JPH0629262A - Plasma etching method - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce the size of the ion concentration sensor that uses an ion-sensitive transistor with a sensitive film at its gate, and to improve the stability of detection sensitivity. A p-channel transistor 21 having sensitive films 7 on the surfaces of n-type and p-type substrates 2 and 3, respectively.
And the n-channel transistor 22 and the gate electrode 30 common to both are formed in the semiconductor chip 10, the sensitive film 7 and the gate electrode 30 are brought into contact with the detection target 40 such as an electrolytic solution, and the polarity of the gate electrode 30 is positive or negative. The ion detection signal S1 by the transistors 21 and 22 with the gate voltage Vg switched to
The difference signal between S2 and S2 is taken out as the ion concentration signal So.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention etches a film to be etched such as a metal film or an insulating film covering a semiconductor wafer surface into a predetermined pattern in the atmosphere of plasma ionized with an etching gas using a photoresist film as a mask. The present invention relates to an etching method.

[0002]

2. Description of the Related Art As a wafer process for manufacturing a semiconductor device, particularly an integrated circuit device, a dry process is being advanced, and various insulating films, polycrystalline silicon films, metal films, etc. provided on the surface of a wafer are etched. In almost all cases, plasma etching has been adopted. As is well known, plasma etching is performed under a reduced pressure of etching gas,
Moreover, these target films are etched by plasma ionized under a high-frequency electric field, and a photoresist film formed by a photo process is generally used to specify the etching pattern.

As is well known, the procedure for plasma etching using a photoresist film as a mask will be briefly described with reference to FIG. Illustrated wafer
Reference numeral 10 is a very small part of the MOS integrated circuit device. For example, a gate oxide film 3 is provided in a region surrounded by the isolation insulating film 2 on the surface of the p-type semiconductor region 1, and a gate 4 of polycrystalline silicon is formed thereon. And the source layer 5 is used as a mask in the figure.
Is diffused as an n-type and an interlayer insulating film 6 is formed so as to cover it. The figure shows an etching process for the metal film 7 for aluminum wiring which is entirely deposited so as to manufacture the source layer 5 in the window opened in the interlayer insulating film 6, and the photoresist film 20 formed by the photo process is used as a mask. ,
For example, the metal film 7 is etched into a predetermined pattern, that is, a wiring pattern for the source layer 5 in the illustrated example, in plasma of chlorine-based etching gas containing carbon tetrachloride or the like.

Such plasma etching is, of course, performed on various target films in addition to the metal film 7.
Even in the case of (a), it is also used for patterning the polycrystalline silicon for the gate 4 and opening a window for the phosphosilicate glass film for the interlayer insulating film 6. At this time, the photoresist film is also used as a mask. The only difference is that a fluorine-based etching gas is used.

[0005]

Since the above plasma etching has a smaller side etching than chemical etching, the target film can be accurately etched according to the pattern specified by the photoresist film 20, and the etching rate is also high frequency power for plasma generation. It can be increased almost in proportion. However, for example, if the high frequency power is increased to increase the etching rate when the film thickness of the target film is large, the photoresist film 20 is abnormally worn by the high temperature plasma and the patterning becomes inaccurate, or the original etching is performed. There is a problem that even abnormal portions are locally abnormally etched.

This state is shown in FIG. 3 (b) of the wafer 10 in FIG. 3 (a).
The cross section corresponding to The photoresist film 20 is generally worn by the high temperature plasma from the surface, but abnormal wear 21 may occur in a part as shown in the figure. Therefore, even the metal film 7 thereunder receives the abnormal etching 7a. Even if the wire does not break, it may cause overheating or deterioration during long-term use. As a measure against such a problem, the wear of the photoresist film 20 is mainly caused by the high temperature of the plasma,
It has been previously known that cooling 10 is quite effective. However, if the wafer 10 is cooled as much as possible, a part of the metal film 7 that should be removed by etching will remain, resulting in a problem that etching residues 8 are likely to occur as shown in FIG. 3B. An object of the present invention is to solve the conventional problems and to obtain a plasma etching method capable of preventing abnormal etching and generation of etching residues.

[0007]

According to a first method of the present invention, a first step of etching a target film in a state where a wafer loaded on an electrode of a plasma etching apparatus is pressed against the electrode with a predetermined clamp pressure. And the second step of removing the etching residue by overetching with the clamping pressure weaker than in the first step, and in the second method of the present invention, the wafer loaded on the electrode is removed. The target film is etched into a predetermined pattern while the temperature of the clamp jig that is pressed from the peripheral edge toward the electrode is maintained at about the same temperature as the electrode, and the etching residue is removed by over-etching to achieve the above-mentioned purposes. To achieve.

The first method described above is suitable for increasing the plasma power to increase the etching rate, and it is particularly advantageous to enhance the cooling effect of the wafer in the first step. For this purpose, it is advantageous to cool the wafer with the electrodes or to supply a cooling gas between the wafer and the electrodes. In this first method, the clamp jig is pneumatically controlled in order to switch the clamp pressure for the wafer for each process or to control it in each process. The structure is simple and the operation is quick.
And the pressure control is accurate. In both of the first and second methods, it is preferable to use an annular clamp jig that holds the peripheral edge between the wafer and the electrode in order to apply the clamp pressure to the wafer. In the second method, in order to keep the temperature of the clamp jig at substantially the same temperature as the electrode, it is advantageous to provide a fluid path inside the electrode and the jig and allow the heat medium of the same temperature to flow in both paths. .

[0009]

While the wafer is heated by the high temperature plasma to increase its temperature during the high speed plasma etching, the first method of the present invention focuses on the fact that the wafer temperature can be adjusted by the clamping pressure for pressing the wafer against the electrodes. First
In the process, the wafer is cooled by the electrode under a predetermined clamp pressure to reduce the abrasion of the photoresist film to prevent the occurrence of abnormal etching, and in the second process, the clamp pressure is weakened to increase the wafer temperature. The residue of the target film that cannot be completely removed in one step is quickly removed by overetching, thereby preventing abnormal etching and generation of etching residue and solving the above-mentioned problems.

In the second step where the wafer temperature is high, the rate of wear of the photoresist film is naturally higher than in the first step, but since the etching residue is originally small in amount, the over-etching time required for its removal is smaller than that in the first step. It is slight, and there is almost no possibility of abnormal etching occurring within this short time. It is also possible to adjust the temperature of the wafer by the temperature of the electrodes, but the temperature change of the wafer is much quicker if it is adjusted by the clamp pressure, so the flow shifts from the first step to the second step without time. The work efficiency can be improved.

In the second method of the present invention, attention is paid to the fact that if the temperature distribution in the wafer surface is not uniform, in-plane variation easily occurs in the plasma etching rate of the target film and the removal rate of its residue due to overetching. The temperature of the clamp jig that pushes the edge from the peripheral edge to the electrode is kept at about the same temperature as the electrode as in the configuration of the previous section, and the temperature distribution in the wafer surface is made uniform, so that the target film due to the local progress of plasma etching. It is intended to prevent the etching residue from being left unremoved due to the local non-progress of abnormal etching and over-etching.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a structure example of a plasma etching apparatus and a clamp jig for a wafer suitable for carrying out the first method of the present invention, and FIG. 2 shows a structure example of a clamp jig suitable for carrying out the second method of the present invention. Show. Although the clamp pressure is pneumatically controlled in the illustrated embodiment, the present invention is not limited to this and can be implemented in various modes.

The plasma etching apparatus 30 shown in FIG.
A vacuum container composed of a container 31 and a container lid 32 is provided with a lower electrode 33 supporting the wafer 10 and a plate-shaped upper electrode 34 facing the lower electrode 33.
After the inside of the vacuum container is depressurized to vacuum V from the exhaust pipe 32a on the side, the etching gas EG is introduced from the air supply pipe 32a on the side of the container lid 32, and the support 34a of the upper electrode 34 supported on the container lid 32 via the insulation 32b. High frequency voltage from the power supply 35 connected to both electrodes
The etching gas EG is turned into plasma by being applied between 33 and 34. The wafer 10 is, for example, an opening / closing window on the container lid 31 side.
From 36, it is loaded on the lower electrode 33 by an automatic wafer loading / unloading machine or the like, or is taken out of the vacuum container. In the first method, since it is advantageous to place the wafer 10 so that strong cooling can be exerted, the lower electrode 33 is formed in a block shape as shown in the figure, and a fluid path for circulating a cooling medium whose constant temperature is controlled. 33a
It is good to set up. In order to make the cooling effect stronger, a gas supply port is opened in the center of the upper surface of the lower electrode 33, and an inert gas such as helium as a cooling medium is allowed to flow in small gaps with the lower surface of the wafer 10 little by little. You may

In the first method of the present invention, the cooling effect on the wafer 10 is adjusted by the clamp pressure. Therefore, in the illustrated embodiment, an annular clamp treatment for holding the peripheral portion of the wafer 10 with the lower electrode 33 is used. The pressure applied to the ingredient 40 is adjustable.
Therefore, the lower ends of the plurality of operation rods 41, which are guided by the lower electrode 33 and whose upper ends are fixed to the clamp jig 40, are fixed to the operation plate 42, and are vertically moved between the peripheral edge of the operation plate 42 and the base 31. An expandable and contractible cylindrical bellows 43 is provided, and a bellows 44 is also provided between the central portion and the lower electrode 33. Further, a connecting pipe 45 is provided at the center of the operation plate 42 and is connected via flexible pipes to valves 51 and 52 communicating with the pressure sources for the clamp pressures P1 and P2 and a valve 53 communicating with the atmosphere A. The space surrounded by bellows 43 and 44 is the operating rod 41
The pressure reducing chamber communicates with the vacuum container through a gap between the electrode 33 and the electrode 33, and the space inside the bellows 43 is a pressurizing chamber that applies a pressure to the clamp jig 40.

In such an operating mechanism shown in FIG. 1, the valve 51 and the valve 51 are used to operate the clamp jig 40 to the upper position shown by the thin line in the drawing.
Open valve 53 with 52 closed. Due to the atmospheric pressure P applied to the operation plate 42, air is pushed out of the pressurizing chamber in the bellows 44 into the atmosphere A through the valve 53, whereby the clamp jig 40 is moved to the operation plate 42.
Is operated upward through the operating rod 41, and stops at a position where the upper end of the thick portion of the operating rod 41 contacts the lower surface of the lower electrode 33. This operating speed is set by the throttle 53a attached to the valve 53. The loading / unloading of the wafer 10 is performed with the clamp jig 40 being operated to the upper position in this way.

In the first method of the present invention, the clamping pressure for the wafer 10 is switched in the first step and the second step.
After the wafer 10 is loaded on the lower electrode 33, the valve 51 is first opened to introduce the pressure P1 for the first step into the pressurizing chamber, and the clamp jig 40
Is operated downward at a speed set by the diaphragm 51a to press the wafer 10 against the lower electrode 33 by the suppression force of the pressure P1. To switch the clamping pressure for the second step, the valve 51 may be closed and the valve 52 may be opened to switch the pressure P1 to P2. The values of both pressures P1 and P2 are set according to the area ratio of the pressure reducing chamber and the pressure chamber on the operation plate 42 and the atmospheric pressure P based on the clamp pressures to be applied to the wafer 10 in the first and second steps, respectively. Although it is different from the actual suppression pressure on the wafer 10, they are referred to as clamping pressures for convenience.

When the metal film 7 of FIG. 3A is patterned by the first method using the photoresist film 20 as a mask, the wafer 10 is, for example, 5 kg / cm 2 in the first step.
^The photoresist film of the metal film 7 under the condition that the high-frequency power of the power supply 35 is strengthened within the limit that the surface temperature does not exceed, for example, 50 ° C. by pressing the lower electrode 33 with a strong clamping pressure P1 of ² to cool it strongly. A large area portion not covered with 20 is removed by high speed plasma etching. Although the etching residue 8 of FIG. 3 (b) described above may slightly remain after the first step,
Since the cooling effect on the wafer 10 under the strong clamping pressure P1 is strong, abnormal wear of the photoresist film 20 as in the conventional case 21
It is possible to almost completely prevent the occurrence of abnormal etching 7a of the metal film 7. When the etching of the metal film 7 is almost finished in this first step, the plasma emission peculiar to aluminum rapidly weakens in this example, so this is detected by an end point detector (not shown) and put into the next second step.

In the second step, the residue 8 of the metal film 7 is removed by overetching while the clamping pressure is lowered to a pressure P2 lower than P1, for example 3 Kg / cm ² . Since the cooling effect on the wafer 10 decreases when the suppression pressure is decreased, the temperature thereof usually rises rapidly above 100 ° C.
Is removed at high speed. The wear of the photoresist film 20 during the second step where the wafer temperature is high naturally increases more than that in the first step, but since the etching residue 8 is minute, its removal can be completed within a very short time, and abnormal etching 7a may occur during this time. Very few. The high frequency power in the second step is the same as that in the first step, or is slightly reduced if necessary. After completion of the second step, the valve 52 may be closed, the valve 53 may be opened, the clamp jig 40 may be operated to the upper position, and the wafer 10 may be taken out.

FIG. 2 shows a structure of a clamp jig 40 suitable for the second method of the present invention in a sectional view of an essential part corresponding to a part of FIG. The parts corresponding to those in FIG. 1 are designated by the same reference numerals. In the example of the figure, in order to control the clamp jig 40 to the same temperature as the lower electrode 33, an annular fluid passage 40a surrounding the wafer 10 is provided inside the clamp jig 40, and the temperature is the same when the fluid is supplied to the fluid passage 33a of the lower electrode 33. The heat medium HM is adapted to flow from the fluid passage 41a of the operation rod 41 formed in a hollow body with the upper end closed to the fluid passage 40a through the communication hole 40b.

In the second method, the temperature of the clamp jig 40 that holds the wafer 10 loaded on the lower electrode 33 from the periphery is controlled to be substantially the same as the temperature of the lower electrode 33.
After patterning the target film of 10 by plasma etching, the residue is removed by over etching. The structure of the plasma etching apparatus other than that shown in FIG. 2 may be the same as that of FIG. 1, but in the second method, it is not necessary to switch the clamping pressure, so the pressure P2 and the valve 52 in FIG. 1 can be omitted. The temperatures of the lower electrode 33 and the clamp jig 40 are set according to the type and film thickness of the target film, and of course heating or cooling may be performed. When the etching is promoted by heating, the temperature control speed can be increased by electric heating as well as by the heating medium described above. In this case, Fig. 3 (a)
It is preferable that the photoresist film 20 of 1 is attached to be thicker than in the case of the first method.

In the case of patterning the aluminum film containing silicon or copper as the metal film 7 of FIG. 3 (a) by the second method by the plasma etching method using the chlorine-based etching gas EG containing carbon tetrachloride or the like, To remove the residue sufficiently by over etching, lower electrode 33 and clamp jig
It is better to set the temperature of 40 to a higher temperature, but below 100 ℃, and from experience, 70-80 ℃ is the optimum temperature setting. If the temperature of the clamp jig 40 is not controlled as in the past, the wafer 10
Although the residue 8 of FIG. 3 (b) is likely to be generated in the peripheral portion of the wafer and it is difficult to remove it by overetching, the second method makes the temperature distribution in the surface of the wafer 10 uniform, so that after the plasma etching, The generation of the residue 8 is reduced, and the residue 8 can be almost completely removed by overetching in a short time, and the generation of the abnormal etching 7a of the target film 7 as shown in FIG.

In the second method, the temperature of the lower electrode 33 and the clamp jig 40 may be raised during over etching as compared with the plasma etching, and the clamping pressure may be slightly weakened as in the first method. You may Further, in the above embodiments of the first and second methods, the target film is a metal film for convenience, but in other cases, the etching gas, the clamp pressure, the temperature, the high frequency power, etc. are appropriately set according to the film type and the film thickness. Of course, the present invention can be applied by setting.

[0023]

As described above, in the first method of the present invention,
In the first step, the target film is patterned by plasma etching while suppressing the wafer loaded on the electrodes of the plasma etching apparatus toward the electrodes by a predetermined clamping pressure. In the second step, the clamping pressure is first By removing the residue of the target film by over-etching while weakening it from the process, the following effects can be achieved.

(A) In the first step, the wafer is pressed against the electrode with a strong clamping pressure to cool it strongly to keep the wafer temperature low during plasma etching, thereby reducing the wear of the photoresist film for patterning the target film. Can almost completely prevent the abnormal etching of the target film.
In the second step, the residue of the target film that could not be completely removed during the first step can be completely removed by overetching in a short time while the wafer temperature is slightly raised by the clamping pressure.
Since the risk of abnormal etching of the target film in the first step is small, the etching rate can be increased more than before by increasing the high frequency power for converting the etching gas into plasma.

According to the second method of the present invention, the target film is predetermined while the temperature of the clamp jig for suppressing the wafer loaded on the electrode from the peripheral portion of the wafer toward the electrode is maintained at substantially the same temperature as the electrode. By removing the etching residue of the target film by over-etching after plasma etching in the pattern of, the temperature distribution in the wafer surface is always made uniform.
(a) It is possible to prevent abnormal etching of the target film due to local progress of plasma etching, and (b) it is possible to reduce the possibility that the residue of the target film is locally removed even after overetching. As described above, both the first and second methods of the present invention effectively prevent the abnormal etching of the target film and the generation of residues, and the first method has the effect of improving the plasma etching rate. Effective to improve the production efficiency by applying it to plasma etching when patterning various insulating films, polycrystalline silicon films, metal films, etc. in the wafer process of circuit devices, reduce damage and improve manufacturing yield Can be played.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structural example of an etching apparatus and a wafer clamping jig suitable for plasma etching according to a first method of the present invention.

FIG. 2 is a sectional view of essential parts showing a structural example of a clamp jig suitable for plasma etching according to a second method of the present invention.

3A and 3B are cross-sectional views showing a MOS integrated circuit device as a target example of plasma etching. FIG. 3A shows a normal state after etching and FIG. 3B shows an abnormal state after etching by a conventional method. It is a partially expanded sectional view of each shown wafer.

[Explanation of symbols]

 7 Metal film as target film for etching 8 Etching residue of target film 10 Wafer 20 Photoresist film 30 Plasma etching device 33 Electrode or lower electrode on which wafer is loaded 40 Clamping jig 40a Clamping jig used in the second method Fluid path inside 41a Fluid path inside operating rod used in the second method EG Etching gas HM Heat medium used in the second method P1 Clamping pressure during the first step of the first method P2 Second of the first method Clamping pressure during the process

Claims (5)

[Claims] 1. A method for etching a target film covering a wafer surface in a predetermined pattern in an atmosphere of plasma ionized with an etching gas, using a photoresist film as a mask, wherein a wafer loaded on the electrode is used as an electrode. A first step of etching the target film with a predetermined clamp pressure being applied toward it, and a second step of removing the etching residue by over-etching with the clamp pressure weaker than in the first step
A plasma etching method comprising the steps of: 2. The plasma etching according to claim 1, wherein a clamping pressure is applied to the wafer by an annular clamping jig that holds the peripheral portion of the wafer between the electrode and the electrode. Method. 3. The plasma etching method according to claim 1, wherein the wafer is cooled during etching. 4. A method for etching a target film covering a wafer surface in a predetermined pattern in an atmosphere of plasma ionized with an etching gas using a photoresist film as a mask, wherein a wafer loaded on an electrode is provided with a peripheral portion. Plasma etching, characterized in that the target film is etched into a predetermined pattern while the temperature of the clamp jig that is pressed from the electrode toward the electrode is maintained at about the same temperature as the electrode, and the etching residue is removed by overetching. Method. 5. The plasma etching method according to claim 4, wherein a fluid path is provided inside the electrode and the clamp jig, and a heat medium having the same temperature is made to flow therethrough.