an etching gas, but although the etching rate increases this time, the selectivity ratio decreases and the results are unsatisfactory. is not obtained.

[Problems to be Solved by the Invention] As described above, with conventional etching gases, when the selectivity is high, the etching rate is low, and when the etching gray is high, the selectivity is low. There was no satisfactory enching gas for silicon nitride.

The present invention has been made in consideration of the above circumstances, and it is an object of the present invention to provide a method for manufacturing a semiconductor device that can realize a high etching selectivity and a high etching rate.

[Means for Solving the Problems] A method for manufacturing a semiconductor device according to the present invention uses a mixed gas of sulfur hexafluoride, oxygen, and hydrogen bromide as an etching gas for etching a silicon nitride film, and changes the flow rate of oxygen to sulfur hexafluoride, oxygen, and hydrogen bromide. It is characterized in that the flow rate of sulfur is about 200% or less, and the flow rate of hydrogen bromide is about 60% or less of the flow rate of sulfur hexafluoride.

[Function] According to the present invention, by mixing an appropriate amount of oxygen with sulfur hexafluoride, the low etching rate of sulfur hexafluoride is improved, and by further mixing an appropriate amount of hydrogen bromide, This prevents the selectivity from decreasing due to the mixing of oxygen, and enables etching with high quality selectivity and etching rate.

[Example] In the method for manufacturing a semiconductor device according to the present invention, the etching gas for reactive ion etching of the silicon nitride film formed on the underlying silicon oxide layer is based on sulfur hexafluoride, oxygen and Contains hydrogen bromide.

The reaction of sulfur hexafluoride, oxygen, and hydrogen bromide to a silicon oxide film and a silicon nitride film will be described.

Sulfur hexafluoride is decomposed as shown in the following equation in reactive ion etching.6 SF6-+SFn +F* The radical F reacts with the silicon oxide film and silicon nitride film as shown in the following equation.

5isN4 +F -3iFx ↑ ±N2TS
iO20F →S iF x↑+02↑The reaction is more to the silicon nitride film, and the reaction to the silicon oxide film is less.

Odor 1 Arsenic decomposes in reactive ion etching as shown in the following equation.

HB r −+ I-I −t-B
The r*radical r3r reacts with the silicon oxide film and the silicon nitride film as shown in the following equation.

5iiN4+Br ”5iBr, ↑+N2↑5ty2
+Br -3iBr, ↑Mo02↑Mainly reacts with silicon nitride film, and hardly reacts with silicon oxide film.

Oxygen affects the concentration of fluorine, which contributes to etching. That is, as the flow rate of oxygen increases, the fluorine concentration increases and reaches a peak, and as the flow rate of oxygen increases further, the fluorine degree decreases. The fluorine concentration is controlled by the oxygen flow rate.

Next, the etching rate of silicon nitride film and silicon oxide film when oxygen or hydrogen bromide is mixed with sulfur hexafluoride, and the change in the selectivity ratio of silicon nitride film to silicon oxide 1 are shown in Figures 1 to 1. Shown in Figure 3.

Figure 1 is a graph showing changes in the etching rate and selectivity of a silicon nitride film when the flow rates of oxygen and hydrogen bromide mixed with a constant flow rate of sulfur are changed. Mix only hydrogen bromide with a constant flow rate of sulfur hexafluoride, and change the etching ratio of silicon nitride (arsenic film and silicon oxide film) and selectivity when changing the temperature. Figure 3 shows the etching rate and selectivity of silicon nitride and silicon oxide when only oxygen is mixed with sulfur hexafluoride at a constant flow rate and the flow rate is changed. It is a graph showing changes.

Figure 1 is a diagram for comprehensively evaluating the effects of the etching gas according to the present invention, and Figures 2 and 3 are for reference in order to independently evaluate the effects of hydrogen bromide and oxygen. It is.

The experimental conditions shown in Figs. 1 to 3 are common: the 2RM of sulfur hexafluoride is 253 CCM, and the silicon nitride film is heated with reactive ions at a pressure of 0.2 Torr and a power density of 0.4 W/cm'. Etching.

In FIG. 1, the flow rate of oxygen is varied between 0 and 203 CCM, and the flow rate of hydrogen bromide is varied between 0 and 203 CCM. The horizontal axis of the graph in Figure 1 is the iAE of odor 1 arsenic.
m (S CCM ), the left vertical axis is the erating gray h (n rn /' m i n ), and the right MI
IIi! I! is the silicon nitride film/silicon oxide 1 model selectivity ratio.

In Figure 2, the flow rate of hydrogen bromide is varied between 0 and 503 CCM. The right vertical axis is the silicon nitride film/silicon oxide film selection ratio.

In FIG. 3, the oxygen flow rate is varied between 0 and 11005 CC. The horizontal axis of the graph in Figure 3 is hydrogen bromide: “HE
quantity (SCCM), and the left vertical axis is the etching rate (n
m/m1n), and the right vertical peak is the silicon nitride film/silicon oxide film selection ratio.

As can be seen from the graph in FIG. 2, when the flow rate of odor 1 arsenic exceeds 203 CCCM, the selectivity falls below 51 J and is no longer satisfactory. From Figure 2, 253 CC'V
The flow rate of hydrogen bromide is approximately 153C for 1 sulfur hexafluoride.
If it is less than CM, the selection ratio will be a satisfactory value of 6 or more. In addition, if U and t of hydrogen bromide are OS CCM, that is, if hydrogen bromide is not mixed, silicon nitride °
[Of course, this is not desirable because the elastin gray of 1~ drops rapidly.

From the above, it can be seen that it is desirable that the flow rate of hydrogen bromide to be mixed is 60?5 or less of the flow rate of hexafluoride sulfur.

As can be seen from the graph in FIG. 3, when even a small amount of oxygen is mixed, the elation grays 1 to 7 of the silicon nitride film rise sharply. However, as the mixing flow rate of oxygen increases, the selectivity tends to decrease.

When the oxygen flow rate was 60 SCC, the etching rate of silicon nitride reached its peak, and the oxygen flow rate was reduced to 608 CC.
Even with the above, silicon nitride model elatin- 1.
will no longer increase, and on the contrary, the selectivity will decrease. Therefore, it is desirable that the oxygen flow rate be 50S CCM or less. Further, as with hydrogen bromide, if there is no oxygen meteor, that is, if oxygen is not mixed, the etching rate of the silicon nitride film will drop rapidly, which is not desirable.

From the above, it can be seen that the flow rate of oxygen to be mixed is desirably 200% or less of the flow Jl of sulfur hexafluoride.

In this way, the mixed flow rate of hydrogen bromide and oxygen could be predicted from the graphs in FIGS. 2 and 3. Confirm this point using Figure 1.4. jj.

As can be seen from Figure 1, the flow rate of odor 1 arsenic is 153C.
If the amount is greater than CM, the selection ratio will be too low regardless of the oxygen mixing flow rate. If the flow rate of hydrogen bromide is 153 CCM or less, a selectivity of around 6 or more can be ensured.

Furthermore, as can be seen from Figure 1, as the flow rate of oxygen increases, the etching rate of the silicon nitride film increases, but the selectivity tends to decrease.6 However, if the flow rate of arsenic is less than 155 CCM, , even if the number of oxygen meteors increases, the selectivity ratio will not decrease fatally, that is, if the oxygen meteors are less than 503 CCCM as predicted by Figure 3,
It can be seen that a satisfactory selection ratio can be secured.

For example, when using an etching gas containing a mixture of oxygen at a flow rate of 1103 CCM and hydrogen bromide at a flow rate of 53 CCM for sulfur hexafluoride with 't'E>M25SCCM, the etching ratio is approximately 9, and the etching rate of the silicon nitride film is is about 120
nm/min. Therefore, the series of 1100n:
When etching a 100% silicon nitride film, even with 50% over-etching, the silicon oxide film is only etched by 5.55 nm on 2/9/100, and the silicon nitride film underneath is only etched by 5.55 nm. This is sufficient and is suitable as a method for manufacturing semiconductor devices using thin silicon oxide films in recent years.

Judging from the above, the etching gas for etching the silicon nitride layer is a mixed gas of sulfur hexafluoride, oxygen, and hydrogen bromide, and the flow rate of oxygen is approximately the same as the flow rate of sulfur hexafluoride. 200% or less, and the flow rate of hydrogen arsenide is approximately 60% or less of the flow rate of sulfur hexafluoride, the etching rate of the silicon nitride film is △ and the selectivity of the silicon oxide film is high. be able to.

5 Effects of the Invention] As described above, according to the present invention, an appropriate amount of oxygen (which has the effect of increasing the etching gray 1 to 1) of the silicon nitride film is mixed with arsenic sulfur, and has an effect that does not reduce the selectivity. Since a certain amount of hydrogen bromide is mixed with Wi, it is possible to etch the silicon nitride film with high selectivity and etching rate.

Figure 3 is a graph showing the quenching rate and selectivity ratio of silicon nitride film and silicon acid arsenic film when only oxygen is mixed with sulfur. .

[Brief explanation of the drawing]

FIG. 1 is a graph showing the etching rate and selectivity of silicon nitride when oxygen and arsenic are mixed with arsenic sulfur according to the semiconductor device manufacturing method of the present invention.

Claims (1)

[Claims] In a method for manufacturing a semiconductor device in which a silicon nitride film is subjected to reactive ion etching, a mixed gas of sulfur hexafluoride, oxygen, and hydrogen bromide is used as an etching gas, and the flow rate of oxygen is set to about 200% or less of the flow rate of sulfur hexafluoride; A method for manufacturing a semiconductor device, characterized in that the flow rate of hydrogen bromide is approximately 60% or less of the flow rate of sulfur hexafluoride.