JPS6013072B2 - Plasma etching end point control method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to endpoint control in plasma etching.

More particularly, it relates to endpoint control by detecting substantial changes in the intensity of optical emissions from the plasma. In plasma etching, there is usually considerable variation in the etching sequence due to various reasons such as starting temperature, plasma conditions, and changes in the etch area.

To this end, it is important to ensure that the etch ends at the correct time (i.e. end point) for optimal etching, i.e. the layer to be etched is removed but the pattern within the layer is not over-etched. And it is difficult to terminate when the underlying layers are not etched to a significant extent. The present invention provides precise endpoint control by detecting changes in the emission line as it reaches the underlying layer by changes in the material at that level.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. A typical plasma etching apparatus is illustrated in FIG.

Here, the reaction chamber is shown in cross-section perpendicular to its centerline. Suitable etching gas for plasma stripping of photoresist, typically CF
45% 02 or pure 02 in a cylindrical quartz reaction chamber 10
is introduced into the interior through the needle valve 12. Then, the reaction chamber 10 is maintained at pressure P by a vacuum pump 13 that evacuates the reaction chamber 10 through a throttle valve 14. The flow rate of the etching gas is set by adjusting the needle valve 12, and the flow rate of the etching gas is set by adjusting the needle valve 12.
5 to be accurately monitored. The pressure is independently controlled by the throttle valve 14.
and monitored by a precision pressure gauge 16. Flow rate is 5-500cc/min, pressure is 0.25-1.5
Torr is a typical example. Plasma is generated within the reactor by applying power from a high frequency power source 17 to a capacitor plate 18 arranged around the reaction chamber 10 . Power levels are typically between 10 and 500 watts. An impedance matched to the circuit of the radio frequency power supply 17 is used to optimize the power coupling into the plasma. The etch rate can be made more uniform and controlled in the following way. The method is to use a metal radio frequency shield 19, shown in dotted lines, which confines the plasma in an annular region outside the shield to reduce the temperature and non-uniformity of the workpiece 20, which is typically placed in a quartz holder. It works to reduce the amount of water. In a typical etching method, etching begins when the workpiece material is placed in a reaction chamber, the reaction chamber is evacuated, an etching gas is introduced, and the radio frequency power is turned on.

Reactor temperature increases during etching. And since the etching rate is highly temperature dependent, the etching thickness during a particular time depends sensitively on the temperature characteristics of the reactor and the processing material. In materials such as Si, poly-Si, Si3N4, and Ti, the etching rate is large and the area of the workpiece exposed to the etching gas, the separation of adjacent workpieces. , and also depends on the location and number of processed materials. The last dependence arises because there is competition among processing materials for the types of etching that are useful. Thereby, the etching rate decreases as the number of processed materials increases. The processed material in the center of the turret also etches slower than the edge wafers due to the lagoon effect. As a result of temperature dependence, the plasma conditions, workpiece placement, and times required to apply the same etch typically vary considerably. Therefore, it is necessary to monitor the progress of etching in order to properly complete the etching cycle. Over-etching will cause irreversible damage to the workpiece material. Therefore, endpoint monitoring or control methods are important and must be accurate. for example,
In the manufacture of semiconductor devices, plasma etching is generally applied to a photoresist-masked etch pattern in a thin layer on a slowly etching substrate. The substrate then partially acts as an etch stop. And over-etching is an undesirable etch under the mask edge (
(undercut) and excessive etching of the substrate layer. In some cases, the substrate layer is a thin layer overlying an underlying layer that is rapidly etched, and etch penetration into this underlying layer can cause irreparable damage. Although it is possible to monitor the etching by visually observing it, this is often difficult.

Although certain visual changes, such as changes in the color of an etched surface, are reliable, this is not always available and is highly dependent on the perceptual acuity of the observer. Constant observation by observers is also necessary. The present invention monitors optical emissions from a plasma.

It is possible to select emission lines that are sensitive to changes in the etched material. This indicates that at the end point etching has begun into the underlying layer. One type of apparatus for monitoring plasma emissions is illustrated in FIG. Optical emissions from the plasma at 21 (within reaction chamber 10) are observed by photodetector 22 through filter 23. The passage zone of filter 23 is selected to select the emission line. The intensity of the emission radiation is particularly sensitive to changes in the material being etched. The photodetector signal is constantly monitored on strip chart recorder 24. It can also be input to the comparator circuit 25. The comparator circuit 25 generates a trigger to cut off the etching cycle via an output to the high frequency power supply 17 through a connection terminal 26. A phototube with an electronic meter output amplifier can be used as a detector. but,
Solid state detectors are preferred. This is because they are smaller and cheaper. Monochromator (hro to mom)
Experiments using Mator) showed the following. The wafer is etched in CF402 to transform it from Si02 to S.
When changed to i, the wavelength line of about 0.7 Buddha changed greatly.

Si02 wafers are removed or many Si02
Or when a Si03N4 wafer is inserted, the signal amplitude of this emission line remains unchanged. Adding a Si wafer greatly reduced the intensity of this emission line. The slight reduction is greatest when placing a large wafer, applying high RF power, and applying a low CF45%02 etch gas pressure. The Si/SiQ signal ratio decreases slightly with increasing temperature. And all signals decrease sharply by adding N2 to the etching gas. The decrease in the 0.70 line emission when increasing the etch rate or wafer placement suggests the following. The intensity of this line is the S
i depends on the number of etching groups. Plasmas dry up as the etch rate or footprint increases. Alternatively, this emission line is destroyed by the Si etch reactants. An example of an endpoint monitoring signal obtained in a typical polysilicon etch operation is shown in FIG.

The original recording had a signal to noise ratio of better than 30:1. A 40% signal change was achieved with the next etch.

Poly-Si single photoresist pattern wafer on SiO2 50W, 0.25Tom CF4 15%
Etching was performed using 02 etching gas and 5000 ml of etching gas. The signal level of 30 is due to rear lighting.

The signal increases at 31. At this time, the plasma is heated and reaches the level of Si etching characteristics of No. 33. The signal then increases again at 34. At this time, SIC
2 Part of the substrate is exposed. And finally, the end of the etch is marked by the signal suddenly becoming horizontal with respect to time at 35. Similar curves are found for continued operation, very reproducible in shape and amplitude. Similar curves are observed for larger wafer baths. The relative change in signal at the end point is much larger. And the sudden change in slope at the end point becomes a little blurred. This is due to the non-uniformity of the etch rate across the ridge thickness and the ridge. Etch rate decreases with increasing wafer placement. This can then be compensated for by increasing the signal amplitude from the endpoint monitor to correspond to the increase in power. The peak 32 at the beginning of silicon etching generally appears for the first time when: Before etching, remove bubbles from photoresist for a short time to improve etching uniformity.
2 Perform plasma treatment. The peak is due to the etching of the thin Si02 layer formed during the plasma oxidation preclean. Points 35 and 36 in FIG. 3 correspond to the end points of the wafer for two patterns etched using the end point control method of the present invention.

At 35, the etched wafer is free of poly-Si in all exposed areas with negligible undercut.

The wafer finished at 36 exhibits an undercut small enough to allow a two-way pattern etch.

This shows that the endpoint is easily recognized using the window. Etching should be completed during this time.
The window can accommodate very wide typical variations in polysilicon thickness or non-uniformity in etch rate within the bath installation. The 0.70 French emission line is also used to monitor plasma patterns in other structures.

For example, Si3N4 on Si02 is typically used in silicon integrated circuit manufacturing. This is done by using dummy wafers as illustrated in Figures 4a and 4b. FIG. 4a is for Si3N4 on Si02 and FIG. 4b is for Si02 on Si. In FIG. 4a, wafer 40 includes a silicon substrate 41. In FIG.

There is a layer of SiQ42 on one surface and a rear protective layer 43 on the other surface. The Sj3N4 layer is Si0
A masking layer 45 is formed over layer 44. This defines the region 46 to be etched. A dummy wafer 47 is applied to wafer 40. The wafer 47 has a silicon substrate 41 and a back protection layer 43, but the SiQ layer 42 is omitted. The Si3N4 layer 44 is directly on the substrate.
A masking layer 45 is formed over layer 44 and defines region 46 . The Si3N4 layer 44 on each wafer is of the same thickness. One or more wafers 40 are placed into the reaction chamber along with dummy wafers 47. Etching is S
The etching is terminated immediately after the optical emission intensity decreases in conjunction with penetrating through the i3N4 layer 44 into the silicon substrate 41 of the dummy wafer 40. A similar approach force is used for Si02 on Si.

As shown in FIG. 4b, a wafer 501 has a silicon substrate 51 thereon. A silicon substrate 51 has a Si02 layer 52 on one surface and a back protection layer 53 on the other surface. The masking layer 54 is S
A region 55 formed on the i02 layer 52 and etched
stipulates. A dummy wafer 56 is also provided.
It has the same configuration as wafer 50, with a silicon substrate 51, a Si02 layer 52, a back protection layer 53 and a masking layer 54 defining regions 55. Layer 52 has the same thickness, but as in this example, the S of dummy wafer 56
The i02 layer 52 has been given a minute pre-etch.
For example, 500 to 1000 in advance as shown in 57.
The wafer or wafers 5 on which A is given
0 is placed in the reaction chamber together with a dummy wafer 56. The etch is terminated when the Si etch emission signal level is detected in conjunction with the dummy wafer. At this time,
A thin layer of SiO2 is applied to the wafer or wafers 5.
0 remains on the substrate 51. And Si/Si
Etching up to the 02 interface can be completed with chemical recess etching. This chemical recess etch does not exacerbate pattern degradation if required. Since silicon plasma etches much faster than Si02, plasma etching
Having an etching gas of CF4 5%02 at the Si02 interface cannot be completed without unacceptable damage to the underlying silicon region due to the non-uniformity of the etch and layer thickness. When using a dummy wafer, the Sj3N4 etch must continue slightly past the endpoint signal to provide etch rate and layer thickness non-uniformity.

And the Si02 etchback of Si02 on the Sj dummy wafer must be larger than the non-uniform amount. As an example of both, the dummy wafer must have the same layers and masking characteristics as the bath wafer. and,
The wafers must be equally spaced within the reactor. Back protection layers 43 and 53 are provided to avoid spurious Si signals from the back of the wafer. Some of the major benefits of the new endpoint monitoring indicating the beginning (or end) of silicon layer etching are as follows.

1. The end point indicator is clear and accurate, requiring little operator judgment or skill.

In addition, the signal is reproducible and changes sharply near the end point. Therefore, it is suitable for use in 80% of the Si02 signals that trigger the delayed completion of the etching cycle using a comparator circuit set.
The set point can be compensated by installing a dummy. 2
This method also automatically compensates for variations in wafer number, spacing, exposed area, and layer thickness between baths.

3 This method automatically compensates for changes in starting temperature and plasma conditions.

Therefore, it allows relaxation of the accuracy required to set all plasma parameters. 4 {As a result of 3', the need for temperature control and preheating is eliminated and shortened.
Lower temperature, higher frequency power etch cycles are now possible with faster throughput without compromising endpoint control accuracy.

By allowing fast etching at low temperatures and high RF power, the present invention makes it possible to maintain adequate etch rate uniformity with up to 4.5 photoresist erosion. This allows finer line patterning on layers with more steps than normally possible. Endpoint control of optical emission also has application in photoresist stripping, as shown in FIG.

In FIG. 5, curve 60 corresponds to one wafer of 3 inches in diameter, and curve 61 corresponds to four wafers of 3 inches in diameter. The coordinate axes of the curve are the intensity of the emission line and the stripping time, respectively. Stripping time is also shown related to plasma temperature. The individual curves 60 and 61 are for emission lines at a wavelength of about 0.30 peaks, and the stripping of the photoresist is 0.5.
It was performed inside the etching tunnel with 300 Watts of RF power in a Ton02 plasma. After an initial rise at 62, the signal decreased to 63.
It peaks at , decreases, and increases with increasing temperature and stripping time, reaching a maximum at 64.

At this time, the photoresist area is partially peeled off.
The signal then decreases until all photoresist is stripped at 65. Then it becomes horizontal. The end point can be clearly seen even in a partial installation. The signal amplitude increases with increasing photoresist area, reactor temperature, and RF power, but decreases with increasing O2 pressure. The emission line increases with increasing stripping, suggesting that it is associated with reaction products. The emission line is about 0.3 μm and is therefore particularly sensitive to photoresist stripping.

However, between about 0.250 and about 0.340 Buddha and about 0.
There is a group of lines between 450 and about 0.485, and a single line with similar sensitivity at about 0.650. Emission occurs due to species present in the plasma.

The species is related to the change in the material being etched.
Thus, the signal generated by the change in emission intensity can be used to indicate the end of etching of a particular material or beyond a particular material to indicate the beginning of etching of that particular material. It can be used for. The emission line with a wavelength of about 0.70 French is Si02
Although it has been found to be particularly effective for plasma etching on Si or vice versa, other lines have been evaluated to be effective for other materials. Similarly, CF45%
Although Q was described as an etching gas when etching Si, the oxygen content can be changed from zero as is well known.

Then, CF45%02 was chosen as the conventional etching gas. 1 and 2, what is known as a volume loading device is described.

The present invention can also be practiced using surface-loaded devices. This method is suitable for photoresists commonly used in integrated circuit manufacturing.

For example, a typical photoresist is Philip A. H
untCO. (Canada) LW. Way powered by
CoatHR series and ShipleyCompa
Ship supplied by d to nyIncorpora
It is the ley1350 series. A key feature of the present invention is to select the most effective emission line for maximum sensitivity. There are a variety of emission lines that exhibit useful characteristics, and methods of selection and detection may vary.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a plasma reaction chamber and its associated equipment. FIG. 2 is a schematic diagram of the reaction chamber and release detector. FIG. 3 is a representative emission signal for one etching gas for a particular wafer type. Figures 4a and 4b illustrate the use of dummy wafers to locate specific material endpoints. FIG. 5 shows the emission signal for photoresist stripping. 10: Reaction chamber, 12: Needle valve, 13
: Vacuum pump, 14: Throttle valve, 15: Mass flow meter, 16: Precision pressure gauge, 17: High frequency power supply, 18:
Capacitor plate, 19: Metal high frequency shield, 20: Processing material. d Kita ↓ J Takashi Shige ○ Uchida 4 Bina r 3 d Protect stuffiness 〆 〆 〆 5″

Claims (1)

Claims: 1. A method for uniformly applying a pattern to a plurality of workpieces by selective etching, comprising: (b) exposing a plurality of workpieces in a reaction space to a chemically reactive plasma that etches at least one atomic emission line of an atomic emission spectrum of the plasma during reaction of the plasma with the workpiece; (c) the emission line has an amplitude that is sensitive to the concentration in the plasma of a member selected from the products of the reaction or etching radical; determining an endpoint of selective etching. 2. The method of claim 1, wherein the emission line has an amplitude that is sensitive to the concentration in the plasma of the products of the reaction. 3. The method of claim 1, further comprising: (d) terminating the selective etching at a predetermined time after determining the end point. 4. At least one of the workpieces comprises a support composed of a first material and a second material directly applied to the support.
a layer of material in the plasma, the layer of second material is exposed to the plasma, and the amplitude of the atomic emission line during etching of the first material in the plasma is 3. The method of claim 2, wherein the amplitude of etching the second material is substantially different. 5 at least one of the remaining workpieces has a thickness substantially equal to the layer of the second material of the first workpiece and a third layer adjacent the second layer; The amplitude of the atomic emission radiation during etching of the third material in the plasma is not substantially different from the amplitude of the second material in the plasma, and all endpoints of the workpiece are 5. The method of claim 4, wherein the change in the amplitude of the atomic emission lines of etching of the first and second materials is determined. 6 the second material consists essentially of Si_3N_4;
6. The method of claim 5, wherein said third material consists essentially of SiO_2. 7. The method of claim 4, wherein the layer of second material in the first workpiece is slightly thinner than the layer of second material in the remaining workpieces. 8. A method according to claim 4, wherein, before said step (a), a layer of second material in said first workpiece is subjected to a slight pre-etching treatment. 9. terminating the selective etching at the determined end point, after which at least one of the remaining workpieces is removed from the second etching without reducing the resolution of the pattern. 8. The method of claim 7, further comprising a wet chemical etching process to complete the removal of the layer of material. 10. The method of claim 1, wherein the emission line has an amplitude that is sensitive to the concentration of etching radicals in the plasma. 11. A method for end point control in a plasma etching method for removing material from a workpiece, comprising (a)
selectively removing material from the workpiece by a chemical reaction between etching radicals in a plasma and the material to be removed; and (b) having an amplitude that is sensitive to the concentration in the plasma of the products of the reaction. monitoring atomic emission radiation;
(c) determining an end point of the plasma etching method based on the change in amplitude; and (d) terminating the chemical reaction at a predetermined time after the detected end point. how to. 12. A method for endpoint control in a plasma etching method for removing material from a workpiece,
(a) selectively removing material from the workpiece by a chemical reaction between etching radicals in the plasma and the material to be removed; and (b) atomic emission having an amplitude that is sensitive to the concentration of etching radicals in the plasma. (c) determining an endpoint of the plasma etching method by the change in amplitude; and (d) terminating the chemical reaction at a predetermined time after the detected endpoint. A method comprising: 13. The method of claim 1, wherein at least one of the workpieces is exposed to the plasma through photoresist. 14. The method of claim 4, wherein said second material consists essentially of silicon and said first material consists essentially of SiO_2. 15. The method of claim 1, wherein the chemically reactive plasma comprises CF_4. 16. The method of claim 1, wherein the atomic emission line has a wavelength of about 0.7 μm. 17. of the first material in at least one wafer adjacent to the second layer, the first material and the second material each having substantially similar atomic emission spectra within the etching plasma; A method for controlling the end point of applying a pattern by plasma etching layer A, comprising: (a) forming a dummy wafer with a layer B of said first material having substantially the same thickness as layer A; etching by exposing layer A to a chemically reactive plasma during the presence of (i) wherein layer A and layer B are exposed to the reactive plasma for substantially the same amount of time; and (ii) etching the first material. (b) there is at least one emission line in the atomic emission spectrum in the plasma of the third material that is substantially different in amplitude from a corresponding emission line in the atomic emission spectrum in the plasma of the third material; (c) monitoring the change in amplitude of at least one of the emission lines over time during the reaction of the layers A and B with the reaction plasma; and determining. 18. The method of claim 17, further comprising terminating the etching step at a predetermined time after determining the end point. 19. In a method of removing photoresist material from a photoresist-masked workpiece: (a) exposing the photoresist material to a chemically reactive plasma; (b)
monitoring changes over time in the amplitude of at least one atomic emission line of an atomic emission spectrum of the plasma during the reaction of the photoresist material with the plasma, the emission line being sensitive to a concentration in the plasma of a product of the reaction; and having an amplitude of
(c) the end point of the removal is characterized by a change in the amplitude. 20. The method of claim 19, wherein the plasma includes oxygen. 21 The atomic emission line is about 0.25 and about 0.34 μm
, about 0.45 and about 0.485 μm, and 0.65 μm
20. The method of claim 19, wherein the wavelength line is selected from the wavelength lines between. 22. The method of claim 19, wherein the atomic emission line has a wavelength of about 0.30 μm. 23. In an apparatus for uniformly applying a pattern to a plurality of workpieces by selective etching, the method comprises: (a) reacting with a chemically reactive plasma etching the exposed surface of each of the workpieces chemically reacting with the material the surface has; (b) means for exposing a plurality of workpieces in a space; A monitoring means for monitoring, wherein the emission radiation is
(c) monitoring means having an amplitude responsive to the concentration in the plasma of selected members of the reaction products or etching radicals; (c) means for determining the end point of selective etching by changes in the amplitude; and means for determining the selective etching at a predetermined time after determining the end point.