TWI570804B - A method of forming a notch at the bottom of the hole during the etching process, and a method of forming the hole - Google Patents

Description

Method for suppressing the occurrence of a notch at the bottom of a hole during etching, and method for forming a hole

The present invention relates to the field of semiconductor fabrication, and more particularly to a method for etching a via hole in a material layer to be etched to form a through hole through the material layer for suppressing the bottom of the via hole (ie, the material layer is insulated from the bottom) At the interface of the layer, a phenomenon of notching occurs.

The use of anisotropic plasma etching to form vias in a material layer is one of the most common processes for semiconductor processing. As shown in Fig. 1, when ruthenium (or other material) 1 is etched, a large amount of charge is accumulated on 矽1 due to the electrical isolation of the lower insulating layer (e.g., yttrium oxide) 2. Due to the influence of the electric charge, when etching proceeds to the interface between the crucible 1 and the insulating layer 2, notches 4 are formed on both sides of the hole 3.

In some applications, the gap is to be avoided because the presence of the gap itself has destroyed the shape of the feature (ie, the hole), thereby degrading the performance of the device. Not only that, but the gap also poses problems for subsequent processing processes, such as filling holes.

It is an object of the present invention to improve the notching phenomenon that occurs at the bottom of a hole during plasma etching.

According to an aspect of the invention, a method for etching a hole structure by a Bosch method is provided, comprising: performing a main etching process to form a hole, the main etching process comprising: (a) a plasma etching step; (b) a passivation step; (c) alternately repeating the plasma etching step (a) and the passivation step (b); performing an over-etching process to deepen the hole, the over-etching process comprising: (d a plasma etching step; (e) a passivation step; (f) alternately repeating the plasma etching step (d) and the passivation step (e); wherein the over etching process corresponds to the plasma etching step (d) The working gas pressure in the reaction chamber is smaller than the working gas pressure in the reaction chamber in the plasma etching step (a) corresponding to the main etching process.

According to another aspect of the present invention, a method of forming a hole structure is provided, comprising: providing a substrate comprising a layer of a material to be etched and an insulating layer adhered to a lower surface of the layer of material to be etched; Etching the layer of material to be etched to initially form a hole; continuing the anisotropic plasma etch to deepen the hole under a relatively low working pressure environment; at least at the end of the process of deepening the hole The insulating layer has been exposed through the holes.

According to still another aspect of the present invention, there is provided a method for reducing or eliminating a notch defect at the bottom of a hole during etching of a hole structure, comprising: in a device obtained by the above batch process, a notch defect or a notch defect at the bottom of the hole is out of an allowable range At the same time, the working gas pressure of the previous process medium ion etching step is lowered; the next batch of workpieces is plasma etched with the adjusted parameters.

Current research theories generally suggest that in plasma etching, the occurrence of notching at the bottom of the hole is directly related to the accumulation of charge on the ruthenium (or other material). Therefore, the idea of suppressing the notch phenomenon is usually the charge accumulated on the surface of the neutralized ruthenium. Or directly reduce the amount of charge delivered to the helium. Specific measures include lowering the radio frequency, applying a pulsed generator to the RF power source, and reducing the duty cycle. )Wait.

In investigating the problem of eliminating the gap phenomenon, the inventors have discovered a new factor that can affect the gap: the plasma pressure of the plasma etching. When the other parameters are constant, the lower the working pressure, the more obvious the improvement of the notch phenomenon.

In plasma etching, the surface of the bottom formed by etching is not flat and curved, and the higher the gas pressure in the etching step, the larger the arc shape, and vice versa. As shown in FIG. 2, when the etching is performed to the lower insulating layer 2, the 矽1 in the central portion of the bottom of the hole 3' has been exhausted, and the 矽1 of the edge region remains, and the closer to the edge remains, that is, It is said that the etched bottom surface produces a height difference H. The 矽1 material remaining in the edge region is generally stepped.

The etching is continued to remove the residual 矽1. As shown in Fig. 3, the inventors have found that in this process, along with the elimination of residual ruthenium, damage D occurs at the sidewall of the corresponding height hole (for the cause of the damage D) The inventor's understanding is that as the exposed area of the underlying insulating layer becomes larger and larger, the area of the actually etched 矽1 is gradually reduced, and the number of particles that are etched remains unchanged, which makes 矽1 The etching is equivalent to being enhanced, resulting in damage). As the etch progresses, these damages D develop into the final gap. The height of the finally formed notch is substantially equal to the above-described bottom surface height difference H.

Multiple tests of different parameter conditions have also verified the above relationship between the gap height of the notch and the bottom surface (especially the height difference of the etched bottom surface just after etching to the lower insulating layer, as shown in Figure 2).

In view of the above findings, the inventors propose to improve the flatness (height difference) of the etched bottom surface by reducing the working gas pressure in the plasma etching stage, thereby reducing or even avoiding the etching enhancement described above, thereby suppressing or eliminating the hole. The gap at the bottom. In the specific implementation, the hole etching may be completed at a lower working pressure from beginning to end, or the majority of the depth of the hole may be etched first at a higher working pressure, to be etched to the lower insulating layer or close to the lower insulating layer. Subsequent etching is then performed at a lower working pressure. Regardless of the above, the gap phenomenon can be suppressed or even eliminated.

Hereinafter, how to specifically implement the method of the present invention in plasma etching to suppress the notch phenomenon at the bottom of the via hole will be described with reference to the accompanying drawings. It is emphasized that the description herein is merely exemplary and that other embodiments that utilize the invention are not excluded.

A plasma etched via process capable of suppressing the occurrence of a notch according to the principles of the present invention, as shown in FIG. 4, mainly includes two etching stages: a main etching stage and an over etching stage. The first etch phase is performed to form the main outline and depth of the via hole, and the over-etching stage is performed to etch the remaining portion in a relatively low pressure environment to form a complete via structure. The implementation of each step of the process and the effects to be achieved will be described in detail below in connection with the semiconductor component to be processed.

A substrate is provided. The substrate includes at least a layer of material to be etched on the surface, and an insulating layer adhered to the lower surface of the layer of material to be etched. The material of the insulating layer is different from the material layer to be etched, and is difficult to be etched in the subsequent etching process (relative to the material layer to be etched), and is suitable as an etch stop layer. There may also be other layers of material beneath the insulating layer.

In this embodiment, the substrate is an SOI substrate, as shown in FIG. The top layer 矽10 is a material layer to be etched; the buried oxide layer 20 is an insulating layer and a stop layer, which can prevent the underlying germanium 30 from being damaged by the etching process of the top layer 矽10. However, the present invention is not limited thereto, and it is also within the scope of the present invention to provide the material layer to be etched and the stop layer in other ways.

Moreover, the material of the material layer to be etched is not limited to germanium, and any other material suitable for etching through holes therein, such as germanium, antimony oxide, etc., can also be used. The material of the underlying insulating layer can be adjusted according to the layer of material to be etched. In addition, other structures, such as shallow trench isolation structures (not shown), etc., may already be formed in the substrate (accurately within the layer of material to be etched) prior to etching.

As shown in FIG. 6, a mask P, such as a photoresist, is formed over the top layer 矽10. The mask P covers a partial area of the top layer 10; the uncovered area of the top layer 10 is the area where the through holes are to be etched.

The substrate is placed in a plasma etching apparatus, and a main etching process is performed to etch the top layer 10 to a certain depth through the mask P anisotropic plasma to form a hole. The device formed is as shown in Fig. 7, wherein reference numeral 12 denotes a preliminary formed hole. In Figure 7, the central region of the aperture 12 is etched faster and the edge region is etched relatively slowly such that the junction of the central region to the edge region forms a step-up step.

Then, the gas pressure in the reaction chamber of the etching device is adjusted, and in a lower pressure environment, an etching process is performed to completely remove the germanium material at the bottom of the hole 12 (refer to FIG. 7) to form a final through hole. The above overetching process is also an anisotropic plasma etching process. The device formed after the end of this step is as shown in Fig. 8, wherein reference numeral 14 is referred to as the finally formed through hole. Since the over-etching step uses a lower working pressure, the flatness of the etching at the bottom of the hole is ensured, thereby eliminating the step (or height difference) formed in the main etching process, thereby avoiding the gap on both sides of the bottom of the hole. (notching) is produced.

In the plasma etching process, the setting of the gas pressure in the reaction chamber directly affects the etching rate. Under the condition that other parameters are unchanged, the higher the gas pressure, the faster the etching rate; the lower the gas pressure, the slower the etching rate, but correspondingly, the flatness of the surface formed by etching is higher. In the above main etching stage, the etching of the main part of the through hole is completed by using a higher air pressure, and the etching efficiency is basically ensured; and the low air pressure taken in the finishing stage (ie, the over etching stage) only completes the shallow depth. The etch, so it does not significantly reduce the efficiency of the entire etch while avoiding or suppressing the generation of the gap.

In order to ensure that the sidewalls of the anisotropic etching can maintain a high verticality, whether in the main etching stage or the over-etching stage, the gas to be introduced preferably includes both an etching gas and a passivation gas, wherein The ions formed by the dissociation of the etching gas and the material formed by the reaction of the material to be etched are easily separated from the substrate to achieve the purpose of etching; the ions formed by the dissociation of the passivation gas react with the material to be etched to form a polymer, and remain on the sidewall. To achieve temporary protection of the side walls. The choice of the specific etching gas and passivation gas and the adjustment of the ratio between the two, as well as the setting of various parameters in the etching, can be selected and adjusted according to the material to be etched and the actual needs.

As a better alternative, the above-mentioned main etching process and over-etching process can all adopt the Bosch process to ensure high etching of the vertical sidewalls while ensuring etching. rate. That is to say, whether it is a main etch or an over etch, it can be realized by two alternating cycles of etching and passivation steps. Wherein, in the etching step, at least a portion of the plasma dissociated by the reactive gas bombards the substrate in an almost vertical direction; in the passivation step, the passivating gas is introduced to form a layer on the exposed substrate surface (including the sidewall, the bottom) polymer. In the subsequent etching step, the polymer at the bottom is bombarded by particles in the vertical direction, the underlying substrate is exposed and etched, and the polymer on the sidewall is rarely bombarded, thereby remaining and playing against the sidewall. Temporary protection.

When the main etching or over etching adopts the Bosch method, or at least one of the main etching and the over etching includes other non-etching steps while including the basic etching step, the present invention Etching in a lower gas pressure environment requires only that the actual etching step be performed in a lower pressure environment, without requiring other non-etching steps (such as passivation steps) to be performed in this lower pressure environment.

When the material to be etched is tantalum, when the gas pressure in the over-etching stage is usually set to 40 mTorr or less, the generation of the notch at the bottom of the hole can be substantially eliminated, and even if the gap is left, the size is limited to almost no influence on the device. Degree. It should be noted here that since air pressure is not the only factor that can affect the generation of the gap, it is also important to adjust the air pressure while ensuring that other parameters (such as Duty Cycle, etc.) are not in the worst state. However, even if the other influencing factors are in a poor state due to actual demand or other reasons and cannot be optimized, according to the present invention, the working pressure in the reaction chamber in the etching stage can be lowered to improve the notch phenomenon.

The etch rate in the main etch phase is faster and can therefore typically be utilized to complete most of the depth of the entire via. The main etching phase can be stopped immediately when the etched region is just etched to the underlying stop layer. In the specific implementation, it may be selected according to actual needs when the main etching phase is terminated and the over-etching phase is started. The principle that can be followed is that the earlier the main etching phase is terminated, the greater the depth of the layer of material to be etched which is etched in the over-etching phase, and the better the effect of suppressing the notch is generated; in contrast, the main etching phase is terminated. The later, the higher the etching efficiency of the entire etching process, but the greater the probability of the gap, the more serious the gap defects are. In practice, one that has been proven to be effective is to check the last batch of products and measure the depth of their gaps; when processing the same batch of the next batch, set the main etch phase to arrive. This depth is terminated before or when this depth is reached. For example, if multiple products obtained by the above batch processing, the gaps are mostly started at X microns (or nanometers) from the stop layer, then, in order to suppress the generation of the gap, the next batch can be processed. The main etch process is set to terminate at X microns (or nanometers) or more from the stop layer and replaced with an over etch process with a lower working pressure.

When a through hole (especially a deep hole) is etched, the notch is always generated at the bottom of the through hole, and usually occurs after a certain depth, such as a depth of five-fifths of the depth of the entire hole, so that it is simple. The main etch process can be set to etch to the end of five-fifths of the entire hole depth. In theory, it is feasible to set the main etch process to etch to two-thirds to twenty-seven to nineteenth of the entire hole depth. If the main etch is terminated too early, on the one hand, the gap phenomenon cannot be further improved (for example, if the process X1 of the main etch is finished later, the gap phenomenon can be completely avoided, and the process of the main etch is terminated earlier than X2 naturally. It can't improve the notch phenomenon better than X1. On the other hand, it reduces the etching efficiency. If the main etching ends too late, it may cause subsequent over-etching to be meaningless and can not effectively improve the gap phenomenon. .

For the plasma etching device provided with the etching end point monitoring device in the reaction chamber, the end point monitoring device can be used to monitor the entire etching process, and when the etching proceeds to the stop layer, the main etching process is immediately terminated and the etching is started. Etching process.

When the etching is performed by the Bosch method, it is also possible to improve the notch phenomenon by increasing the working gas pressure in the passivation step of the over-etching stage (the improvement here is relative to the passivation step of the main etching stage). This is because the increase in the pressure of the passivation step improves the amount (thickness) of the deposition of the protective layer (i.e., the polymer), and the increase in the thickness of the protective layer on the side walls is more effective in preventing the occurrence of notches or damage in the sidewalls. In a specific implementation, the working pressure of the passivation step of the over-etching step can be set to 70 mTorr or more. Of course, other air pressure parameters can be selected as needed. This is also not to be construed as limiting the invention.

9 is a flow diagram of another plasma etched via process that inhibits the generation of a gap in accordance with the principles of the present invention. The process mainly includes the following steps:

Step (1), placing the Nth batch of the to-be-processed product in a plasma reaction chamber.

The article to be processed may be a substrate similar to that shown in FIG. 5 as given in the previous embodiment, comprising at least a layer of material to be etched on the surface for processing, and an insulating layer underlying the layer of material to be etched.

Step (2), performing plasma etching according to the set parameters, forming a through hole in the product to be processed.

The plasma etching may be a two-stage etching method as shown in the previous embodiment (ie, a main etching step and an over etching step), or a more-stage etching method, or a single-stage etching method. Etching (ie, etching the entire via through the constant parameters from start to finish). Moreover, each stage of the plasma etch (if there are two or more stages) may or may not employ a Bosch method, as described in the previous embodiments.

Step (3), removing the processed product to be processed out of the reaction chamber, and detecting whether there is a notching at the bottom of the formed through hole, and whether the size of the gap exceeds the allowable range.

If no gap is found, or the gap size is within the allowable range, the previous etching parameters are maintained, and the subsequent batches of the same product to be processed (such as the N+1 batch) continue to be applied;

If the notch size is outside the allowable range, the previously used etching parameters are adjusted so that a better effect can be obtained in the subsequent batches (such as the N+1 batch) (in terms of notch defects). Moreover, when the parameters are adjusted and the next batch is processed, the gap of the finished product can be continuously detected. If the gap still fails to meet the requirements, the parameters can be further optimized.

The parameter adjustment described above for optimizing the notch defect includes at least reducing the internal pressure of the reaction chamber. Of course, it can also be supplemented by other parameter adjustments well known in the industry that can achieve improvement effects, such as reducing the frequency of the radio frequency and reducing the space-to-occupancy ratio.

Moreover, similar to that discussed in the previous embodiments, the lowering of the air pressure here may be to lower the working air pressure of the entire etching stage, or to only lower the back stage of the etching stage (which roughly corresponds to the front side). The working pressure of the over-etching phase discussed.

Although the present invention has been described in detail by the preferred embodiments thereof, it should be understood that the foregoing description should not be construed as limiting. Various modifications and alterations of the present invention will be apparent to those skilled in the art. Accordingly, the scope of the invention should be defined by the appended claims.

1‧‧‧矽
2‧‧‧Insulation
3‧‧‧ hole
3'‧‧‧ hole
4‧‧‧ gap
10‧‧‧ top layer
12‧‧‧ hole
14‧‧‧through hole
20‧‧‧ buried oxide layer
30‧‧‧Underground
D‧‧‧Injury
H‧‧‧ height difference
P‧‧ mask

Other features, objects, and advantages of the present invention will become more apparent from the detailed description of the accompanying drawings. FIG. 2 is a schematic view showing the unevenness of the bottom surface formed by etching when the etching is performed to the lower insulating layer; FIG. 3 is a schematic view showing the generation of the gap caused by continuing etching the device shown in FIG. 2; 2 is combined with FIG. 3 to reflect the correspondence between the position where the gap is generated and the unevenness of the etched bottom surface; FIG. 4 is a schematic flow chart of a process for etching the through-hole structure according to an embodiment of the present invention; 5 to 8 are schematic views showing the structure of a semiconductor device formed by performing the steps of an etching process according to an embodiment of the present invention; and FIG. 9 is a process for etching a via structure according to another embodiment of the present invention. Schematic diagram of the process.

Claims (7)

A method for etching a hole structure by using a Bosch method, comprising: performing a main etching process to form a hole, the main etching process comprising: (a), a plasma etching step; (b), a passivation step; Repeating the above-described plasma etching step (a) and the passivation step (b) up to a main etching stop point; performing an over-etching process to deepen the hole from the main etching stop point to form a final via hole, The over-etching process includes: (d) a plasma etching step; (e) a passivation step; (f) alternately repeating the plasma etching step (d) and the passivation step (e); wherein the over-etching process The working gas pressure in the reaction chamber in the corresponding plasma etching step (d) is smaller than the working gas pressure in the reaction chamber in the plasma etching step (a) corresponding to the main etching process. The method of claim 1, wherein the working pressure in the reaction chamber in the plasma etching step (d) corresponding to the over-etching process is not more than 40 mTorr. The method of claim 1, wherein the working gas pressure in the reaction chamber in the passivation step (e) corresponding to the over-etching process is greater than the passivation step (b) corresponding to the main etching process. The method of claim 1, wherein an insulating layer of a different material is adhered under the layer of the material to be etched, and the main etching process is immediately stopped in contact with the insulating layer in the region where the etching is fastest, or Contact with the insulating layer stops. A method for forming a hole structure for suppressing or avoiding the occurrence of a notch at the bottom of the hole, comprising: providing a substrate comprising a layer of material to be etched and an insulating layer adhered to a lower surface of the layer of material to be etched; Plasma etching the layer of material to be etched to initially form a hole; in a relatively low working pressure environment, continuing an anisotropic plasma etch to deepen the hole; at least at the end of the process of deepening the hole The insulating layer is already exposed through the aperture. The forming method according to claim 5, wherein the etching step for preliminary forming the holes and the etching step for deepening the holes are all performed by a Bosch method. The method of forming according to claim 5, wherein the material layer to be etched and the insulating layer are top layer germanium and buried oxide layers of the SOI substrate.