JPS6053459B2 - Plasma etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plasma etching method, and more particularly to a plasma etching method for silicon or silicon compounds through an organic resin photomask.

In the manufacture of semiconductor devices, silicon (Si single crystal or Si polycrystal) and silicon compounds (SiO2, Si
3N.

etc.) as an effective means of selectively etching
Plasma etching is employed using CF4 (carbon tetrafluoride) gas containing a small amount (usually 4 to 10%) of 0.0 as an etching gas. By the way, when plasma etching a Si wafer or a Si compound formed on its surface, a resin resist is used as a mask, but in this case, the pattern dimensions on the Si wafer after etching become smaller than the dimensions of the photoresist pattern. Another disadvantage is that pattern dimensions may vary.

The reasons for this lack of color are that an undercut occurs under the resist mask, which reduces the pattern size, and (2) if overetching is performed, the undercut becomes especially severe, so the etched area inside the wafer is It is thought that variations in the thickness of the desired film are amplified and appear as variations in pattern dimensions.

In the present invention, when plasma etching of Si3N4 was performed using aluminum as a mask, almost no reduction in pattern dimensions was found. Therefore, the reduction in dimensions, that is, undercutting, is a characteristic characteristic when using a resin resist. It is assumed that there is some kind of physical or chemical interaction between the etching gas and the resist, and studies have been conducted to variously change the components and component ratios of the etching gas.

Therefore, it is an object of the present invention to eliminate the reduction and variation in pattern dimensions caused by plasma etching, and to increase the design margin for integrated circuits.

The structure of the invention for achieving the above object uses a mixture of carbon tetrafluoride (CF0) containing oxygen and nitrogen as an etching gas in a method of plasma etching silicon or silicon compounds through an organic/resin mask. The gist is that.

Furthermore, as a preferred embodiment of the present invention, the content of oxygen is 4 to 10%, and the mixing ratio of nitrogen and carbon tetranitride is 1 or more.

According to such a configuration, by mixing N2 with CF, the unfavorable interaction between the etching gas and the resist that occurs when only CF is used is prevented, and therefore undercuts are prevented from occurring. The above objective can be achieved without any problem.

FIG. 1 shows the effect of N2 dilution (partial pressure ratio) on pattern dimension changes during CF plasma etching in an example in which the present invention is used for patterning Si, N, and films.

In this figure, solid line A is the upper limit for the measurement results, solid line B,
C indicates a representative value and a lower limit, respectively. The plasma etching conditions are as follows.

(1) Equipment: 1 PC (electrode type: capacitor type) using aluminum etch tunnel (2) RF power: 100
W (3) Gas composition and pressure (total pressure 0.6t0rr') CF
, (0.30rr (partial pressure) containing 024%) N2O. 3t
Orr (partial pressure) (4) Etch tunnel temperature at the start of etching: 50℃ (5) Etching time
,C, and in each figure, 1 is a Si substrate (wafer).
, 2 is SiQ. Coating, 3 is Si3N4 coating (1500A
), 4 is a photoresist.

In the figure, A shows the state before plasma etching, B shows the state after the plasma etching is completed, and C shows the state after the resist has been removed. The pattern dimension change ΔW is the pattern dimension W of the resist before etching.
1 and Si3N after etching, the pattern dimension W2 of the film is expressed as the difference between the measurement accuracy of Wl and W2. is ±0.1PT
r1. shall be. ΔW for each partial pressure Pcp shows only the average value within a wafer and between wafers, and the variation is ±0.3P.
It is about TrL.

In the above examples, the decrease in pattern size before and after etching and its variation between batches was 0.1±0.0 when etched under the above conditions. or MCF, only (no N2)
In the case of etching, it is 0.3±0.3 μm, and the effect of mixing N2 is clear.

According to FIG. 1, it is shown that when PN2/PCP (partial pressure ratio) is 1 or more, the pattern size reduction is stable at 0.27!7 to 0. 3 to 4 are enlarged views of the cross-sectional shape of the Si3N film after plasma etching.

Figure 3 shows the case where only CF is used as the etching gas according to the conventional method.
The undercut has progressed at the interface part (the part surrounded by the broken line 5), and the edge 6 of the Si3N4 pattern has retreated.
That is, the pattern size decreases by Δw. Further, the angle θ1 of the edge is approximately 30W. On the other hand, FIG. 4 shows that CF, O. 3l'0rr (partial pressure) N2O. l) When etching with a mixed gas of Rr (partial pressure), there is no regression of the Si3N film pattern (ΔW=0), and the edge angle 02 is approximately 60. It is ℃.

Although the embodiments have been described above, the present invention is not limited thereto.

For example, the same effect can be obtained when the material to be etched is Si (single crystal or polycrystal) or SiO2. When the etching gas mixture JltN2/CF4 is less than 1, although it is not possible to reduce the pattern dimension to 0, it is important to note that the dimension reduction is more effective depending on the mixing ratio than when N2 is not added. This is also clear from Figure 1. This invention particularly relates to bipolar ICs based on the oxide film isolation method, . It is effective when applied to the manufacture of LSIs or MOS memories.

[Brief explanation of drawings]

Fig. 1 is a curve diagram showing the relationship between the N2/CF ratio and pattern size reduction during etching of a Si3N4 film by CN4 plasma, Fig. 1A is a model cross-sectional view showing the relationship between pattern dimensions Wl and W2, and Fig. 2 Figures A-C are cross-sectional views showing the configuration of the device before and after plasma etching, Figures 3 and 4 are enlarged perspective views of the cross-sectional configuration of the Si3N film and photoresist after plasma etching, and Figure 3 is a conventional example. , FIG. 4 shows an example of the present invention. 1...Si substrate, 2...SiO2 film,
3... Si3N, film, 4... resist, 5... photoresist Si3N4 interface, 6...
...Edge part of Si3N.

Claims (1)

[Claims] 1 When plasma etching is performed on the underlying silicon nitride film using the patterned organic photoresist film as an etching-resistant mask, the etching gas is a nitrogen gas with respect to carbon tetrafluoride containing 4 to 10% oxygen. A plasma etching method characterized by using a mixed gas having a partial pressure ratio of 1.0 or more.