JPS5823931B2 - How to use a hand hacking tool - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for etching thin layers deposited on a semiconductor substrate.

As is well known in the field of semiconductor devices, for example, in the case of transistors, semiconductor integrated circuits (ICs), etc., an insulating thin layer is deposited on the surface of the semiconductor device for surface stabilization, and photocells, etc.・For phototransistors, etc.
An optical coating layer is deposited to make the surface of the device irradiated with light non-reflective.

As these surface stabilizing thin layers or optical coating layers, thin layers of SiO□, Si3N4, etc. are known, and these Si02 and Si3N4 are NH4HF, respectively.
Selective etching is said to be possible with two liquids, a hot phosphoric acid solution.

The present applicant has previously proposed a semi-insulating polycrystalline silicon layer which is extremely suitable for the above-mentioned surface stabilizing layer and optical coating layer.

This semi-insulating polycrystalline silicon layer contains oxygen for example
Polycrystalline silicon containing 35 at% or 10 at% nitrogen
It is made of polycrystalline silicon containing the above.

However, when using this semi-insulating polycrystalline silicon layer,
Selective etching of the semi-insulating polycrystalline silicon layer, for example, selective etching when performing a window for electrode extraction, could not be performed satisfactorily.

That is, for etching such a semi-insulating polycrystalline silicon layer, it has been considered to use, for example, an HNO3+HF-based etching solution or plasma etching, or if these are used, the etching of the semi-insulating polycrystalline silicon layer is The end point of etching is not clear, there is a strong possibility that etching is insufficient or too much, and the silicon of the substrate is also etched, resulting in a rough silicon surface.

Further, in the selective etching for S13N4 described above, a hot phosphoric acid solution with a liquid temperature of about 180° C. is used as the etching solution, which is inconvenient in that a normal photoresist layer cannot be used as an etching mask.

In view of this point, the present invention provides a thin layer made of polycrystalline silicon containing oxygen, polycrystalline silicon containing nitrogen, and silicon nitride such as 513N4, when deposited on a silicon semiconductor substrate. The present invention provides a thin layer etching method on a semiconductor substrate that allows selective etching of layers.

The present invention will be explained in detail below.

In the present invention, a special etching solution is used to selectively etch the thin layer of oxygen-containing polycrystalline silicon and silicon nitride as described above, and this etching solution will be described first.

The etching solution of the present invention contains hydrogen peroxide (H2O2), hydrofluoric acid (HF), and a neutralizing solution, ie, NH4F, NH4on.
.

It consists of a mixed solution with a salt or base such as KOHl or NaOH, and has a weakly acidic or neutral solution, that is, a pH of 3.5 to 5.5.

The reason why the pH of the solution was selected in the range of 3.5 to 5.5 is that, for example, when etching the above-mentioned semi-insulating polycrystalline silicon, if the pH is lower than 3.5, stains (rust) may appear on the surface after etching. ) will occur, and if the pH is higher than 5.5, the etching rate will be extremely low, making it impractical.

Additionally, if the etching solution is strongly acidic, photoresist, which is commonly used as an etching mask, will peel off and become unusable, but as the solution approaches neutrality, the peeling will stop and photoresist can be used. becomes.

Since the above etching solution has a pH of 3.5 to 5.5, it is possible to use a photoresist as an etching mask.

In addition, in the above etching solution, the H2O2 etches Si in the layer to be etched (for example, polycrystalline silicon containing oxygen).
, acts to oxidize SiO to SiO□, HF acts to corrode the SiO□, and salt or base reduces the pH of the liquid.
It acts to adjust H.

For this reason, this etching solution consists of H2O2 and HF.
The ratio of luck is also an important factor, so H2O2 and H
It is possible to select the ratio with F within the following range.

Here, when H2F2F does not reach 3, a bluish residue that is considered to be stain remains in the layer to be etched, especially semi-insulating polycrystalline silicon, which is undesirable.

Further, when the H2O2 and F content exceeds 20, the etching rate becomes slow and it is not suitable for actual production.

Next, examples of the etching solution of the present invention will be shown.

The table below shows the properties (pH, etching rate) of a mixture of H2O2, HF, and NH4F when the composition ratio was varied.

The H2O2 used was a 30% aqueous solution, the HF was a 50% aqueous solution, and the NH4F was a 40% aqueous solution, all of which were commercially available.

The thin layer to be etched is an oxygen-containing polycrystalline silicon layer (with an oxygen atom concentration of 20 atoms) when the flow rate ratio of N20 and SIH40 is N20/5iH4 = 15o.
s% polycrystalline silicon) with a thickness of 4,000.

In the above table [1], the etching solutions of sample numbers 3, 4, and 5.7 can be used, and among them, the etching solution of sample number 4 is most suitable.

In addition, other layers to be etched using the optimum etching solution (sample number 4), namely silicon (Sl) and S by the CVD method, were also etched.
+02, 5IO2 and nitrogen-containing polycrystalline silicon by thermal oxidation (NH3/5iH4=20015o), 513
The etching characteristics for N4 are shown in the table [■] below.

In addition, FIG. 1 shows the etching solution of the present invention, that is, Table (1)
) shows the etching characteristics of the etching solution shown in Sample No. 4 with respect to the oxygen concentration in polycrystalline silicon containing oxygen.

The vertical axis shows the etching rate (in/out), and the horizontal axis shows the concentration of oxygen in polycrystalline silicon (atomic %).

In the figure, curve a is the etching solution of the present invention, and curve a is the conventional etching solution for 5i02 (HF:NH4F=12:1
oo), curve C is the conventional etching solution for Si (HF:H
NO3:CH3CO0I-(-I:5:40).

As is clear from this characteristic diagram, the etching solution according to the present invention has no etching effect on polycrystalline silicon with an oxygen content of 10 atom % or less, and the etching effect occurs rapidly when the oxygen content exceeds 10 atom %. In particular, polycrystalline silicon with an oxygen content of 14 to 35 atom %, which is suitable for a surface stabilizing layer, exhibits a high etching effect.

In addition, the examples shown in Table CI, I above are cases where NH4F is used, but other NH4OH, KOH, NaOH
The same is true when using etc.

For example, in an etching solution that is a mixture of H2O2, HF, and NH4OH in a ratio of 6:1:6, the pH of the solution is 4,
The etching rate for the oxygen-containing polycrystalline silicon used in Table CI) was about 45 μm, and the etching properties were similar to those of the above examples.

In this mixed solution, the pH was selected to be in the range of 3.5 to 5.5, and the ratio of H20□ and HF was also selected to be H2O2/HF-3 to 2.
It is possible to select anything within the range of 0.

Similarly, in an etching solution of H20□, HF, and KOH or an etching solution of H2O2, HF, and NaOH, appropriate amounts of each component are distributed to achieve a pH of 3.5 to 5.5.
and H2O2/Hp=3~20
If selected so as to have the same etching properties as those of the above embodiments, it is possible to obtain etching characteristics similar to those of the above embodiments.

Therefore, in the present invention, one or more types of a polycrystalline silicon layer containing oxygen or a polycrystalline silicon layer containing nitrogen and a silicon nitride layer such as a 513N4 layer are directly or indirectly deposited on a silicon semiconductor substrate. For example, when a surface stabilizing layer or an optical coating layer is formed, selective etching of the thin layer can be carried out using the above-mentioned special etching solution and using a photoresist layer or a polycrystalline silicon layer as an etching mask. This will be explained using a first embodiment.

FIG. 2 shows a case where the method is applied to selective etching of a surface stabilizing layer made of an 8102 layer and a polycrystalline silicon layer containing oxygen.

In FIG. 2A, 1 indicates, for example, an N-type silicon single crystal substrate, 2 indicates a P shadow region formed by selective diffusion, and j indicates a PN junction.

A polycrystalline silicon layer 3 containing oxygen and a 5IO2 layer 4 are sequentially deposited on the entire surface of the substrate 1 to form a surface stabilizing layer 5.

The polycrystalline silicon layer 3 containing oxygen has an oxygen content of 14 to
35 atomic %, especially 20 atomic %, and both of these layers 3 and 4 can be formed by the so-called C, V, D method.

Next, an etching mask 6 is formed on the 8102 layer 4 except for the portion to be etched away, for example, the portion where a window is to be opened for electrode extraction.

As this mask 6, a photoresist layer (for example, KPR) is used.
A pure polycrystalline silicon layer or a polycrystalline silicon layer containing 10 atomic % or less of oxygen can be used.

Thereafter, the surface stabilizing layer 5 in the portions of the mask 6 which are not covered is selectively etched and removed using the above-mentioned etching solution according to the present invention.

In this way, only the 8102 layer 4 and the polycrystalline silicon layer 3 containing oxygen are etched, and the silicon of the substrate 1 is not etched, so that the surface of the substrate 1 is not roughened and accurate selective etching can be performed (FIG. 2B). .

In this case, according to the above table [1] and (n), the SiO□ layer 4
etching rate (2oooA10) and etching rate of polycrystalline silicon layer 3 containing oxygen (2640jv15+
) are approximately the same, so they are etched at the same time using the same etching process.

FIG. 3 shows a case where the present invention is applied to selective etching of a surface stabilizing layer made of a polycrystalline silicon layer containing oxygen and a polycrystalline silicon layer containing nitrogen.

As shown in FIG. 3A, a polycrystalline silicon layer 3 containing oxygen and a polycrystalline silicon layer 7 containing nitrogen are deposited on a substrate 1 on which a PN junction has been formed, thereby forming a two-layer surface stabilizing layer 8. Form.

In this case, the oxygen-containing polycrystalline silicon layer 3 may have an oxygen content of 14 to 35 at%, particularly 20 at%, and the nitrogen-containing polycrystalline silicon layer 7 may have a nitrogen content of 10 at%. % or more, especially 40 atomic %, and can be formed by connecting growth using C, V, and D methods, respectively.

That is, for example, in the case of polycrystalline silicon layer 3 containing oxygen, the substrate temperature is 6506C, SiH4:50C, N20
:20cc15+, carrier gas N2: A mixed gas of 401/min was sent to grow polycrystalline silicon with an oxygen content of 20 at% by pyrolysis, and in the case of the polycrystalline silicon layer 7 containing nitrogen, the substrate temperature was similarly adjusted to 650 %. ℃, S t H
4: A mixed gas of NH3:200CC4 and carrier gas N2:4A/6 is fed to grow a polycrystalline silicon layer 7 having a nitrogen content of 40 atom % by thermal decomposition.

Next, an etching mask 6 similar to that shown in FIG. 2 is selectively applied on the polycrystalline silicon layer γ containing nitrogen, and the surface stabilizing layer 8 is selectively etched using the above-mentioned etching solution according to the present invention. Figure B).

In this way, although the polycrystalline silicon layer 3 containing oxygen and the polycrystalline silicon layer 7 containing nitrogen are etched, the silicon of the substrate is not etched, so that good selective etching can be performed.

In this case, since the etching rate of the lower polycrystalline silicon layer 3 containing oxygen is higher than that of the upper polycrystalline silicon layer 7 containing nitrogen, side etching of the polycrystalline silicon layer 7 containing nitrogen is reduced and a clean window pattern is obtained. Selective etching is possible.

FIG. 4 shows a case where the present invention is applied to selective etching of a surface stabilizing layer consisting of a SiO2 layer and a polycrystalline silicon layer containing nitrogen or a 5t3N4 layer.

That is, as shown in FIG. 4A, an 8102 layer 4 and a polycrystalline silicon layer containing 10 atomic percent or more of nitrogen or an S + 3N4 layer 7' are deposited on the substrate 1 on which the PN junction J is formed to stabilize the surface. A coating layer 9 is formed.

Then, after depositing an etching mask layer 6 similar to that shown in FIG. 2 on layer 7', selective etching of surface stabilizing layer 9 is carried out using the etching solution according to the invention described above (FIG. 4B).

Even in such a case, good selective etching can be performed on the layer 9 as in the upper side.

In this case, since the force of the lower 8102 layer 4 has a faster etching speed than the upper layer 7', side etching of the layer 7' is less and a clean window can be formed.

Note that hot phosphoric acid has conventionally been used as an etching solution for Si3N4 (the etching rate at this time is 100A/
6) However, when hot phosphoric acid is used, a photoresist layer generally used as an etching mask cannot be used.

However, with the etching solution of the present invention described above, the Si3N4 layer can be etched at room temperature at a rate comparable to that of hot phosphoric acid (100
Since etching can be performed at a rate (A/min), the photoresist can be advantageously used as an etching mask.

As described above, according to the present invention, selective etching of an oxygen-containing polycrystalline silicon layer or a nitrogen-containing polycrystalline silicon layer, which has excellent properties as a surface stabilizing layer or an optical coating layer of a semiconductor device, can be performed on the surface of a semiconductor substrate. Etching can be performed cleanly and accurately without roughening, and selective etching of Si3N4 can also be performed at room temperature, making it suitable for use in manufacturing various semiconductor devices.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the characteristics of an etching solution according to the present invention, and FIGS. 2 to 4 are sectional views showing embodiments of the present invention. 1 is a semiconductor substrate of a first conductivity type, 2 is a semiconductor region of a second conductivity type, 3 is an S102 layer, 4 is a polycrystalline silicon layer containing oxygen, 6 is an etching mask, and 7 is a polycrystalline silicon layer containing nitrogen. It is.

Claims (1)

[Claims] 1. Forming a silicon layer containing more than 10 atomic % of oxygen on a semiconductor substrate, using a mixture of hydrogen peroxide, hydrofluoric acid, and a salt or base, and having a pH of 3.5 to 5.5. , the ratio of hydrogen peroxide and hydrofluoric acid is 3≦H2O2/HF≦20
A thin layer etching method on a semiconductor substrate, characterized in that the layer is etched with an etching solution.