JPH0770531B2 - Method for forming buried oxide film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a buried oxide film having high surface flatness accuracy required for a high-density integrated circuit.

[Conventional technology]

Conventionally, the so-called BOX separation process, which is a trench isolation oxide film embedded type separation process, has been drawing attention as an alternative separation method to LOCOS separation. This is a method of etching the isolation region of the silicon substrate to form a groove (step), depositing a silicon oxide film by the CVD method, and leaving the silicon oxide film only in the groove formed on the silicon substrate through the flattening etchback process. is there.

In the conventional technique, since the end point determination in the flattening etch-back process depends on time, the step difference between the buried silicon oxide film and the silicon in the active region is varied, which adversely affects the device characteristics.

As disclosed in JP-A-63-192236 as a conventional example for solving this problem, a silicon nitride film is deposited before and after the embedded silicon oxide film is deposited, and the emission intensity of CN radical is monitored during etching. It has been proposed to detect the end point of etching.

[Problems to be Solved by the Invention]

However, if the nitride film is deposited on the silicon substrate, the compatibility with the substrate is poor and the substrate warps due to the stress. Therefore, a thermal oxide film for relaxing the stress is interposed between the nitride film and the silicon substrate. Must be
Many processes become complicated.

Therefore, in order to solve the above-mentioned conventional problems, it is an object of the present invention to provide a method capable of detecting the end point of etchback and forming a buried oxide film without complicating the process. .

[Means for Solving the Problems]

In order to achieve the above object, the invention related to this application is
Deposit a silicon oxide film on the substrate with the grooves, and then
A method of performing etch back of the resist film and the silicon oxide film, wherein a resist film is deposited on the silicon oxide film to flatten the surface, and etching is terminated when the surface of the substrate appears. A buried oxide film for device isolation is formed in the trench while interposing a thin film of a different composition different from that of the oxide film and the resist film and monitoring the intensity of active species generated by etching the thin film of the different composition. In the method, the thin film having a different composition is formed of a phosphorus glass (PSG) film, and the silicon oxide film and the resist film are etched while monitoring the intensity of a specific active species generated by etching the phosphorus glass film, It is characterized in that the time point when the peak of the intensity of the specific active species ends is detected as the end point of the etchback.

[Action]

Since the stress between the phosphorus glass film and the substrate is significantly smaller than the stress between the nitride film and the substrate, specifically about 1/20, the thermal oxide film between the phosphorus glass film and the substrate is small. There is no need to relieve stress by intervening.

Therefore, since the thermal oxide film is not formed, the process can be shortened to form the buried oxide film.

The end point of the etch back is to etch the silicon oxide film and the resist film while monitoring the intensity of the specific active species generated by the etching of phosphorus glass, and to etch when the peak of the intensity of the active species ends. By setting the end point of the back, it is easy to detect the end point of the etch back.

Here, the specific active species means ions, radicals and the like that are generated by etching the phosphorous glass film and are in a chemically active state, the intensity of which can be detected by an instrument analyzer.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional configuration diagram for explaining the process of one embodiment.

In the step of FIG. 1 (1), a phosphorous glass film 2 was deposited on the semiconductor silicon substrate 1 by the CVD method to a thickness of 150 nm. In this step, since the stress between the phosphorus glass film 2 and the silicon substrate 1 is small, even if the phosphorus glass film 2 is formed by omitting the step of forming the thermal oxide film on the substrate, the substrate 1 does not warp.

Next, in step (2), a resist pattern is formed on the phosphor glass film 2 and the phosphor glass film 2 and the silicon substrate 1 are dry-etched by 800 nm to form a groove (step portion) 3 on the substrate surface. .

Go to step (3) and use the low pressure CVD method to form the groove 3
A silicon oxide film 4 for embedding, which is embedded flatly with the substrate 1 and becomes an element isolation region, is formed in a 1000 nm stacked layer therein. At this time, the silicon oxide film enters the groove, and a step corresponding to this groove is formed in the portion of the silicon oxide film 4 on the groove 3.

Moving to the step (4), the resist film 7 is formed in a later step. To complete the surface flattening in this step, the resist pattern 5 is formed at the height of 800 nm on the step portion 10, Further, a silicon oxide film 6 having a thickness of 20 nm is formed only on the surface of the resist pattern 5. The step of forming the silicon oxide film 6 may be omitted.

Then, the surface is flattened by forming a resist film 7 by resist coating.

Next, the semiconductor device having the film structure formed through the steps up to (4) is etched back by the dry etching method. This etch back is performed until the surface of the silicon substrate 1 appears as shown in the following steps (5) and (6), and the buried silicon oxide film 4 exists only in the groove 3.
And make the surface flat.

At the time of this etch back, the exhaust gas of the etching gas is introduced into the mass spectrometer, and the intensity of phosphorus ions in the exhaust gas is monitored.

As shown in the step (5), as the etch back proceeds, the resist film 7, the silicon oxide film 6, the resist pattern 5 and the silicon oxide film 4 on the phosphorus glass film 2 are etched to form the phosphorus glass film 2. It becomes exposed on the surface.

FIG. 2 shows the time course of the mass spectrum of phosphorus ion intensity from the step (4) to the step (5).

As shown in the step (5), the phosphorus glass film 2 is formed on the outermost surface.
When the glass starts to be exposed, the phosphorus glass film 2 in the etching exhaust gas
Since phosphorus ions produced by etching are mixed, the intensity of the phosphorus ion mass spectrum sharply increases. That is, at the time when the phosphorus ion intensity sharply increases (t ₁ ), the etch back is progressing until the phosphorus glass film 2 is exposed.

When the etch back is further advanced, the intensity of phosphorus ions drops sharply and the intensity of phosphorus ions becomes equal to the value of the reference line. At this time (t ₂ ), as shown in the process diagram of (6), the phosphor glass film 2 is etched by 150 nm to expose the surface of the substrate 1, and the silicon oxide film for embedding is formed only in the groove 3 of the substrate 1. 4 is a state in which it is embedded flat with the substrate. Therefore, if the etching is finished with the end point of the phosphorus ion intensity in FIG. 2 as the end point of the etch back, the burying silicon oxide film 4 is buried only in the groove 3 of the substrate 1 so as to be flat with the substrate. The separation structure can be completed.

In the above embodiment, the phosphor glass film 2 is laminated on the substrate 1 in the step of FIG. 1 (1), but as shown in FIG. 3, the embedding silicon oxide film 4 is formed on the substrate 1. After the formation, the phosphorus glass film 2 can be formed on the silicon oxide film.

In this case, when the etch back progresses to the surface of the phosphorus glass film 2 (A in FIG. 3), the phosphorus ion intensity starts to increase as shown in the graph of the temporal change in phosphorus ion intensity in FIG. 4, and etching is further advanced. Accordingly, a first peak 40 of phosphorus ionic strength occurs.

Further, as the etching progresses and the etch back progresses to the surface of the phosphorus glass film 20 existing in the lower layer of the resist pattern 5 (B in FIG. 5) as shown in FIG. It starts to rise again, and as the etching is continued, a second peak 41 of the phosphorus ion intensity is generated as shown in FIG.

Therefore, when the etch back is completed at the end point (t ₃ ) of this second peak, the buried oxide film is formed flat only in the groove 3 of the substrate 1 as in the step shown in FIG. 1 (6). be able to.

According to the above-mentioned embodiment, as compared with the conventional example in which the end point of the etchback is detected through the nitride film, it is not necessary to form a thermal oxide film between the substrate and the nitride film. Can be shortened.

Further, since the end point of the etch back is detected based on the phosphorus ion intensity monitor of the mass spectrometer, the end point can be detected accurately and accurately, so that the etch back process required for an integrated circuit having a fine pattern is performed. Can be performed accurately and with good reproducibility. Moreover, by automatically detecting the end point of the peak of the phosphorus ion intensity, it is possible to automate the etchback, thus improving the yield in the formation of the buried oxide film. Can be improved.

In the above embodiment, the mass spectrometric method is used for monitoring the phosphorus ion intensity, but the present invention is not limited to this, and other instrumental analysis methods such as gas chromatography and optical emission analysis method can be widely used.

Also, phosphorus ions are used as the specific active species, and the end point of the etchback is detected by monitoring the intensity of the phosphorus ions.However, boron, As, Ge, etc. are doped in the phosphorus glass film to remove the impurities other than phosphorus. It is also possible to detect the end point of etchback by monitoring the ion intensity.

It is also possible to detect the end point of the etchback by using a specific active species such as a radical other than ions generated in the process of etching the phosphorus glass film.

〔The invention's effect〕

As described above, according to the method for forming a buried oxide film according to the present invention, a phosphorus glass film having a small stress is interposed between a substrate and a specific active species generated by etching the phosphorus glass film is monitored. Since the end point of the etch back is detected, it is not necessary to form a thermal oxide film between the substrate and the phosphor glass film.As a result, the buried oxide film is formed only in the groove formed in the substrate in a shortened process. It becomes possible to form a flat surface.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram for explaining a process of one embodiment of the present invention, and FIG. 2 shows a time-dependent change in the mass spectrum of phosphorus ion intensity generated in the process of etching back performed in the process of FIG. A graph, FIG. 3 is a sectional view of a film structure of a semiconductor device formed by a process of another embodiment of the present invention, and FIG.
FIG. 3 is a graph showing the change over time in the mass spectrum of the phosphorus ion intensity that occurs during the process of etching back the semiconductor device of FIG. 3, and FIG. 5 is a graph of the semiconductor device at the time when the second peak of the phosphorus ion intensity occurs in the graph of FIG. It is a membrane structure sectional view. In the figure, 1 is a silicon substrate, 2 is a phosphorus glass film, 3 is a groove,
Reference numeral 4 is a buried silicon oxide film, 5 is a resist pattern, 6 is a silicon oxide film, and 7 is a resist film.

Claims (1)

[Claims] 1. A silicon oxide film is deposited on a substrate having a groove, and then a resist film is deposited on the silicon oxide film to flatten the surface, and etching is terminated when the surface of the substrate appears. A method of performing etch back of the resist film and the silicon oxide film, wherein the thin film having a different composition is interposed between the silicon oxide film and the resist film, and the thin film having the different composition is etched to generate an activity. In a method of forming a buried oxide film for device isolation in the groove while monitoring the strength of a seed, the thin film of different composition is formed of a phosphorus glass (PSG) film,
The silicon oxide film and the resist film are etched while monitoring the intensity of the specific active species generated by etching the phosphorus glass film, and the time point at which the peak of the intensity of the specific active species ends is detected as the end point of the etchback. A method for forming a buried oxide film, which comprises: