JPH0574732A - Formation method of contact hole - Google Patents

Abstract

PURPOSE:To provide a formation method of a contact hole having the least dispersion in the hole sectional shape capable of properly corresponding to various individual hole sectional shapes. CONSTITUTION:A semiconductor substrate 1 provided with an insulating film 2 on the surface thereof and a mask 3 having windows 3a in the contact hole formation positions on the insulating film 2 is prepared. In order to make the contact holes in this semiconductor substrate 1, this insulating film 2 is laminated of two oxide films 2a, 2b in different etching rates so that the oxide film 2a of lower etching rate may be located in the lower side (nearer to the substrate 1) to be anisotropically or isotropically etched away. Through these procedures, the through-holes piercing both oxide films 2b, 2a making the hole diameter of the upper oxide film layer 2b wider than that of the lower side film layer 2a are to be made as the contact holes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a contact hole for contacting an electrode with an insulating film on the surface of a semiconductor substrate.

[0002]

2. Description of the Related Art When a semiconductor element is formed on a semiconductor substrate such as a silicon wafer, an insulating film is formed on the surface of the semiconductor substrate, and an aluminum electrode (wiring) is formed on the insulating film at a predetermined position. It penetrates through and is in contact.
Therefore, in the manufacturing process, there is a step of forming a contact hole for contacting the electrode at a predetermined position of the insulating film on the surface of the semiconductor substrate.

In the conventional contact hole forming process,
Specifically, as shown in FIG. 9, a mask 53 having a silicon oxide film (insulating film) 52 on its surface and having a window 53a at a contact hole formation position on the insulating film 52.
The semiconductor substrate 51 having the above is prepared, and the semiconductor substrate 51 is etched to remove the insulating film 52 at the window 53a and open the contact hole 55.

After forming the contact hole, an aluminum film is deposited by sputtering, and subsequently, a photoresist solution is applied and patterned to form a photoresist mask of an electrode (wiring) pattern, and then an etching treatment is performed. If the mask is removed by, the aluminum electrode 58 which is in contact with the surface of the semiconductor substrate 51 through the insulating film 52 is formed as shown in FIG.

However, as the size of the contact hole becomes smaller due to the miniaturization of the semiconductor element and the like, there arises a problem that the film thickness of the contact hole side wall portion 58a of the aluminum electrode 58 becomes thinner. Therefore, recently, in order to eliminate the insufficient thickness of the hole side wall portion 58a,
The contact hole is opened as follows. That is, as shown in FIG. 11, a semiconductor substrate 61 having a silicon oxide film (insulating film) 62 on its surface and a mask 63 having a window 63a at a contact hole formation position on the insulating film 62 is prepared. This semiconductor substrate 61 is subjected to an isotropic dry etching process or a wet etching process (for example, with a hydrofluoric acid-based solution) to form a window 63.
The insulating film 62 at a is partially removed, and then, as shown in FIG. 12, anisotropic etching (for example, reactive ion etching) is performed to remove the remaining portion, and the contact hole 65 is removed. Open the door.

Then, after forming the contact hole, an aluminum film is deposited by sputtering, and subsequently, a photoresist solution is applied and patterned to form a photoresist mask of an electrode (wiring) pattern, followed by etching treatment. When the mask is removed with, the aluminum electrode 68 that contacts the insulating film 62 is formed on the surface of the semiconductor substrate 61 as shown in FIG.
Since the contact hole 65 has a cup-like shape that opens to the outside, the contact hole side wall 68a of the aluminum electrode 68 has a sufficient film thickness, and the conventional problem of insufficient film thickness can be solved.

[0007]

However, in the case of the latter method of forming a contact hole, the hole cross-sectional shape varies widely and is not constant, the controllability of the hole cross-sectional shape is poor, and various hole cross-sectional shapes are not individually controlled. There is a problem that it is difficult to deal with. The reason why the hole cross-sectional shape greatly varies is that the depth K (shown in FIG. 11) dug by the first isotropic etching that partially removes the oxide film is not constant. The oxide film 62 has a considerable variation in the etching rate (etching rate), and this directly appears as a variation in the depth K. On the other hand, in the latter method of forming a contact hole,
The control element of the hole cross-sectional shape is, in effect, only the adjustment of the depth K depending on the length of the isotropic etching processing time. However, as described above, the depth K itself varies due to the variation in the etching rate of the oxide film 62. Since it is not constant throughout, the control of the hole cross-sectional shape is limited by the length of the processing time of isotropic etching, and it is not possible to individually cope with various hole cross-sectional shapes.

In view of the above circumstances, it is an object of the present invention to provide a method for forming a contact hole, which has a small variation in hole cross-sectional shape and can appropriately cope with various hole cross-sectional shapes.

[0009]

In order to solve the above problems, in the method of forming a contact hole of the present invention, a mask having a surface with an insulating film and having a window at a contact hole forming position is formed on the insulating film. When a semiconductor substrate to be provided is prepared, the semiconductor substrate is subjected to an etching treatment, the insulating film at the window is removed, and a contact hole is opened, the insulating film is oxidized by two oxides having different etching rates. An insulating film formed by laminating an oxide film having a slow etching rate on the side closer to the semiconductor substrate. By performing anisotropic etching and isotropic etching as the etching treatment, both oxides are formed. A through hole that penetrates through the film and has a larger hole diameter in the oxide film layer on the side far from the semiconductor substrate than in the oxide film layer on the side closer to the semiconductor substrate. And so as to form a contact hole.

Usually, as shown in FIG. 4, the upper and lower oxide films 2a and 2b are penetrated by anisotropic etching, and then, as shown in FIG. 5, isotropic etching is performed to the upper side (away from the semiconductor substrate). The hole diameter of the (side) oxide film 2b is made larger than the hole diameter of the lower (closer to the semiconductor substrate) oxide film 2a. To make a difference in etching rate between the upper and lower oxide films, for example, the lower (closer to the semiconductor substrate) oxide film is annealed after deposition, and the upper (farther from the semiconductor substrate) oxide film is lower after deposition. The annealing process may be performed at a temperature lower than the annealing temperature of the oxide film or the annealing process may not be performed.

Examples of the anisotropic etching treatment used in the present invention include reactive ion etching and the like, and examples of the isotropic etching treatment include wet etching using an aqueous solution of hydrofluoric acid and isotropic dry etching. It

[0012]

In the case of the present invention, the insulating film for contact hole formation has two oxide films having different etching rates (etching rates) as viewed from the semiconductor substrate, with the oxide film having a slower etching rate (slow etching rate) facing downward. It is an insulating film that is laminated so as to be bent. As a result, the depth L (shown in FIG. 5) of the portion where the hole diameter is widened becomes constant and becomes more stable than before. For example, as shown in Figure 4,
Through holes 4 are formed in both upper and lower oxide films 2a and 2b by anisotropic etching.
As shown in FIG. 5, when the hole diameter in the upper oxide film 2b is made wider than the hole diameter in the lower oxide film 2a by isotropic etching, the etching rate of the lower oxide film 2a is increased. Since the oxide film 2a is slow, the hole diameter hardly expands, and the portion with the large hole diameter is substantially only the upper oxide film 2b.
The depth L is always substantially equal to the thickness of the oxide film 2b. Therefore, if the thickness of the oxide film 2b is constant, the depth L is also constant. In fact, the thickness accuracy of the oxide film is good and the thickness is constant, and the depth L is constant. As a result of the depth L becoming constant in this way, variations in hole cross-sectional shape become smaller than in the conventional case.

In the case of the present invention, from the above description, if the thickness of the upper oxide film 2b is changed, the depth L is changed, and if the processing time of the isotropic etching is changed, the hole diameter of the upper oxide film 2b is increased. It can be seen that the depth L does not change so much and the thickness of the upper oxide film 2b and the processing time of the isotropic etching can be individually changed. On the other hand, the depth L and the spread of the hole diameter in the oxide film 2b are factors that determine the hole cross-sectional shape. Therefore, if the thickness L of the upper oxide film 2b is changed to adjust the depth L with high accuracy, or if the degree of expansion of the hole diameter in the upper oxide film 2b is adjusted by the processing time of isotropic etching, It is possible to control the hole cross-sectional shape. That is, in the present invention, various hole cross-sectional shapes can be appropriately dealt with individually.

[0014]

Embodiments of the present invention will be described below. First,
As shown in FIG. 1, the n-type impurity high concentration region 1 is formed on the surface portion.
p-type silicon semiconductor substrate (wafer) on which a is formed
900 is deposited on the surface of No. 1 by the CVD method.
The silicon oxide film 2a is formed by annealing at a temperature of .degree. C. (the lower side closer to the substrate 1). Then, as shown in FIG. 2, P is formed on the silicon oxide film 2a by the CVD method.
By depositing an SG (phosphorus glass) film (without annealing treatment) to form a laminated silicon oxide film 2b, an insulating film 2 composed of the silicon oxide films 2a and 2b is formed on the surface of the p-type silicon semiconductor substrate 1. It will be.

After forming the insulating film 2, as shown in FIG. 3, a mask solution 3 having a window 3a at a contact hole forming position is formed on the insulating film 2 by applying a photoresist solution and patterning. Thus, the semiconductor substrate 1 having the insulating film 2 on the surface and the mask 3 having the window 3a at the contact hole forming position on the insulating film 2 is prepared.

Subsequently, the semiconductor substrate 1 on which the mask 3 is formed
Then, anisotropic etching (for example, reactive ion etching) is performed to form a through hole 4 penetrating both upper and lower oxide films 2a and 2b as shown in FIG. Since the etching is anisotropic etching, the cross section of the through hole 4 has substantially the same shape as the window 3a. After forming the through hole 4 in the insulating film 2, wet etching is performed using a very thin hydrofluoric acid aqueous solution, and as shown in FIG. 5, the hole diameter in the upper oxide film 2b is changed to that in the lower oxide film 2a. Contact hole 6 if wider than hole diameter
Opens. At this time, the lower oxide film 2a is also slightly etched, but since the etching rate in the previous annealing process is very slow, the depth L (shown in FIG. 5) hardly changes, and the thickness of the oxide film 2b does not change. Is approximately equal to. The degree of enlargement of the hole diameter of the oxide film 2b is determined by the wet etching time.

After the contact hole 6 is formed, the mask 3 is removed, and the oxide film 2 is annealed at a temperature of about 900.degree.
After b is vitrified, an aluminum film is deposited by sputtering, and then a photoresist solution is applied and patterned to form a photoresist mask of an electrode (wiring) pattern, and then an etching process is performed to remove the mask. If removed, as shown in FIG. 6, an aluminum electrode 8 is formed on the surface of the semiconductor substrate 1 so as to penetrate the insulating film 2 and make contact therewith. Since the contact hole 6 has a cup-shaped shape that opens outward, the film thickness is sufficient even at the contact hole side wall portion 8a of the aluminum electrode 8.

The present invention is not limited to the above embodiment. For example, in the state of FIG. 3, isotropic etching is performed to open the upper oxide film 2b as shown in FIG.
As will be seen from the above, the lower oxide film 2a may be opened by anisotropic etching to form the contact hole 6 penetrating the insulating film 2. In order to make the depth L constant, the processing time of isotropic etching may be set long enough to surely open up to the bottom surface of the oxide film 2b. Oxide film 2
Although the isotropic etching may continue even after the opening to the bottom surface of b, the oxide film 2a has a low etching rate and is hardly opened even if the isotropic etching continues.
The depth L is constant, and variations in hole cross-sectional shape are reduced.

[0019]

As described above, in the method of forming a contact hole according to the present invention, since the depth of the portion having a wide hole diameter is constant, the variation in the sectional shape of the hole is smaller than before, and Since the hole cross-section shape can be accurately controlled by changing the thickness of the upper oxide film and adjusting the processing time of isotropic etching, it is possible to respond appropriately to various hole cross-section shapes. Useful for.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a first half of an insulating film forming step in an example.

FIG. 2 is a cross-sectional view showing the latter half of the insulating film forming step in the example.

FIG. 3 is a cross-sectional view showing a state of a mask forming process in an example.

FIG. 4 is a cross-sectional view showing the first half of the step of opening a contact hole in an example.

FIG. 5 is a cross-sectional view showing the latter half of the contact hole opening step in the example.

FIG. 6 is a cross-sectional view showing a state of an aluminum electrode forming step in the example.

FIG. 7 is a cross-sectional view showing the first half of the step of opening a contact hole in another example.

FIG. 8 is a cross-sectional view showing a latter half of a contact hole opening step in another example.

FIG. 9 is a cross-sectional view showing a state of a contact hole opening step in the conventional method.

FIG. 10 is a cross-sectional view showing a state of an aluminum electrode forming step in a conventional method.

FIG. 11 is a cross-sectional view showing a first half of a contact hole opening step in another conventional method.

FIG. 12 is a cross-sectional view showing a latter half of a contact hole opening step in another conventional method.

FIG. 13 is a cross-sectional view showing a state of an aluminum electrode forming step in another conventional method.

[Explanation of sign]

 1 semiconductor substrate 2 insulating film 2a oxide film 2b oxide film 3 mask 3a window 6 contact hole 8 aluminum electrode

Claims (3)

[Claims] 1. A semiconductor substrate having an insulating film on its surface and a mask having a window at a contact hole formation position on the insulating film is prepared, and the semiconductor substrate is subjected to etching treatment, In a method of forming a contact hole in which an insulating film at a window is removed and a contact hole is opened, the insulating film has two oxide films having different etching rates, and the oxide film having a slow etching rate is used as a semiconductor substrate. It is an insulating film that is laminated so as to come closer to the side, by performing anisotropic etching and isotropic etching as the etching treatment,
A through hole is formed as the contact hole, the through hole penetrating both the oxide films and having a hole diameter of the oxide film layer on the side far from the semiconductor substrate is larger than that of the oxide film layer on the side closer to the semiconductor substrate. Method of forming contact hole. 2. The upper and lower oxide films are penetrated by anisotropic etching, and then the isotropic etching is performed to change the hole diameter of the oxide film layer on the side far from the semiconductor substrate to the hole diameter of the oxide film layer on the side closer to the semiconductor substrate. The method of forming a contact hole according to claim 1, wherein the contact hole is wider than the contact hole. 3. An oxide film on the side closer to the semiconductor substrate is annealed after deposition, and an oxide film on the side farther from the semiconductor substrate is annealed after deposition at a temperature lower than the annealing temperature of the oxide film on the side closer to the semiconductor substrate below. 3. The method of forming a contact hole according to claim 1, wherein the upper and lower oxide films have a difference in etching rate depending on whether they are processed or not annealed.