JPS6376329A - Etching method - Google Patents

Abstract

PURPOSE:To prevent that a bottle-like and horizontally swollen trench is formed or that an undercut is formed at a buried layer during a trench etching process of a silicon substrate by a method wherein a chloroform (CHCl3) gas is added to chlorine or a chlorine gas. CONSTITUTION:A plasma 28 is generated between a cathode 23 and a substrate 11 by means a reactive etching system 21. Then, a mixture of Cl2 and CHCl3 or another mixture of SiCl4+Cl2+CHCl3 is fed into the system 21 through an inlet pipe 25. If, e.g., the mixture of Cl2+CHCl3 is used, a satisfactory result can be obtained with the mixture ratio of Cl2:CHCl3=1:1. Normally, it is desirable to set the ratio in such a way that, if Cl2 is 1, CHCl3 ranges form 0.5 to 1.5. Through this constitution, it is possible to prevent that, during a trench etching process of a silicon substrate, a bottle-shaped etched part or an undercut is formed and to execute an etching process of a trench having a size as designed. Therefore, it is possible to improve the reliability and to achieve the miniaturization of a semiconductor device to be fabricated.

Description

[Detailed description of the invention] [Summary] Silicon trench treatment using chlorine or chlorine-based gas
In etching, the gas is chloroform (CH(
J! 3) prevents the occurrence of undercuts.

[Industrial application field]

The present invention relates to an etching method, and more specifically, a reactive etching method using chlorine or chlorine-based gas.
Ion etching
The present invention relates to a method for preventing bottle-shaped etching and undercutting in buried layers, which have conventionally been observed, in processing and notching silicon substrates by Hing+ RIE.

[Conventional technology]

Etching for forming a trench (groove) in the silicon substrate is carried out by the method shown in FIG.
An oxide film (5i02 film) 12 and a silicon nitride film 13 are formed in this order on top, and phosphorus silicate glass (PS) is formed on top of that.
G”) It!t!14 is made and window 1 is made on the PSG film 14.
Open window 5. Next, a trench 16 is formed in the substrate 11 by RIE using chlorine (C122) or chlorine-based (Stα4+α2) gas.

[Problem that the invention seeks to solve]

Initially, etching was performed using only C22, but
When the n+ type buried layer 17 is formed on the substrate 11, undercutting occurs in the buried layer 17, and the wing-like portions 18 are also etched.

Therefore, chlorine 5iCet, BIJ 3,
Etching with a chlorine-based gas to which CCe4Nat was added was attempted, and the problem of undercutting in the buried layer was temporarily solved using such a chlorine-based gas.

However, in such RIE, etching progresses not only in the vertical direction of the silicon substrate but also in the lateral direction, and the etching progresses in the trench 1.
As shown in FIG.
Although the window opening in step 5 is set to width W, the width W is larger than W.
A trench of "" is formed, which poses a problem of hindering the miniaturization of devices formed on the substrate 11.

The present invention was created in view of the above points, and it is possible to prevent the trench from being formed in a bottle-like shape that bulges in the lateral direction, or to prevent the formation of undercuts in the buried layer in trench etching of a silicon substrate. The purpose is to provide a method for

[Means for solving problems]

FIG. 1 is a cross-sectional view of an embodiment of the present invention, in which 21 is a reactive ion etching device, 22 is a silicon substrate 1
23 is a counter electrode plate, 24 is a grounded radio frequency (RF) oscillator, 25 is a gas introduction pipe for etching, 26 is an exhaust system, and 27 is a cooling system.

In the present invention, within the device 21, the RF
Plasma 28 (
(shown with a sandy area in the figure), and introduce St flight 4 + V 2 + CH flight 3 from the gas introduction pipe 25. Etch the silicon substrate 11 using IE.

[Effect]

In the above method, as shown in FIG. 2, a CxHySi deposit 19 is deposited by the gas on the side wall 16a of the trench 16 being etched, and this deposit serves as a protective film for the silicon substrate. Prevents lateral etching and undercutting in buried layers.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

The inventor has provided St flight 4+ 8 flight 3 to Zheng 2. Cα4
trenching of silicon substrate using gas added with etc.
After confirming that undercutting in the buried layer was prevented by etching, but etching progressed to a bottle-like shape, a literature search was conducted to find out whether there was a gas that could prevent bottle-like etching, but the existence of such a gas was not found. I could not find any literature reporting this. Therefore, the inventor conducted experiments on etching with the addition of various gases, and confirmed that when chloroform (CHCf!3) was added, the trench 16 was etched straight in the vertical direction.

When the sidewall 16a of the trench was observed after the etching was completed, it was found that deposits were present on the sidewall 16a and on the sidewalls of the PSG film, silicon nitride film, and 5i02 film.
Analysis of it confirmed that it was a composition of carbon, hydrogen, and silicon (CxHySi). When such deposits are deposited, they are etched by ions traveling straight in RIE, so the deposits on the PSG film are removed by ions, and silicon etching and deposit formation occur simultaneously at the bottom of the trench. While etching progresses, the deposits on the trench sidewalls 16a remain unetched.

In fact, after a trench of a given depth has been etched, deposits remain only on the sidewalls 16a, which are exposed to plasma
It is necessary to remove it by 2.

The method of the present invention uses a reactive ion etching apparatus 21 shown in FIG.
Plasma 28 is generated between 1 and 1, and then CP, 2 and CH 3, or Si feces and 10 feces 2+CHα3 are mixed and supplied into the device 21 through the introduction pipe 25.

and 2 + CI + CE 3 examples, Stool 2:C
Good results were obtained with a ratio of Hα3=1:1. Generally, II, f:2 is set to 1, CHα3 is 0.5 to 1
．． It was confirmed that the object of the present invention could be achieved by setting it within the range of 5.

Furthermore, we will also experiment with Siαq+α2+CHIJ3L/, (SicJ!,, + +CJ!2): C
) IC [! 3 = 3: 1 and similarly satisfactory results were obtained, (SiCJ?, 4+α2):C
The desired objective could be achieved by adjusting Hα3 to 2 to 4:1.

〔Effect of the invention〕

As described above, according to the present invention, bottle-shaped etching and undercuts can be prevented from occurring in trench etching of a silicon substrate, and trenches with the designed dimensions can be etched, thereby allowing semiconductors to be manufactured. This is effective in improving device reliability and miniaturization.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an embodiment of the present invention, FIG. 2 is a cross-sectional view of a trench according to the present invention, FIG. 3 is a cross-sectional view of a conventional example, and FIG. 4 is a cross-sectional view showing problems in the conventional example. 1 to 4, 11 is a silicon substrate, 12 is a SiO2 film, 13 is a silicon nitride film, 14 is a PSG film, 15 is a window, 16 is a trench, IT is a buried layer, 18 is a wing-shaped portion, and 19 is a 21 is a quartz jar, 22 is a susceptor, 23 is a cathode, 24 is an I? 25 is a gas introduction pipe, 26 is an exhaust system, 27 is a cooling system, and 28 is a plasma. Agent Patent Attorney Akifuku Agent Patent Attorney Yoshio Suga ] 72 Figure 3 Io final example P'' Moon, @, 1 foot Ta Figure 4

Claims (1)

[Claims] A vertically straight trench (1) is formed in a semiconductor substrate (11).
6) When etching with reactive ion etching, chlorine or chlorine-based gas is mixed with chloroform (CHCl_3).
An etching method characterized by adding gas.