JPH0936103A - Etching of semiconductor wafer and resist removing method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the speed of etching and removal of resist by a method wherein RF plasma is generated above a wafer, the free radical grown by microwave plasma is ionized, and ionized radical is generated by combining the above-mentioned treatments. SOLUTION: Gas is introduced from a gas source 5, a mirowave generator 7 is brought into an active state, and free radical high concentration reactive gas 9, which is discharged from a microwave plasma 8, is grown. The free radical in the reactive gas is ionized by generating RF plasma 14 in the reactive gas 9 grown by microwaves. Then, when the RF plasma 14 is started in the discharge gas, the ions generated as a result becomes CF4 having no discharge of microwaves, and the plasma 14 of oxygen gas is different from the CF4, having no discharge of microwaves, and the RF plasma 14 of oxygen gas together with the ions in the microwave discharge gas itself. The ashing speed of this plasma can be increased sharply when etching or resist removal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for processing a semiconductor wafer, and more particularly to a method and an apparatus for etching a semiconductor wafer and removing resist.

[0002]

In the processing of semiconductor wafers, it is often desirable to form a layer of semiconductor material in a desired pattern. To form the desired pattern, a layer is deposited on the surface of the wafer and then the desired pattern is coated with a resist, ie a material that is resistant to the etchant used. The wafer is then exposed to an etchant and the portions of the layer not covered by resist are etched away, leaving a layer of the desired pattern. The resist that has served the initial purpose is removed from the surface of the wafer by a resist removal process.

An apparatus that can be used for both etching deposited layers and removing resist is described in US Pat. No. 5,228,052, the teachings of which are incorporated herein by reference. The apparatus described in the above U.S. patent has a wafer processing chamber. In this processing chamber, the wafer is supported above the horizontal heating means by a lifting device,
This elevating device has a pin which passes through the heating means and extends upward through the opening in the substrate electrode. The wafer is lifted and lowered by a lifting device from a position in contact with the substrate electrode to a position 1 mm above the substrate electrode. The wafer can be raised to a higher position above the substrate electrode when loading or unloading it into the process chamber, but conventional equipment is designed to handle this higher position. Not not.

An introduction pipe extends into the processing chamber, and the processing gas is charged by the introduction pipe. The processing gas is typically at least oxygen (O2) gas, and N2 gas, H2
Gas or a forming gas such as N2 + H2 gas. Although not essential, CF4 may be contained in the processing gas. When the etching processing gas contains CF4, the gas contains low concentration oxygen and high concentration CF4.
And are included to mainly generate fluorine radicals or ions. For resist removal treatment, the gas contains a high concentration of oxygen and a low concentration of CF4 to mainly generate oxygen radicals or ions. These treatments can be carried out with O2 gas and N2 gas, H2 gas or N2 + H2 gas without CF4, but in this case, energy is replenished by heat from the heating means.

Prior art devices use a process gas for etching or resist removal in one of two ways. That is, (1) a reactive ion etching (RIE) method of ionizing a processing gas above the wafer, or (2)
This is a radical method in which radicals of a processing gas are discharged from a microwave plasma through an introduction tube. These processes etch the layers on the wafer and ash the resist. The rate of etching or resist removal is known as the ashing rate, which is typically measured in units of Å / min.

According to the RIE method, a plasma is generated by a radio frequency (RF) voltage source, and this plasma produces oxygen or fluorine ions above the wafer. The RF source is connected to a counter electrode and a substrate electrode (hot plate) installed above the wafer. As described in the above U.S. patents, the counter electrode and the substrate electrode act as double cathodes, facilitating the production of ions. These ions are attracted to the wafer, etching the layer and removing the resist.

In the radical method, a microwave generation source connected to an introduction pipe is operated to generate a microwave plasma which produces oxygen or fluorine radicals, and the oxygen or fluorine radicals are discharged from the plasma into the processing chamber. I will let you. These radicals react with the resist or other layers and decompose them into other gases, which are then exhausted through an exhaust connected to a vacuum pump. The vacuum pump also lowers the atmospheric pressure in the processing chamber,
Typically kept at about 50-500 mT (millitorr).
This process may or may not require supplementation of heat by the heating means (hot plate) depending on the process gas used.

In these two methods, either one of them or both of them can be continuously performed, but since the high frequency source and the microwave source are interlocked. , Only one of the two methods can be operated at a time. When these methods are continuously applied to resist removal processing, RI is generally used.
Method E is performed first. The wafer is placed at a high position above the hot plate, and the processing gas is introduced through the introduction pipe. Ions having energy for etching or resist removal are generated from the RF plasma generated above the wafer. This RIE method is particularly useful for removing the hardened portion of the resist.

If RF plasma is used, RF
Turn off the source. At this time, if CF4 is not used, the wafer is lowered to the heated hot plate to supply heat, but if CF4 is used, the wafer can be held at a position 1 mm higher. The description here is given assuming that CF4 is used. Introduce processing gas,
Plasma is generated in the introduction tube by the microwave generation source. This plasma produces radicals of oxygen and fluorine, which are discharged downstream from the microwave source. The resist is typically composed of CxHyNz, which reacts with fluorine radicals to generate HF.
To form This reaction releases energy,
This energy is generated by oxygen radicals
Helps decompose into NO2 and H2O. Fluorine thus acts as a catalyst. The gas generated by this decomposition reaction is discharged to the outside of the processing chamber through the exhaust pipe.

[0010]

In an etching process using only radicals, the etching occurs isotropically, that is, at the same rate in all directions. However, it is often desired to form an anisotropic wall slope, that is, to form a steeply sloped wall surface by etching the wafer larger in the depth direction and smaller in the lateral direction. Such anisotropy can be achieved in an anisotropic etching system that controls the slope of the corroded wall by using very low pressure (about 1-10 mT) and a strong etchant. Due to the strongly corrosive nature of the etchant, a typical anisotropic etching system does not require a high degree of anisotropy as the components are composed of corrosion resistant materials, which makes the system expensive. Not economical for processing. RI in the above device
Although some degree of anisotropy can be achieved by using the E plasma method, since the RIE method can be performed only at a position 1 mm above the hot plate, the user can almost control the degree of anisotropy. Can not.

One of the objects of the present invention is to provide a method and apparatus for improving the rate of etching and resist removal.

Another object of the present invention is to provide a method and apparatus that gives the user more freedom in processing wafers.

[0013]

According to the present invention, microwave plasma is activated to discharge a gas having free radicals. At the same time, RF plasma is generated above the wafer to ionize the free radicals generated by the microwave plasma. By combining these processes to generate ionized radicals, the plasma can ash the resist or layers on the wafer much faster than if these processes were performed individually.

The present invention also includes an elevating device for setting a wafer having a motor driven by a controller, the wafer typically having a plurality of different processing positions, represented in height from a hot plate. Installed in one of the The controller is programmable so that different positions can be set and later changed if desired. Since processing can be performed at various processing positions, the processing temperature can be changed at each step or between steps, and etching can be performed by changing the degree of anisotropy by controlling the electric field of ions. These different processing locations can be used with the combined processing described above to quickly ash resist or other layers.

Other objects, features and advantages will be apparent from the following detailed description, drawings and claims.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a semiconductor wafer 1 to be processed is placed in a sealed processing chamber 2 above a horizontally arranged hot plate 3. Wafer 1
The plate (which is typically a flat disc with a diameter of 4 to 8 inches) is mounted horizontally on a support pin 4 extending through the opening formed in the hot plate 3 in the thickness direction. Has been done. Therefore, the wafer 1 and the hot plate 3 are
It exists in planes parallel to each other.

The processing gas is introduced into the processing chamber 2 from the gas source 5 via the introduction pipe 6. The microwave plasma 8 is formed in the introduction tube by the microwave generation source 7 installed in the introduction tube 6, and thus the reactive gas 9 containing a high concentration of active free radicals is discharged. The reactive gas 9 is attached above the wafer and has an opening (not shown) provided in the counter electrode 10 having the structure described in the above-mentioned US patent.
Pass through. Under appropriate conditions, these active free radicals decompose and vaporize the resist film by gasifying the resist on the wafer 1. The vacuum system 11 evacuates these gases through the exhaust pipe 12 and maintains the pressure in the processing chamber on the order of 50 to 500 mT.

The radio frequency (RF) source 13 is the counter electrode 10.
Are electrically coupled to the hot plate 3 and thus the hot plate acts as a substrate electrode. Both electrodes 10
And 3 thus form a double cathode. A high frequency (RF) plasma 14 is generated above the wafer 1 by the high frequency voltage from the RF generation source 13. RF plasma 1
4 generates reactive ions, which ash the resist and remove it from the wafer 1.

The transparent cover 15 and the end point detector 16 are used to detect the start point and the end point of the ashing by the RF plasma. The end point detector 16 is composed of a filter and an optical detector, and detects photons emitted into the RF plasma when the OH radical is excited to become water.

According to the present invention, the gas is introduced from the gas source 5 and the microwave generation source 7 is activated to generate the reactive gas 9 containing a high concentration of free radicals discharged from the microwave plasma. To do. RF plasma is generated in the reactive gas 9 generated by the microwave to ionize the free radicals therein. For example,
When CF4 and oxygen are contained in the processing gas from the gas source 5, the discharged gas from the microwave plasma contains fluorine and oxygen radicals at high concentrations in the gas above the wafer. To do. If an RF plasma is then started in this discharge gas, the resulting ions are different from the ions in the microwave discharge gas itself, and from the RF plasma of CF4 and oxygen gas without microwave discharge. This heterogeneous plasma has been found to significantly increase the ashing rate in both etching and resist removal.

In one experiment, the resist-coated wafer was raised to a high position above the hot plate. The process gas introduced contained a generally known combination of gases such as oxygen, CF4, H2, N2 and H2 + N2. When only radicals generated by microwaves were used, the ashing rate was 18,000 Å / min, and when only the RIE method using RF plasma was used, the ashing rate was 14,000 Å / min. However, as mentioned above, when these two methods are performed simultaneously,
An ashing rate of 8000Å / min was measured. Experience has shown that ashing rates of this order cannot be achieved with either type of equipment in this type of equipment, regardless of the hot plate temperature or power level of each plasma. . Such ashing rates were already highly seasoned with highly reactive free radicals discharged from the microwave plasma.
(seasoned) Obtained only in the combined process of generating plasma in mixed gas. By combining both of these processing methods in one processing chamber to improve the ashing rate, the total processing time for ashing is reduced. In another experiment, heavily ion-implanted photoresist cross-linked by UV treatment was set on a hot plate for etching. Radical method and RIE
When the etching is performed in combination with the method, the total processing time is 30 compared with the two-step method in which the radical method is performed after the RIE method.
%Diminished.

Heat, fluorine and R in the ashing process
The reduction of the ashing time is important because any electric field generated by the F plasma has a risk of damaging the electric components to be manufactured. Reducing ashing time can reduce these risks. Further, the throughput can be increased and the manufacturing cost can be greatly reduced.

The apparatus of the present invention is further provided with a mechanism 17 capable of changing the relative position of the wafer 1 with respect to the hot plate and the counter electrode 10. These positions are typically represented as a number of processing positions having different heights from the hot plate 3. This mechanism has a motor 19 for vertically moving the rod 18 vertically by a gear (not shown).
8 is connected to the pin 4 by a horizontal base 20. This mechanism 17 is controlled by a controller 21, which regulates the height from the hot plate and presets it. These preset positions can be further reset by the user with this controller to define and preset new positions. In one embodiment, the wafer can be set on the hot plate itself as well as 1 mm, 2 mm, 3 mm, 5 mm, 7 mm and 13 mm above the hot plate. Processing can be performed at any of these locations. The variable height of the processing position in this way gives the user greater freedom in various aspects of the processing operation.

By adjusting the height of the pin, a degree of freedom can be obtained in controlling the inclination of the wall of the etching layer. FIG.
A description will be given below with reference to (a) and 2 (b). According to FIG. 2 (a), which shows an example of isotropic etching, the wafer has a patterned layer 32 formed on a substrate 31 and a resist 33 formed on the layer 32. The resist is provided with an opening 34, from which an etching agent is supplied. As shown, the etching occurs omnidirectionally, so that by the time the etching reaches the thickness of layer 32, overhangs 35 have occurred.

The apparatus of the present invention can independently control all the important parameters for controlling etching. The number of active free radicals in the gas mixture is controlled by the microwave source and the resulting downstream discharge, and the proportion of ions in the plasma is controlled by the power level of the RF plasma. Also, and most importantly, the control of the energy of the ions depends on the position of the wafer above the hot plate in the plasma:
This is done by controlling the electric field of the ions.

Referring to FIG. 2 (b) showing an example of anisotropic etching, when the apparatus is used for etching to activate the RF plasma, by controlling the electric field that directs the ions to the wafer surface, A steep slope can be formed. The energy of these ions and the proportion of ions in the reactive mixed gas are the layers 3 formed on the substrate 31.
6 determines the degree of anisotropy of the sidewalls 37 caused by the etching process (with the resist 33 on it). With such a system, the inclination is 70 ° -80
A side wall of ° can be achieved.

The ion energy is highest when the wafer is placed on the hot plate surface and decreases when the wafer is placed above the hot plate. Such a relationship between the height of the wafer from the hot plate and the ion energy is shown by a curve in FIG. The figure shows the sputter etch rate of silicon dioxide from the wafer surface as a function of wafer height from the hot plate. The sputter etch rate, measured directly from the ion bombardment energy, drops rapidly as the wafer is lifted. However, there are inherent challenges in this relationship. Heat and high energy can impair the electrical components being manufactured, but at the same time they contribute to the acceleration of the ashing process,
The process time is reduced and some of the risk of damage is reduced.

Etching can be controlled so as to give a desired degree of anisotropy by using a microwave generation source and an RF generation source together and by adjusting the height of the wafer by a pin elevating mechanism. Furthermore, the height of the wafer and thus the electric field can be varied during one process step or during several subsequent process steps to adapt the layer walls to the desired shape.

The ability to adjust the height of the wafer over a range of positions gives the user more freedom in adjusting the temperature of the wafer. Such temperature control can be important because higher temperatures increase the risk of electrical damage to the circuitry formed on the wafer.
Due to the low pressure in the process chamber, heat is generally transferred from the hot plate to the wafer by radiation, rather than by heat transfer by conduction or convection. As a result, the closeness of the wafer and the hot plate is extremely important for temperature determination.

By holding the wafer at a high position above the hot plate, ashing can be performed at a relatively low temperature by the RIE method. Hot plate temperature is 260 ℃
Then, the temperature of the wafer is kept low for a long time. 1
The temperature versus time curve is shown in FIG. 4 for an 8 inch wafer placed 1 mm above a 260 ° C. hot plate in a 00 mT process chamber. As shown in this figure, the temperature is kept below 120 ° C. for over 60 seconds, which is believed to be a fairly low temperature in typical semiconductor wafer processing.

Therefore, the temperature of the wafer can be changed by moving the wafer between each processing position. After the desired amount of resist has been removed, the process temperature can be changed from low to high by dropping the wafer close to or on the hot plate, and rapidly increasing the temperature of the wafer. For highly ion-implanted photoresists, it is desirable to ash away the top surface at a low temperature before the wafer is heated, so the above method of etching down the wafer to lower the wafer is such a method. Is especially useful for the removal of

Alternatively, it is desirable to use the RIE method at a low position as the first step to ash away the hardened resist with ions. Then, as the second step,
Raise the wafer to a higher position further away from the hot plate and use the radical / RIE merge method for a short period of time.
For example, high speed ashing is performed for 10 seconds.

Rapid cooling of a heated wafer on a hot plate is generally difficult because the pressure in the process chamber is low and the heat transfer from the wafer is very slow. To proceed with wafer cooling, the wafer is raised, removed from the hot plate, and helium is introduced into the process chamber for about 15 seconds. Since helium conducts heat from the wafer, it rapidly reduces the heat, for example from 260 ° C to 180 ° C.

Since the processing can be performed at a position relatively distant from the hot plate (for example, 5 mm or more as compared with 1 mm), the degree of freedom in processing the rear surface of the wafer can be obtained. At locations further away from the hot plate, simultaneous processing of the front and back surfaces of the wafer becomes easier. Such double-sided treatment can be used for both the etching and resist removal steps. When the wafer is very close to the counter electrode,
Processing can be performed primarily on the backside of the wafer.

While we have described specific embodiments of the present invention, it will be apparent that modifications can be made without departing from the scope of the appended claims. For example, although some gases have been mentioned that can be used for etching or resist removal, other gases can be used. In the above description, the substrate electrode is also a hot plate, but this hot plate is
It can be omitted when using some other heat source such as an ion lamp. In this case, the substrate electrode does not have to be a hot plate.

[Brief description of drawings]

FIG. 1 is a cutaway side view of a semiconductor wafer processing apparatus according to the present invention.

FIG. 2A is a sectional view of the wafer showing the case of isotropic etching. FIG. 2B is a sectional view of the wafer showing the case of anisotropic etching.

FIG. 3 is a graph showing the relationship between the electric field and the distance from the hot plate.

FIG. 4 is a graph showing the relationship between the wafer temperature and the time at a certain distance from the hot plate and a certain pressure.

[Explanation of symbols]

 1 Semiconductor Wafer 2 Processing Chamber 3 Hot Plate (Substrate Electrode) 4 Support Pin 6 Introduction Tube 7 Microwave Source 8 Microwave Plasma 9 Reactive Gas 10 Counter Electrode 13 Radio Frequency (RF) Source 14 Radio Frequency (RF) Plasma 17 Relative Mechanism for changing position 19 Motor 21 Controller 31 Substrate 32 Patterned layer 33 Resist 34 Opening 35 Overhang 36 Etching layer 37 Sidewall

Claims (13)

[Claims] 1. A method of treating a semiconductor wafer having a layer formed on a substrate and a resist formed on this layer, comprising: (a) using a microwave source to generate a large number of free radicals. Generating microwave containing discharge gas, (b) supplying the microwave discharge gas above the semiconductor wafer, and (c) generating plasma of microwave discharge gas above the semiconductor wafer. Generating ions and ashing one of the resist and one of the layers to remove from the semiconductor wafer, using at least one electrode to generate the plasma, and in the step (c), A method of processing a semiconductor wafer, including the step of changing the action of an electric field on ions by varying the distance to the semiconductor wafer. 2. The method for processing a semiconductor wafer according to claim 1, wherein in the step (a), the microwave discharge gas contains oxygen radicals. 3. The method of processing a semiconductor wafer according to claim 1, wherein in the step (a), the microwave discharge gas contains fluorine radicals. 4. A method for treating a semiconductor wafer having a layer formed on a substrate and a resist formed on the layer, comprising: (a) using a microwave source to generate a large number of free radicals. Generating microwave containing discharge gas, (b) supplying the microwave discharge gas above the semiconductor wafer, and (c) generating plasma of microwave discharge gas above the semiconductor wafer. Generating ions and ashing one of the resist and one of the layers from the semiconductor wafer, using at least one electrode to generate the plasma, and prior to step (a), in etching. Setting the semiconductor wafer in one of a plurality of relative positions with respect to the electrodes to obtain a desired degree of anisotropy. Semiconductor wafer processing method. 5. The method according to claim 4, further comprising moving the semiconductor wafer to another position of the plurality of relative positions, and repeating the steps (a) to (c). A method for processing a semiconductor wafer as described. 6. An apparatus for processing a semiconductor wafer having a layer formed on a substrate and a resist formed on the layer, the processing chamber containing a semiconductor wafer to be processed. A means for supporting a semiconductor wafer in the processing chamber, a first means for generating a discharge gas having a large number of free radicals and supplying the discharge gas into the processing chamber, and Plasma is generated above the semiconductor wafer to ionize the large number of free radicals, and second means for ashing one of the layer and the resist to remove from the semiconductor wafer is provided. The two means can be performed at the same time, the second means includes a generally horizontally arranged electrode and a supporting means for horizontally supporting the semiconductor wafer, and further,
A semiconductor wafer processing apparatus comprising means for moving a semiconductor wafer between a plurality of positions separated from the electrodes. 7. The semiconductor wafer processing apparatus according to claim 6, wherein the moving means can be adjusted so that the plurality of positions can be defined in a certain numerical value or can be redefined in another numerical value. 8. The plurality of locations are about 1 m from the electrodes.
7. The semiconductor wafer processing apparatus according to claim 6, wherein the semiconductor wafer processing apparatus is separated by a distance ranging from m to about 13 mm. 9. An apparatus for processing a semiconductor wafer, comprising a processing chamber accommodating a semiconductor wafer to be processed, an introduction pipe for introducing a reactive gas into the processing chamber, and a horizontal electrode arranged in the processing chamber. Means for generating a plasma of the gas above the semiconductor wafer, and supporting the wafer, and processing the wafer from an initial position on the horizontal electrode above the horizontal electrode. 1. A semiconductor wafer processing apparatus having a wafer supporting mechanism for raising to one of a plurality of positions that can be performed. 10. The wafer support mechanism has pins extending through the electrodes.
The semiconductor wafer processing apparatus described. 11. The semiconductor wafer processing apparatus according to claim 9, wherein the electrode is also a hot plate. 12. The semiconductor wafer processing apparatus according to claim 9, wherein the wafer supporting mechanism has a motor and a controller. 13. The semiconductor wafer processing apparatus according to claim 12, wherein the controller is coupled to the motor so that the plurality of positions can be variably defined.