JPS6031908B2 - Etching method and etching device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to etching processing, and is to perform fine etching of a workpiece with high precision.

In recent years, research and development has been promoted so much that the technical term Ubuyama SI has become familiar not only to engineers in charge of technology development, but also to the general public.

In order to realize Ultra 1, it goes without saying that the development of software and circuit configuration technology that satisfies the necessity of its existence is important, but it is also important to develop ultra-fine processing to construct the presumed fine and ultra-high density circuits. First of all, technological development is required for the time being. This ultra-fine processing technology includes an ultra-fine mask construction technology for performing desired processing of 1-submicron, and etching technology for performing desired processing faithfully to mask dimensions. For the former, electron beam and X-ray exposure technologies are attracting attention because they overcome the wavelength limit of visible light, and for the latter, so-called dry etching technology has become the mainstream in development, replacing etching methods using liquids. Now, dry etching technology includes ion beam etching technology, which is the most intense physical process in which atoms of the workpiece are mechanically scraped off using high-energy particles, and chemically active radicals with unpaired electrons excited by plasma. Various methods have been devised and implemented, including plasma etching technology, in which atoms are supplied to the surface of a workpiece, and through a chemical reaction, the atoms constituting the workpiece are converted into a compound with a high vapor pressure, and then removed as a gas. However, as will be described later, each of these conventional techniques has advantages over the others, and each has its own drawbacks, so the current situation is that they are not yet satisfactory. The present invention relates to a new dry etching technology that makes it possible to actively utilize the features of conventional dry etching technology and eliminate defects. It has the features of high selectivity and flexibility in the etch rate between materials, almost no deformation or deterioration of the leg resist, and no machining distortion left on the {c} machined surface.
It also has the feature of being able to control the shape of the processed end face, making it possible to perform processing that faithfully reproduces the resulting mask on the workpiece with submicron dimensional accuracy.

An object of the present invention is to eject atoms, molecules, or ions (hereinafter referred to as etchants) that have been chemically excited into an active state by some means from a specific ejection opening as a collimated molecular stream in the direction of a workpiece. In this method, an etchant is made to fly onto a specific surface of a workpiece with a certain fixed incidence, and the workpiece is chemically etched according to the probability of the etchant flying over.

Further, the present invention provides an etching method using radicals excited in plasma as a molecular flow, or an etching method using an ion flow and a molecular flow of radicals, and an apparatus therefor. Conventional so-called dry etching methods are broadly classified into ion beam etching, sputter etching, plasma etching, and the like.

The elementary process of ion beam etching is that atoms constituting the workpiece are removed by sputtering using ions accelerated with high energy, and it is clearly a matter of V supply.

In this method, it is necessary to transport the accelerated particles to the workpiece surface without losing their kinetic energy, so the mean free path of the particles is 1
The process is carried out in a high vacuum where the distance L between the ion source and the workpiece is sufficiently large (1 》L). Therefore, the direction of incidence of ions onto the workpiece can be clearly defined, and the machined cross-sectional shape of the workpiece can be controlled to some extent by the angle of incidence of the ions. However, due to the sputtering of high-energy particles, it inherently has the following drawbacks. That is, {11 the selectivity of the etching rate depending on the material is small.

{21 Leaves machining distortion on the machined surface. {3' Sputtered workpiece atoms redeposit.

○''This means that the resist itself, which serves as a mask, is also deformed during etching of the target material.In order to perform etching with high dimensional accuracy, it is necessary to adjust the resist to the thickness of the object to be removed. The thickness must be sufficiently thick. However, if the resist is too thick, there will be an undesirable phenomenon of redeposition of sputtered atoms, so the resist film thickness must be controlled extremely highly. On the other hand, the process-strained layer described in (1) above deteriorates the inherent characteristics of the material to be processed. For this reason, various post-processing is required, but it is difficult to completely eliminate the influence of distortion. In order to avoid these difficulties of ion beam etching, chemically active radicals are excited in a gas plasma maintained at a pressure of 0.1 to 1 willow Hg, and chemical reactions caused by these radicals and ions in the plasma are induced. There is a so-called plasma etching method that performs etching by a physical reaction caused by etching. In order to avoid the drawbacks caused by direct exposure of the workpiece to ions or plasma, a structure in which the plasma excitation part and the etching reaction part are separated is also known. The advantages of this method are that since it is a pure chemical method using radicals, it does not cause processing distortion, and that the etching rate between the workpiece and the mask is highly selective. Therefore, it is possible to selectively etch the workpiece without causing deformation or deterioration of the etching resist. However, although the plasma excitation part and the reaction part are separated, they are in a low vacuum of about 10-1 Hg, so the mean free path 1 of the gas molecules in the system is at most 10-1 Hg.
It's only about the size of my ribs. Therefore, the radicals are incident on the surface of the workpiece without any directionality, etching the workpiece uniformly. For this reason, when etching the workpiece layer to a thickness r,
Side etching with radius r always occurs. Also 10-1 rib H
In a low vacuum of around g, the gas in the system is in the viscous flow region,
The transport speed of radicals, which are etchants, is limited by the flow rate of the viscous flow, and it is impossible to effectively utilize short-lived radicals. Furthermore, during transportation, radicals repeatedly collide with many other gas molecules, which may unnecessarily shorten their lifetime. A further improved method is a method of keeping the sample processing chamber at a high vacuum compared to the plasma generation chamber (Tokusei Sho 51).
-88182) and a method of maintaining the pressure in the sample processing chamber (reaction tube) below 10-3 Torr (Special Seki No. 51-11
No. 14071) is known.

These known examples describe various effects of increasing the degree of vacuum in the sample processing chamber, but in order to be able to define the angle of incidence of the etchant on the sample surface, which is the subject of the present invention described later, it is necessary to supply the etchant as a molecular beam. The idea of doing so has not been clearly disclosed. Therefore, the effect of etching using a molecular beam as an etchant in the present invention is also not described at all. In this sense, the above two improved conventional methods are simply etching in a high vacuum, and the mean free path of the etchant is lengthened to allow the reaction to occur under diffusion-limited conditions in the etchant gas. However, the direction of incidence of the etchant on the surface of the workpiece is not clearly defined and is completely close to isotropic incidence. As described above, side etching due to isotropic incidence of etchant cannot be avoided within the scope of conventional plasma etching technology.
This side etch is a serious drawback in ultra-high precision machining in the submicron region. The advantages and disadvantages of conventional methods have been explained above, taking as an example etching methods that involve elementary processes at both extremes, physical reactions and chemical reactions.

In addition, sputter etching is known, but it is a mixed type of both physical and chemical reactions, and has the above-mentioned advantages and disadvantages depending on the degree of elementary processes involved. The present invention was conceived in the process of pursuing the fundamental properties of molecular beams, and the inventions related to molecular beams by the present inventors were published in Tokugao No. 51-186736 and Tokugao No. 51-118126. Proposed.

The present invention enables fine etching using molecular beams based on the technical consideration of molecular beam epitaxy previously proposed by the inventors. The above invention by the present inventors is
If a molecular beam is ejected from a source entrance with a finite area and reaches the substrate surface without being substantially scattered, the growth rate will depend on the ratio of the local arrival rate of the molecular beam at the substrate surface. This demonstrated that epitaxial crystal growth is possible.

In other words, the following molecular beam techniques were used. {11 When the area of the source Sekiguchi seen from any one point on the substrate is small,
A molecular beam can be regarded as a substantially parallel molecular flow.

Therefore, the direction of incidence of the molecular beam on the above point can be defined. (2) If we take the local incident angle of the molecular beam at any one point above, the probability of the molecular beam coming is proportional to coo.

[3' If there is a molecular beam obstruction between the radiation source and any point, the probability of the molecular beam coming to this point is Proportional to area.

'41 Since the kinetic energy of a molecular beam is equivalent to the source temperature, it does not sputter or mechanically strain the substrate or already deposited film. The present invention utilizes the above-described characteristics of molecular beams for precision etching of materials.

In the present invention, the etchant, which is a reactive substance that forms a high vapor pressure compound containing the constituent elements of the workpiece by chemically reacting with the workpiece, is used as a molecular beam with a specific incident direction on the surface of the workpiece. supplied to FIG. 1 shows the case of normal incidence as an example. 1 is the incident direction of the etchant, 2 is the workpiece to be etched, and 3 is the protective film.

At the start of etching as shown in a of FIG. If the chemical reaction is rate-determining, the surface 20 will be etched at a uniform rate depending on the probability of the molecular beam hitting. (However, if there is a probability that the etchant molecules flying onto the protective film 3 will be supplied onto the surface 20 through the surface movement process 11, the etch rate may locally increase at the edge 21.) In this way, If etching is continued, the state shown in figure b will be reached. The probability of a molecular beam landing on the surface 22 does not change, but the probability of a primary molecular beam landing on the side surface 23 is zero, only due to the surface movement process 11 and the surface scattering process 1.
There is only a probability of 2. It is sufficiently possible to make the probability of flying toward the side surface 23 due to processes 11 and 12 smaller than the probability of flying toward the surface 22 due to 1 by setting conditions. Therefore, it can be easily understood from FIG. 1 that it is possible to make the amount of side etching extremely small. For comparison, FIG. 2 shows the radical supply process by conventional plasma etching.

In the conventional method, the direction of incidence of the radicals 15 is not specified, and the radicals 15 are incident from completely random directions. Therefore, even if the average flying probability is kept the same as in the present invention, the probability of radicals flying onto the bottom surface 25 shows position dependence. That is, no component having an incident angle shallower than the path 16 is incident on the partial surface 26 in FIG. On the other hand, the side surface 27 has a surface movement 11 and a surface scattering 12.
Directly incident radicals 17 are supplied in addition to the components caused by this. In this way, at the same time as the inside of the flat part of the bottom surface 25 is reduced, a side etch 28 is inevitably generated, and the etched side surface 2
7 can only be a gently sloped surface that is far from vertical. This is an essential drawback for the purpose of precisely reproducing the microscopic shape of the protective film on the workpiece. This drawback is a principle disadvantage of the conventional method in which radicals are incident from completely random directions. Comparing FIG. 1 and FIG. 2, the principle advantage of specifying the incident direction of the etchant is obvious. FIG. 3 shows an example of an apparatus in which the present invention is applied to etching polysilicon. The working chamber is formed of a stainless steel bell jar 30 whose inner wall is covered with Teflon 31, and is evacuated by a diffusion pump 35. Rooms 36 and 37 are preliminary rooms where three rivers are attached, and silicon wafers 40, etc. are transferred to the conveyor 38.
drive mechanism and cartridges for continuous transport in
(not shown) is housed in an airtight room. 32 is an inner cylinder made of quartz glass, the surface of which is thickly coated with polysilicon.

The baffle 33 and the sieve baffle 34 are also made of quartz glass, and their surfaces are similarly thickly coated with polysilicon. The fluorocarbon gas mixed with oxygen introduced from the introduction tube 43 becomes plasma in the discharge tube 41, which is an etchant generation source, and dissociates into active neutral radicals and ions. These radicals and ions are emitted toward the workpiece silicon substrate 40 in the working chamber through the minute openings 42 at the speed of thermal motion in the plasma. At this time, the working chamber is evacuated to a high vacuum by the pump 35 so that the mean free path 1 of the molecules is larger than the distance L from the barrier hole 42 to the silicon substrate 40. Therefore, the etchant molecular flow 45 can reach the substrate 40 with almost no scattering along its path, and the state shown in FIG. 1 can be realized in principle. In other words, the kinetic energy is only comparable to the thermal velocity in the plasma, and therefore, the workpiece is sputtered, and the low-velocity etchant, which has no possibility of causing mechanical distortion, flies onto the substrate with a predetermined direction of incidence. do. On the substrate 40, monatomic active F
* and Si'con Si are chemically bonded to form S, which has a high vapor pressure.
The desired portion is etched using iF4. Baffles 33, 34 and cylinder 32 coated with polysilicon
has two important effects as described below.

The first one enters the working chamber from the checkpoint 42 and is inserted into the silicon substrate 40.
The purpose is to quickly change the etchant that cannot contribute to etching and is scattered around the work chamber into inert molecules (for example, Sip4), and to reduce the etchant component that enters the substrate in no direction. Second, if active molecules are left active, the etching chamber and pump system will corrode, requiring a great deal of expense to maintain the apparatus. However, if the device shown in Fig. 3 quickly converts most of the active molecules incident from the Sekiguchi 42 into inactive molecules and then exhausts them, the maintenance effort can be greatly reduced. . Furthermore, since the exhaust gas from the pump is already inert, it has low toxicity and can reduce the need for pollution countermeasures. Next, specific examples using the present invention will be described.

Example 1 After depositing polysilicon with a film thickness of about 0.51 m on a silicon substrate, a pattern of parallel non-parallel resists with a diameter of 2 mm and a pitch of 2 mm was formed, and this sample was Etching was carried out using the apparatus shown in the figure and a conventionally known apparatus with a plasma generation chamber/sample chamber separation type in which radicals are incident in no direction.

As a result of scanning electron microscope observation of the cross sections, almost no deformation of the resist was observed in both cases, but a large difference in cross-sectional shape was observed between the two. In other words, the sample using the device of the present invention has almost no one side etching and has a cross section that is nearly perpendicular to the other, whereas the sample using the conventional device has
It had a cross-sectional shape close to that expected from an isotropic chemical etch. Example 2 A sample similar to that used in Example 1 was installed in an inclined manner in the apparatus shown in FIG. 3, and etching was performed under the condition that the molecular beam was obliquely incident on the main surface of the sample.

Figure 4 schematically shows the results. 50 is a Si substrate, 51 is a silicon substrate, 52 is a partially etched polysilicon,
53 is Shijist. 54 indicates the direction of incidence of the molecular beam.

In this case, the cross section is formed approximately parallel to the direction of incidence of the molecular beam. Therefore, it is possible to form a mesa-shaped cross section 55 or an inverted mesa-shaped cross section 56. A similar cross-sectional shape can be obtained using an ion beam, but it has the disadvantage of reattachment.
In the method of the present invention, there is no problem of redeposition, and any cross-sectional shape can be formed depending on the direction of incidence of the molecular beam. Furthermore, since it is a pure chemical etch, no processing distortion remains on the processed surface. As detailed above, under conditions where the basic process of etching is essentially supply-limited, the kinetic energy of the gaseous etchant is at most the temperature of the etchant source, and the kinetic energy is at most the temperature of the etchant source. If the incident direction is specified and the resist is blown away, ■ there is almost no change in the shape of the resist due to heat or ion collision, ■ side etching is minimal, ■ the cross-sectional shape is almost parallel to the incident direction of the etchant molecules, and ■ Therefore, it was possible to obtain a new ultra-precision processing means that has controllability of the cross-sectional shape and also does not leave processing distortion on the workpiece.

Furthermore, by installing a wall inside the device that quickly reacts with active molecules to form inactive molecules, the ratio of secondary molecules that scatter inside the device and remain behind compared to primary molecules can be reduced. This clarifies the direction of incidence of etchant molecules on the surface of the workpiece, and greatly reduces the problem of corrosion that is the fate of equipment that handles chemically active gas molecules. We were able to reduce maintenance costs and improve operational efficiency.

On the other hand, it also reduces the toxicity of exhaust gas, which is advantageous in terms of maintaining worker health and preventing pollution. It goes without saying that the idea of rapidly converting unreacted active molecules into chemically stable molecules inside the device and then discharging them can be easily applied to conventional active sputtering equipment and plasma etching equipment. be.

That is, heated Si or polysilicon may be installed between the working chamber of these subordinate devices and the exhaust pump so that the active gas has a sufficient opportunity to react with them. When fluorine is mainly used, as another example, it may be reacted with sulfur to convert it into an extremely stable gas such as SF6, and then exhausted. Although the above-mentioned example shows only an example of etching polysilicon, this method is not limited to etching polysilicon, and can be applied to semiconductors, metals, rolling conductors, insulators, and magnetic materials if an appropriate etchant is selected. Naturally, it can be applied to the processing of various solid substances such as.

Although polysilicon was used as the coating for the inner cylinder 32 and baffles 33 and 34, this coating material is not limited to polysilicon, and generally reacts with the etchant to remove the desired workpiece as quickly or as quickly as the desired workpiece. It is sufficient to use a substance that inactivates it. These coated portions can also be selectively held at elevated temperatures to make them more reactive than the workpiece. Furthermore, the machined cross-sectional shape can also be controlled by rotating or tilting the workpiece during processing so as to change the incident angle of the molecular beam relative to the workpiece during processing.

Furthermore, as illustrated in FIG. 3, if active radicals and low-velocity ions are expelled directly from the tube wall as a molecular stream with a thermal velocity in a part of the discharge tube 41 and at the 4-point of the potential gradient, For example, the transport speed of the etchant is the same as the speed of thermal motion of the molecules, which increases significantly compared to the transport speed of the conventional viscous flow.

As a result, the lifetime can be shortened and radicals can also be used effectively. Furthermore, by installing an ion control electrode near the opening 42, only neutral radicals can be used. ■
We apply a variety of processing methods depending on the target material, such as using neutral radicals in combination with accelerated ions, and using neutral radicals and ions with kinetic energy comparable to the energy of thermal waves in plasma. can. On the other hand, if it is desired to use only long-lived radicals, it is natural to place an appropriate distance between the discharge detector and the entrance of the processing chamber and connect them with a transport pipe. As a discharge tube for etchant formation, a general diode glow discharge tube, a PIG-type triode discharge tube, and a discharge tube without a hot cathode such as a high-frequency discharge tube or a microwave discharge tube are required. Can be used as required.

Since the present invention has a structure in which the discharge tube section, which is the etchant generation chamber, and the processing chamber are separated, the processed surface is damaged by charged particles existing in the plasma in the discharge tube, and the resist is damaged and deformed by ultraviolet rays and heat. Nor.

It goes without saying that this method also has the characteristics of an improved conventional method in that the etching rate is uniform within a sample or between samples, and there is almost no dependence on the number of samples, etching area, or pattern size and shape. As explained above, the method of the present invention is an extremely useful method that utilizes only the features of conventional dry etching technology and eliminates its drawbacks. In other words, while maintaining the regularity of the incident direction of ion beam etching, it is possible to realize pure chemical etching using an etchant that has only thermal kinetic energy, resulting in extremely small side etch, controllability of the machined cross-sectional shape, and the ability to control the machined surface. No machining distortion remains. Further, since the etch rate of the resist and the workpiece material is highly selective, there is no deformation of the resist. The pattern shape of this test resist can be precisely reproduced on the workpiece with submicron precision. Due to the above features, this technology is S
Regarding i-semiconductors, for m/V group semiconductors such as ultra-B1 and GaA1as, it is necessary to form gratings for ultra-high frequency elements and distributed loop racers, and also for surface wave application equipment, magnetic bubble equipment, Josephson junction equipment, etc. The present invention provides a new processing method that is extremely useful for manufacturing devices that require ultra-fine processing without leaving any processing distortion.

[Brief explanation of drawings]

1A and 1B are schematic cross-sectional views showing the principle of the present invention, FIG. 2 is a schematic view showing the etchant supply process in the conventional method, and FIG. 3 is the structure of an etching apparatus according to an embodiment of the present invention. 4 are schematic views of processing polysilicon using an oblique incidence etchant using the method of the present invention. 1... Molecular beam of etchant with a defined incident direction, 2... Workpiece, 3... Protective film, 2
0, 22... Exposed surface of workpiece, 21...
...Exposed surface of the workpiece near the edge of the protective film, 23...Etched end face, 30...Bell jar covered with Teflon 31, 32, 33, 34...The surface is covered with polysilicon. Coated inner cylinder, 33, 34...baffle, 35...diffusion pump, 41...excitation chamber for producing etchant from freon gas introduced from supply pipe 43, 42 ... Echantant spout closure, 45.
... Molecular beam of etchant, 50 ... Silicon, 51 ... Si02 film, 52 ... Polysilicon remaining after processing, 53 ... Resist, 54.
...Molecular beams of etchant with the same direction of oblique incidence. Figure 2 Figure 1 Figure 4 Figure 3

Claims (1)

[Claims] 1. A gaseous substance excited to a chemically active atomic, molecule, or ion state is ejected from an excitation chamber as a molecular stream into a processing chamber through a finite opening, and the gaseous substance in the processing chamber is The molecular flow is caused to fly onto a specific surface of the workpiece in a state where the mean free path is larger than the distance between the opening and the workpiece, and the workpiece material and the gaseous substance are caused to chemically react, and the An etching method characterized in that the workpiece is removed as a high vapor pressure substance according to the probability of a gaseous substance flying into the workpiece. 2. The etching method according to claim 1, wherein the gaseous substance is flown onto the surface of the workpiece with an average kinetic energy approximately equal to the average temperature of the gas inside the excitation chamber. 3. The etching method according to claim 1, characterized in that a chemically active unreacted gaseous substance that does not react with the material to be processed is converted into a chemically stable substance. 4
2. The etching method according to claim 1, wherein the direction of incidence of the gaseous substance on the workpiece is relatively changed during processing. 6. The etching method according to claim 1, wherein the gaseous substance is composed of electrically neutral radicals or these radicals and ions. 6. An excitation chamber that converts a chemically inert substance into a chemically active state having an atomic, molecular or ionic state, and causes this excited gas to chemically react with a desired material to be processed;
An etching apparatus comprising: a processing chamber for removing the material to be processed as a high vapor pressure material; and a mechanism for converting the chemically active unreacted vaporized material into a chemically stable material. 7. The etching apparatus according to claim 6, wherein the excited gas is introduced from the excitation chamber into the processing chamber through a finite opening. 8. The etching apparatus according to claim 6, further comprising a mechanism for installing and converting a substance having a basic reaction probability between a gaseous substance and a processed substance in the processing chamber.