JP2003037099A - Method for etching - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for etching capable of executing uniform treatment of a surface of a substrate in which oxide films and films made of non- oxidized materials are mixed. SOLUTION: The method for etching comprises a step of etching a surface layer of the substrate 10 in which first layers 1, 6 and second layers 4, 5 constituted of non-oxidized materials are mixed. The method further comprises a step of first oxidizing of the surface of the substrate 10 to grow oxide films 4a, 5a on the exposed surfaces of the second layers 4, 5. The method also comprises a step of thereafter etching the surface layer of the substrate 10 so as to remove at least the films 4a, 5a. In this etching, an etching time is set so that film reducing amounts of the first layers 1, 6 become the same degree as those of the second layers 4, 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method, and particularly to a surface of a substrate exposed in a state where an oxide film and a non-oxide film made of a material that is not oxidized are mixed in a manufacturing process of a semiconductor device or the like. An etching method for evenly etching a layer.

[0002]

2. Description of the Related Art In the process of manufacturing a semiconductor device, various processes such as introduction of impurities using a resist pattern as a mask and pattern etching are repeatedly performed. In each of these steps, after the introduction of impurities, etching, and the like, the resist pattern used as the mask is peeled and removed, and subsequently the substrate surface is washed.

For example, in manufacturing a MOS transistor, as shown in FIG. 4A, a gate electrode 3 is formed on a semiconductor substrate 1 via a gate oxide film 2 made of silicon oxide.
To form a pattern. The gate electrode 3 is formed by sequentially stacking a polysilicon film 4 and a metal silicide film 5 such as tungsten silicide, and an offset oxide film 6 made of silicon oxide is stacked thereon. The gate electrode 3 having such a structure is formed by pattern etching the laminated film using the resist pattern formed on the offset oxide film 6 as a mask.

Therefore, after the pattern etching,
Stripping and removal of the resist pattern and subsequent cleaning treatment are performed. In this cleaning process, as shown in FIG. 4B, in order to reliably remove foreign matter on the exposed surface of the substrate 10, including the surface of the semiconductor substrate 1, the side wall of the gate electrode 3, and the surface of the offset insulating film 6. In addition, an etching process using a hydrofluoric acid-based solution as a cleaning solution is performed.

[0005]

However, in such an etching method (cleaning method), since the etching rate of each film with respect to the etching solution is different, each film cannot be uniformly etched. That is, when a hydrofluoric acid-based solution is used, the etching rates of the gate insulating film 2 made of silicon oxide and the offset insulating film 6 are the same as the etching rates of the polysilicon film 4 and the metal silicide film 5 forming the gate electrode 3. Therefore, the etching of the gate insulating film 2 and the offset insulating film 6 proceeds faster.

Therefore, it becomes difficult to keep the side wall extending from the offset oxide film 6 to the gate insulating film 2 in a vertical shape immediately after pattern etching. Since such a cleaning process (etching process) is performed every time a process using a new resist pattern as a mask, the uneven shape of the side wall is enlarged as the manufacturing process progresses.

Therefore, according to the present invention, it is possible to uniformly perform in-plane treatment on the surface of a substrate in which an oxide film and a non-oxidized film made of a non-oxidized material are mixed, and thereby the side wall shape is obtained. It is an object of the present invention to provide an etching method capable of maintaining the above.

[0008]

According to the present invention for achieving the above object, a first layer made of an oxide and a second layer made of a material which is not oxidized are mixed. In this method, the exposed surface layer of the substrate is etched. First, the surface of the substrate is oxidized to grow an oxide film on the exposed surface of the second layer.
The surface layer of the substrate is etched so that at least this oxide film is removed.

In such a method, the exposed surface layer of the second layer is converted into the second layer consisting of the oxide originally present on the substrate surface by the oxidation treatment of the substrate surface performed prior to the etching treatment. It changes into an oxide film which is a close property. Therefore, the etching rate of the exposed surface layer (that is, the oxide film) of the second layer shifts so as to approach the etching rate of the second layer with respect to the etching rate of the first layer. Therefore, as compared with the case where the etching process is performed in a state where the first layer and the second layer are exposed as they are, the reduction amount of the first layer and the reduction amount of the second layer including the oxide film are reduced. Etching treatment is performed with the same amount as the amount.

During the etching process, the first
By setting the etching time so that the amount of film loss of the second layer including the oxide film and the amount of film loss of the second layer including the oxide film are set to be approximately the same, a step difference is formed between the first layer and the second layer. An etched surface free from scratches is obtained.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIG.
It will be described in detail with reference to the sectional process drawing.

As shown in FIG. 1 (1), the substrate 10 to be etched is the same substrate 10 as described in the prior art with reference to FIG. 4 (1). Here, the gate electrode 4 is used. Taking as an example the etching for cleaning the surface of the substrate 10 after forming the pattern, a method of performing the etching without forming a step in the side wall shape will be described.

First, the structure of the substrate 10 will be described in detail.
The substrate 10 to be etched here has a gate electrode 3 provided on a semiconductor substrate 1 with a gate oxide film 2 made of silicon oxide interposed therebetween. The gate oxide film 2 is formed by thermal oxidation, for example. In addition, the gate electrode 3 is
A polysilicon film 4 and a metal silicide film 5 such as tungsten silicide are sequentially laminated, and an offset oxide film 6 made of silicon oxide is laminated on the upper portion. This offset oxide film 6 is formed by CVD (chemical vapor depo
sition) It should be made of silicon oxide obtained by film formation. In the substrate 10 having such a structure, the gate oxide film 2 and the offset oxide film 6 correspond to the first layer composed of the oxide shown in the claims, and the polysilicon film 4 and the metal silicide film 5 are Corresponds to the second layer composed of the non-oxidized material shown in the claims.

In the etching method for cleaning the surface of the substrate 10 having such a structure, first, as shown in FIG. 1 (2), the substrate 10 is subjected to an oxidation treatment so that the polysilicon film 4 and the metal film are removed. Oxide films 4a and 5a are grown on the exposed surface of the silicide film 5, respectively. On this occasion,
Wet oxidation treatment using an oxidizing solution such as ozone water or hydrogen peroxide water is performed, whereby the sidewalls of the polysilicon film 4 and the metal silicide film 5 have an oxide film 4a of a predetermined thickness,
Grow 5a. Here, the ozone water is ozone-dissolved water in which ozone gas is dissolved in pure water.
Further, in this oxidation treatment, the exposed surfaces of the polysilicon film 4 and the metal silicide film 5 are oxidized and the oxide films 4a, 5
It is assumed that an oxidizing solution is preferably used in which only a is formed and the gate oxide film 2 and the offset oxide film 6 are not etched.

Next, as shown in FIG. 1C, the oxide film 4 is formed.
The first stage etching is performed to the extent that a and 5a are removed. Here, wet etching is performed using a hydrofluoric acid-based etching solution, and the gate oxide film 2 and the offset oxide film 6 are also etched along with the oxide films 4a and 5a.

Here, as the hydrofluoric acid-based etching solution, the silicon oxide forming the gate oxide film 2 and the offset oxide film 6, and the oxide film 4a grown on the exposed surfaces of the polysilicon film 4 and the metal silicide film 5 are used. , 5a are used as chemical solutions having different etching rates. As such a hydrofluoric acid-based etching solution, for example, a hydrofluoric acid aqueous solution, an ammonium fluoride aqueous solution, a buffered hydrofluoric acid aqueous solution (a mixed solution aqueous solution of hydrofluoric acid and ammonium fluoride), a mixed solution of hydrofluoric acid and a surfactant is used. An aqueous solution, a mixed solution aqueous solution of hydrofluoric acid and hydrogen peroxide, and a mixed solution aqueous solution of hydrofluoric acid and hydrochloric acid are used.

In the etching using the hydrofluoric acid type etching solution, the etching rate of the oxide layer 5a of the metal silicide film 5 becomes faster than the etching rate of the gate oxide film 2 and the offset oxide film 6 made of silicon oxide. . Further, the etching rate of the oxide film 4a of the polysilicon film 4 shifts to the silicon oxide film side and becomes faster than the etching rate of the polysilicon film 4 itself.

Therefore, in the state where the oxide films 4a and 5a are removed, the amount of reduction of the metal silicide 5 is larger than that of the gate oxide film 2 and the offset oxide film 6. The amount of reduction of the polysilicon film 4 depends on the thickness of the oxide film 4a and the difference between the etching rate of the oxide film 4a and the etching rates of the gate oxide film 2 and the offset oxide film 6, but the polysilicon film Compared with the case where 4 is etched in the initial state, the amount of reduction of the gate oxide film 2 and the offset oxide film 6 becomes closer. The film reduction amount is the amount of change in the pattern shape of each film with respect to the film shape of the gate electrode 3 immediately after the pattern formation shown in FIG.

Here, in the gate electrode 3, since the pattern width of the metal silicide 5 is particularly related to the characteristics of the MOS transistor, there is a desire to make the pattern width of the metal silicide 5 equal to the pattern width of the gate oxide film 2. is there.

Therefore, as shown in FIG. 1D, the second stage etching is performed. Here, the etching using the hydrofluoric acid aqueous solution as an etching solution is performed in succession to the etching of the first stage, and the etching of the gate oxide film 2 and the offset oxide film 6 is advanced. At this time, the polysilicon film 4 and the metal silicide film 5 forming the gate electrode 3 are also etched, but their etching rates are slower than the etching rates of the gate oxide film 2 and the offset oxide film 6.

Therefore, the second-stage etching is
In order that the total amount of film reduction due to the etching in the step 2 and the step 2 in the step 2 may be substantially equal in the gate oxide film 2 and the offset oxide film 6, and in the polysilicon film 4 and the metal silicide film 5 (in particular, the metal silicide film 5), The etching time is set.

That is, the etching time in the etching that combines the first step and the second step is
Further, the film thickness reduction amounts of the offset oxide film 6 and the polysilicon film 4 and the metal silicide film 5 are finally set to be approximately the same.

Further, if the amount of etching required for cleaning is insufficient by the above etching alone, FIG.
And the oxidation treatment described with reference to FIG. 1 (3) and FIG.
By repeating the subsequent etching described using (4), the etching is advanced by a predetermined etching amount (film reduction amount).

Next, the details of the procedure for setting the etching time in which the etching in the first step and the etching in the second step are combined will be described with reference to the graph showing the relationship between the etching time and the etching amount in FIG.

Here, for simplification of description, the etching amount (film) of the two layers of the gate oxide film 2 made of the thermal oxide film described with reference to FIG. 1 and the non-metal silicide film (tungsten silicide film) 5 is described. The procedure for setting the etching time for the purpose of adjusting the amount of decrease) will be described. The setting of the etching time here means the setting of the total time of the etching process of the first stage and the second stage after the above-mentioned oxidation process.

First, the etching amount E1 in the etching process of the gate oxide film (in the graph) made of a silicon thermal oxide film is as follows: etching time is T, etching speed is a
When set to 1, it can be approximated by the following formula (1). E1 (T) = a1.times.T + b1 (1) Here, b1 is assumed to be a value generated due to a device error or the like in actual etching.

The etching amount E2 in the etching process of the oxide film (in the graph) grown on the exposed surface of the metal silicide film is expressed by the following formula (2) when the etching time is T and the etching rate is a2. Can be approximated. E2 (T) = a2 * T + b2 (2) Here, it is assumed that b2 is a value that occurs due to a device error or the like in actual etching.

The above equation (2) holds until the etching amount E2 reaches the film thickness D of the oxide film. Here, the formula (2)
The etching time _{Tox for which} is expressed by the following equation (3). E2 (T _ox ) = a2 × T _ox + b2 = D T _ox = (D−b2) / a2 (3) Here, the thickness D of the oxide film is the oxidation treatment condition (for example, concentration of the oxidizing solution, treatment time). It is a value determined by. still,
The etching at the etching time _Tox is the first described above.
Corresponds to staged etching.

Further, the etching amount E3 of the metal silicide film itself can be approximated by the following equation (4), where T is the etching time and a3 is the etching rate. E3 (T) = a3.times.T + b3 (4) Here, b3 is assumed to be a value that is generated due to a device error or the like in actual etching.

However, this equation (4) is established after the etching amount E2 of the equation (2) reaches the film thickness D of the oxide film, that is, in the above-described second stage etching. Therefore, the etching amount E3 'as the metal silicide film including the etching amount of the oxide film is expressed by the following formula (5).
become that way.

The etching time Td at which the etching amount E3 'as the metal silicide film including the oxide film and the etching amount E1 of the gate oxide film become the same etching amount Ed is expressed by the above equation (1). ) And equation (5), the following equation (6) is calculated. Ed (Td) = E1 (Td) = E3 '(Td) a1 * Td + b1 = D + a3 * (Td-T _ox ) + b3 Td = {D-a3 * T _ox + b3-b1} / (a1-a3) ... (6) )

In the above equations, a1, b1, a
2, b2, a3, and b3 are constants determined by the type of film, the type of etching solution used, the concentration, the temperature, the apparatus used for etching, and the setting thereof, and generally a1 ≠ a
2 ≠ a3 and b1 ≠ b2 ≠ b3. Also, D
Is a constant controlled by the type, concentration, temperature and treatment time of the oxidizing solution used for the oxidizing treatment. These constants should be obtained for each film type to be subjected to the etching treatment, the oxidation treatment condition and the etching treatment condition.

Specifically, when the oxidizing treatment is carried out using ozone water having an ozone concentration of 20 ppm, the etching treatment is carried out using hydrofluoric acid having a concentration of 1% at 24 ° C. a1≈6 nm / mi
n, b1≈0, a2≈8.6 nm / min, b2≈0, a
3≈1.1 nm / min and b3≈0. Further, when the oxidation treatment is performed for 10 seconds using ozone water having an ozone concentration of 20 ppm at 23 ° C., D = 0.
77. Substituting these values into the equation (6), Td≈7.7 seconds is obtained.

That is, after this oxidation treatment, an etching treatment using hydrofluoric acid having a concentration of 1% at 24 ° C. as an etching solution is performed for 7.7 seconds, whereby the etching amount of the metal silicide film and the gate oxide film is increased. (The amount of film loss) can be adjusted.

In the graph of FIG. 2, a3 <a1
Although the case of <a2 is shown, as shown in the graph of FIG. 3, even when a2 <a1 <a3, an appropriate etching time can be calculated by the procedure described above.

Furthermore, when a1 = a2, that is, the etching rate a1 of the first layer made of an oxide material
And the etching rate 2a of the oxide film grown on the second layer made of the unoxidized material are almost equal to each other, the etching time for removing the oxide film is calculated. Etching is performed. That is, in the process described with reference to FIG.
The etching is completed only by the first-stage etching. This makes it possible to equalize the amount of film loss of the first layer and the amount of film loss of the second layer.

Further, in the above description, in order to simplify the explanation, the gate oxide film (silicon oxide film by thermal oxidation) and the metal silicide film (tungsten silicide film) are used.
The etching time when the etching amounts of the layers were made uniform was calculated. However, in the substrate 10 described with reference to FIG. 1, the polysilicon film 4 can be considered like the metal silicide film 5, and the offset insulating film (CVD silicon oxide film) 6 is similar to the gate oxide film 2. Can be thought of. Therefore, the etching amounts of these films are almost the same as the etching amounts of the gate oxide film 2 and the metal silicide film 5.

That is, even when three or more different film types are mixed and exposed, these films and the oxide films grown on the surface layers of these films are etched by the same etching solution. The amount is expressed by the formula (1),
If the conditions (2) and (4) are satisfied, the etching amounts can be made uniform by the method described above. In this case, for the group of film species whose etching rate does not change in the etching process after the oxidation process, the etching amount may be approximated by the common formula (1). On the other hand, in the group of film species in which an oxide film grows on the exposed surface by the oxidation treatment, the etching amount may be approximated by the common equations (2) and (4).

As the film type in which the etching amount is approximated by the formula (1), in addition to the above-described silicon oxide film formed by thermal oxidation, a silicon oxide film formed by CVD, boron-containing silicon oxide (BSG), phosphorus-containing silicon oxide. (PS
G), boron-phosphorus-containing silicon oxide (BPSG) and the like can be exemplified. On the other hand, examples of the film type whose etching amount is approximated by the formulas (2) and (4) include titanium silicide, silicon nitride, silicon, and amorphous silicon in addition to the metal silicide (tungsten silicide) described above.

Further, in the above description, for example, the oxide film 4 on the exposed surface of the gate electrode 3 shown in FIG.
It was explained that the growth of a and 5a was not accompanied by volume expansion. However, when the growth of the oxide films 4a and 5a is accompanied by volume expansion, it is possible to finish the etching at the end of the first stage when the oxide films 4a and 5a are removed to make the film reduction amount uniform. In this case, considering the difference between the etching rate of the gate oxide film 2 and the offset oxide film 6 and the etching rate of the oxide films 4a and 5a of the polysilicon film 4 and the metal silicide film 5, the film thickness of the oxide films 4a and 5a is considered. By setting, when the oxide films 4a and 5a are removed (that is, at the time when the first-stage etching process is completed), the reduction amount of the gate oxide film 2 and the offset oxide film 6 and the polysilicon film 4 are set. And the amount of metal silicide film 5 reduced.

[0041]

As described above, according to the etching method of the present invention, an oxide film is grown on the surface layer of the material which is not oxidized by oxidizing the surface of the substrate, and then the substrate is etched. Even if the oxide surface and the surface made of non-oxidized material are mixed on the exposed surface by adopting the structure that performs the treatment, the etching rates of these surfaces are brought close to each other and the amount of film loss is about the same. The etching can be performed. Therefore, even when the oxide material and the non-oxidized material are mixed on the exposed surface, it is possible to perform etching while maintaining the pattern shape without causing a step.

[Brief description of drawings]

FIG. 1 is a cross-sectional process diagram showing an etching method of an embodiment.

FIG. 2 is a graph showing the relationship between the etching time and the etching amount of each film in the etching method of the embodiment.

FIG. 3 is a graph showing the relationship between the etching time and the etching amount of each film in the etching method of the embodiment.

FIG. 4 is a cross-sectional view for explaining a conventional etching method and its problems.

[Explanation of symbols]

2 ... Gate oxide film (first layer), 4 ... Polysilicon film (second layer), 5 ... Metal silicide film (second layer), 6
... Offset oxide film (first layer), 10 ... Substrate

Claims (5)

[Claims] 1. A method of etching a surface layer of a substrate, which is exposed in a state where a first layer made of an oxide and a second layer made of an unoxidized material are mixed. And oxidizing the surface of the substrate to grow an oxide film on the exposed surface of the second layer, and etching the surface layer of the substrate so that at least the oxide film is removed. An etching method comprising performing a processing step. 2. The etching method according to claim 1, wherein the etching time in the etching process is set so that the amount of film loss of the first layer and the amount of film loss of the second layer are substantially the same. An etching method comprising: 3. The etching method according to claim 1, wherein the step of growing the oxide film and the step of etching are continuously and repeatedly performed. 4. The etching method according to claim 1, wherein the oxidation treatment is performed by a wet treatment using an oxidizing solution, and the etching treatment is performed by a wet treatment using a hydrofluoric acid solution. Characteristic etching method. 5. The etching method according to claim 1, wherein the first layer is made of silicon oxide, and the second layer is made of a silicon-based material.