JPH0744174B2 - Etching method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a precision etching method required for high density integrated circuits.

2. Description of the Related Art Conventionally, the so-called BOX separation process, which is a grooving oxide film embedded type separation process, has been attracting attention as an alternative separation method to LOCOS separation. This etches the isolation area of the silicon substrate,
In this method, a silicon oxide film is deposited by the D method, and a flattening etchback process is performed to leave the silicon oxide film only in the silicon trench.

Problems to be Solved by the Invention In the conventional technique, since the end point determination is performed by time etching in the planarization process, the buried silicon oxide film and the active region are not
Variations in the Si gap were found to have a negative effect on device characteristics.

Means for Solving the Problems In order to solve the above problems, the present invention determines the end point of etchback by depositing a silicon nitride film on a buried oxide film or between a polysilicon film and a buried oxide film. This is performed by changing the intensity of the emission spectrum of radicals.

Effect According to the present invention, since the end point of etch back is automatically determined, precise etch back can be performed with good reproducibility.

Embodiment FIG. 1 shows an embodiment of the present invention. This will be described in the order of steps. A thermal oxide film 2 is deposited to a thickness of 50 nm and a polysilicon 3 is deposited to a thickness of 140 nm on a semiconductor silicon substrate 1, and then a resist pattern is applied to the polysilicon 3, the thermal oxide film 2 and the silicon substrate 1.
800 nm is etched to form a step 10 on the substrate 1. Then L
The silicon oxide film 4 for embedding in the PCVD method is 1100 nm
After the deposition, the silicon nitride film 5 for detecting the end point in the subsequent etch back process is deposited to 100 nm. Next, a resist pattern 6 is applied at a height of 990 nm, and subsequently a silicon oxide film 7 is formed to a thickness of 20 nm by a sputtering method. Subsequently, resist coating is performed to form a resist 8. The film thus formed is etched by the etch back method. That is, the resist 8
Is dry-etched with a gas containing O ₂ . Then, the oxide film 7 and below are etched with a mixed gas of CHF ₃ , C ₂ F ₆ and O ₂ . FIG. 2 shows a state of being etched to the position shown in FIG.

Next, the polysilicon 3 is removed, and SiO ₂ 2 is etched to a thickness of 50 nm. Then, as shown in FIG.
An oxide film 4 for element isolation is embedded and formed therein. FIG. 4 shows the change over time of CN ^* emission, for example, light having a wavelength of 387 nm when the silicon nitride film 5 is etched in the etch back process. The peak of X in FIG. 4 is during the etching of the line portion of X in FIG. 1, and the peak of Y is during the etching of y in FIG. If etching is performed while reading this emission and the etching end is judged when the second peak ends, accurate etching back can be performed.

Next, another embodiment of the present invention will be described with reference to FIGS. 5, the same parts as those in FIG. 1 are designated by the same reference numerals.

A thermal oxide film 2 is deposited to a thickness of 50 nm on a silicon substrate 1, a polysilicon 3 is deposited to a thickness of 140 nm, and a silicon nitride film 5 for detecting an end point is deposited to a thickness of 100 nm. In this embodiment, polysilicon 3
A nitride film 5 for detecting the end point is formed thereon. Next, a resist pattern is formed and the silicon nitride film 5 (100 nm), polysilicon 3 (140 nm), thermal oxide film 2 (50 nm) and silicon substrate 1 are etched by 800 nm to form a step 10. Then LPC
A silicon oxide film 4 is deposited to a thickness of 1100 nm by the VD method. Next, after forming a resist pattern 6 of 1090 nm, a silicon oxide film 7 is subsequently deposited to a thickness of 20 nm by a sputtering method. Further, the resist 8 is coated to form a flat surface. Next, this film is etched by the etch-back method using the same gas as described above, as shown in FIG. Subsequently, the state in which the polysilicon 3 is removed and the thermal oxide film 2 (50 nm) is etched is shown in FIG.

FIG. 8 shows the time change of the emission intensity of CN radicals generated during the etching of the silicon nitride film, which is used for detecting the end point in the etchback process. The peak in FIG. 8 indicates the time when the nitride film 5 is etched. Precise etch back is possible with the end point at the peak of the emission intensity of the CN radical generated by the etching of the silicon nitride film 5.

EFFECTS OF THE INVENTION According to the present invention, it is possible to accurately and accurately detect the end point of etching in the etchback process, and the etchback process required for an integrated circuit having a fine pattern is automatically performed with high precision and reproducibility. This greatly contributes to the improvement of the manufacturing yield of dense semiconductor devices.

[Brief description of drawings]

1 and 5 are sectional views of a semiconductor substrate before etching back according to an embodiment of the present invention, FIGS. 2 and 6 are sectional views after etching back, and FIGS. 3 and 7 are after separation. Sectional view of the fourth
FIG. 8 and FIG. 8 are views showing the change over time in the emission intensity of CN radicals during etchback. 1 ... Silicon substrate, 2 ... Thermal oxide film, 3 ... Polysilicon, 4 ... Silicon oxide film, 5 ... Silicon nitride film,
6 ... resist, 7 ... silicon oxide film, 8 ... resist.

Claims (2)

[Claims] 1. A step of depositing a silicon oxide film on a substrate having steps, a step of depositing a silicon nitride film on the oxide film, a step of coating a resist to planarize the surface, and While etching the formed film
An etching method characterized by monitoring the emission intensity of CN radicals to detect the end point of the etching. 2. A step of depositing a silicon nitride film on a polysilicon film on a substrate having a step, a step of depositing a silicon oxide film on the nitride film, and a resist coating to planarize the surface. An etching method comprising the steps, and etching the film formed in the above step to monitor the emission intensity of CN radicals to detect the end point.